6.4 Making movies from plots

If you have data that evolves, you might want to save it as a movie as well as showing it in a figure window, similar to the command savefig. One way to do this is with the module visvis, see [37]. 

Here is a simple example of evolving a circle using an implicit representation. Let the circle be represented by the zero level, 

of a function .

Alternatively, consider the disk  inside the zero set of . If the value of decreases at a rate , then the circle will move outward at the rate .

This can be implemented as:

import visvis.vvmovie as vv

# create initial function values
x = linspace(-255,255,511)
X,Y = meshgrid(x,x)
f = sqrt(X*X+Y*Y) - 40 #radius 40

# evolve and store in a list
imlist = []
for iteration in range(200):
    imlist.append((f>0)*255)
    f -= 1 # move outwards one pixel
vv.images2swf.writeSwf('circle_evolution.swf',imlist)

The result is a flash movie (*.swf file) of a growing...