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dtrexc.f(3)				      LAPACK				      dtrexc.f(3)

       dtrexc.f -

       subroutine dtrexc (COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, WORK, INFO)

Function/Subroutine Documentation
   subroutine dtrexc (characterCOMPQ, integerN, double precision, dimension( ldt, * )T,
       integerLDT, double precision, dimension( ldq, * )Q, integerLDQ, integerIFST, integerILST,
       double precision, dimension( * )WORK, integerINFO)


	    DTREXC 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 DHSEQR), 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.


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


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


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


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


		     IFST is INTEGER


		     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 is DOUBLE PRECISION array, dimension (N)


		     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.

	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

	   November 2011

       Definition at line 146 of file dtrexc.f.

       Generated automatically by Doxygen for LAPACK from the source code.

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