Abstract
Given a set \(\mathcal {A}\subseteq {\mathcal S}_n\) of m permutations of [n] and a distance function d, the median problem consists of finding a permutation \(\pi ^*\) that is the “closest” of the m given permutations. Here, we study the problem under the Kendall-\(\tau \) distance which counts the number of pairwise disagreements between permutations. This problem has been proved to be NP-hard when \(m \ge 4\), m even. In this article, we investigate new theoretical properties of \(\mathcal {A}\) that will solve the relative order between pairs of elements in median permutations of \(\mathcal {A}\), thus drastically reducing the search space of the problem.
supported by NSERC through an Individual Discovery Grant (Hamel) and by FRQNT through a Master’s scholarship (Milosz).
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Acknowledgements
Thanks to Bryan Brancotte, Sarah Cohen-Boulakia and Alain Denise (LRI - Paris Sud) for giving us useful advices and thoughts to guide the work. Thanks to Nicole Burke (Montreal) for a careful english revision of the article.
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Milosz, R., Hamel, S. (2016). Medians of Permutations: Building Constraints. In: Govindarajan, S., Maheshwari, A. (eds) Algorithms and Discrete Applied Mathematics. CALDAM 2016. Lecture Notes in Computer Science(), vol 9602. Springer, Cham. https://doi.org/10.1007/978-3-319-29221-2_23
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