Abstract
The following proposition is proved: A nonsingular matrix \(A\) is normal if and only if its cosquare is a unitary matrix. An unusual feature of this criterion is that normality, the most important concept in the theory of similarity transformations, is characterized in terms of transformations of an entirely different type, namely, congruence transformations.
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Ikramov, K.D. An Unusual Criterion for Normality of Nonsingular Matrices. MoscowUniv.Comput.Math.Cybern. 46, 8–11 (2022). https://doi.org/10.3103/S0278641922010022
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DOI: https://doi.org/10.3103/S0278641922010022