,
Andrew Ryzhikov
Creative Commons Attribution 4.0 International license
A zero-one matrix is a matrix with entries from {0, 1}. We study monoids containing only such matrices. A finite set of zero-one matrices generating such a monoid can be seen as the matrix representation of an unambiguous finite automaton, an important generalisation of deterministic finite automata which shares many of their good properties.
Let 𝒜 be a finite set of n×n zero-one matrices generating a monoid of zero-one matrices, and m be the cardinality of 𝒜. We study the computational complexity of computing the minimum rank of a matrix in the monoid generated by 𝒜. By using linear-algebraic techniques, we show that this problem is in NC and can be solved in 𝒪(mn⁴) time. We also provide a combinatorial algorithm finding a matrix of minimum rank in 𝒪(n^{2 + ω} + mn⁴) time, where 2 ≤ ω ≤ 2.4 is the matrix multiplication exponent. As a byproduct, we show a very weak version of a generalisation of the Černý conjecture: there always exists a straight line program of size 𝒪(n²) describing a product resulting in a matrix of minimum rank.
For the special case corresponding to complete DFAs (that is, for the case where all matrices have exactly one 1 in each row), the minimum rank is the size of the smallest image of the set of states under the action of a word. Our combinatorial algorithm finds a matrix of minimum rank in time 𝒪(n³ + mn²) in this case.
@InProceedings{kiefer_et_al:LIPIcs.STACS.2025.61,
author = {Kiefer, Stefan and Ryzhikov, Andrew},
title = {{Efficiently Computing the Minimum Rank of a Matrix in a Monoid of Zero-One Matrices}},
booktitle = {42nd International Symposium on Theoretical Aspects of Computer Science (STACS 2025)},
pages = {61:1--61:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-365-2},
ISSN = {1868-8969},
year = {2025},
volume = {327},
editor = {Beyersdorff, Olaf and Pilipczuk, Micha{\l} and Pimentel, Elaine and Thắng, Nguy\~{ê}n Kim},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2025.61},
URN = {urn:nbn:de:0030-drops-228867},
doi = {10.4230/LIPIcs.STACS.2025.61},
annote = {Keywords: matrix monoids, minimum rank, unambiguous automata}
}