def METHOD_NAME(self, cosmo, M, a):
    if self.alpha == 'cosmo':
        Mvir = self._to_virial_mass(cosmo, M, a)
        sM = cosmo.sigmaM(Mvir, a)
        nu = get_delta_c(cosmo, a, kind='EdS_approx') / sM
        return 0.155 + 0.0095 * nu * nu
    return np.full_like(M, self.alpha)