Re: Selection Functions

[M. Lang & S. Railsback]

Michael Stillwell wrote:
> 
> I'm working on a GA-like system in which the probability that a bug is
> chosen to breed is related to its fitness.  It appears that the
> traditional way to do this is to use "roulette wheel selection"--each
> bug gets a slice of the wheel in proportion to its fitness, the wheel
> is spun, and the bug associated with the point where the wheel ended
> up is gets to breed.
> 
> Do other "selection functions" exist?  My problem with roulette wheel

What we do in our fish model is assume that, when breeding season comes,
each fish is given the possibility of breeding and its probability is
related to its fitness. We use logistic function of probability of
spawning vs. "fitness" (actually, a measure of its energy reserves). So
if all the fish have low reserves then very few breed; if it's a good
year and a lot of fish have high reserves, there's lots of breeding and
lots of new baby fish.

I think this approach resembles nature more closely than the roulette
wheel, but for a GA system, it may have some disadvantages: it makes the
competition among "bugs" offspring highest when they are most
successful.

Steve
-- 
address@hidden
Lang, Railsback & Assoc.
250 California Ave., Arcata CA 95521
707-822-0453; Fax 822-1868


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