## Sunday, April 20, 2008

### The Lorenz Attractor

As Professor Edward Lorenz died of Cancer on Wednesday, I thought it would only be fitting that today's article be about the Lorenz Attractor which is one of the earliest (if not the first) example of chaos theory. Chaotic systems are those in which a very small change can have a drastic impact on the outcome of the system over time. The butterfly effect is probably the best known example of this. Essentially, a butterfly flapping it's wings can as a result alter the weather weeks in the future. This happens because the extremely small change in the weather pattern can slowly be amplified over time. This is also the reason why we are so poor at predicting the weather.

Professor Lorenz discovered this fact in the early sixties when he was trying to develop a computer model of the weather. Back then computers were not that powerful so the professor simplified the model so that it consisted of three differential equations:

• dx/dt = 10(y - x)
• dy/dt = xz + 28x - y
• dz/dt = xy - (8/3)z

When running these equations, Professor Lorenz found that if he tried to pick up the equations from where he left them in an earlier run that the outputs were not the same. After verifying that the computer was in fact working properly and that there were not any bugs in his program, he isolated the problem down to the precision in which he was entering the information. He was only entering the data to 3 decimal places where as the computer was keeping the data up to 6 decimal places. Did I mention that this was the sixties and that the computer was primitive?

The result of this is the discovery of Strange Attractors. Other forms of chaos, such as fractals and the Mandelbrot set, have since been discovered and have been used in the generation of some of the most incredible graphics and animations. There are a number of open source programs that can plot these equations for you and there are certainly many books on the subject. I personally feel that it is more fun to write your own generator, but then I like programming and find the programming aspects as much fun (if not more fun) as looking at the results.