zrotg.f (cxxblas/netlib/blas/zrotg.f)

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      SUBROUTINE ZROTG(CA,CB,C,S)

*     .. Scalar Arguments ..

      DOUBLE COMPLEX CA,CB,S

      DOUBLE PRECISION C

*     ..

*

*  Purpose

*  =======

*

*     ZROTG determines a double complex Givens rotation.

*

*  =====================================================================

*

*     .. Local Scalars ..

      DOUBLE COMPLEX ALPHA

      DOUBLE PRECISION NORM,SCALE

*     ..

*     .. Intrinsic Functions ..

      INTRINSIC CDABS,DCMPLX,DCONJG,DSQRT

*     ..

      IF (CDABS(CA).EQ.0.0d0) THEN

         C = 0.0d0

         S = (1.0d0,0.0d0)

         CA = CB

      ELSE

         SCALE = CDABS(CA) + CDABS(CB)

         NORM = SCALE*DSQRT((CDABS(CA/DCMPLX(SCALE,0.0d0)))**2+

     $       (CDABS(CB/DCMPLX(SCALE,0.0d0)))**2)

         ALPHA = CA/CDABS(CA)

         C = CDABS(CA)/NORM

         S = ALPHA*DCONJG(CB)/NORM

         CA = ALPHA*NORM

      END IF

      RETURN

      END