The Tinkerbell map is a chaotic dynamical system with an interesting strange attractor. The iterated function is

x_{n+1} = x_n^2 - y_n^2 + a x_n + b y_n

y_{n+1} = 2 x_n y_n + c x_n + d x_n

In this example, the parameters are $a=0.9$, $b=-0.6013$, and $c=2.0$. $d$ is randomly chosen on $(0.35, 0.55)$, and the colour is based on $d$.

See also Wikipedia.

My notes on setting up a new mac, probably only useful for me. 

Suppose you have a few commits in a git repository, and some of them are on the wrong branch. They're listed below from the oldest (a) to newest (g). The letters represent the commit checksums.

a b c d e f g

You want to move the bold commits b, d, and e to a new branch. So start by checking out the commit before the first bad one and creating a branch there.

Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway. Computer Networks, 3rd ed., p. 83. (paraphrasing Dr. Warren Jackson, Director, University of Toronto Computing Services (UTCS) circa 1985)
Spent a couple of days tracking down a strange error using PHPunit and SQLite for testing a complex application. The test suite kept throwing
PDOException: SQLSTATE[HY000]: General error: 5 database is locked
and halting in test that didn't touch the database. The problem was in an unrelated test that ran before it. The test uses iterators to examine database contents, but didn't iterate all the way through the result set. The iterator left the database locked.