Geodesic
Unitary automorphisms of the space of $3\times3$ Toeplitz-plus-Hankel matrices
Zapiski Nauchnykh Seminarov POMI, Computational methods and algorithms. Part XXVII, Tome 428 (2014), pp. 137-151 
Kh. D. Ikramov; A. K. Abdikalykov; V. N. Chugunov. Unitary automorphisms of the space of $3\times3$ Toeplitz-plus-Hankel matrices. Zapiski Nauchnykh Seminarov POMI, Computational methods and algorithms. Part XXVII, Tome 428 (2014), pp. 137-151. http://geodesic.mathdoc.fr/item/ZNSL_2014_428_a9/
@article{ZNSL_2014_428_a9,
     author = {Kh. D. Ikramov and A. K. Abdikalykov and V. N. Chugunov},
     title = {Unitary automorphisms of the space of $3\times3$ {Toeplitz-plus-Hankel} matrices},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {137--151},
     year = {2014},
     volume = {428},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2014_428_a9/}
}
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Voir la notice du chapitre de livre provenant de la source Math-Net.Ru

Let $\mathcal TH_3$ be the set of Toeplitz-plus-Hankel $3\times3$ matrices. We describe all the matrices $U$ in the unitary group $\mathbf U_3$ such that $$ \forall A\in\mathcal TH_3\longrightarrow B=U^*AU\in\mathcal TH_3. $$

[1] Kh. D. Ikramov, “Unitarnye avtomorfizmy prostranstva teplitsevykh matrits”, Dokl. RAN, 456:4 (2014), 389–391 | DOI | Zbl

[2] Kh. D. Ikramov, “Unitarnye avtomorfizmy prostranstva gankelevykh matrits”, Mat. zametki, 96:5 (2014), 687–696 | DOI

[3] Kh. D. Ikramov, V. N. Chugunov, A. K. Abdikalykov, “O lokalnykh usloviyakh, kharakterizuyuschikh mnozhestvo $(T+N)$-matrits”, Dokl. RAN, 457:1 (2014), 17–18 | DOI | Zbl