Abstract
This paper is concerned with the k-traveling salesman problem (k-TSP), which is a variation of widely studied traveling salesman problem (TSP). Given a set of n cities including a home city and a fixed value k such that \(1 < k \le n\), this problem seeks a tour of minimum length which starts and ends at the home city and visits k cities (including the home city) exactly out of these n cities. Finding a feasible solution to k-TSP involves finding a subset of k cities including the home city first, and then a circular permutation representing a tour of these k cities. In this paper, we have proposed two multi-start heuristic approaches for the k-TSP. The first approach is based on general variable neighborhood search algorithm (GVNS), whereas the latter approach is a hyper-heuristic (HH) approach. A variable neighborhood descent strategy operating over two neighborhood structures is utilized for doing the local search in the GVNS. As part of the hyper-heuristic, two low level heuristics are considered. To the best of our knowledge, these are the first metaheuristic and hyper-heuristic approaches for the k-TSP. To evaluate the performance of our approaches, a set of benchmark instances is created utilizing instances from TSPLIB. Computational results on these benchmark instances show HH approach to be better than GVNS approach.
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Acknowledgements
The authors would like to express their sincere gratitude to two anonymous reviewers and the editor for their valuable comments and suggestions which helped in improving the quality of this manuscript. The first author is grateful to the Council of Scientific and Industrial Research (CSIR), Government of India for supporting his research through a Senior Research Fellowship. The second author acknowledges the support of the research Grant No. MTR/2017/000391 received under MATRICS scheme from Science and Engineering Research Board (SERB), Government of India.
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Appendices
Appendix I
This appendix presents the results obtained by our approaches on each TSPLIB instance under each of the six groups. Therefore, there are six tables, each corresponding to a group. Tables 4, 5 and 6 correspond to groups (Small, SR), (Medium, SR) and (Large, SR) respectively. These three tables report the performance of GVNS, HH_RAND and HH_GREEDY under short run. On the other hand, tables 7, 8 and 9 correspond to groups (Small, LR), (Medium, LR) and (Large, LR) respectively, and report the performance of our approaches under long run. In all these tables, the first column lists the instance names. The numerical values at the end of an instance name specifies the number of cities in the corresponding instance. The second column (k) reports the number of cities (including the home city) that the salesman has to visit. The columns Best, Worst & Average under an approach reports the best, worst and average solution quality obtained over ten independent runs respectively by that approach. The best values are reported in bold font for ease of identification. Please note that we have also reported the worst solution obtained by various approaches over ten runs here. The knowledge about the worst solution obtained aids in ascertaining the robustness of an approach in comparison to other approaches. As can be seen from these tables, even the worst solution obtained by HH_RAND is better than the worst solution obtained by other two approaches in most of the cases.
Appendix II
This appendix presents the convergence behavior of our approaches. For studying the convergence behavior, three instances of different sizes, namely gr229, ali535 and p654, have been considered. Figures 3, 4 and 5 plot the convergence behavior of our three approaches, viz. GVNS, HH_RAND and HH_GREEDY respectively for the instances gr229, ali535 and p654 under small, medium and large scenarios. The convergence graphs depict that both HH_RAND and HH_GREEDY converges faster than the GVNS. When it comes to the comparison between HH_RAND and HH_GREEDY based on their convergence behavior, there is only a minute difference in their convergence behavior except for the large scenario of p654, where HH_RAND clearly converges faster than HH_GREEDY.
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Pandiri, V., Singh, A. Two multi-start heuristics for the k-traveling salesman problem. OPSEARCH 57, 1164–1204 (2020). https://doi.org/10.1007/s12597-020-00463-8
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DOI: https://doi.org/10.1007/s12597-020-00463-8