code: public int getNumberOfInputGroupVertices(final int stage) {
  
  		if (stage < 0 || stage >= this.stages.size()) {
  			return 0;
  		}
  
  		return this.stages.get(stage).getNumberOfInputGroupVertices();
  	}
docs: Returns the number of input group vertices in the management stage with the given index.
  
  @param stage
  the index to the management stage
  @return the number of input group vertices in this stage, possibly 0.