where v k i is the velocity vector of particle i at iteration k, ω is an inertia weight, x p,i is the personal best position of the particle i, x g is the global best position of the swarm, r k p and r k g are uniform random number vectors, φ p and φ g are acceleration parameters, respectively. The inertial weighting was not included in the original formulation of the velocity equation and was first introduced by Shi and Eberhart in 1998 . Their form of Eq. ( ) later became accepted as the new standard for the PSO. Due to the resulting dynamic adjustment of the particle velocities, it refines the search in the direct vicinity of the minimum. Thus, an optimisation of the convergence speed as well as an enhancement of the final solution is achieved.