A parallel-machine scheduling with periodic constraints under uncertainty

Most studies on scheduling problem have assumed that the machine is continuously available. However, the machine is likely to be unavailable for many practical reasons (e.g. breakdown and planned preventive maintenance). Once a machine is not available, the optimal scheme in the deterministic scenario may not be the optimal choice. To address the actual scenario, a scheduling problem with two identical parallel machines, one of which requires periodic maintenance, is considered in this article. For uncertainties in reality, the processing and maintenance time are considered as uncertain variables. A novel method to study the worst-case ratio in an uncertain scenario is proposed. It is shown that the worst-case ratio of the longest processing time algorithm is 3/2 at a high confidence level. Given theoretical analysis results, an modified algorithm is proposed. Finally, numerical experiments are used to verify the feasibility of the modified algorithm.