t><br>
</blockquote>

IN: <tt>index_map(VertexIndexMap index_map)</tt> 
<blockquote>
  This maps each vertex to an integer in the range <tt>[0,
    num_vertices(graph))</tt>. This is necessary for efficient updates of the
  heap data structure&nbsp;[<A
  HREF="bibliography.html#driscoll88">61</A>] when an edge is relaxed.
  The type 
  <tt>VertexIndexMap</tt> must be a model of
  <a href="../../property_map/doc/ReadablePropertyMap.html">Readable Property Map</a>. The value type of the map must be an
  integ