English

Barrett-Johnson inequalities for totally nonnegative matrices

Combinatorics 2022-10-04 v3

Abstract

Given a matrix AA, let AI,JA_{I,J} denote the submatrix of AA determined by rows II and columns JJ. Fischer's Inequalities state that for each n×nn \times n Hermitian positive semidefinite matrix AA, and each subset II of {1,,n}\{1,\dotsc,n\} and its complement IcI^c, we have det(A)det(AI,I)det(AIc,Ic)\det(A) \leq \det(A_{I,I})\det(A_{I^c,I^c}). Barrett and Johnson (Linear Multilinear Algebra 34, 1993) extended these to state inequalities for sums of products of principal minors whose orders are given by nonincreasing integer sequences (λ1,,λr)(\lambda_1,\dotsc,\lambda_r), (μ1,,μs)(\mu_1,\dotsc,\mu_s) summing to nn. Specifically, if λ1++λiμ1++μi\lambda_1+\cdots+\lambda_i\leq \mu_1+\cdots+\mu_i for all ii, then λ1!λr!(I1,,Ir)det(AI1,I1)det(AIr,Ir)  μ1!μs!(J1,,Js)det(AJ1,J1)det(AJs,Js), \lambda_1!\cdots\lambda_r! \sum_{(I_1,\dotsc,I_r)} \det(A_{I_1,I_1}) \cdots \det(A_{I_r,I_r}) ~\geq~ \mu_1!\cdots\mu_s! \sum_{(J_1,\dotsc,J_s)} \det(A_{J_1,J_1}) \cdots \det(A_{J_s,J_s}), where sums are over sequences of disjoint subsets of {1,,n}\{1,\dotsc,n\} satisfying Ik=λk|I_k| = \lambda_k, Jk=μk|J_k| = \mu_k. We show that these inequalities hold for totally nonnegative matrices as well.

Keywords

Cite

@article{arxiv.2209.06466,
  title  = {Barrett-Johnson inequalities for totally nonnegative matrices},
  author = {Mark Skandera and Daniel Soskin},
  journal= {arXiv preprint arXiv:2209.06466},
  year   = {2022}
}
R2 v1 2026-06-28T01:15:56.657Z