# Some $\mathbb{A}$-numerical radius inequalities for $d\times d$ operator
matrices

Research paper by **Kais Feki**

Indexed on: **01 Apr '20**Published on: **31 Mar '20**Published in: **arXiv - Mathematics - Functional Analysis**

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#### Abstract

Let $A$ be a positive (semidefinite) bounded linear operator acting on a
complex Hilbert space $\big(\mathcal{H}, \langle \cdot\mid \cdot\rangle \big)$.
The semi-inner product ${\langle x\mid y\rangle}_A := \langle Ax\mid y\rangle$,
$x, y\in\mathcal{H}$ induces a seminorm ${\|\cdot\|}_A$ on $\mathcal{H}$. Let
$T$ be an $A$-bounded operator on $\mathcal{H}$, the $A$-numerical radius of
$T$ is given by \begin{align*} \omega_A(T) = \sup\Big\{\big|{\langle Tx\mid
x\rangle}_A\big|: \,\,x\in \mathcal{H}, \,{\|x\|}_A = 1\Big\}. \end{align*} In
this paper, we establish several inequalities for
$\omega_\mathbb{A}(\mathbb{T})$, where $\mathbb{T}=(T_{ij})$ is a $d\times d$
operator matrix with $T_{ij}$ are $A$-bounded operators and $\mathbb{A}$ is the
diagonal operator matrix whose each diagonal entry is $A$.