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Improved numerical radius bounds using the Moore-Penrose inverse

Author : Dr Pintu Bhunia

Year : 2025

Publisher : Elsevier Inc.

Source Title : Linear Algebra and Its Applications

Document Type :

Abstract

Using the Moore-Penrose inverse of a bounded linear operator, we obtain few bounds for the numerical radius, which improve the classical ones. Applying these improvements, we study equality conditions of the existing bounds. It is shown that if T is a bounded linear operator with closed range, then [Formula presented] For a finite-dimensional space operator T, this improvement is proper if and only if Range(T)∩Range(T⁎)={0}. Clearly, if ‖TT†+T†T‖=1, then [Formula presented]. Among other results, we obtain inner product inequalities for the sum of operators, and as an application of these inequalities, we deduce relevant operator norm and numerical radius bounds.