
      For a given set of clusters, the total energy is then simply
      the sum of the cluster energies E(J).  The goal is to choose the
      clusters in such a way that the total energy is minimized.
      Usually, a point X(I) goes into the cluster with the closest
      representative point Z(J).  So to define the clusters, it's
      enough simply to specify the locations of the cluster representatives.
    </p>

    <p>
      This is actually a fairly hard problem.  Most algorithms do
      reasonab