As explained in Chapter 3, there are two fundamental forces that form the basis of evolutionary systems: variation and selection. In this chapter we discuss the EA components behind the second one. Having discussed some typical population management models, and selection operators, we then go on to explicitly look at some situations where diversity is needed, such as multimodal problems, and some approaches to population management, and altering selection, that have been proposed to increase useful diversity.
Contents:
5.1 Population Management Models……………………… 79
5.2 Parent Selection………………………………….. 80
5.2.1 Fitness Proportional Selection …………………. 80
5.2.2 Ranking Selection …………………………… 81
5.2.3 Implementing Selection Probabilities…………….. 83
5.2.4 Tournament Selection………………………… 84
5.2.5 Uniform Parent Selection……………………… 86
5.2.6 Overselection for Large Populations……………… 86
5.3 Survivor Selection ………………………………… 87
5.3.1 Age-Based Replacement………………………. 88
5.3.2 Fitness-Based Replacement ……………………. 88
5.4 Selection Pressure ………………………………… 90
5.5 Multimodal Problems, Selection, and the Need for Diversity . . 91
5.5.1 Multimodal Problems ………………………… 91
5.5.2 Characterising Selection and Population Management Approaches for Preserving Diversity …………….. 92
5.5.3 Fitness Sharing …………………………….. 92
5.5.4 Crowding………………………………….. 93
5.5.5 Automatic Speciation Using Mating Restrictions . . . . . . 95
5.5.6 Running Multiple Populations in Tandem: Island ModelEAs ………………………………… 95
5.5.7 Spatial Distribution Within One Population: Cellular EAs ……………………………………… 97