SUBROUTINE ZROTG(CA,CB,C,S)
* .. Scalar Arguments ..
DOUBLE COMPLEX CA,CB,S
DOUBLE PRECISION C
* ..
*
* Purpose
* =======
*
* 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).NE.0.0d0) GO TO 10
C = 0.0d0
S = (1.0d0,0.0d0)
CA = CB
GO TO 20
10 CONTINUE
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
20 CONTINUE
RETURN
END