Constructive heuristics comparison in hybrid flow shop scheduling environments with missing operations

In this paper, we address the hybrid flowshop scheduling problem with makespan minimisation as objective. This is a well-known problem with many practical applications that it has been tackled in the past. More specifically, we are interested in the special case where there are missing operations, i.e. not all jobs have to be processed in all stages, a condition inspired in a realistic problem in a plastic manufacturer. The main contribution of our paper is twofold. On the one hand we carry out a computational analysis to show that the hardness of the problem with missing operations is for most cases higher than that of the classical hybrid flowshop and flowshop scheduling problems. On the other hand, we propose a set of constructive heuristics that captures the special properties of the missing operations and compare these algorithms with already existing heuristics for the hybrid flowshop and for the flowshop. Computational results show that it is possible to reduce the makespan by interacting with the jobs containing missing operations, thus taking advantage of the special behaviour of missing operations for this kind of problems.