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