Section: New Results

Evolving Genetic Programming Classifiers with Novelty Search

Participants : Enrique Naredo, Leonardo Trujillo, Pierrick Legrand.

Novelty Search (NS) is a unique approach towards search and optimization, where an explicit objective function is replaced by a measure of solution novelty to provide the selective pressure in an artificial evolutionary system. However, NS has been mostly used in evolutionary robotics, while it's applicability to classic machine learning problems has been mostly unexplored. This work presents a NS-based Genetic Programming (GP) algorithm for supervised classification, with the following noteworthy contributions. It is shown that NS can solve real-world classification tasks, validated over several commonly used benchmarks. These results are made possible by using a domain-specific behavioral descriptor, closely related to the concept of semantics in GP. Moreover, two new variants of the NS algorithm are proposed, Probabilistic NS (PNS) and a variant of Minimum Criterion NS (MCNS). The former models the behavior of each solution as a random vector, eliminating all the NS parameters and reducing the computational overhead of the traditional NS algorithm; the latter uses a standard objective function to constrain the search and bias the process towards high performance solutions. The paper also discusses the effects of NS on an important GP phenomenon, bloat. In particular, results indicate that some variants of the NS approach can have a beneficial effect on the search process by curtailing code growth. See [52] .