Path: utzoo!mnetor!uunet!husc6!mailrus!umix!umich!dwt
From: dwt@zippy.eecs.umich.edu (David West)
Newsgroups: comp.ai
Subject: Re: Cognitive System using Genetic Algorithms
Message-ID: <775@zippy.eecs.umich.edu>
Date: 11 Feb 88 19:34:52 GMT
References: <230@wright.EDU> <8300018@osiris.cso.uiuc.edu> <1062@ucdavis.ucdavis.edu>
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Reply-To: dwt@zippy.eecs.umich.edu (David West)
Organization: University of Michigan EECS Dept. Ann Arbor
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Summary: No Free Lunch
UUCP-Path: ihnp4!umich!zippy!dwtt


In article <1062@ucdavis.ucdavis.edu> g451252772ea@deneb.ucdavis.edu.UUCP (PUT YOUR NAME HERE) writes:
>The author discusses neural nets, 
>simulated annealing, and one example of GA, all applied to the TSP, but
>comments that "... a thorough comparason ... _would be_ very interesting"
  [...]
>o	As noted, the TSP is a canonical candidate.

I believe the TSP is popular because it is easy and compact to program.
The performance of a general method such as GAs can be strongly influenced
by the problem representation, and it turns out that the most straightforward
representations for genetic operations are particularly badly matched to the
most straightforward representations for TSPs.  This makes the TSP a rather
unfortunate choice of introductory example for people who are unfamiliar
with GAs.

>Finally, I noted above that the production rules take system inputs as
>bit-strings.  This representation allows for induction,... 

It is *one* way of getting a form of induction, and has the property that
only very simple operations on the internal representation are used; the 
extent to which this is useful depends, again, on the joint appropriateness 
of the representations of the genetic operators and the world.  
An "appropriate" representation has the property that the expected 
fitness of the result of (say) a crossover is not severely worse than 
that of its parents. This is something that must be ensured by the experimenter
if (as is most common) the representational mapping itself is not subject to
genetic selection.

 -David West