diffusion

    Diffusion Limited Aggregation. Randomly moving points accumulate.
    Two parameters: border width (default 10), type


This type begins with a single point in the center of the screen.
Subsequent points move around randomly until coming into contact with the
first point, at which time their locations are fixed and they are colored
randomly. This process repeats until the fractals reaches the edge of the
screen. Use the show orbits function to see the points' random motion.

One unfortunate problem is that on a large screen, this process will tend
to take eons. To speed things up, the points are restricted to a box
around the initial point. The first and only parameter to diffusion
contains the size of the border between the fractal and the edge of the
box. If you make this number small, the fractal will look more solid and
will be generated more quickly.

Diffusion was inspired by a Scientific American article a couple of years
back which includes actual pictures of real physical phenomena that behave
like this.

Thanks to Adrian Mariano for providing the diffusion code and
documentation. Juan J. Buhler added the additional options.