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Zhurnal Vychislitel'noi Matematiki i Matematicheskoi Fiziki, 2005, Volume 45, Number 4, Pages 587–591
(Mi zvmmf664)
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On the Euclidean distance to the set of matrices with a multiple zero eigenvalue
Kh. D. Ikramov Faculty of Computational Mathematics and Cybernetics, Moscow State University, Moscow, 119992, Russia
Abstract:
Let $M_n(\mathbb C)$ be the set of $n$-by-$n$ complex matrices ($n>2$), and let $\mathcal K$ and $\mathcal L$ be the subsets of $M_n(\mathbb C)$ consisting of the matrices with a rank not greater than $n-2$ and of the matrices with a multiple zero eigenvalue, respectively. It is known that the minimal distance from a matrix $A\in M_n(\mathbb C)$ to the matrices in $\mathcal K$ is attained at the same matrix $K_A$ for both the spectral and Euclidean norm. It is shown that, for the set $\mathcal L$, similar minimal distances are attained, in the general case, at different matrices in $\mathcal L$. Moreover, the Euclidean distance from $A$ to $\mathcal L$ is, in general, strictly less than the Euclidean distance from $A$ to $\mathcal K$.
Key words:
spectral norm, Euclidean norm, singular values, normal matrix, departure from normality.
Received: 13.09.2004
Citation:
Kh. D. Ikramov, “On the Euclidean distance to the set of matrices with a multiple zero eigenvalue”, Zh. Vychisl. Mat. Mat. Fiz., 45:4 (2005), 587–591; Comput. Math. Math. Phys., 45:4 (2005), 563–567
Linking options:
https://www.mathnet.ru/eng/zvmmf664 https://www.mathnet.ru/eng/zvmmf/v45/i4/p587
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