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Non-negative decomposition of a non-negative matrix

This seems to be the well-known (and difficult) task of computing the nonnegative rank of a matrix. It seems that the true complexity of computing the nn-rank is unknown, while verifying whether nn-r …
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40 votes
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Wanted: Positivity certificate for the AM-GM inequality in low dimension

The following paper: Fujiwara, Kazumasa, and Tohru Ozawa. Identities for the Difference between the Arithmetic and Geometric Means, (2014). proves the following representation for odd $n$: \be …
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6 votes
Accepted

On a trace condition for positive definite $2\times 2$ block matrices

For any unitarily invariant norm it can be shown that \begin{equation*} \|X\| = \left\Vert \begin{bmatrix} A & C\\ C^* & B \end{bmatrix} \right\Vert \le \|A\| + \|B\|. \end{eq …
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