>
  This value is used to initialize the distance for the source
  vertex before the start of the algorithm.  The type <tt>DT</tt>
  must be the value type of the <tt>WeigthMap</tt>.<br>
  <b>Default:</b> <tt>0</tt>
</blockquote>

UTIL/OUT: <tt>color_map(ColorMap c_map)</tt> 
<blockquote>
  This is used during the execution of the algorithm to mark the
  vertices. The vertices start out white and become gray when they are
  inserted in the queue. They then turn black when they are removed
  from the queue. 