Geodesic
Criteria for Unitary Congruence of Complex $2\times 2$ Matrices
Matematičeskie zametki, Tome 88 (2010) no. 2, pp. 249-260 Cet article a éte moissonné depuis la source Math-Net.Ru

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Canonical forms of $2\times 2$ matrices with respect to unitary congruence transformations are described. This makes it possible to formulate simple criteria for checking whether the given matrices are unitarily congruent.
Keywords: unitary similarity transformation, unitary congruence transformation, Specht's criterion, singular value, cosquare, Jordan block. 
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Kh. D. Ikramov. Criteria for Unitary Congruence of Complex $2\times 2$ Matrices. Matematičeskie zametki, Tome 88 (2010) no. 2, pp. 249-260. http://geodesic.mathdoc.fr/item/MZM_2010_88_2_a7/

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