Evolution in Time and Space-The Parallel Genetic Algorithm

The parallel genetic algorithm (PGA) uses two major modiications compared to the genetic algorithm. Firstly, selection for mating is distributed. Individuals live i n a 2-D w orld. Selection of a mate is done by each i n d i-vidual independently in its neighborhood. Secondly, e a c h individual may improve its tness during its lifetime by e.g. local hill-climbing. The PGA is totally asynchronous, running with maximal eeciency on MIMD parallel computers. The search strategy of the PGA is based on a small number of active and intelligent individuals, whereas a GA uses a large population of passive individuals. We will investigate the PGA with deceptive problems and the traveling salesman problem. We outline why and when the PGA is succesful. Abstractly, a PGA is a parallel search with information exchange between the individuals. If we represent the optimization problem as a tness landscape in a certain connguration space, we see, that a PGA tries to jump from two local minima to a third, still better local minima, by using the crossover operator. This jump is (probabilistically) successful, if the tness landscape has a certain correlation. We s h o w t h e correlation for the traveling salesman problem by a connguration space analysis. The PGA explores implicitly the above correlation.