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*> \brief \b SROTG
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
* Definition:
* ===========
*
* SUBROUTINE SROTG(SA,SB,C,S)
*
* .. Scalar Arguments ..
* REAL C,S,SA,SB
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> SROTG construct givens plane rotation.
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] SA
*> \verbatim
*> SA is REAL
*> \endverbatim
*>
*> \param[in] SB
*> \verbatim
*> SB is REAL
*> \endverbatim
*>
*> \param[out] C
*> \verbatim
*> C is REAL
*> \endverbatim
*>
*> \param[out] S
*> \verbatim
*> S is REAL
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date December 2016
*
*> \ingroup single_blas_level1
*
*> \par Further Details:
* =====================
*>
*> \verbatim
*>
*> jack dongarra, linpack, 3/11/78.
*> \endverbatim
*>
* =====================================================================
SUBROUTINE SROTG(SA,SB,C,S)
*
* -- Reference BLAS level1 routine (version 3.7.0) --
* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
* December 2016
*
* .. Scalar Arguments ..
REAL C,S,SA,SB
* ..
*
* =====================================================================
*
* .. Local Scalars ..
REAL R,ROE,SCALE,Z
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS,SIGN,SQRT
* ..
ROE = SB
IF (ABS(SA).GT.ABS(SB)) ROE = SA
SCALE = ABS(SA) + ABS(SB)
IF (SCALE.EQ.0.0) THEN
C = 1.0
S = 0.0
R = 0.0
Z = 0.0
ELSE
R = SCALE*SQRT((SA/SCALE)**2+ (SB/SCALE)**2)
R = SIGN(1.0,ROE)*R
C = SA/R
S = SB/R
Z = 1.0
IF (ABS(SA).GT.ABS(SB)) Z = S
IF (ABS(SB).GE.ABS(SA) .AND. C.NE.0.0) Z = 1.0/C
END IF
SA = R
SB = Z
RETURN
END
|
