I. Introduction
Nature-inspired optimization algorithms [2], notably Evolutionary Algorithms (EAs), have been widely used to solve various scientific and engineering problems. Currently, there are three well-known EAs, namely, Genetic Algorithms (GAs), Evolutionary Programming (EP) and Evolution Strategies (ES). The inspiration of all the EAs is Darwin's evolution theory: survival of the fitness. Recently, a new global optimization algorithm paradigm, Swarm Intelligence (SI), has been proposed. There are two different SI algorithms: Ant Colony Optimizer (ACO) and Particle Swarm Optimizer (PSO). They are inspired by real ant foraging behaviour and Artificial Life, respectively.