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
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 couldn’t be paired or if the input
matrix S was not originally in Schur form. 0 indicates
Implemented by: G. Henry, May 1, 1997