Best of 2019

The blog posts Hacker News loved most in 2019. 184 posts.

Math & Algorithms
155

Time Travel (2006)

Last time we talked about free will, superintelligent predictors, and Dr. Evil planning to destroy the earth from his moon base. Today I'd like to talk about a more down-to-earth topic: time travel. The first point I have to make is one that Carl Sagan made: we're all time travelers—at the rate of one second per…

163

Towards a Better Pythagorean Cup

There was an article on Hacker News the other day by David Richeson entitled Make Your Own Pythagorean Cup . A Pythagorean cup is a cup with a built-in siphon. Supposedly invented by Pythagoras, the cup functions just like an ordinary cup as long as it is only filled to a certain level. If anyone gets greedy and tries…

164

RSA: Theory and Implementation

RSA has been a staple of public key cryptography for over 40 years, and is still being used today for some tasks in the newest TLS 1.3 standard. This post describes the theory behind RSA - the math that makes it work, as well as some practical considerations; it also presents a complete implementation of RSA key…

167

Curve fitting A: Linear Least Squares

The graph on the left shows a third example, taken from analytical chemistry: a straight-line calibration data set where X = concentration and Y = instrument reading (Y = a + b X). Click to download that data . The blue dots are the data points. They don't all fall in a perfect straight line because of random noise…

174

A Visual Introduction to Morse Theory

In a previous article , I already introduced manifolds and their, ahem, manifold ways. Among the many interesting comments I received about this article, some were dealing with a basic question, namely how to measure the properties of a manifold. In this article, I want to present a few concepts from Morse theory …

178

Stock Option Pricing Inference

I’m a stock market enthusiast 📈, so lately I have spent my spare time on the topic of stock option pricing, and I was curious to find out whether or not I could build a script that accurately reflected real market option prices. It turns out I came close, and learned a lot along the way, which I share in this article.

179

Math versus Dirty Data

At Google, our organization designs, owns, and maintains a number of optimization models that automate the planning of Google’s datacenter growth and health. As is pretty standard in supply chain optimization and planning, these models are often integer linear programs. It’s a core competency of operations research…