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On the cone of positive semidefinite matrices. (English) Zbl 0615.15008
An as yet unsolved problem in matrix theory is to classify those linear transformations of the $n\times n$ complex matrices which leave the cone, PSD, of positive semidefinite Hermitian matrices invariant. The present note surveys the known results on the structure of the cone PSD, and some of the results concerning linear transformations which map PSD into itself. Certain useful isometric isomorphisms are given in detail.
Reviewer: G.P.Barker

##### MSC:
 15B57 Hermitian, skew-Hermitian, and related matrices 15A04 Linear transformations, semilinear transformations (linear algebra) 15B48 Positive matrices and their generalizations; cones of matrices
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##### References:
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