assignments == second) = first;
0153         
0154         <span class="comment">% Finally, indicate that potential aggregations between the new cluster and</span>
0155         <span class="comment">% other (nonempty) clusters are untested while pairs involving clusters that</span>
0156         <span class="comment">% have already been emptied should not be tested.</span>
0157         untested(first,:) = 3;               untested(:,first) = 3;
0158         untested(tree(:,2),:) = 0;           untested(:,tre