A key ingredient in any successful genetic programming is robust initialisation. Many successful initialisation methods used in genetic programming have been adapted to use with grammatical evolution, to varying levels success. This papaer examines the effectiveness of some of the most popular of these initialisation techniques on structured grammatical evolution. Namely, we investigate Sensible Initialisation and Probabilistic Tree Creation 2, as well as the standard initialisation procedure used in structured grammatical evolution, Grow. We also propose a novel procedure called Local Optimised Probabilistic Tree Creation 2, which runs a quick greedy optimisation on the trees created.
We examine their performance, as well as the diversity of solutions they create, on 7 well-known benchmarks. We observe that Local Optimised Probabilistic Tree Creation 2 created the fittest, or joint fittest, initialisation populations on every benchmark considered. This did not necessarily result in overall better runs, however, and SGE runs with below average initialisation performance were seen to overcome their ''bad start". The diversity of solutions, particularly fitness diversity, at the end of the run was lower for Local Optimised Probabilistic Tree Creation 2 and Probabilistic Tree Creation 2 than for both sensible initialisation and grow.