Dynamically Defined Functions In Grammatical Evolution

Grammatical evolution is an extension of genetic programming, in that it is an algorithm for evolving complete programs in an arbitrary language. By utilising a Backus Naur form grammar the advantages of typing are achieved as well as a separation of genotype and phenotype. This paper introduces a meta-grammar into grammatical evolution allowing the grammar to dynamically define functions, self-adaptively at the individual level without the need for special purpose operators or constraints. The user need not determine the architecture of the dynamically defined functions. As the search proceeds through genotype/phenotype space the number and use of the functions can vary. The ability of the grammar to dynamically define such functions allows regularities in the problem space to be exploited even where such regularities were not apparent when the problem was set up.