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DLASORTE - sort eigenpairs so that real eigenpairs are together and complex are together

SUBROUTINE DLASORTE ( S, LDS, J, OUT, INFO ) INTEGER INFO, J, LDS DOUBLE PRECISION OUT( J, * ), S( LDS, * )

DLASORTE sorts eigenpairs so that real eigenpairs are together and complex are together. This way one can employ 2x2 shifts easily since every 2nd subdiagonal is guaranteed to be zero. This routine does no parallel work and makes no calls.

S (local input/output) DOUBLE PRECISION array, dimension LDS On entry, a matrix already in Schur form. On exit, the diagonal blocks of S have been rewritten to pair the eigenvalues. The resulting matrix is no longer similar to the input. LDS (local input) INTEGER On entry, the leading dimension of the local array S. Unchanged on exit. J (local input) INTEGER On entry, the order of the matrix S. Unchanged on exit. OUT (local input/output) DOUBLE PRECISION array, dimension Jx2 This is the work buffer required by this routine. INFO (local input) INTEGER This is set if the input matrix had an odd number of real eigenvalues and things couldnâ€™t be paired or if the input matrix S was not originally in Schur form. 0 indicates successful completion. Implemented by: G. Henry, May 1, 1997