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Inequalities for the norm and numerical radius for Hilbert $C^{*}$-module operators
Mohsen Shah Hosseinia, Baharak Moosavib a Department of Mathematics, Shahr-e-Qods Branch, Islamic Azad University,
Tehran, Iran
b Department of Mathematics, Safadasht Branch, Islamic Azad University,
Tehran, Iran
Abstract:
In this paper, we introduce some inequalities between the operator norm and the numerical radius of adjointable operators on Hilbert $C^{*}$-module spaces. Moreover, we establish some new refinements of numerical radius inequalities for Hilbert space operators. More precisely, we prove that if $T \in B(H)$ and $$ \min \Big( \frac{\Vert T+ T^* \Vert^ 2 }{2}, \frac{\Vert T- T^* \Vert^ 2 }{2}\Big) \leq \max \Big(\inf_{ \Vert x \Vert=1}{\Vert Tx \Vert^2}, \inf_{ \Vert x \Vert=1}\Vert T^*x \Vert^2\Big), $$ then \begin{equation*} \Vert T \Vert \leq \sqrt{ 2} \omega(T); \end{equation*} this is a considerable improvement of the classical inequality \begin{equation*} \Vert T \Vert \leq 2\omega(T). \end{equation*}
Keywords:
bounded linear operator, Hilbert space, norm inequality, numerical radius.
Received: 01.12.2019 Revised: 04.06.2020 Accepted: 05.06.2020
Citation:
Mohsen Shah Hosseini, Baharak Moosavi, “Inequalities for the norm and numerical radius for Hilbert $C^{*}$-module operators”, Probl. Anal. Issues Anal., 9(27):2 (2020), 87–96
Linking options:
https://www.mathnet.ru/eng/pa298 https://www.mathnet.ru/eng/pa/v27/i2/p87
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Abstract page: | 84 | Full-text PDF : | 41 | References: | 14 |
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