Implementing `dTgSen' command of Gauss in Matlab

I wonder if there is a way to implement dTgSen (reordering Schur decomposition) command of Gauss in Matlab.

Thank you.

Answer 1

[Oleg Komarov]

Is this what you're looking for: ordschur

[Martin]

Dear Oleg,

Something like that. I just googled the fortran command which describes as follows.

dtgsen reorders the generalized real Schur decomposition of a real matrix pair (A, B) (in terms of an orthonormal equivalence trans- formation Q' * (A, B) * Z), so that a selected cluster of eigenvalues appears in the leading diagonal blocks of the upper quasi-triangular matrix A and the upper triangular B. The leading columns of Q and Z form orthonormal bases of the corresponding left and right eigen- spaces (deflating subspaces). (A, B) must be in generalized real Schur canonical form (as returned by DGGES), i.e. A is block upper triangular with 1-by-1 and 2-by-2 diagonal blocks. B is upper triangular.

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Thanks.

Martin