Any function to reorder the uppertriangular matrix in Schur?

[fatalme]

After a Schur factorization, I want to reorder the eigenvalues of the upper Triangular Matrix from lagest to smallest.

[sven]

You can use DTREXC to do that. Or use DGEESX from the outset to perform the Schur factorization and reorder the eigenvalues.

There are BLAS routines to generate and apply Givens rotations (DROTG and DROT), as well as some LAPACK auxiliary routines (see Appendix B of the Users' Guide).

Best wishes,

Sven Hammarling.