Despite a lot of recent progress in obtaining faster sequential matroid intersection algorithms, the fastest parallel poly(n)-query algorithm was still the straightforward O(n)-round parallel implementation of Edmonds' augmenting paths algorithm from the 1960s. Very recently, Chakrabarty-Chen-Khanna [FOCS'21] showed the lower bound that any, possibly randomized, parallel matroid intersection algorithm making poly(n) rank-queries requires Ω̃(n^{1/3}) rounds of adaptivity. They ask, as an open question, if the lower bound can be improved to Ω̃(n), or if there can be sublinear-round, poly(n)-query algorithms for matroid intersection. We resolve this open problem by presenting the first sublinear-round parallel matroid intersection algorithms. Perhaps surprisingly, we do not only break the Õ(n)-barrier in the rank-oracle model, but also in the weaker independence-oracle model. Our rank-query algorithm guarantees O(n^{3/4}) rounds of adaptivity, while the independence-query algorithm uses O(n^{7/8}) rounds of adaptivity, both making a total of poly(n) queries.
@InProceedings{blikstad:LIPIcs.ICALP.2022.25, author = {Blikstad, Joakim}, title = {{Sublinear-Round Parallel Matroid Intersection}}, booktitle = {49th International Colloquium on Automata, Languages, and Programming (ICALP 2022)}, pages = {25:1--25:17}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-235-8}, ISSN = {1868-8969}, year = {2022}, volume = {229}, editor = {Boja\'{n}czyk, Miko{\l}aj and Merelli, Emanuela and Woodruff, David P.}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2022.25}, URN = {urn:nbn:de:0030-drops-163662}, doi = {10.4230/LIPIcs.ICALP.2022.25}, annote = {Keywords: Matroid Intersection, Combinatorial Optimization, Parallel Algorithms} }
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