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JOURNALS // Zapiski Nauchnykh Seminarov POMI // Archive

Zap. Nauchn. Sem. POMI, 2012 Volume 401, Pages 5–52 (Mi znsl5224)

This article is cited in 6 papers

Operator Lipschitz functions and linear fractional transformations

A. B. Aleksandrov

St. Petersburg Department of V. A. Steklov Institute of Mathematics, Russian Academy of Sciences, St. Petersburg, Russia

Abstract: It is known that the function $t^2\sin\frac1t$ is an operator Lipschitz function on the real line $\mathbb R$. We prove that the function $\sin$ can be replaced by any operator Lipschitz function $f$ with $f(0)=0$. In other words, for every operator Lipschitz function $f$ the function $t^2 f(\frac1t)$ is also operator Lipschitz if $f(0)=0$. The function $f$ can be defined on an arbitrary closed subset of the complex plane $\mathbb C$. Moreover, the linear fractional transformation $\frac1t$ can be replaced by every linear fractional transformation $\varphi$. In this case, we assert that the function $\dfrac{f\circ\varphi}{\varphi'}$ is operator Lipschitz for every operator Lipschitz function $f$ provided $f(\varphi(\infty))=0$.

Key words and phrases: operator Lipschitz functions.

UDC: 517.5+517.98      

Received: 23.04.2012


 English version:
Journal of Mathematical Sciences (New York), 2013, 194:6, 603–627

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