void foo(){
  const int N = 4;
  double x[N] = {1, 2, 3, 4};
  double y[N] = {1, 4, 8, 18};
  double dy[N] = {0.2, 0.5, 1, 1.5};

  TGraphErrors *g1 = new TGraphErrors(N, x, y, 0, dy);
  g1->SetMarkerStyle(8);
  g1->Draw("ap");
  g1->Fit("pol2");

  /*
  // the following 5 lines work
  TGraphErrors *gci = new TGraphErrors(*g1);
  gci->SetFillColor(5);
  (TVirtualFitter::GetFitter())->GetConfidenceIntervals(gci, 0.68);
  gci->Draw("e3 same");
  g1->Draw("p");
  */

  const double xx[N] = {1., 2., 3., 4.};
  double ci[N] = {0., 0., 0., 0.};
  (TVirtualFitter::GetFitter())->GetConfidenceIntervals->(N, 1, &xx[0], &ci[0], 0.68);

}