A new neighborhood structure for job shop scheduling problems

TL;DR

This paper introduces a new neighborhood structure, N8, for job shop scheduling that considers moving critical operations both within and outside critical blocks, improving solution quality and efficiency.

Contribution

The paper proposes the N8 neighborhood structure, expanding beyond existing structures by including outside critical block movements, and demonstrates its superior performance in JSP solutions.

Findings

N8 outperforms N5, N6, and N7 in benchmark tests.

N8 reduces computational time through a neighborhood clipping method.

N8 achieves better makespan improvements on standard benchmarks.

Abstract

Job shop scheduling problem (JSP) is a widely studied NP-complete combinatorial optimization problem. Neighborhood structures play a critical role in solving JSP. At present, there are three state-of-the-art neighborhood structures, i.e., N5, N6, and N7. Improving the upper bounds of some famous benchmarks is inseparable from the role of these neighborhood structures. However, these existing neighborhood structures only consider the movement of critical operations within a critical block. According to our experiments, it is also possible to improve the makespan of a scheduling scheme by moving a critical operation outside its critical block. According to the above finding, this paper proposes a new N8 neighborhood structure considering the movement of critical operations within a critical block and the movement of critical operations outside the critical block. Besides, a neighborhood clipping method is designed to avoid invalid movement, reducing the computational time. Tabu search (TS) is a commonly used algorithm framework combined with neighborhood structures. This paper uses this framework to compare the N8 neighborhood structure with N5, N6, and N7 neighborhood structures on four famous benchmarks. The experimental results verify that the N8 neighborhood structure is more effective and efficient in solving JSP than the other state-of-the-art neighborhood structures.