Given a non-negative real matrix M of non-negative rank at least r, can we witness this fact by a small submatrix of M? While Moitra (SIAM J. Comput. 2013) proved that this cannot be achieved exactly, we show that such a witnessing is possible approximately: an m×n matrix of non-negative rank r always contains a submatrix with at most r³ rows and columns with non-negative rank at least Ω(r/(log n log m)). A similar result is proved for the 1-partition number of a Boolean matrix and, consequently, also for its two-player deterministic communication complexity. Tightness of the latter estimate is closely related to the log-rank conjecture of Lovász and Saks.
@InProceedings{hrubes:LIPIcs.CCC.2024.13, author = {Hrube\v{s}, Pavel}, title = {{Hard Submatrices for Non-Negative Rank and Communication Complexity}}, booktitle = {39th Computational Complexity Conference (CCC 2024)}, pages = {13:1--13:12}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-331-7}, ISSN = {1868-8969}, year = {2024}, volume = {300}, editor = {Santhanam, Rahul}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CCC.2024.13}, URN = {urn:nbn:de:0030-drops-204097}, doi = {10.4230/LIPIcs.CCC.2024.13}, annote = {Keywords: Non-negative rank, communication complexity, extension complexity} }
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