A graph G is locally irregular if no two of its adjacent vertices have the same degree. The authors of [Fioravantes et al. Complexity of finding maximum locally irregular induced subgraph. SWAT, 2022] introduced and provided some initial algorithmic results on the problem of finding a locally irregular induced subgraph of a given graph G of maximum order, or, equivalently, computing a subset S of V(G) of minimum order, whose deletion from G results in a locally irregular graph; S is called an optimal vertex-irregulator of G. In this work we provide an in-depth analysis of the parameterised complexity of computing an optimal vertex-irregulator of a given graph G. Moreover, we introduce and study a variation of this problem, where S is a subset of the edges of G; in this case, S is denoted as an optimal edge-irregulator of G. We prove that computing an optimal vertex-irregulator of a graph G is in FPT when parameterised by various structural parameters of G, while it is W[1]-hard when parameterised by the feedback vertex set number or the treedepth of G. Moreover, computing an optimal edge-irregulator of a graph G is in FPT when parameterised by the vertex integrity of G, while it is NP-hard even if G is a planar bipartite graph of maximum degree 6, and W[1]-hard when parameterised by the size of the solution, the feedback vertex set or the treedepth of G. Our results paint a comprehensive picture of the tractability of both problems studied here.
@InProceedings{fioravantes_et_al:LIPIcs.IPEC.2024.18, author = {Fioravantes, Foivos and Melissinos, Nikolaos and Triommatis, Theofilos}, title = {{Parameterised Distance to Local Irregularity}}, booktitle = {19th International Symposium on Parameterized and Exact Computation (IPEC 2024)}, pages = {18:1--18:15}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-353-9}, ISSN = {1868-8969}, year = {2024}, volume = {321}, editor = {Bonnet, \'{E}douard and Rz\k{a}\.{z}ewski, Pawe{\l}}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2024.18}, URN = {urn:nbn:de:0030-drops-222440}, doi = {10.4230/LIPIcs.IPEC.2024.18}, annote = {Keywords: Locally irregular, largest induced subgraph, FPT, W-hardness} }
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