An Ant-Colony Algorithm to Transform Jobshops into Flowshops: A Case of Shortest-Common-Supersequence Stringology Problem

In this work we address the problem of transforming a jobshop layout into a flowshop layout with the objective of minimizing the length of the resulting flowline. This problem is a special case of the well-known classical Shortest Common Supersequence (SCS) stringology problem. In view of the problem being NP-hard, an ant-colony algorithm, called PACO-SFR, is proposed. A new scheme of forming an initial supersequence of machines (i.e., flowline) is derived from a permutation of jobs, followed by the reduction in the length of the flowline by using a concatenation of forward reduction and inverse reduction techniques, machine elimination technique and finally an adjacent pair-wise interchange of machines in the flowline. The proposed antcolony algorithm’s performance is relatively evaluated against the best known results from the existing methods by considering many benchmark jobshop scheduling problem instances.