def mass2_from_mass1_eta(mass1, eta, force_real=True):
    """Returns the secondary mass from the primary mass and symmetric mass
    ratio.
    """
    return mass_from_knownmass_eta(mass1, eta, known_is_secondary=False,
                                   force_real=force_real)
def mass2_from_mass1_eta ( mass1 , eta , force_real = True ) : return mass_from_knownmass_eta ( mass1 , eta , known_is_secondary = False , force_real = force_real )
Returns the secondary mass from the primary mass and symmetric mass
    ratio.