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.

def aux_dict(self):
        """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.
        """
        if self._aux_dict is None:
            self._aux_dict = Executor._get_dict(
                self._symbol.list_auxiliary_states(), self.aux_arrays)
        return self._aux_dict