A Hybrid Searching Method for the Unrelated Parallel Machine Scheduling Problem

The work addresses the NP-hard problem of scheduling a set of jobs to unrelated parallel machines with the overall objective of minimizing makespan. The solution presented proposes a greedy constructive algorithm followed by an application of a Variable Neighborhood Decent strategy that continually improves the incumbent solution until a local optimum is reached. The strength of the approach lies in the adoption of different objectives at various stages of the search to avoid early local optimum entrapment and, mainly, in the hybridization of heuristic methods and mathematical programming for the definition and exploration of neighborhood structures. Experimental results on a large set of benchmark problems attest to the efficacy of the proposed approach.