ceMap</tt>.  All edges
  are assumed to have weight less than (by <tt>distance_compare</tt>) this
  value.<br>
  <b>Default:</b> <tt>std::numeric_limits&lt;D&gt;::max()</tt><br>
</blockquote>

IN: <tt>distance_zero(D distance_zero)</tt> 
<blockquote>
  The <tt>distance_zero</tt> value must be the identity element for the
  <a href="./Monoid.html">Monoid</a> formed by the distance values
  and the <tt>distance_weight_combine</tt> function object.
  The type <tt>D</tt> is the value type of the <tt>DistanceMap