Geodesic
On upper and lower bounds of the numerical radius and an equality condition
Takeaki Yamazaki1
1Department of Mathematics Kanagawa University Yokohama 221-8686, Japan
Studia Mathematica, Tome 178 (2007) no. 1, pp. 83-89
Cet article a éte moissonné depuis la source Institute of Mathematics Polish Academy of Sciences

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We give an inequality relating the operator norm of $T$ and the numerical radii of $T$ and its Aluthge transform. It is a more precise estimate of the numerical radius than Kittaneh's result [Studia Math. 158 (2003)]. Then we obtain an equivalent condition for the numerical radius to be equal to half the operator norm.
DOI : 10.4064/sm178-1-5
Keywords: inequality relating operator norm numerical radii its aluthge transform precise estimate numerical radius kittanehs result studia math obtain equivalent condition numerical radius equal half operator norm

Takeaki Yamazaki  1

1 Department of Mathematics Kanagawa University Yokohama 221-8686, Japan 
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Takeaki Yamazaki. On upper and lower bounds of the numerical radius
 and an equality condition. Studia Mathematica, Tome 178 (2007) no. 1, pp. 83-89. doi: 10.4064/sm178-1-5

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