code: def aux_dict(self):
          
          if self._aux_dict is None:
              self._aux_dict = Executor._get_dict(
                  self._symbol.list_auxiliary_states(), self.aux_arrays)
          return self._aux_dict
docs: Get dictionary representation of auxiliary states arrays.
  
          Returns
          -------
          aux_dict : dict of str to NDArray
              The dictionary that maps name of auxiliary states to NDArrays.
  
          Raises
          ------
          ValueError : if there are duplicated names in the auxiliary states.