code: def get_notify_observers_kwargs(self):
          
          return {'x_new': self._linear.adj_op(self._x_new),
                  'z_new': self._z_new, 'idx': self.idx}
docs: Return the mapping between the metrics call and the iterated
          variables.
  
          Return
          ----------
          notify_observers_kwargs: dict,
             the mapping between the iterated variables.