flexible flowshop scheduling with equal number of unrelated parallel machines

this article addresses a multi-stage flowshop scheduling problem with equal number of unrelated parallel machines. the objective is to minimize the makespan for a given set of jobs in the system. this problem class is np-hard in the strong sense, so a hybrid heuristic method for sequencing and then allocating operations of jobs to machines is developed. a number of test problems are randomly generated and results obtained by proposed heuristic are compared with optimal solutions reported by the lingo 8.0 package applying the branch & bound approach. the results show that the proposed hybrid method is more efficient when the problem sizes have been increased.