The Standard Map

Submitted by michael on Mon, 02/04/2019 - 17:40

The standard map is the first chaotic thing I remember seeing, probably in an AfterDark screen saver. It has an interesting physical interpretation involved rotors, but that isn't important for the pretty pictures.

$$ x_{n+1} = x_n + K \sin(y_n) \mod 2\pi $$

$$ y_{n+1} = y_n + x_n + K \sin(y_n) \mod 2\pi $$

Clifford Attractor

Submitted by michael on Sun, 01/27/2019 - 15:43

Clifford Attractors are attributed to Clifford Pickover. They're reminiscent of smoke gently wafting in still air. paulbourke.net has some more images, and generates colour in a different way.

The formula has four parameters, each chosen randomly on $[-2,2]$. Not all random combinations generate a strange attractor. In some they fall into a fixed cycle or even a single fixed point. If that happens click the Restart button to get a new set of parameters.

Tinkerbell Map

Submitted by michael on Sat, 01/19/2019 - 14:29

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.

Git: Move commits to new branch

Submitted by michael on Mon, 10/29/2018 - 11:34

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.