Code speedup tips

[Raymond Hettinger]

"Carl Banks"
> Here is how I rewrote CA_Function.  There are some details in it I've
> left unexplained; feel free to ask for a clarification:
>
>
>     def CA_Function(Length,Steps):
>         # Create the two lattices
>         current = zeros((Length,Length),Int)
>         workspace = zeros((Length-2,Length-2),Int)
>
>         # Create slices of the current lattice
>         # We don't have to do this every step because slicing shares
memory
>         left = current[0:-2,1:-1]
>         up = current[1:-1,0:-2]
>         right = current[2:,1:-1]
>         down = current[1:-1,2:]
>
>         # Set the start cell to black
>         current[Length/2,Length/2] = 1
>
>         # Apply the rule
>         for step in xrange(Steps):
>             # In the workspace, add the shifted lattices
>             # This uses a bunch of += because it's faster
>             workspace[:] = left
>             workspace[:] += up
>             workspace[:] += right
>             workspace[:] += down
>             # Set the current lattice
>             current[1:-1,1:-1] = where(workspace,1,0)

Nice job.