Read true time step data from individual time steps.

        Returns
        -------
        steps : array
            The time steps.
        times : array
            The times of the time steps.
        nts : array
            The normalized times of the time steps, in [0, 1].

        Notes
        -----
        The default implementation returns empty arrays.

def read_times(self, filename=None):
        """
        Read true time step data from individual time steps.

        Returns
        -------
        steps : array
            The time steps.
        times : array
            The times of the time steps.
        nts : array
            The normalized times of the time steps, in [0, 1].

        Notes
        -----
        The default implementation returns empty arrays.
        """
        aux = nm.array([], dtype=nm.float64)
        return aux.astype(nm.int32), aux, aux