def obfn_dfd(self):
        r"""Compute data fidelity term :math:`(1/2) \| \sum_m \mathbf{d}_m *
        \mathbf{x}_m - \mathbf{s} \|_2^2`.
        """

        Ef = sl.inner(self.Df, self.obfn_fvarf(), axis=self.cri.axisM) - \
            self.Sf
        return sl.rfl2norm2(Ef, self.S.shape, axis=self.cri.axisN) / 2.0
r"""Compute data fidelity term :math:`(1/2) \| \sum_m \mathbf{d}_m *
        \mathbf{x}_m - \mathbf{s} \|_2^2`.