The Cook Book
Recipe for the week of November 14  20
Shortterm Nucleation in the Rug Rule
 Here is an interesting soup that I discovered while playing with
WinCA, our Windowsbased interactive modeling environment for
cellular automata. To pick up the first beta version of WinCA look
in the kitchen sink. Then you can try
cooking for yourself.
 For this week's recipe, a specified number of colors are arranged
cyclically in a "color wheel." The highest color is inert, a sort of
ground state. All other colors update by a small perturbation of modular
smoothing. Namely, a color's index is replaced by 1 + the (rounded)
average of the indices of its neighbors, modulo the total number of
colors. The result is a kind of digital heat equation with nonlinearity.
Complex diffusive wave patterns emerge. Patterns reminiscent of Oriental
carpets evolve if the initial configuration is simple and symmetric, so
this family of CA dynamics is widely known as the rug rule..
A WinCA experiment called rug.xpt produces such a carpet.
 To make this week's soup, however, we start the 256color rug rule
from a uniformly random initial configuration using the WinCA
palette rainbow.pal, which has a full spectrum of colors
culminating with purples and reds for state values up to 216, and then
has a black to white grayscale for values 217 through 255. The initial
white sites form a random field of inert nucleation centers with density
1/255. Over time, gray blobs aggregate and consolidate around the
centers. Cook for 100 updates, or until the blobs achieve optimal
heaviosity. Be careful, though, not to let the soup boil over  an
unappetizing gray mush will result.
