Contents

• NAME
• SYNOPSIS
  • F95 INTERFACE
  • C INTERFACE
• PURPOSE
• ARGUMENTS

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 * 1 COMPQ
     DOUBLE COMPLEX T(LDT,*), Q(LDQ,*)
     INTEGER N, LDT, LDQ, IFST, ILST, INFO

     SUBROUTINE ZTREXC_64(COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO)

     CHARACTER * 1 COMPQ
     DOUBLE COMPLEX T(LDT,*), Q(LDQ,*)
     INTEGER*8 N, LDT, LDQ, IFST, ILST, INFO

  F95 INTERFACE
     SUBROUTINE TREXC(COMPQ, [N], T, [LDT], Q, [LDQ], IFST, ILST, [INFO])

     CHARACTER(LEN=1) :: COMPQ
     COMPLEX(8), DIMENSION(:,:) :: T, Q
     INTEGER :: N, LDT, LDQ, IFST, ILST, INFO

     SUBROUTINE TREXC_64(COMPQ, [N], T, [LDT], Q, [LDQ], IFST, ILST, [INFO])

     CHARACTER(LEN=1) :: COMPQ
     COMPLEX(8), DIMENSION(:,:) :: T, Q
     INTEGER(8) :: N, LDT, LDQ, IFST, ILST, INFO

  C INTERFACE
     #include <sunperf.h>

     void ztrexc(char compq, int n, doublecomplex  *t,  int  ldt,
               doublecomplex *q, int ldq, int ifst, int ilst, int
               *info);

     void ztrexc_64(char compq, long n,  doublecomplex  *t,  long
               ldt,  doublecomplex  *q, long ldq, long ifst, long
               ilst, long *info);

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)
               = 'V':  update the matrix Q of Schur vectors;
               = 'N':  do not update Q.

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

     T (input/output)
               On entry, the upper triangular matrix T.  On exit,
               the reordered upper triangular matrix.

     LDT (input)
               The leading dimension  of  the  array  T.  LDT  >=
               max(1,N).

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

     IFST (input)
               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.

     ILST (input)
               See the description of IFST.

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