Xiao-Min Hu et al.: Orthogonal Methods Based Ant Colony Search for Solving Continuous Optimization Problems 3

Other methods developed recently include the continuous interacting ant colony (CIAC) algorithm [16,17] , the extended ACO to continuous domains (ACOR) [18,19], the continuous ant colony system (CACS) [20] , the binary ant system (BAS) [21] , the direct application of ACO (DACO) [22] , and those algorithms reported in [23, 24]. Hybrid ant algorithms combined with genetic algorithms [23] , artificial immune systems [25] and particle swarms (PSACO) [26] have also been proposed. These methods are able to tackle continuous optimization problems to a certain degree. In order to solve continuous optimization problems effectively, this paper develops a continuous orthogonal ant colony (COAC) algorithm by using the orthogonal design method [27−32]. The orthogonal desig