code: public int getNumberOfOutputManagementVertices() {
  
  		int retVal = 0;
  
  		final Iterator<ManagementGroupVertex> it = this.groupVertices.iterator();
  		while (it.hasNext()) {
  
  			final ManagementGroupVertex groupVertex = it.next();
  			if (groupVertex.isOutputVertex()) {
  				retVal += groupVertex.getNumberOfGroupMembers();
  			}
  		}
  
  		return retVal;
  	}
docs: Returns the number of output management vertices in this stage, i.e. the number
  of management vertices which are connected to vertices in a higher stage
  or have no output channels.
  
  @return the number of output vertices in this stage