Given a graph G and two spanning trees T and T' in G, normalSpanning Tree Reconfiguration asks whether there is a step-by-step transformation from T to T' such that all intermediates are also spanning trees of G, by exchanging an edge in T with an edge outside T at a single step. This problem is naturally related to matroid theory, which shows that there always exists such a transformation for any pair of T and T'. Motivated by this example, we study the problem of transforming a sequence of spanning trees into another sequence of spanning trees. We formulate this problem in the language of matroid theory: Given two sequences of bases of matroids, the goal is to decide whether there is a transformation between these sequences. We design a polynomial-time algorithm for this problem, even if the matroids are given as basis oracles. To complement this algorithmic result, we show that the problem of finding a shortest transformation is NP-hard to approximate within a factor of c log n for some constant c > 0, where n is the total size of the ground sets of the input matroids.
@InProceedings{hanaka_et_al:LIPIcs.ISAAC.2024.38, author = {Hanaka, Tesshu and Iwamasa, Yuni and Kobayashi, Yasuaki and Okada, Yuto and Saito, Rin}, title = {{Basis Sequence Reconfiguration in the Union of Matroids}}, booktitle = {35th International Symposium on Algorithms and Computation (ISAAC 2024)}, pages = {38:1--38:16}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-354-6}, ISSN = {1868-8969}, year = {2024}, volume = {322}, editor = {Mestre, Juli\'{a}n and Wirth, Anthony}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2024.38}, URN = {urn:nbn:de:0030-drops-221658}, doi = {10.4230/LIPIcs.ISAAC.2024.38}, annote = {Keywords: Combinatorial reconfiguration, Matroids, Polynomial-time algorithm, Inapproximability} }
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