• Journal of the Chungcheong Mathematical Society
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• v.23 no.4
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• pp.609-616
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• 2010

We characterize extreme rays of the cone $\mathbb{T}$ of all positive semi-definite block matrices whose partial transposes are also positive semi-definite. We also construct an algorithm checking whether a given PPTES generates an extreme ray in the cone $\mathbb{T}$ or not. Using this algorithm, we give an example of $4{\otimes}4$ PPT entangle state of the type (5, 5), which generates extreme ray of the cone $\mathbb{T}$.