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    1: *> \brief \b ZROTG
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at
    6: *            http://www.netlib.org/lapack/explore-html/
    7: *
    8: *  Definition:
    9: *  ===========
   10: *
   11: *       SUBROUTINE ZROTG(CA,CB,C,S)
   12: *
   13: *       .. Scalar Arguments ..
   14: *       COMPLEX*16 CA,CB,S
   15: *       DOUBLE PRECISION C
   16: *       ..
   17: *
   18: *
   19: *> \par Purpose:
   20: *  =============
   21: *>
   22: *> \verbatim
   23: *>
   24: *>    ZROTG determines a double complex Givens rotation.
   25: *> \endverbatim
   26: *
   27: *  Arguments:
   28: *  ==========
   29: *
   30: *> \param[in] CA
   31: *> \verbatim
   32: *>          CA is COMPLEX*16
   33: *> \endverbatim
   34: *>
   35: *> \param[in] CB
   36: *> \verbatim
   37: *>          CB is COMPLEX*16
   38: *> \endverbatim
   39: *>
   40: *> \param[out] C
   41: *> \verbatim
   42: *>          C is DOUBLE PRECISION
   43: *> \endverbatim
   44: *>
   45: *> \param[out] S
   46: *> \verbatim
   47: *>          S is COMPLEX*16
   48: *> \endverbatim
   49: *
   50: *  Authors:
   51: *  ========
   52: *
   53: *> \author Univ. of Tennessee
   54: *> \author Univ. of California Berkeley
   55: *> \author Univ. of Colorado Denver
   56: *> \author NAG Ltd.
   57: *
   58: *> \date November 2017
   59: *
   60: *> \ingroup complex16_blas_level1
   61: *
   62: *  =====================================================================
   63:       SUBROUTINE ZROTG(CA,CB,C,S)
   64: *
   65: *  -- Reference BLAS level1 routine (version 3.8.0) --
   66: *  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
   67: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
   68: *     November 2017
   69: *
   70: *     .. Scalar Arguments ..
   71:       COMPLEX*16 CA,CB,S
   72:       DOUBLE PRECISION C
   73: *     ..
   74: *
   75: *  =====================================================================
   76: *
   77: *     .. Local Scalars ..
   78:       COMPLEX*16 ALPHA
   79:       DOUBLE PRECISION NORM,SCALE
   80: *     ..
   81: *     .. Intrinsic Functions ..
   82:       INTRINSIC CDABS,DCMPLX,DCONJG,DSQRT
   83: *     ..
   84:       IF (CDABS(CA).EQ.0.0d0) THEN
   85:          C = 0.0d0
   86:          S = (1.0d0,0.0d0)
   87:          CA = CB
   88:       ELSE
   89:          SCALE = CDABS(CA) + CDABS(CB)
   90:          NORM = SCALE*DSQRT((CDABS(CA/DCMPLX(SCALE,0.0d0)))**2+
   91:      $       (CDABS(CB/DCMPLX(SCALE,0.0d0)))**2)
   92:          ALPHA = CA/CDABS(CA)
   93:          C = CDABS(CA)/NORM
   94:          S = ALPHA*DCONJG(CB)/NORM
   95:          CA = ALPHA*NORM
   96:       END IF
   97:       RETURN
   98:       END