*> \brief \b CROTG * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * * Definition: * =========== * * SUBROUTINE CROTG(CA,CB,C,S) * * .. Scalar Arguments .. * COMPLEX CA,CB,S * REAL C * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> CROTG determines a complex Givens rotation. *> \endverbatim * * Arguments: * ========== * *> \param[in] CA *> \verbatim *> CA is COMPLEX *> \endverbatim *> *> \param[in] CB *> \verbatim *> CB is COMPLEX *> \endverbatim *> *> \param[out] C *> \verbatim *> C is REAL *> \endverbatim *> *> \param[out] S *> \verbatim *> S is COMPLEX *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \date November 2017 * *> \ingroup complex_blas_level1 * * ===================================================================== SUBROUTINE CROTG(CA,CB,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 .. COMPLEX CA,CB,S REAL C * .. * * ===================================================================== * * .. Local Scalars .. COMPLEX ALPHA REAL NORM,SCALE * .. * .. Intrinsic Functions .. INTRINSIC CABS,CONJG,SQRT * .. IF (CABS(CA).EQ.0.) THEN C = 0. S = (1.,0.) CA = CB ELSE SCALE = CABS(CA) + CABS(CB) NORM = SCALE*SQRT((CABS(CA/SCALE))**2+ (CABS(CB/SCALE))**2) ALPHA = CA/CABS(CA) C = CABS(CA)/NORM S = ALPHA*CONJG(CB)/NORM CA = ALPHA*NORM END IF RETURN END