Self-Improvement to Control Code Growth in Genetic Programming

Abstract

An important problem with genetic programming systems is that in the course of evolution the size of individuals is continuously growing without a corresponding increase in fitness. This paper reports the application of a self-improvement operator in combination with a characteristic based selection strategy to a classical genetic programming system in order to reduce the effects of code growth. Two examples, a symbolic regression problem and an 11-bit multiplexer problem are used to test and validate the performance of this newly designed operator. Instead of simply editing out non-functional code this method tries to select subtrees with better fitness. Results show that for both test cases code growth is substantially reduced obtaining a reduction factor of 3-10 (depending on the problem) while the same level of fitness is attained. © Springer-Verlag 2004.