*> \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 November 2017 * *> \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 3.8.0) -- * -- Reference BLAS is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * November 2017 * * .. 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