def f_idx_to_run(self, name_or_idx):
return self._single_run_ids[name_or_idx]<EOL>
Converts an integer idx to the corresponding single run name and vice versa.

        Note during a single run ONLY useful if ``v_full_copy`` was set to True.

        :param name_or_idx: Name of a single run or an integer index

        :return: The corresponding idx or name of the single run

        Example usage:

        >>> traj.f_idx_to_run(4)
        'run_00000004'
        >>> traj.f_idx_to_run('run_00000000')
        0