code: public GraphVar[] retrieveGraphVars() {
  		ArrayList<GraphVar> gvars = new ArrayList<>();
  		for (Variable v : getVars()) {
  			if ((v.getTypeAndKind() & Variable.KIND) == GraphVar.GRAPH) {
  				gvars.add((GraphVar) v);
  			}
  		}
  		return gvars.toArray(new GraphVar[gvars.size()]);
  	}
docs: Iterate over the variable of <code>this</code> and build an array that contains the GraphVar only.
  
  @return array of GraphVar in <code>this</code> model