code: def xstep(self):
          r
  
          b = self.AHSf + self.rho*np.sum(
              np.conj(self.Gf)*sl.rfftn(self.Y-self.U, axes=self.axes),
              axis=self.Y.ndim-1)
          self.Xf = b / (self.AHAf + self.rho*self.GHGf)
          self.X = sl.irfftn(self.Xf, self.axsz, axes=self.axes)
  
          if self.opt['LinSolveCheck']:
              ax = (self.AHAf + self.rho*self.GHGf)*self.Xf
              self.xrrs = sl.rrs(ax, b)
          else:
              self.xrrs = None
docs: r"""Minimise Augmented Lagrangian with respect to
          :math:`\mathbf{x}`.