Draw multiple fitted histograms in single canvas

Newbie
1

Dear experts,

I have 3 histograms, h18, h17, h16 and i want to fit each of them with gaussian function. After fitting, i want to draw all three of them in a single canvas - the points as well as the fitted curve. I wrote this code:

void fit_plot(){
  TFile* f18 = new TFile("18D_v3.root","open");
  TH1F* h18 = (TH1F*)(f18->Get("demo/h4"));
  h18->SetMarkerColor(2);
  h18->SetLineColor(2);
  h18->Sumw2();

  TFile* f17 = new TFile("17F_v3.root","open");
  TH1F* h17 = (TH1F*)(f17->Get("demo/h4"));
  h17->SetMarkerColor(1);
  h17->SetLineColor(1);
  h17->Sumw2();

  TFile* f16 = new TFile("16H_v3.root","open");
  TH1F* h16 = (TH1F*)(f16->Get("demo/h4"));
  h16->SetMarkerColor(3);
  h16->SetLineColor(3);
  h16->Sumw2();

  h16->Scale(1.0/h16->Integral());
  h17->Scale(1.0/h17->Integral());
  h18->Scale(1.0/h18->Integral());

  TCanvas c;

  h16->Fit("gaus");
  h17->Fit("gaus");
  h18->Fit("gaus");

  h17->Draw("HIST");
  h16->Draw("HISTsame");
  h18->Draw("HISTsame");

  c.SaveAs("scaled.png");
}

But what i get is just the points and not the fitted curve (plot attached).
16H_v3.root (6.5 KB)
17F_v3.root (6.5 KB)
18D_v3.root (6.5 KB)

scaled
scaled698×475 3.24 KB

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ROOT Version: ROOT 6.18/04
Platform: Linux
Compiler: Not Provided

2

Hello,

@couet can you have a look? Thanks!

4 
void fit_plot(){
  TFile* f18 = new TFile("18D_v3.root","open");
  TH1F* h18 = (TH1F*)(f18->Get("demo/h4"));
  h18->SetMarkerColor(2);
  h18->SetLineColor(2);
  h18->Sumw2();

  TFile* f17 = new TFile("17F_v3.root","open");
  TH1F* h17 = (TH1F*)(f17->Get("demo/h4"));
  h17->SetMarkerColor(1);
  h17->SetLineColor(1);
  h17->Sumw2();

  TFile* f16 = new TFile("16H_v3.root","open");
  TH1F* h16 = (TH1F*)(f16->Get("demo/h4"));
  h16->SetMarkerColor(3);
  h16->SetLineColor(3);
  h16->Sumw2();

  h16->Scale(1.0/h16->Integral());
  h17->Scale(1.0/h17->Integral());
  h18->Scale(1.0/h18->Integral());

  h16->Fit("gaus");
  h17->Fit("gaus","","same");
  h18->Fit("gaus","","same");
}

Screenshot 2022-08-08 at 13.10.41
Screenshot 2022-08-08 at 13.10.411376×908 50.2 KB

1 Like
5 
  TF1 *f = (TF1*)gROOT->GetFunction("gaus");
  f->SetNpx(1000);
  f->SetLineColor(h16->GetLineColor());
  h16->Fit(f, "I"); // "I" because the bin width is big compared to the sigma
  f->SetLineColor(h17->GetLineColor());
  h17->Fit(f, "I", "same");
  f->SetLineColor(h18->GetLineColor());
  h18->Fit(f, "I", "same");
1 Like