Geodesic
A note on the canonical form for a pair of orthoprojectors
Zapiski Nauchnykh Seminarov POMI, Computational methods and algorithms. Part XVII, Tome 309 (2004), pp. 17-22 
A. George; Kh. D. Ikramov. A note on the canonical form for a pair of orthoprojectors. Zapiski Nauchnykh Seminarov POMI, Computational methods and algorithms. Part XVII, Tome 309 (2004), pp. 17-22. http://geodesic.mathdoc.fr/item/ZNSL_2004_309_a1/
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Voir la notice du chapitre de livre provenant de la source Math-Net.Ru

Let $P$ and $Q$ be orthoprojectors in $\mathbb C^n$. The canonical form for $P$ and $Q$ is constracted as their common block diagonal form with diagonal blocks of order one or two. The entries in the $2\times 2$ blocks of the canonical form are then interpreted in terms of the canonical angles between the subspaces $\mathcal L=\operatorname{im}P$ and $\mathcal M=\operatorname{im}Q$.

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