LAPACK: BLAS/SRC/crotg.f Source File

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00001       SUBROUTINE CROTG(CA,CB,C,S)
00002 *     .. Scalar Arguments ..
00003       COMPLEX CA,CB,S
00004       REAL C
00005 *     ..
00006 *
00007 *  Purpose
00008 *  =======
00009 *
00010 *  CROTG determines a complex Givens rotation.
00011 *
00012 *  =====================================================================
00013 *
00014 *     .. Local Scalars ..
00015       COMPLEX ALPHA
00016       REAL NORM,SCALE
00017 *     ..
00018 *     .. Intrinsic Functions ..
00019       INTRINSIC CABS,CONJG,SQRT
00020 *     ..
00021       IF (CABS(CA).NE.0.) GO TO 10
00022       C = 0.
00023       S = (1.,0.)
00024       CA = CB
00025       GO TO 20
00026    10 CONTINUE
00027       SCALE = CABS(CA) + CABS(CB)
00028       NORM = SCALE*SQRT((CABS(CA/SCALE))**2+ (CABS(CB/SCALE))**2)
00029       ALPHA = CA/CABS(CA)
00030       C = CABS(CA)/NORM
00031       S = ALPHA*CONJG(CB)/NORM
00032       CA = ALPHA*NORM
00033    20 CONTINUE
00034       RETURN
00035       END