def cnst_A1(self, X, Xf=None):
        r"""Compute :math:`A_1 \mathbf{x}` component of ADMM problem
        constraint. In this case :math:`A_1 \mathbf{x} = (\Gamma_0^T \;\;
        \Gamma_1^T \;\; \ldots )^T \mathbf{x}`.
        """

        if Xf is None:
            Xf = sl.rfftn(X, axes=self.cri.axisN)
        return sl.irfftn(sl.inner(
            self.GDf, Xf[..., np.newaxis], axis=self.cri.axisM), self.cri.Nv,
                         self.cri.axisN)