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The noncommutative Löwner theorem for matrix monotone functions over operator systems
Journal article   Open access   Peer reviewed

The noncommutative Löwner theorem for matrix monotone functions over operator systems

Linear algebra and its applications, v 541, pp 54-59
15 Mar 2018
url
https://doi.org/10.1016/j.laa.2017.12.002View
Published, Version of Record (VoR) Restricted

Abstract

Matrix inequalities Matrix monotone functions Noncommutative function theory
Given a function f:(a,b)→R, Löwner's theorem states f is monotone when extended to self-adjoint matrices via the functional calculus, if and only if f extends to a self-map of the complex upper half plane. In recent years, several generalizations of Löwner's theorem have been proven in several variables. We use the relaxed Agler, McCarthy, and Young theorem on locally matrix monotone functions in several commuting variables to generalize results in the noncommutative case. Specifically, we show that a real free function defined over an operator system must analytically continue to a noncommutative upper half plane as map into another noncommutative upper half plane.

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Mathematics
Mathematics, Applied
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