Enhancing differential evolution algorithm for solving continuous optimisation problems

Differential Evolution (DE) has become one of the most important metaheuris- tics during the recent years, obtaining attractive results in solving many engi- neering optimization problems. However, the performance of DE is not always strong when seeking optimal solutions. It has two major problems in real world applications. First, it can easily get stuck in a local optimum or fail to generate better solutions before the population has converged. Secondly, its performance is significantly influenced by the control parameters, which are problem depen- dent and which vary in different regions of space under exploration. It usually entails a time consuming trial-and-error procedure to set suitable parameters for DE in a specific problem, particularly for those practioners with limited knowledge and experience of using this technique.This thesis aims to develop new DE algorithms to address the two afore- mentioned problems. To mitigate the first problem, we studied the hybridiza- tion of DE with local search techniques to enhance the efficiency of search. The main idea is to apply a local search mechanism to the best individual in each generation of DE to exploit the most promising regions during the evo- lutionary processs so as to speed up the convergence or increase the chance to scape from local optima. Four local search strategies have been integrated and tested in the global DE framework, leading to variants of the memetic DE algo- rithms with different properties concerning diversification and intensification. For tackling the second problem, we propose a greedy adaptation method for dynamic adjustment of the control parameters in DE. It is implemented by con- ducting greedy search repeatedly during the run of DE to reach better parameter assignments in the neighborhood of a current candidate. The candidates are as- sessed by considering both, the success rate and also fitness improvement of trial solutions against the target ones. The incorporation of this greedy parame- ter adaptation method into standard DE has led to a new adaptive DE algorithm, referred to as Greedy Adaptive Differential Evolution (GADE).The methods proposed in this thesis have been tested in different bench- mark problems and compared with the state of the art algorithms, obtainingcompetitive results. Furthermore, the proposed GADE algorithm has been ap- plied in an industrial scenario achieving more accurate results than those ob- tained by a standard DE algorithm.