110 lines
2.2 KiB
Fortran
110 lines
2.2 KiB
Fortran
*> \brief \b DROTG
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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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* SUBROUTINE DROTG(DA,DB,C,S)
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*
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* .. Scalar Arguments ..
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* DOUBLE PRECISION C,DA,DB,S
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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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*> DROTG construct givens plane rotation.
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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] DA
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*> \verbatim
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*> DA is DOUBLE PRECISION
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*> \endverbatim
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*>
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*> \param[in] DB
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*> \verbatim
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*> DB is DOUBLE PRECISION
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*> \endverbatim
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*>
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*> \param[out] C
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*> \verbatim
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*> C is DOUBLE PRECISION
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*> \endverbatim
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*>
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*> \param[out] S
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*> \verbatim
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*> S is DOUBLE PRECISION
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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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*> \date November 2017
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*
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*> \ingroup double_blas_level1
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*
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*> \par Further Details:
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* =====================
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*>
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*> \verbatim
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*>
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*> jack dongarra, linpack, 3/11/78.
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*> \endverbatim
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*>
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* =====================================================================
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SUBROUTINE DROTG(DA,DB,C,S)
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*
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* -- Reference BLAS level1 routine (version 3.8.0) --
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* -- Reference BLAS 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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* November 2017
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*
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* .. Scalar Arguments ..
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DOUBLE PRECISION C,DA,DB,S
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* ..
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*
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* =====================================================================
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*
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* .. Local Scalars ..
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DOUBLE PRECISION R,ROE,SCALE,Z
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC DABS,DSIGN,DSQRT
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* ..
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ROE = DB
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IF (DABS(DA).GT.DABS(DB)) ROE = DA
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SCALE = DABS(DA) + DABS(DB)
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IF (SCALE.EQ.0.0d0) THEN
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C = 1.0d0
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S = 0.0d0
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R = 0.0d0
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Z = 0.0d0
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ELSE
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R = SCALE*DSQRT((DA/SCALE)**2+ (DB/SCALE)**2)
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R = DSIGN(1.0d0,ROE)*R
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C = DA/R
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S = DB/R
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Z = 1.0d0
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IF (DABS(DA).GT.DABS(DB)) Z = S
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IF (DABS(DB).GE.DABS(DA) .AND. C.NE.0.0d0) Z = 1.0d0/C
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END IF
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DA = R
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DB = Z
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RETURN
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END
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