Double_t customFunction(Double_t *x, Double_t *par)
{
  return par[0] * x[0];
}

void example_modified(){
  
  TCanvas * myCanvas = new TCanvas();
  TF1* myTF1 = new TF1("myTF1",customFunction,0.,100.,1);
  myTF1->SetParameter(0,1.0);
  myTF1->Draw();
  myCanvas->Modified();
  myCanvas->Update();
  myCanvas->SaveAs("exampleCanvas_does_not_work.C");
  TGraph *g = new TGraph(myTF1);
  g->Draw("a,L");
  myCanvas->Update();
  myCanvas->SaveAs("exampleCanvas_works_fine.C");
}