def K(eps):
    """ Rayleigh complex dielectric factor
    This is basically the K complex factor that defines the Radar dielectric
    factor |K|**2. It is useful in Rayleigh theory to define absorption cross
    section from its imaginary part

    Parameters
    ----------
    eps : complex
        nd array of complex relative dielectric constants

    Returns
    -------
    nd - float
        Rayleigh complex dielectric factor K
    """
    return (eps-1.0)/(eps+2.0)