def obfn_g0(self, Y0):
        r"""Compute :math:`g_0(\mathbf{y}_0)` component of ADMM objective
        function.
        """

        return np.linalg.norm(sp.proj_l2(Y0, self.epsilon,
                                         axis=self.cri.axisN) - Y0)
r"""Compute :math:`g_0(\mathbf{y}_0)` component of ADMM objective
        function.