t</span> = 0;
<a name="l00187"></a>00187 
<a name="l00188"></a>00188   <span class="comment">// set cost factor</span>
<a name="l00189"></a>00189   <span class="keyword">virtual</span> <span class="keywordtype">void</span> set_cost_factor(<span class="keywordtype">float</span> cost_factor) = 0;
<a name="l00190"></a>00190 
<a name="l00191"></a>00191   <span class="comment">// get cost factor</span>
<a name="l00192"></a>00192   <span class="keyword">virtual</span> <span class="keywordtype">float</span> cost_f