On the Effects of Bit-Wise Neutrality on Fitness Distance Correlation, Phenotypic Mutation Rates and Problem Hardness

摘要

The effects of neutrality on evolutionary search are not fully understood. In this paper we make an effort to shed some light on how and why bit-wise neutrality - an important form of neutrality induced by a genotype-phenotype map where each phenotypic bit is obtained by transforming a group of genotypic bits via an encoding function - influences the behaviour of a mutation-based GA on functions of unitation. To do so we study how the fitness distance correlation (fdc) of landscapes changes under the effect of different (neutral) encodings. We also study how phenotypic mutation rates change as a function of the genotypic mutation rate for different encodings. This allows us to formulate simple explanations for why the behaviour of a GA changes so radically with different types of neutrality and mutation rates. Finally, we corroborate these conjectures with extensive empirical experimentation.