Reassembling operator equalisation

Abstract

The recent Crossover Bias theory has shown that bloat in Genetic Programming can be caused by the proliferation of small unfit individuals in the population. Inspired by this theory, Operator Equalisation is the most recent and successful bloat control method available. In this work we revisit two bloat control methods, the old Brood Recombination and the newer Dynamic Limits, hypothesizing that together they contain the two main ingredients that make Operator Equalisation so successful. We reassemble Operator Equalisation by joining these two ingredients in a hybrid method, and test it in a hard real world regression problem. The results are surprising. Operator Equalisation and the hybrid variants exhibit completely different behaviors, and an unexpected feature of Operator Equalisation is revealed, one that may be the true responsible for its success: a nearly flat length distribution target. We support this finding with additional results, and discuss its implications.