The migration model divides the population in multiple subpopulations. The parallel implementation of the migration model showed not only a speedup in computation time, but it also needed less objective function evaluations when compared to a single population algorithm.
Many possibilities exist for the structure of the migration of individuals between subpopulations.
Here, individuals may migrate from any subpopulation to another. For each subpopulation, a pool of potential immigrants is constructed from the other subpopulations. The individual migrants are then uniformly at random determined from this pool. Figure 2 gives a detailed description for the unrestricted migration scheme for 4 subpopulations with fitness-based selection. 1 individual is uniformly at random chosen from this pool and replaces the worst individual in subpopulation 1.