Q1.5: What's Genetic Programming (GP)?

GENETIC PROGRAMMING is the extension of the genetic model of learning into the space of programs. That is, the objects that constitute the POPULATION are not fixed-length character strings that encode possible solutions to the problem at hand, they are programs that, when executed, "are" the candidate solutions to the problem. These programs are expressed in genetic programming as parse trees, rather than as lines of code. Thus, for example, the simple program "a + b * c" would be represented as:


	    +
	   / \
	   a  *
	    / \
	    b  c

or, to be precise, as suitable data structures linked together to achieve this effect. Because this is a very simple thing to do in the programming language Lisp, many GPers tend to use Lisp. However, this is simply an implementation detail. There are straightforward methods to implement GP using a non-Lisp programming environment.

The programs in the population are composed of elements from the FUNCTION SET and the TERMINAL SET, which are typically fixed sets of symbols selected to be appropriate to the solution of problems in the domain of interest.

In GP the CROSSOVER operation is implemented by taking randomly selected subtrees in the INDIVIDUALs (selected according to FITNESS) and exchanging them.

It should be pointed out that GP usually does not use any MUTATION as a GENETIC OPERATOR.

More information is available in the GP mailing list FAQ. (See Q15.2) and from http://smi-web.stanford.edu/people/koza/


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Hitch Hiker's Guide to Evolutionary Computation, Issue 9.1, released 12 April 2001
Copyright © 1993-2001 by J. Heitkötter and D. Beasley, all rights reserved.