We study the problem of estimating the size of a maximum matching in sublinear time. The problem has been studied extensively in the literature and various algorithms and lower bounds are known for it. Our result is a 0.5109-approximation algorithm with a running time of Õ(n√n). All previous algorithms either provide only a marginal improvement (e.g., 2^{-280}) over the 0.5-approximation that arises from estimating a maximal matching, or have a running time that is nearly n². Our approach is also arguably much simpler than other algorithms beating 0.5-approximation.
@InProceedings{mahabadi_et_al:LIPIcs.ICALP.2025.116, author = {Mahabadi, Sepideh and Roghani, Mohammad and Tarnawski, Jakub}, title = {{A 0.51-Approximation of Maximum Matching in Sublinear n^\{1.5\} Time}}, booktitle = {52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025)}, pages = {116:1--116:17}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-372-0}, ISSN = {1868-8969}, year = {2025}, volume = {334}, editor = {Censor-Hillel, Keren and Grandoni, Fabrizio and Ouaknine, Jo\"{e}l and Puppis, Gabriele}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2025.116}, URN = {urn:nbn:de:0030-drops-234932}, doi = {10.4230/LIPIcs.ICALP.2025.116}, annote = {Keywords: Sublinear Algorithms, Maximum Matching, Maximal Matching, Approximation Algorithm} }
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