The converse of the Cowling--Obrechkoff--Thron theorem
arXiv:2303.12852 · doi:10.2140/involve.2025.18.473
Abstract
In this work, the converse of the Cowling--Obrechkoff--Thron theorem is established. In addition to its theoretical interest, the result fills a gap in the proof of Kellogg's celebrated eigenvalue inequality for matrices whose principal minors are positive or nonnegative.