def uniform_mass_mc_eta_log_prior(M_c, eta):
    """
    If :math:`p(m_1, m_2)` is unformly distributed (subject to
    :math:`m_i \\geq m_{\\mathrm{min}}` and
    :math:`m_1 + m_2 \\leq M_{\\mathrm{max}}`), then that implies

    .. math::
       p(\\mathcal{M}_{\\mathrm{c}}, \\eta) =
       \\frac{4}{(M_{\\mathrm{max}} - m_{\\mathrm{min}})^2}
       \\frac{\\mathcal{M}_{\\mathrm{c}}}{\\eta^{6/5} \\sqrt{1 - 4\\eta}}

    This evaluates that function, in the log, neglecting the constant factor
    dealing with the lower and upper mass cutoffs.
    """
    import numpy
    return numpy.log(M_c) - 1.2 * numpy.log(eta) - 0.5 * numpy.log(1.0 - 
        4.0 * eta)
