code: def xstep(self):
          r
  
          self.X = np.asarray(sl.cho_solve_ATAI(
              self.D, self.rho, self.DTS + self.rho * (self.Y - self.U),
              self.lu, self.piv), dtype=self.dtype)
  
          if self.opt['LinSolveCheck']:
              b = self.DTS + self.rho * (self.Y - self.U)
              ax = self.D.T.dot(self.D.dot(self.X)) + self.rho*self.X
              self.xrrs = sl.rrs(ax, b)
          else:
              self.xrrs = None
docs: r"""Minimise Augmented Lagrangian with respect to
          :math:`\mathbf{x}`.