In this paper, first we consider cross-diagonal, in particular off-diagonal, operator matrices;
those operator matrices such that all entries except those on the main and off diagonals are …

Let k and n be two coprime positive integers. In this paper, we show that any n× nk-circulant
operator matrix A k, n with the first row A 1,…, A n∈ B (H) is unitarily equivalent to a …

We introduce the notion of approximate ω-orthogonality (referring to the numerical radius ω)
and investigate its significant properties. Let T, S∈ B (Ж) and ε∈[0, 1). We say that T is …

In this paper, we give a description of the maximal numerical range of a hyponormal element
and a characterization of a normaloid element in a C∗-algebra. We also give an explicit …

Approximate isosceles $$\omega $$ -orthogonality and approximate $$\omega $$ -parallelism
| Boletín de la Sociedad Matemática Mexicana Skip to main content SpringerLink Account …

1. INTRODUCTION Let B (H) denote the C∗-algebra of all bounded linear operators acting
on a complex Hilbert space H, and let H (n) be the direct sum of n copies of H. We identify …

In this work, a Gruss inequality for positive Hilbert space operators is proved. So, some
numerical radius inequalities are proved. On the other hand, based on a non-commutative …

We introduce the notion of approximate numerical radius (Birkhoff) orthogonality and
investigate its significant properties. Let $ T, S\in\mathbb {B}(\mathscr {H}) $ and …