A tabu search algorithm based on new block properties and speed-up method for permutation flow-shop with finite intermediate storage

This paper deals with a permutation flow-shop scheduling problem with finite intermediate storage (PFSFIS) between successive machines so as to minimize makespan. In such a problem the intermediate storage capacity constraints are considered besides the machine-related constraints usually discussed in the general permutation flow-shop. This feature adds extra difficulties to the scheduling problem. In this paper, we present some new block properties and a speed-up method using a forward-backward hybrid algorithm to compute makespan. Applied in a tabu search algorithm, the new block properties greatly reduce the neighborhood size and thus shorten the search time. Also, the speed-up method eliminates redundant computation for the objective function and reduces a majority of the running time. Computational experiments (up to 200 jobs and 20 machines) are given to demonstrate the effectiveness of new block neighborhood characteristics and the speed-up method. Compared with the results yielded by the best-known algorithm, the objective function is improved by 0.14% if the new block neighborhood characteristics are used; furthermore, the running time is reduced by 53.7% on the average if the speed-up method is used. Under the condition that both of the algorithms have the same running time the objective function is improved by 0.24% if both of the two above improvement methods are applied in the original tabu search.