The Strength Pareto Evolutionary Algorithm (SPEA) [9] is an
elitist Multi-Objective Evolutionary Algorithm (MOEA) since it
ensures that good solutions found in early runs are only replaced
if better solutions are discovered. The algorithm achieves it by
maintaining an external population P¯l consisting of a fixed number
of non-dominated solutions found before the beginning of the
simulation. If new non-dominated solutions are found during the
simulation, they are compared with the existing external population
and the resulting non-dominated solutions are stored. The
external population participates in the genetic operators with the
current population expecting to influence the population towards
good regions of the search space. Below one iteration of the algorithm
step-by-step is described [9]. Initially, a population P0 of
size N is randomly created, and the external population P¯0 with
maximum capacity of N¯ is empty. In generation t,