vtx.setDatum(new Datum(DATUM_SNA_INDEX, new Integer(index)));
vtx.setDatum(new Datum(DATUM_INDEX, new Integer(index)));
	private void indecize() {		Set v = _graph.getVertices();		Iterator i = v.iterator();		int index = 0;		_vtx_index_tbl = new Vertex[v.size()];		while(i.hasNext()) {			Vertex vtx = (Vertex) i.next();			// index -> vertex map			_vtx_index_tbl[index] = vtx;			// vertex -> index map			vtx.setDatum(new Datum(DATUM_SNA_INDEX, new Integer(index)));			index++;		}	}