# Concavity of certain maps on positive definite matrices and applications to Hadamard products

```@article{And1979ConcavityOC,
title={Concavity of certain maps on positive definite matrices and applications to Hadamard products},
author={T. And{\^o}},
journal={Linear Algebra and its Applications},
year={1979},
volume={26},
pages={203-241}
}```
• T. Andô
• Published 1979
• Mathematics
• Linear Algebra and its Applications
Abstract If f is a positive function on (0, ∞) which is monotone of order n for every n in the sense of Lowner and if Φ1 and Φ2 are concave maps among positive definite matrices, then the following map involving tensor products: (A,B)↦f[Φ 1 (A) −1 ⊗Φ 2 (B)]·(Φ 1 (A)⊗I) is proved to be concave. If Φ1 is affine, it is proved without use of positivity that the map (A,B)↦f[Φ 1 (A)⊗Φ 2 (B) −1 ]·(Φ 1 (A)⊗I) is convex. These yield the concavity of the map (A,B)↦A 1−p ⊗B p (0 (A,B)↦A 1+p ⊗B −p (0 (A,B… Expand
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