,
Roland Guttenberg
,
Nathan Lhote
,
Mahsa Shirmohammadi
,
James Ben Worrell
Creative Commons Attribution 4.0 International license
This paper concerns decision problems related to finite monoids of rational matrices. We show that determining finiteness of a given finitely presented monoid is in PSpace, improving the known coNExp^NP bound. We also show that the membership problem for finite matrix monoids is PSpace-complete, improving the known NExp-upper bound. Our two complexity results are corollaries of a new polynomial bit-size bound on matrix entries in finite monoids. This is obtained by reduction to the case of matrix groups, using the structure theory of noncommutative algebras and of matrix monoids. Our techniques also give us a polynomial-time algorithm for deciding whether a monoid of rational matrices is conjugate to a monoid of integer matrices.
@InProceedings{aitelmanssour_et_al:LIPIcs.ICALP.2026.158,
author = {Ait El Manssour, Rida and Guttenberg, Roland and Lhote, Nathan and Shirmohammadi, Mahsa and Worrell, James Ben},
title = {{Revisiting Finiteness of Matrix Monoids}},
booktitle = {53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)},
pages = {158:1--158:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-428-4},
ISSN = {1868-8969},
year = {2026},
volume = {374},
editor = {Bhattacharya, Sayan and Nanongkai, Danupon and Benedikt, Michael 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.2026.158},
URN = {urn:nbn:de:0030-drops-265745},
doi = {10.4230/LIPIcs.ICALP.2026.158},
annote = {Keywords: Matrix Semigroups, Finiteness, Integrality, Bitsize Bound}
}