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dlaexc.f(3)				      LAPACK				      dlaexc.f(3)

NAME
       dlaexc.f -

SYNOPSIS
   Functions/Subroutines
       subroutine dlaexc (WANTQ, N, T, LDT, Q, LDQ, J1, N1, N2, WORK, INFO)
	   DLAEXC swaps adjacent diagonal blocks of a real upper quasi-triangular matrix in Schur
	   canonical form, by an orthogonal similarity transformation.

Function/Subroutine Documentation
   subroutine dlaexc (logicalWANTQ, integerN, double precision, dimension( ldt, * )T, integerLDT,
       double precision, dimension( ldq, * )Q, integerLDQ, integerJ1, integerN1, integerN2,
       double precision, dimension( * )WORK, integerINFO)
       DLAEXC swaps adjacent diagonal blocks of a real upper quasi-triangular matrix in Schur
       canonical form, by an orthogonal similarity transformation.

       Purpose:

	    DLAEXC swaps adjacent diagonal blocks T11 and T22 of order 1 or 2 in
	    an upper quasi-triangular matrix T by an orthogonal similarity
	    transformation.

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

       Parameters:
	   WANTQ

		     WANTQ is LOGICAL
		     = .TRUE. : accumulate the transformation in the matrix Q;
		     = .FALSE.: do not accumulate the transformation.

	   N

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

	   T

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

	   LDT

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

	   Q

		     Q is DOUBLE PRECISION array, dimension (LDQ,N)
		     On entry, if WANTQ is .TRUE., the orthogonal matrix Q.
		     On exit, if WANTQ is .TRUE., the updated matrix Q.
		     If WANTQ is .FALSE., Q is not referenced.

	   LDQ

		     LDQ is INTEGER
		     The leading dimension of the array Q.
		     LDQ >= 1; and if WANTQ is .TRUE., LDQ >= N.

	   J1

		     J1 is INTEGER
		     The index of the first row of the first block T11.

	   N1

		     N1 is INTEGER
		     The order of the first block T11. N1 = 0, 1 or 2.

	   N2

		     N2 is INTEGER
		     The order of the second block T22. N2 = 0, 1 or 2.

	   WORK

		     WORK is DOUBLE PRECISION array, dimension (N)

	   INFO

		     INFO is INTEGER
		     = 0: successful exit
		     = 1: the transformed matrix T would be too far from Schur
			  form; the blocks are not swapped and T and Q are
			  unchanged.

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   September 2012

       Definition at line 138 of file dlaexc.f.

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

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