Completely positive matrices of order 5 with \widehat{CP}-graph


We characterize completely positive matrices of order five whose associated graph is a \widehat{CP}-graph not completely positive, unifying and improving results obtained by Xu. We show by counterexamples that two characterizations obtained by Xu are incorrect

Keywords: doubly non-negative matrices; completely positive matrices; $\widehat{CP}$-graphs

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