Some generalized numerical radius inequalities involving Kwong functions

Abstract

We prove several numerical radius inequalities involving positive semidefinite matrices via the Hadamard product and Kwong functions. Among other inequalities, it is shown that if $X$ is an arbitrary $n\times n$ matrix and $A,B$ are positive semidefinite, then \begin{align*} ω(H_{f,g}(A))\leq k\, ω(AX+XA), \end{align*} which is equivalent to \begin{align*} ω\big(H_{f,g}(A,B)\pm H_{f,g}(B,A)\big)\leq k'\,\left\{ω((A+B)X+X(A+B))+ω((A-B)X-X(A-B))\right\}, \end{align*} where $f$ and $g$ are two continuous functions on $(0,\infty )$ such that $h(t)=\frac{f(t)}{g(t)}$ is Kwong, $k=\max \left\{\frac{f(\lambda )g(\lambda )}{\lambda }:\lambda \in \sigma (A)\right\}$ and $k^{\prime }=\max \left\{\frac{f(\lambda )g(\lambda )}{\lambda }:\lambda \in \sigma (A)\cup \sigma (B)\right\}$.

arXiv commentTo appear in Hacettepe Journal of Mathematics and Statistics