Emergency local searching approach for job shop scheduling

Existing methods of local search mostly focus on how to reach optimal solution. However, in some emergency situations, search time is the hard constraint for job shop scheduling problem while optimal solution is not necessary. In this situation, the existing method of local search is not fast enough. This paper presents an emergency local search(ELS) approach which can reach feasible and nearly optimal solution in limited search time. The ELS approach is desirable for the aforementioned emergency situations where search time is limited and a nearly optimal solution is sufficient, which consists of three phases. Firstly, in order to reach a feasible and nearly optimal solution, infeasible solutions are repaired and a repair technique named group repair is proposed. Secondly, in order to save time, the amount of local search moves need to be reduced and this is achieved by a quickly search method named critical path search(CPS). Finally, CPS sometimes stops at a solution far from the optimal one. In order to jump out the search dilemma of CPS, a jump technique based on critical part is used to improve CPS. Furthermore, the schedule system based on ELS has been developed and experiments based on this system completed on the computer of Intel Pentium(R) 2.93 GHz. The experimental result shows that the optimal solutions of small scale instances are reached in 2 s, and the nearly optimal solutions of large scale instances are reached in 4 s. The proposed ELS approach can stably reach nearly optimal solutions with manageable search time, and can be applied on some emergency situations.