code: def cnst_A0T(self, Y0):
          r
  
          # This calculation involves non-negligible computational cost. It
          # should be possible to disable relevant diagnostic information
          # (dual residual) to avoid this cost.
          Y0f = sl.rfftn(Y0, None, self.cri.axisN)
          if self.cri.Cd == 1:
              return sl.irfftn(np.conj(self.Df) * Y0f, self.cri.Nv,
                               self.cri.axisN)
          else:
              return sl.irfftn(sl.inner(
                  np.conj(self.Df), Y0f, axis=self.cri.axisC),
                  self.cri.Nv, self.cri.axisN)
docs: r"""Compute :math:`A_0^T \mathbf{y}_0` component of
          :math:`A^T \mathbf{y}` (see :meth:`.ADMMTwoBlockCnstrnt.cnst_AT`).