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).EQ.0.0d0) THEN
22 C = 0.0d0
23 S = (1.0d0,0.0d0)
24 CA = CB
25 ELSE
26 SCALE = CDABS(CA) + CDABS(CB)
27 NORM = SCALE*DSQRT((CDABS(CA/DCMPLX(SCALE,0.0d0)))**2+
28 $ (CDABS(CB/DCMPLX(SCALE,0.0d0)))**2)
29 ALPHA = CA/CDABS(CA)
30 C = CDABS(CA)/NORM
31 S = ALPHA*DCONJG(CB)/NORM
32 CA = ALPHA*NORM
33 END IF
34 RETURN
35 END
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).EQ.0.0d0) THEN
22 C = 0.0d0
23 S = (1.0d0,0.0d0)
24 CA = CB
25 ELSE
26 SCALE = CDABS(CA) + CDABS(CB)
27 NORM = SCALE*DSQRT((CDABS(CA/DCMPLX(SCALE,0.0d0)))**2+
28 $ (CDABS(CB/DCMPLX(SCALE,0.0d0)))**2)
29 ALPHA = CA/CDABS(CA)
30 C = CDABS(CA)/NORM
31 S = ALPHA*DCONJG(CB)/NORM
32 CA = ALPHA*NORM
33 END IF
34 RETURN
35 END