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A note on "5 x 5 Completely positive matrices"
Journal article   Open access   Peer reviewed

A note on "5 x 5 Completely positive matrices"

Hongbo Dong and Kurt Anstreicher
Linear algebra and its applications, Vol.433(5), pp.1001-1004
10/15/2010
DOI: 10.1016/j.laa.2010.04.031
url
https://doi.org/10.1016/j.laa.2010.04.031View
Published (Version of record) Open Access

Abstract

In their paper "5 x 5 Completely positive matrices", Berman and Xu (2004) [3] attempt to characterize which 5 x 5 doubly nonnegative matrices are also completely positive. Most of the analysis in [3] concerns a doubly nonnegative matrix A that has at least one off-diagonal zero component. To handle the case where A is componentwise strictly positive, Berman and Xu utilize an "edge-deletion" transformation of A that results in a matrix (A) over tilde having an off-diagonal zero. Berman and Xu claim that A is completely positive if and only if there is such an edge-deleted matrix (A) over tilde that is also completely positive. We show that this claim is false. We also show that two conjectures made in [3] regarding 5 x 5 completely positive matrices are both false. (C) 2010 Elsevier Inc. All rights reserved.
Mathematics Mathematics, Applied Physical Sciences Science & Technology

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