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JOURNALS // Zapiski Nauchnykh Seminarov POMI // Archive

Zap. Nauchn. Sem. POMI, 2012 Volume 405, Pages 133–137 (Mi znsl5283)

Unitary congruence to a conjugate-normal matrix

Kh. D. Ikramov

M. V. Lomonosov Moscow State University, Moscow, Russia

Abstract: A matrix $A\in M_n(\mathbb C)$ is said to be conjugate-normal if $AA^*=\overline{A^*A}.$ The following proposition (which is the congruence analog of a recent result of T. G. Gerasimova) is proved: A matrix $B\in M_n(\mathbb C)$ is unitarily congruent to a conjugate-normal matrix $A$ if and only if
$$ \mathrm{tr}[(\bar AA)^i]=\mathrm{tr}[(\bar BB)^i],\qquad i=1,\dots,n, $$
and
$$ \|A\|_F=\|B\|_F. $$
This proposition dramatically reduces the amount of computational work for verifying unitary congruence as compared to the case of general matrices $A$ and $B$.

Key words and phrases: unitary similarity, unitary congruence, normal matrix, conjugate-normal matrix, Specht criterion.

UDC: 512.64

Received: 15.05.2012


 English version:
Journal of Mathematical Sciences (New York), 2013, 191:1, 72–74

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© Steklov Math. Inst. of RAS, 2024