30 July 2014

At Most R

How to encode a cardinality constraint as boolean constraints.

24 July 2014

Depth First Search in Python

Everybody thinks they understand depth-first search. The algorithm is indeed simple. But — I think — it is deceptively simple. In this post I play with some code.

20 July 2014

IMO 2014 problem 1

This is an exercise proposed by Timothy Gowers: Write down all you think of while trying to solve a math problem.

18 July 2014

Predictive Causality

We know correlation does not imply causality. What does?

12 July 2014

Minimizing Weighted Automata via Linear Algebra

In this post I present the minimization problem for weighted automata, closely following a paper by Stefan Kiefer and Björn Wachter. I do add lots of steps that aren't necessary. To me, they make the result look less like magic. I really like the mixture of automata and linear algebra.

05 July 2014

Minimal Sets over Monotone Predicates

This post describes a very nice use of binary search. I learned about it from a paper by Joao Marques-Silva, Mikolas Janota, and Anton Belov.

04 July 2014

The Education Funnel

About the difficulty of national tests, and pass rates.