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Zapiski Nauchnykh Seminarov POMI, 2003, Volume 301, Pages 172–194
(Mi znsl952)
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This article is cited in 2 scientific papers (total in 2 papers)
Bounds for the extreme eigenvalues of block $2\times2$ Hermitian matrices
L. Yu. Kolotilina St. Petersburg Department of V. A. Steklov Institute of Mathematics, Russian Academy of Sciences
Abstract:
Let an $n\times n$ Hermitian matrix $A$ be presented in block $2\times2$ form as
$A=\left[\begin{smallmatrix}A_{11}&A_{12}\\A^*_{12}&A_{22}\end{smallmatrix}\right]$,
where $A_{12}\ne0$, and assume that the diagonal blocks $A_{11}$ and $A_{22}$ are positive definite. Under these assumptions, it is proved that the extreme eigenvalues of $A$ satisfy the bounds
$$
\lambda_1(A)\ge\|A_{12}\|(\|R\|^{-1}+1),\quad
|\lambda_n(A)|\le\|A_{12}\|\,\bigl|\,\|R\|^{-1}-1\bigr|,
$$
where $R=A^{-1/2}_{11}A_{12}A^{-1/2}_{22}$ and $\|\cdot\|$ is the spectral norm. Further, in the positive-definite case, several equivalent conditions necessary and sufficient for both of the above bounds to be attained are provided.
Received: 11.09.2003
Citation:
L. Yu. Kolotilina, “Bounds for the extreme eigenvalues of block $2\times2$ Hermitian matrices”, Representation theory, dynamical systems, combinatorial and algoritmic methods. Part IX, Zap. Nauchn. Sem. POMI, 301, POMI, St. Petersburg, 2003, 172–194; J. Math. Sci. (N. Y.), 129:2 (2005), 3772–3786
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https://www.mathnet.ru/eng/znsl952 https://www.mathnet.ru/eng/znsl/v301/p172
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