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strexc.f(3)				      LAPACK				      strexc.f(3)

NAME
       strexc.f -

SYNOPSIS
   Functions/Subroutines
       subroutine strexc (COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, WORK, INFO)
	   STREXC

Function/Subroutine Documentation
   subroutine strexc (characterCOMPQ, integerN, real, dimension( ldt, * )T, integerLDT, real,
       dimension( ldq, * )Q, integerLDQ, integerIFST, integerILST, real, dimension( * )WORK,
       integerINFO)
       STREXC

       Purpose:

	    STREXC reorders the real Schur factorization of a real matrix
	    A = Q*T*Q**T, so that the diagonal block of T with row index IFST is
	    moved to row ILST.

	    The real Schur form T is reordered by an orthogonal similarity
	    transformation Z**T*T*Z, and optionally the matrix Q of Schur vectors
	    is updated by postmultiplying it with Z.

	    T must be in Schur canonical form (as returned by SHSEQR), that is,
	    block upper triangular with 1-by-1 and 2-by-2 diagonal blocks; each
	    2-by-2 diagonal block has its diagonal elements equal and its
	    off-diagonal elements of opposite sign.

       Parameters:
	   COMPQ

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

	   N

		     N is INTEGER
		     The order of the matrix T. N >= 0.

	   T

		     T is REAL array, dimension (LDT,N)
		     On entry, the upper quasi-triangular matrix T, in Schur
		     Schur canonical form.
		     On exit, the reordered upper quasi-triangular matrix, again
		     in Schur canonical form.

	   LDT

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

	   Q

		     Q is REAL 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
		     orthogonal transformation matrix Z which reorders T.
		     If COMPQ = 'N', Q is not referenced.

	   LDQ

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

	   IFST

		     IFST is INTEGER

	   ILST

		     ILST is INTEGER

		     Specify the reordering of the diagonal blocks of T.
		     The block with row index IFST is moved to row ILST, by a
		     sequence of transpositions between adjacent blocks.
		     On exit, if IFST pointed on entry to the second row of a
		     2-by-2 block, it is changed to point to the first row; ILST
		     always points to the first row of the block in its final
		     position (which may differ from its input value by +1 or -1).
		     1 <= IFST <= N; 1 <= ILST <= N.

	   WORK

		     WORK is REAL array, dimension (N)

	   INFO

		     INFO is INTEGER
		     = 0:  successful exit
		     < 0:  if INFO = -i, the i-th argument had an illegal value
		     = 1:  two adjacent blocks were too close to swap (the problem
			   is very ill-conditioned); T may have been partially
			   reordered, and ILST points to the first row of the
			   current position of the block being moved.

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   November 2011

       Definition at line 146 of file strexc.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2				 Tue Sep 25 2012			      strexc.f(3)
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