def rel_name2abs_name(system, rel_name):
    """
    Map relative variable name to absolute variable name.

    Parameters
    ----------
    system : <System>
        System to which the given name is relative.
    rel_name : str
        Given relative variable name.

    Returns
    -------
    str
        Absolute variable name.
    """
    return rel_name if system.pathname == '' else system.pathname + '.' + rel_name