Better Trained Ants
Previous: One Point Crossover
By making a modest change to the Santa Fe trail problem we have made
it significantly easier for GP.
In terms of the effort required (120,000)
it is approximately three times easier
and GP performs about as well as the best results previously obtained
using variable length hill climbers
(187,500)
[Langdon1998c,Langdon and
Poli1998]
and size restricted EP search (136,000) [Chellapilla1997].
By enforcing an optimal size limit on the programs being evolved we
might be able to do marginally better
(104,000, size 
).
Surprisingly GP performance is only marginally affected by a size limit and is roughly constant for wide ranges in maximium size.
Using the improved fitness function on the original search space, GP is able to out perform the best that might be obtained by random search by about 4:1. If both search techniques are limited to programs of a maximum length of 50 (which best suits GP) this ratio expands to about 25:1.