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Initial revision

    1:       SUBROUTINE ZROTG(CA,CB,C,S)
    2: *     .. Scalar Arguments ..
    3:       DOUBLE COMPLEX CA,CB,S
    4:       DOUBLE PRECISION C
    5: *     ..
    6: *
    7: *  Purpose
    8: *  =======
    9: *
   10: *     ZROTG determines a double complex Givens rotation.
   11: *
   12: *  =====================================================================
   13: *
   14: *     .. Local Scalars ..
   15:       DOUBLE COMPLEX ALPHA
   16:       DOUBLE PRECISION NORM,SCALE
   17: *     ..
   18: *     .. Intrinsic Functions ..
   19:       INTRINSIC CDABS,DCMPLX,DCONJG,DSQRT
   20: *     ..
   21:       IF (CDABS(CA).NE.0.0d0) GO TO 10
   22:       C = 0.0d0
   23:       S = (1.0d0,0.0d0)
   24:       CA = CB
   25:       GO TO 20
   26:    10 CONTINUE
   27:       SCALE = CDABS(CA) + CDABS(CB)
   28:       NORM = SCALE*DSQRT((CDABS(CA/DCMPLX(SCALE,0.0d0)))**2+
   29:      +       (CDABS(CB/DCMPLX(SCALE,0.0d0)))**2)
   30:       ALPHA = CA/CDABS(CA)
   31:       C = CDABS(CA)/NORM
   32:       S = ALPHA*DCONJG(CB)/NORM
   33:       CA = ALPHA*NORM
   34:    20 CONTINUE
   35:       RETURN
   36:       END