GetConfidenceInterval() not visible

Newbie
1

I use the code similar to ConfidenceIntervals.C File Reference. But the output image only contains scatter plot and fitting line. Do you know how to make confidence interval visible?

TCanvas *c1 = new TCanvas(“c1”,“graph”,700,500);
//creat graph

tree->Draw(“Step:Susceptible>>graph”);

graph->GetXaxis()->SetTitle(“Susceptible”);

graph->GetYaxis()->SetTitle(“Step”);

//Create the fitting function

TF1 *fpol = new TF1(“fpol”, “pol1”, -1, 1);

fpol->SetLineWidth(2);

graph->Fit(fpol, “Q”);

/Create a TGraphErrors to hold the confidence intervals/

ngr = tree->GetEntries();

TGraphErrors *grint = new TGraphErrors(ngr);

grint->SetTitle(“Fitted line with .95 conf. band”);

for (i=0; i<ngr; i++)

  grint->SetPoint(i, gr->GetX()[i], 0);

/Compute the confidence intervals at the x points of the created graph/

(TVirtualFitter::GetFitter())->GetConfidenceIntervals(grint);

//Draw the graph, the function and the confidence intervals

grint->SetLineColor(kRed);

grint->Draw(“ap”);

graph->SetMarkerStyle(5);

graph->SetMarkerSize(0.7);

graph->Draw(“psame”);

2

This is a duplicate post of GetConfidenceIntervals() returns nothing - #4 by moneta.
@xinyih8 please avoid doing this !