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LAPACK version 3.0
ztrexc(3)

PURPOSE
  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

SYNTAX
  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, * )

DESCRIPTION
  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