PSOs can be numerically implemented as synchronous or asynchronous algorithms. While in the synchronous case, the global best is determined after the end of each iteration, x g is updated after each misfit evaluation in the asynchronous setup. Asynchronous optimisation increases the diversity of the swarm, whereas synchronous PSO includes more information from the previous iteration . Various studies showed superior performance of the asynchronous PSO ; however, the increased need for communication complicates the parallelisation of the algorithm considerably .