We study the NP-hard Stable Hypergraph Matching (SHM) problem and its generalization allowing capacities, the Stable Hypergraph b-Matching (SHbM) problem, and investigate their computational properties under various structural constraints. Our study is motivated by the fact that Scarf’s Lemma [Scarf, 1967] together with a result of Lovász [Lovász, 1972] guarantees the existence of a stable matching whenever the underlying hypergraph is normal. Furthermore, if the hypergraph is unimodular (i.e., its incidence matrix is totally unimodular), then even a stable b-matching is guaranteed to exist. However, no polynomial-time algorithm is known for finding a stable matching or b-matching in unimodular hypergraphs. We identify subclasses of unimodular hypergraphs where SHM and SHbM are tractable such as laminar hypergraphs or so-called subpath hypergraphs with bounded-size hyperedges; for the latter case, even a maximum-weight stable b-matching can be found efficiently. We complement our algorithms by showing that optimizing over stable matchings is NP-hard even in laminar hypergraphs. As a practically important special case of SHbM for unimodular hypergraphs, we investigate a tripartite stable matching problem with students, schools, and companies as agents, called the University Dual Admission problem, which models real-world scenarios in higher education admissions. Finally, we examine a superclass of subpath hypergraphs that are normal but not necessarily unimodular, namely subtree hypergraphs where hyperedges correspond to subtrees of a tree. We establish that for such hypergraphs, stable matchings can be found in polynomial time but, in the setting with capacities, finding a stable b-matching is NP-hard.
@InProceedings{biro_et_al:LIPIcs.ICALP.2025.31, author = {Bir\'{o}, P\'{e}ter and Cs\'{a}ji, Gergely and Schlotter, Ildik\'{o}}, title = {{Stable Hypergraph Matching in Unimodular Hypergraphs}}, booktitle = {52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025)}, pages = {31:1--31:20}, 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.2025.31}, URN = {urn:nbn:de:0030-drops-234086}, doi = {10.4230/LIPIcs.ICALP.2025.31}, annote = {Keywords: stable hypergraph matching, Scarf’s Lemma, unimodular hypergraphs, university dual admission} }
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