An extension of several essential numerical radius inequalities of 2x2 off-diagonal operator matrices

Abstract

In this work, we provide upper and lower bounds for the numerical radius of an nxn off-diagonal operator matrix, which extends some results by Abu-Omar and Kittaneh (Stud. Math. 216:69-75, 2013; Linear Algebra Appl. 468:18-26, 2015; Rocky Mt. J. Math. 45(4):1055-1065, 2015), and Paul and Bag (Appl. Math. Comput. 222:2731-2943, 2013).