code: public int getNumberOfOutputGroupVertices() {
  
  		int retVal = 0;
  
  		final Iterator<ManagementGroupVertex> it = this.groupVertices.iterator();
  		while (it.hasNext()) {
  			if (it.next().isOutputVertex()) {
  				++retVal;
  			}
  		}
  
  		return retVal;
  	}
docs: Returns the number of output group vertices in this stage. Output group vertices are those vertices which have
  outgoing edges to group vertices of a higher stage.
  
  @return the number of output group vertices in this stage