Complex and real counterexamples to an inequality arising from Drury's conjecture

We give counterexamples to the following inequality, stated by Zhang as a consequence of Drury's 2016 permanent conjecture: if A = (ajk)j,k=1n is a Hermitian positive semidefinite matrix of order n ≥ 2, then ∑j=1n−1 |ajn|2 per A[ĵ, n̂] ≤ per A, where A[ĵ, n̂] is the principal submatrix obtained by deleting indices j and n. Our complex example has order twelve and rank two; our real example has order twenty-one and rank three.

Authors

Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-10-19
DOI
https://doi.org/10.5281/zenodo.23460084
Primary Topic
Matrix Theory and Algorithms
Type
preprint
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preprint

Complex and real counterexamples to an inequality arising from Drury's conjecture

Yair Lavi
Zenodo (CERN European Organization for Nuclear Research)
Matrix Theory and Algorithms
preprint

Complex and real counterexamples to an inequality arising from Drury's conjecture

Yair Lavi
preprint en

Abstract

We give counterexamples to the following inequality, stated by Zhang as a consequence of Drury's 2016 permanent conjecture: if A = (ajk)j,k=1n is a Hermitian positive semidefinite matrix of order n ≥ 2, then ∑j=1n−1 |ajn|2 per A[ĵ, n̂] ≤ per A, where A[ĵ, n̂] is the principal submatrix obtained by deleting indices j and n. Our complex example has order twelve and rank two; our real example has order twenty-one and rank three.

Zenodo (CERN European Organization for Nuclear Research)
Matrix Theory and Algorithms
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Complex and real counterexamples to an inequality arising from Drury's conjecture — Yair Lavi · Zenodo (CERN European Organization for Nuclear Research) (2026) | TGRS Research Map | TGRS