110 lines
2.1 KiB
Fortran
110 lines
2.1 KiB
Fortran
*> \brief \b SROTG
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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 SROTG(SA,SB,C,S)
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*
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* .. Scalar Arguments ..
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* REAL C,S,SA,SB
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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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*> SROTG 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] SA
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*> \verbatim
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*> SA is REAL
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*> \endverbatim
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*>
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*> \param[in] SB
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*> \verbatim
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*> SB is REAL
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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 REAL
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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 REAL
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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 single_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 SROTG(SA,SB,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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REAL C,S,SA,SB
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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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REAL R,ROE,SCALE,Z
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS,SIGN,SQRT
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* ..
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ROE = SB
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IF (ABS(SA).GT.ABS(SB)) ROE = SA
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SCALE = ABS(SA) + ABS(SB)
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IF (SCALE.EQ.0.0) THEN
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C = 1.0
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S = 0.0
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R = 0.0
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Z = 0.0
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ELSE
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R = SCALE*SQRT((SA/SCALE)**2+ (SB/SCALE)**2)
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R = SIGN(1.0,ROE)*R
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C = SA/R
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S = SB/R
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Z = 1.0
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IF (ABS(SA).GT.ABS(SB)) Z = S
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IF (ABS(SB).GE.ABS(SA) .AND. C.NE.0.0) Z = 1.0/C
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END IF
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SA = R
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SB = Z
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RETURN
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END
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