Some upper bounds for the $\mathbb{A}$-numerical radius of $2\times 2$ block matrices

Qingxiang Xu, Zhongming Ye, Ali Zamani

Let $\mathbb{A}=\left(\begin{array}{cc}A& 0\\ 0& A\end{array}\right)$ be the $2\times 2$ diagonal operator matrix determined by a positive bounded operator $A$. For semi-H…