ztrexc(3S)

NAME
     ZTREXC - reorder the Schur factorization of a complex matrix A =
     Q*T*Q**H, so that the diagonal element of T with row index IFST is moved
     to row ILST

SYNOPSIS
     SUBROUTINE ZTREXC( COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO )

         CHARACTER      COMPQ

         INTEGER        IFST, ILST, INFO, LDQ, LDT, N

         COMPLEX*16     Q( LDQ, * ), T( LDT, * )

IMPLEMENTATION
     These routines are part of the SCSL Scientific Library and can be loaded
     using either the -lscs or the -lscs_mp option.  The -lscs_mp option
     directs the linker to use the multi-processor version of the library.

     When linking to SCSL with -lscs or -lscs_mp, the default integer size is
     4 bytes (32 bits). Another version of SCSL is available in which integers
     are 8 bytes (64 bits).  This version allows the user access to larger
     memory sizes and helps when porting legacy Cray codes.  It can be loaded
     by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
     only one of the two versions; 4-byte integer and 8-byte integer library
     calls cannot be mixed.

PURPOSE
     ZTREXC reorders the Schur factorization of a complex matrix A = Q*T*Q**H,
     so that the diagonal element of T with row index IFST is moved to row
     ILST. The Schur form T is reordered by a unitary similarity
     transformation Z**H*T*Z, and optionally the matrix Q of Schur vectors is
     updated by postmultplying it with Z.


ARGUMENTS
     COMPQ   (input) CHARACTER*1
             = 'V':  update the matrix Q of Schur vectors;
             = 'N':  do not update Q.

     N       (input) INTEGER
             The order of the matrix T. N >= 0.

     T       (input/output) COMPLEX*16 array, dimension (LDT,N)
             On entry, the upper triangular matrix T.  On exit, the reordered
             upper triangular matrix.

     LDT     (input) INTEGER
             The leading dimension of the array T. LDT >= max(1,N).
     Q       (input/output) COMPLEX*16 array, dimension (LDQ,N)
             On entry, if COMPQ = 'V', the matrix Q of Schur vectors.  On
             exit, if COMPQ = 'V', Q has been postmultiplied by the unitary
             transformation matrix Z which reorders T.  If COMPQ = 'N', Q is
             not referenced.

     LDQ     (input) INTEGER
             The leading dimension of the array Q.  LDQ >= max(1,N).

     IFST    (input) INTEGER
             ILST    (input) INTEGER Specify the reordering of the diagonal
             elements of T:  The element with row index IFST is moved to row
             ILST by a sequence of transpositions between adjacent elements.
             1 <= IFST <= N; 1 <= ILST <= N.

     INFO    (output) INTEGER
             = 0:  successful exit
             < 0:  if INFO = -i, the i-th argument had an illegal value

SEE ALSO
     INTRO_LAPACK(3S), INTRO_SCSL(3S)

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