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

NAME

ctrexc - 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 CTREXC( COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO)
  CHARACTER * 1 COMPQ
  COMPLEX T(LDT,*), Q(LDQ,*)
  INTEGER N, LDT, LDQ, IFST, ILST, INFO

  SUBROUTINE CTREXC_64( COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO)
  CHARACTER * 1 COMPQ
  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, 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, DIMENSION(:,:) :: T, Q
  INTEGER(8) :: N, LDT, LDQ, IFST, ILST, INFO

C INTERFACE

#include <sunperf.h>

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

void ctrexc_64(char compq, long n, complex *t, long ldt, complex *q, long ldq, long ifst, long ilst, long *info);

PURPOSE

ctrexc 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/output)
  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