private Map<String, Expr> inputs = new HashMap<String, Expr>();
private Map<String, Expr> results = new HashMap<String, Expr>();
private Set<IEngineListener> listeners = new HashSet<IEngineListener>();
public SimpleGraphEngine() {
addFunctions(new ExcelFunctionProvider());
setValue("PI", ExprDouble.PI);
setValue("TRUE", ExprBoolean.TRUE);
setValue("FALSE", ExprBoolean.FALSE);
}