01:       SUBROUTINE ZROTG(CA,CB,C,S)
02: *     .. Scalar Arguments ..
03:       DOUBLE COMPLEX CA,CB,S
04:       DOUBLE PRECISION C
05: *     ..
06: *
07: *  Purpose
08: *  =======
09: *
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
37: