Theoretical Analysis on the Ability of Particle Swarm Optimization to Escape from Local Optimum

Abstract: As one of the most prominent swarm intelligence algorithms, particle swarm optimization (PSO) has been extensively applied to solve global optimization problems. The theoretical analysis on the ability of PSO to escape from local optimum (LO) is deeply intertwined with its global optimization performance, making it highly significant to investigate the underlying mechanisms that enable PSO to escape from LO and achieve global optimization. In this study, a rigorous mathematical analysis is presented to explore the ability and mechanisms of PSO to escape from LO. By modelling each search agent as a Markov chain, the probability of PSO escaping from LO within a finite number of iterations is calculated, and the behavior of agents prior to escaping from LO is analyzed. Through this theoretical analysis, two necessary and sufficient conditions are proposed to ensure that PSO escapes from LO in finite iterations with a probability 1: (a) the personal best (pbest) and global best (gbest) positions stagnate around different local optima, and (b) the inertial weight in PSO is equal to one. Upon these conditions, two potential behaviors of agents, namely inertial motion and oscillation, are proposed, and a state transition chain of the agent toward the global optimum is constructed. Additionally, the theoretical analysis reveals that increasing the distance between pbest and gbest, as well as the values of the learning factors in PSO, enhances the speed at which PSO escapes from LO. Finally, the conclusions drawn from the theoretical analysis are corroborated through numerical experiments.