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Open Access Research Article

General upper bounds for the numerical radius on complex Hilbert space

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pp. 761–774Vol. 26Issue 4June 2023DOI: 10.47974/JIM-1512XML
Received:
01 Dec 2021
Published Online:
19 Aug 2023
Article type:
Research Article
Language:
EN
Article no.:
JIM-1512
Pages:
761–774

Abstract

In this work, we show that if {Ai}mi=1 and {Xi}mi=1  are two sets of bounded linear operators on the complex Hilbert space H, then for every n ∈ ℕ  and m > 2,  we have w(A1n–1 (Si=0 m–1 Am–i Xm–i A*i+1)(A*1)n–1) ≤ ||A1||2n–2 (2||A1|| ||Am|| + Sj=2m–1||Aj||2)w(E), and w(A1n–1A2X2(A*1)n ± A1nX1A*2(A*1)n–1) = 2||A1||2n–1 ||A2||w([0 X2 X1 0]), where w(.)  is the numerical radius and E = [0  Xm  .... X1 0].  This provides an improvement of Theorem 3 by Fong and Holbrook [3] and a generalization of Theorem 3 by Hirzallah et al. [6]. Moreover, we provide some new upper bounds for the numerical radius of off-diagonal operator matrices and provide a generalization of the main result by Abu-Omar and Kittaneh [17].

Keywords

Subject Classifications

47A1247A3047A6347B33

References

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