 as the distance value type.<br>

  <b>Default:</b> <tt>std::plus&lt;D&gt;</tt> with
   <tt>D=typename property_traits&lt;DistanceMap&gt;::value_type</tt>
</blockquote>

IN: <tt>distance_inf(D inf)</tt> 
<blockquote>
  The <tt>inf</tt> object must be the greatest value of any <tt>D</tt> object.
  That is, <tt>compare(d, inf) == true</tt> for any <tt>d != inf</tt>.
  The type <tt>D</tt> is the value type of the <tt>DistanceMap</tt>.<br>
  <b>Default:</b> <tt>std::numeric_limits&lt;D&gt;::max()</tt>
</blockqu