An analysis of the distribution of swapped subtree sizes in tree-based genetic programming

This paper analyses the distribution of swapped subtree sizes involved in crossover events in approximations of an optimal crossover operator that allows the root node to be crossed over. The goal is to examine how the offspring search space can be effectively reduced for given parents. It concludes that good crossover events have a strong preference for the roots of the parent programs and for nodes with small subtrees. This paper also quantifies the ability of crossover to optimise offspring fitness, and concludes that this ability is far below what was expected.