English

Powers of matrices with all principal minors equal to 1

Commutative Algebra 2026-06-27 v1 Combinatorics

Abstract

Consider a square matrix AA whose all principal minors are equal to 11. Over a field, this property is inherited by any power of AA, but this is not the case over an arbitrary commutative ring. We show that it is the case over any regular ring, and also over the ring Z/d\mathbb{Z} / d for any integer dd, and in some other settings (quotients of Pr\"ufer domains and principal quotients of normal domains). This generalizes Problem B5 of the 2021 Putnam contest. Over arbitrary commutative rings, we identify a stronger property that is always inherited by powers: We say that a matrix A=(ai,j)i,j[n]A = \left(a_{i,j}\right)_{i,j\in\left[n\right]} is strongly 11-principled if all its diagonal entries are 11 and if all the cyclic products ai1,i2ai2,i3aik,i1a_{i_1, i_2} a_{i_2, i_3} \cdots a_{i_k, i_1} with k>1k>1 vanish. We show that the latter products are always integral over the ideal generated by the principal minors of AA minus 11.

Keywords

Cite

@article{arxiv.2606.28976,
  title  = {Powers of matrices with all principal minors equal to 1},
  author = {Darij Grinberg},
  journal= {arXiv preprint arXiv:2606.28976},
  year   = {2026}
}

Comments

15 pages. Most ideas and most writing by GPT-5.5; fully proofread and edited by myself. Follow-up to arXiv:2204.07885 (which will be updated in a few days to include back-reference). Comments are welcome!