critical - Draw a system showing self-organizing criticality

critical [-display host:display.screen] [-foreground color] [-background color] [-window] [-root] [-mono] [-install] [-visual visual] [-delay seconds] [-random boolean] [-ncolors int] [-offset int]

The critical program displays a self-organizing critical system that gradually emerges from chaos.

critical performs a simulation on a two-dimensional array of integers. The array is initialized to random values. On each iteration, it draws a line to the array position with the greatest value. It then replaces that location and the eight neighboring locations with randomly-selected values.

The lines are initially random, but over time a chaotic self-organizing system evolves: areas of the screen which happen to have lower values are less likely to be updated to new values, and so the line tends to avoid those areas. Eventually, the histogram of changes approaches the power-law curve typical of such systems.

The simplest documented self-organizing system is the one-dimensional equivalent of critical.

I heard about this algorithm second-hand: apparently there was an article in Scientific American describing it sometime in 1997.

critical accepts the following options:

-window

Draw on a newly-created window. This is the default.

-root

Draw on the root window.

-mono

If on a color display, pretend we're on a monochrome display.

-install

Install a private colormap for the window.

-visual visual

Specify which visual to use. Legal values are the name of a visual class, or the id number (decimal or hex) of a specific visual.

-delay usecs

Number of microseconds to wait after drawing each line.

-random boolean

Whether to use randomly selected colours rather than a cycle around the colour wheel.

-offset integer

The maximum random radius increment to use.

-ncolors integer

How many colors should be allocated in the color ramp (note that this value interacts with offset.)

-trail integer

Length of the trail: between 5 and 100 is nice.

DISPLAY

to get the default host and display number.

XENVIRONMENT

to get the name of a resource file that overrides the global resources stored in the RESOURCE_MANAGER property.

X(1), xscreensaver(1) xscreensaver-command(1) xscreensaver-demo(1)

Copyright © 1998 by Martin Pool.

Permission to use, copy, modify, distribute, and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation. No representations are made about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.

Martin Pool <mbp@humbug.org.au>, 1998-2000. Based in part on the XScreenSaver code by Jamie Zawinski <jwz@jwz.org>.