code: public MultiVariable getRootVariable() {
  		Variable aux = this;
  		while (aux.getParentVariable() != null) {
  			aux = aux.getParentVariable();
  		}
  		return (MultiVariable)aux;
  	}
docs: Get the highest ancestor {@link MultiVariable} of this {@link Variable} (root of the variable hierarchy).
  @return The root of this {@link Variable}'s variable hierarchy.