 the fact that it is possible to quickly determine the decrease in
      energy caused by moving a point from its current cluster to another.
      It repeats the following procedure:
      <ul>
        <li>
          For each point, move it to another cluster if that would lower
          the energy.  If you move a point, immediately update the
          cluster centers of the two affected clusters.
        </li>
      </ul>
      This procedure is repeated until no points are moved, or some
      other te