Given a MD DataFrame, return a Nx4 array which permutes the current
    injection dipoles.

def MD_ConfigsPermutate(df_md):
    """Given a MD DataFrame, return a Nx4 array which permutes the current
    injection dipoles.
    """
    g_current_injections = df_md.groupby(['a', 'b'])
    ab = np.array(list(g_current_injections.groups.keys()))
    config_mgr = ConfigManager(nr_of_electrodes=ab.max())
    config_mgr.gen_configs_permutate(ab, silent=True)
    return config_mgr.configs