2001 Volume 14 Issue 5 Pages 244-251
In this paper, the Lagrangian decomposition and coordination technique is applied to flowshop scheduling problems in which the sum of the changeover cost and the tardiness penalty is minimized. The proposed method possesses a feature that the scheduling problem is decomposed not into single job-level subproblems but into single machine-level subproblems. By decomposing the problem into one-machine multi-operation subproblems, the changeover cost and/or changeover time can easily be embedded in the objective function. In the proposed method, each subproblem for a single machine is solved by combining the simulated annealing method and the neighborhood search algorithm. In order to avoid oscillations in multiplier values, a new Lagrangian function is used to solve each subproblem. The effectiveness of the proposed method is verified by comparing the results of the example problems solved by the proposed method with those solved by the simulated annealing method in which a schedule of the entire machine is successively improved.