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166 lines
3.9 KiB
FortranFixed
166 lines
3.9 KiB
FortranFixed
*> \brief \b DRZT02
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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* Definition:
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* ===========
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*
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* DOUBLE PRECISION FUNCTION DRZT02( M, N, AF, LDA, TAU, WORK,
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* LWORK )
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*
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* .. Scalar Arguments ..
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* INTEGER LDA, LWORK, M, N
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* ..
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* .. Array Arguments ..
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* DOUBLE PRECISION AF( LDA, * ), TAU( * ), WORK( LWORK )
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> DRZT02 returns
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*> || I - Q'*Q || / ( M * eps)
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*> where the matrix Q is defined by the Householder transformations
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*> generated by DTZRZF.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] M
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*> \verbatim
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*> M is INTEGER
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*> The number of rows of the matrix AF.
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*> \endverbatim
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*>
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> The number of columns of the matrix AF.
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*> \endverbatim
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*>
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*> \param[in] AF
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*> \verbatim
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*> AF is DOUBLE PRECISION array, dimension (LDA,N)
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*> The output of DTZRZF.
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*> \endverbatim
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*>
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*> \param[in] LDA
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*> \verbatim
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*> LDA is INTEGER
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*> The leading dimension of the array AF.
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*> \endverbatim
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*>
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*> \param[in] TAU
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*> \verbatim
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*> TAU is DOUBLE PRECISION array, dimension (M)
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*> Details of the Householder transformations as returned by
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*> DTZRZF.
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*> \endverbatim
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*>
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*> \param[out] WORK
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*> \verbatim
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*> WORK is DOUBLE PRECISION array, dimension (LWORK)
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*> \endverbatim
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*>
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*> \param[in] LWORK
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*> \verbatim
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*> LWORK is INTEGER
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*> length of WORK array. LWORK >= N*N+N*NB.
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \ingroup double_lin
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*
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* =====================================================================
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DOUBLE PRECISION FUNCTION DRZT02( M, N, AF, LDA, TAU, WORK,
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$ LWORK )
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*
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* -- LAPACK test routine --
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* -- LAPACK is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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*
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* .. Scalar Arguments ..
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INTEGER LDA, LWORK, M, N
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION AF( LDA, * ), TAU( * ), WORK( LWORK )
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* ..
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*
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* =====================================================================
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*
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* .. Parameters ..
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DOUBLE PRECISION ZERO, ONE
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PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 )
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* ..
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* .. Local Scalars ..
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INTEGER I, INFO
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* ..
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* .. Local Arrays ..
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DOUBLE PRECISION RWORK( 1 )
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* ..
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* .. External Functions ..
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DOUBLE PRECISION DLAMCH, DLANGE
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EXTERNAL DLAMCH, DLANGE
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* ..
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* .. External Subroutines ..
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EXTERNAL DLASET, DORMRZ, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC DBLE, MAX
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* ..
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* .. Executable Statements ..
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*
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DRZT02 = ZERO
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*
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IF( LWORK.LT.N*N+N ) THEN
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CALL XERBLA( 'DRZT02', 7 )
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RETURN
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END IF
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*
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* Quick return if possible
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*
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IF( M.LE.0 .OR. N.LE.0 )
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$ RETURN
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*
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* Q := I
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*
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CALL DLASET( 'Full', N, N, ZERO, ONE, WORK, N )
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*
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* Q := P(1) * ... * P(m) * Q
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*
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CALL DORMRZ( 'Left', 'No transpose', N, N, M, N-M, AF, LDA, TAU,
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$ WORK, N, WORK( N*N+1 ), LWORK-N*N, INFO )
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*
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* Q := P(m) * ... * P(1) * Q
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*
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CALL DORMRZ( 'Left', 'Transpose', N, N, M, N-M, AF, LDA, TAU,
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$ WORK, N, WORK( N*N+1 ), LWORK-N*N, INFO )
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*
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* Q := Q - I
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*
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DO 10 I = 1, N
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WORK( ( I-1 )*N+I ) = WORK( ( I-1 )*N+I ) - ONE
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10 CONTINUE
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*
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DRZT02 = DLANGE( 'One-norm', N, N, WORK, N, RWORK ) /
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$ ( DLAMCH( 'Epsilon' )*DBLE( MAX( M, N ) ) )
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RETURN
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*
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* End of DRZT02
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*
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END
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