zrotg(l) redhat man page | unix.com

subroutine zrotg(ca,cb,c,s)
    double complex ca,cb,s
    double precision c
    double precision norm,scale
    double complex alpha
    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