An improved tabu search method for the weighted constraint satisfaction problem

Aiming at developing a general problem solver for combinatorial optimization problems, we consider in this paper the weighted constraint satisfaction problem (WCSP), which, given a number of constraints and their weights of importance, asks to minimize the total weight of unsatisfied constraints. We propose a tabu search algorithm for WCSP with the features that it uses an evaluation function, defined in terms of the modified weights of constraints, for guiding the search, and that it incorporates an automatic control mechanism of the weights in the evaluation function. Using this code, we solved a number of problems including those from real applications such as generalized assignment, set covering, parallel shop scheduling, timetabling and nurse scheduling. Many problems that arise in cellular manufacturing can also be formulated as WCSP, including the problems of cell formation and tool selection. Our computational results indicate that the control mechanism of weights makes our tabu search more powerful, and our algorithm is practically usable.