ps_evol is mainly intended as a demo script
illustrating the text_evol funtion in Math::Evol.pm.
It assumes you have something like GhostView
which allows you to view PostScript files.
It creates a temporary PostScript file,
then repeatedly generates eight variants of the original file,
scales them smaller, numbers them, and displays them in a 3x3 array.
The original is in the middle, as number 5.
It asks the user which variant they prefer,
then uses that as the original for the next iteration.
When the user decides to call a halt,
the latest preferred variant is written to the standard output.
The parameters to be varied in the PostScript file
must be marked out by special comments, such as
/gray_sky .87 def % evol step 0.05 min 0.0 max 1.0
See perldoc Math::Evol for more details,
and as an example the PostScript file plant.ps,
included with the distribution.