Hybrid Flow Shop with Limited Transportation Scheduling Problem: A Comparison Between Genetics Algorithm, and a Novel Recursive Local Search Heuristic

In this paper, concurrent scheduling of jobs and transportation in a hybrid flow shop system is studied, where multiple jobs, transporters, and stages with parallel unrelated machines are considered. In addition to the mentioned technical features, jobs are able to omit one or more stages, and may not be executable by all the machines, and similarly, transportable by all the transporters. Unlike most studies in the literature, the transport resource is finite and needs to be simultaneously scheduled with the jobs. Initially, a new mixed integer linear programming (MILP) model is proposed to minimize the makespan. Then, a novel Recursive Local Search Heuristic (RLSH) is proposed to tackle the large-sized instances, which otherwise could not be solved via MILP solver (Gurobi) in reasonable time. RLSH is also compared against Genetics Algorithm (GA) on a set of numerical examples generated from the uniform distribution. As the computational results demonstrate, it is concluded that RLSH is extremely efficacious dealing with the problem and outperforms GA in the objective value quality. Finally, using two well-known statistical tests: Wald and analysis of variance(ANOVA), we assess the performance of the suggested approaches.

Learning 2-Opt Heuristics for Routing Problems via Deep Reinforcement Learning

Recent works using deep learning to solve routing problems such as the traveling salesman problem (TSP) have focused on learning construction heuristics. Such approaches find good quality solutions but require additional procedures such as beam search and sampling to improve solutions and achieve state-of-the-art performance. However, few studies have focused on improvement heuristics, where a given solution is improved until reaching a near-optimal one. In this work, we propose to learn a local search heuristic based on 2-opt operators via deep reinforcement learning. We propose a policy gradient algorithm to learn a stochastic policy that selects 2-opt operations given a current solution. Moreover, we introduce a policy neural network that leverages a pointing attention mechanism, which can be easily extended to more general k-opt moves. Our results show that the learned policies can improve even over random initial solutions and approach near-optimal solutions faster than previous state-of-the-art deep learning methods for the TSP. We also show we can adapt the proposed method to two extensions of the TSP: the multiple TSP and the Vehicle Routing Problem, achieving results on par with classical heuristics and learned methods.

Hybrid evolutionary computation methods for quay crane scheduling problems

Quay crane scheduling is one of the most important operations in seaport terminals. The effectiveness of this operation can directly influence the overall performance as well as the competitive advantages of the terminal. This paper develops a new priority-based schedule construction procedure to generate quay crane schedules. From this procedure, two new hybrid evolutionary computation methods based on genetic algorithm (GA) and genetic programming (GP) are developed. The key difference between the two methods is their representations which decide how priorities of tasks are determined. While GA employs a permutation representation to decide the priorities of tasks, GP represents its individuals as a priority function which is used to calculate the priorities of tasks. A local search heuristic is also proposed to improve the quality of solutions obtained by GA and GP. The proposed hybrid evolutionary computation methods are tested on a large set of benchmark instances and the computational results show that they are competitive and efficient as compared to the existing methods. Many new best known solutions for the benchmark instances are discovered by using these methods. In addition, the proposed methods also show their flexibility when applied to generate robust solutions for quay crane scheduling problems under uncertainty. The results show that the obtained robust solutions are better than those obtained from the deterministic inputs. © 2013 Elsevier Ltd.

Hybrid evolutionary computation methods for quay crane scheduling problems

Quay crane scheduling is one of the most important operations in seaport terminals. The effectiveness of this operation can directly influence the overall performance as well as the competitive advantages of the terminal. This paper develops a new priority-based schedule construction procedure to generate quay crane schedules. From this procedure, two new hybrid evolutionary computation methods based on genetic algorithm (GA) and genetic programming (GP) are developed. The key difference between the two methods is their representations which decide how priorities of tasks are determined. While GA employs a permutation representation to decide the priorities of tasks, GP represents its individuals as a priority function which is used to calculate the priorities of tasks. A local search heuristic is also proposed to improve the quality of solutions obtained by GA and GP. The proposed hybrid evolutionary computation methods are tested on a large set of benchmark instances and the computational results show that they are competitive and efficient as compared to the existing methods. Many new best known solutions for the benchmark instances are discovered by using these methods. In addition, the proposed methods also show their flexibility when applied to generate robust solutions for quay crane scheduling problems under uncertainty. The results show that the obtained robust solutions are better than those obtained from the deterministic inputs. © 2013 Elsevier Ltd.