private void AddFunc_Click(object sender, RoutedEventArgs e)
 {
     if (graph != null)
     {
         int           index = graph.CustomFunctions.Count;
         string        name  = "Func" + index;
         FunctionGraph gp    = new FunctionGraph(name);
         gp.AssignParentGraph(graph);
         graph.AddCustomFunction(gp);
         FunctionView cp = new FunctionView(gp);
         cp.OnRemove += Cp_OnRemove;
         Stack.Children.Add(cp);
     }
 }