The Cook Book

Recipe for the week of September 16 - 22

Brian's Brain on Caffeine

As the Java bandwagon picks up steam, Web-based simulations of cellular automata are popping up on a daily basis. Since we reported on early Java versions of Conway's Life by Orbital Technologies and Paul Callahan last January and February, and then Al Hensel's screaming implementation this past summer, more than twenty CA applets have appeared in the Gamelan Java Directory - search on 'Life' and 'Cellular' to find them.

Our favorite new discovery in this collection comes from Mitchel Resnick and Brian Silverman at M.I.T. Their Exploring Emergence interactive tutorial gives a charming 10-part introduction to cellular automata in the spirit of Logo turtle graphics. The culminating example of their mini-course is Brian's Brain, a well-known CA rule devised by Silverman and discssed in the book Cellular Automata Machines by Toffoli and Margolus (M.I.T. Press, 1987).

This week's soup shows part of a CAM8 simulation of Brain after 100,000 updates, with the same coding as in the CAM book. To quote from Resnick and Silverman,

... there are many more gliders - and many more types of gliders -- than with the Life rule. In fact, almost everything ends up as a glider. Glider guns are also very common, and they themselves are gliders. And if you watch carefully, you might even find a glider-gun gun.

Whereas Conway's Life evidently relaxes to a final mix of fixed and periodic local structures starting from generic disordered configurations, Brian's Brain establishes a dynamic statistical equilibrium of great complexity. Kellie Evans has since found similar chaotic steady states for higher range Larger than Life rules near the LtL phase boundary.

Two more Java CA resources are worth mentioning. First, Bruce Christenson's Life has perhaps the nicest user interface to date. In particular there is a way to control the speed of simulation. Java compilers have now improved to the point where versions such as Hensel's desparately need this feature to slow down the movies! Second, for do-it-yourself folks, the new Java By Example book from Sunsoft includes source code for a more general purpose CA simulator. These examples are also included on several Java CDs distributed by SUN.

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