def METHOD_NAME(self, cosmo, M, a):
    nu = get_delta_c(cosmo, a, 'EdS_approx') / cosmo.sigmaM(M, a)
    n_eff = -2 * self._dlsigmaR(cosmo, M, a) - 3
    alpha_eff = cosmo.growth_rate(a)
    A = self.a0 * (1 + self.a1 * (n_eff + 3))
    B = self.b0 * (1 + self.b1 * (n_eff + 3))
    C = 1 - self.c_alpha * (1 - alpha_eff)
    arg = A / nu * (1 + nu**2 / B)
    G = self._G_inv(arg, n_eff)
    return C * G