DLASORTE(3)   ScaLAPACK routine of NEC Numeric Library Collection  DLASORTE(3)



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

SYNOPSIS
       SUBROUTINE DLASORTE( S, LDS, J, OUT, INFO )

           INTEGER          INFO, J, LDS

           DOUBLE           PRECISION OUT( J, * ), S( LDS, * )

PURPOSE
       DLASORTE sorts eigenpairs so that real eigenpairs are together and com-
       plex  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.


ARGUMENTS
       S       (local input/output) DOUBLE PRECISION array, dimension LDS
               On entry, a matrix already in Schur form.  On exit, the  diago-
               nal  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 couldn't  be  paired  or  if  the  input
               matrix  S  was  not originally in Schur form.  0 indicates suc-
               cessful completion.

               Implemented by:  G. Henry, November 17, 1996



ScaLAPACK routine               31 October 2017                    DLASORTE(3)