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arXiv · 1905.08009

Operator norm and numerical radius analogues of Cohen's inequality

Roman Drnovšek
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Abstract

Let $D$ be an invertible multiplication operator on $L^2(X, \mu)$, and let $A$ be a bounded operator on $L^2(X, \mu)$. In this note we prove that $\|A\|^2 \le \|D A\| \, \|D^{-1} A\|$, where $\|\cdot\|$ denotes the operator norm. If, in addition, the operators $A$ and $D$ are positive, we also have $w(A)^2 \le w(D A) \, w(D^{-1} A)$, where $w$ denotes the numerical radius.

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Roman Drnovšek. 2019-05-20. Operator norm and numerical radius analogues of Cohen's inequality. https://arxiv.org/abs/1905.08009

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