dc/dfe/zrotg_8f_source.html

00001       SUBROUTINE ZROTG(CA,CB,C,S)
00002 *     .. Scalar Arguments ..
00003       DOUBLE COMPLEX CA,CB,S
00004       DOUBLE PRECISION C
00005 *     ..
00006 *
00007 *  Purpose
00008 *  =======
00009 *
00010 *     ZROTG determines a double complex Givens rotation.
00011 *
00012 *  =====================================================================
00013 *
00014 *     .. Local Scalars ..
00015       DOUBLE COMPLEX ALPHA
00016       DOUBLE PRECISION NORM,SCALE
00017 *     ..
00018 *     .. Intrinsic Functions ..
00019       INTRINSIC CDABS,DCMPLX,DCONJG,DSQRT
00020 *     ..
00021       IF (CDABS(CA).NE.0.0d0) GO TO 10
00022       C = 0.0d0
00023       S = (1.0d0,0.0d0)
00024       CA = CB
00025       GO TO 20
00026    10 CONTINUE
00027       SCALE = CDABS(CA) + CDABS(CB)
00028       NORM = SCALE*DSQRT((CDABS(CA/DCMPLX(SCALE,0.0d0)))**2+
00029      +       (CDABS(CB/DCMPLX(SCALE,0.0d0)))**2)
00030       ALPHA = CA/CDABS(CA)
00031       C = CDABS(CA)/NORM
00032       S = ALPHA*DCONJG(CB)/NORM
00033       CA = ALPHA*NORM
00034    20 CONTINUE
00035       RETURN
00036       END