The Minimum Rank Problem: a counterexample

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We provide a counterexample to a recent conjecture that the minimum rank of every sign pattern matrix can be realized by a rational matrix. We use one of the equivalences of the conjecture and some results from projective geometry. As a consequence of the counterexample, we show that there is a graph for which the minimum rank over the reals is strictly smaller than the minimum rank over the rationals. We also make some comments on the minimum rank of sign pattern matrices over different subfields of $\mathbb R$.
4 pages, 1 figure

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Combinatorics, 15A09, 15A21, 15A48, 15A57

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http://salesiana.dossiersoluciones.com/handle/123456789/138062

Consulte el texto completo en el siguiente enlace:

https://arxiv.org/abs/0708.1707
 http://arxiv.org/abs/0708.1707

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arXiv