regation hierarchy for a given matrix. </span><span 
class="cmr-12">This is performed</span>
          <span 
class="cmr-12">by the routine </span><span class="obeylines-h"><span class="verb"><span 
class="cmtt-12">hierarchy_build</span></span></span><span 
class="cmr-12">.</span>
                                                                               

                                                                               
          </li>
          <li 
  class="enumerate" id="x17-16010x0"><