A brownian tree example

A brownian tree is a form of computer art that was briefly popular in the 1990s, when home computers started to have sufficient power to simulate brownian motion. Brownian trees are mathematical models of dendritic structures associated with the physical process known as diffusion-limited aggregation.

A brownian tree is built with these steps: first, a "seed" is placed somewhere on the screen. Then, a particle is placed in a random position of the screen, and moved randomly until it bumps against the seed. The particle is left there, and another particle is placed in a random position and moved, and so on.

A circular brownian tree

The resulting tree can have many different shapes, depending on principally three factors:

• the seed position
• the initial particle position (anywhere on the screen, from a circle surrounding the seed, from the top of the screen, etc.)
• the moving algorithm (usually random, but for example a particle can be deleted if it goes too far from the seed, etc.)

Particle color can change between iterations, giving interesting effects.

At the time of their popularity (helped by a Scientific American article in the Amateur Scientist section), a common computer took hours, and even days, to generate a small tree. Today's (2003) computers can generate trees with 10,000's of particles in a few minutes.