Diekert, V, Potapov, I and Semukhin, P (2020) Decidability of membership problems for flat rational subsets of GL(2, Q) and singular matrices. In: ISSAC '20: International Symposium on Symbolic and Algebraic Computation, Kalamata, Greece, July 20-23, 2020 . pp. 122-129. (45th International Symposium on Symbolic and Algebraic Computation, 20 July 2020 - 23 July 2020, Kalamata Greece).

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Abstract

This work relates numerical problems on matrices over the rationals to symbolic algorithms on words and finite automata. Using exact algebraic algorithms and symbolic computation, we prove new decidability results for 2 × 2 matrices over Q. Namely, we introduce a notion of flat rational sets: if M is a monoid and N ≤ M is its submonoid, then flat rational sets of M relative to N are finite unions of the form L0g1 L1 ··· gtLt where all Lis are rational subsets of N and gi ∈ M. We give quite general sufficient conditions under which flat rational sets form an effective relative Boolean algebra. As a corollary, we obtain that the emptiness problem for Boolean combinations of flat rational subsets of GL(2, Q) over GL(2, Z) is decidable. We also show a dichotomy for nontrivial group extension of GL(2, Z) in GL(2, Q): if G is a f.g. group such that GL(2, Z) < G ≤ GL(2, Q), then either G ≅ GL(2, Z) × Zk, for some k ≥ 1, or G contains an extension of the Baumslag-Solitar group BS(1, q), with q ≥ 2, of infinite index. It turns out that in the first case the membership problem for G is decidable but the equality problem for rational subsets of G is undecidable. In the second case, decidability of the membership problem is open for every such G. In the last section we prove new decidability results for flat rational sets that contain singular matrices. In particular, we show that the membership problem is decidable for flat rational subsets of M(2, Q) relative to the submonoid that is generated by the matrices from M(2, Z) with determinants 0, ± 1 and the central rational matrices.

Item Type:	Conference or Workshop Item (Paper)
Uncontrolled Keywords:	membership problem; rational sets; general linear group
Subjects:	Q Science > QA Mathematics > QA75 Electronic computers. Computer science
Divisions:	Computer Science and Mathematics
Publisher:	ACM
Date Deposited:	25 Feb 2022 11:44
Last Modified:	13 Apr 2022 15:18
DOI or ID number:	10.1145/3373207.3404038
URI:	https://researchonline.ljmu.ac.uk/id/eprint/16417

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