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Normalising in TTree

Dear ROOT Users,

I have been trying to normalize the histogram to the number of events.
I extracted the histogram from the root file in which it is stored in the Tree format.
I wrote the following root marco:

TFile*f =new TFile("example.root");
TTree*tree;
f->GetObject("tree",tree);
tree->Draw("event.Q2")

Here I want to normalize the event.Q2 histogram.

KIndly suggest some ways. I have used the following :
tree->Scale(1.0/tree->Integral(),“width”);

Please read tips for efficient and successful posting and posting code

ROOT Version: 6.08/02
Platform: Ubuntu
Compiler: Not Provided


tree->Draw("event.Q2");
TH1 *htemp = (TH1*)gPad->GetPrimitive("htemp"); // 1D
htemp->Scale(1.0 / htemp->Integral(), "width");
gPad->Modified(); gPad->Update();

Thank you so much for your help.
There is one small issue, however, my experimental data is not there now. I have attached the graph for that. The blue line corresponds to the simulated data.

Try with: tree->Draw("event.Q2", "", "HIST");

This is not working, I am attaching the rest of the code I am using to give a better idea.

TFile*f =new TFile("example.root");
TTree*tree;
f->GetObject("tree",tree);
 tree->Draw("event.Q2", "", "HIST");
TH1F *htemp = (TH1F*)gPad->GetPrimitive("htemp"); // 1D
htemp->Scale(1.0 / htemp->Integral(), "width");
gPad->Modified();
gPad->Update();
//second graph                                                                                                                                 
  c1->cd(2);
   const Int_t n1 = 8;
   Double_t px1[] = {0.05, 2.5, 4.0, 6.3,10.0, 15.8,25.0,47.3};
   Double_t py1[] = {73.1,37.3,31.7,21.8,13.3,7.53,3.43,0.60};
   Double_t ex1[] = {0,0,0,0,0,0,0,0};
   Double_t ey1[] = {6.4,3.6,3.0,2.1,1.3,0.72,0.33,0.06};
   TGraphErrors *gr1 = new TGraphErrors(n1,px1,py1,ex1,ey1);
   gr1->SetMarkerColor(kBlue);
   gr1->SetMarkerStyle(21);
    mg->Add(gr1);
   mg->Draw("pz");
}

Sorry for all the trouble

Hi,
to draw two histograms on the same canvas you need to pass "same" among the drawing options.

Cheers,
Enrico

Thanks for your reply.

Unfortunately, I also tried this but then only the experimental data is shown in the histogram.

Can you please share example.root so our graphics expert @couet can take a look?

Cheers,
Enrico

Sure, post the ROOT fille @eguiraud requested.

Kindly find the attached example. root file in the folder.

Thank you in advance for your help.

https://drive.google.com/drive/folders/1QnsOp8m5qsWgu_LeU3A7Q6Hd5RA1hVZi?usp=sharing

In your macro mg is not defined.
Can you post a working macro ?

Sure, I forgot to write the whole code above.

{

//first graph                                                                                                                                  
TCanvas *c1 = new TCanvas("c1","multigraph",700,500);
   c1->SetGrid();

   TMultiGraph *mg = new TMultiGraph();

   // create first graph                                                                                                                       
  c1->cd(1);
TFile*f =new TFile("example.root");
TTree*tree;
f->GetObject("tree",tree);
 tree->Draw("event.Q2", "", "HIST");
TH1F *htemp = (TH1F*)gPad->GetPrimitive("htemp"); // 1D
htemp->Scale(1.0 / htemp->Integral(), "width");
gPad->Modified();
gPad->Update();
//second graph                                                                                                                                 
  c1->cd(2);
   const Int_t n1 = 8;
   Double_t px1[] = {0.05, 2.5, 4.0, 6.3,10.0, 15.8,25.0,47.3};
   Double_t py1[] = {73.1,37.3,31.7,21.8,13.3,7.53,3.43,0.60};
   Double_t ex1[] = {0,0,0,0,0,0,0,0};
   Double_t ey1[] = {6.4,3.6,3.0,2.1,1.3,0.72,0.33,0.06};
   TGraphErrors *gr1 = new TGraphErrors(n1,px1,py1,ex1,ey1);
   gr1->SetMarkerColor(kBlue);
   gr1->SetMarkerStyle(21);
    mg->Add(gr1);
    mg->Draw();
}
TCanvas *c1 = new TCanvas(...);
c1->Divide(1, 2); // two pads
// ...
mg->Draw("AP");
{
   TCanvas *c1 = new TCanvas("c1","multigraph",700,500);
   c1->Divide(2,1);

   TMultiGraph *mg = new TMultiGraph();

   c1->cd(1)->SetGrid();
   TFile*f =new TFile("example.root");
   TTree*tree;
   f->GetObject("tree",tree);
   tree->Draw("event.Q2", "", "HIST");
   TH1F *htemp = (TH1F*)gPad->GetPrimitive("htemp"); // 1D
   htemp->Scale(1.0 / htemp->Integral(), "width");
   gPad->Modified();
   gPad->Update();

   c1->cd(2)->SetGrid();
   const Int_t n1 = 8;
   Double_t px1[] = {0.05, 2.5, 4.0, 6.3,10.0, 15.8,25.0,47.3};
   Double_t py1[] = {73.1,37.3,31.7,21.8,13.3,7.53,3.43,0.60};
   Double_t ex1[] = {0,0,0,0,0,0,0,0};
   Double_t ey1[] = {6.4,3.6,3.0,2.1,1.3,0.72,0.33,0.06};
   TGraphErrors *gr1 = new TGraphErrors(n1,px1,py1,ex1,ey1);
   gr1->SetMarkerColor(kBlue);
   gr1->SetMarkerStyle(21);
   mg->Add(gr1);
   mg->Draw("ap");
}

Thank you for your reply.

Actually, I am looking for plotting these two plots on the same graphs. Is there any way to do that?

The graph has a much wider range. You should plot it first

{

   const Int_t n1 = 8;
   Double_t px1[] = {0.05, 2.5, 4.0, 6.3,10.0, 15.8,25.0,47.3};
   Double_t py1[] = {73.1,37.3,31.7,21.8,13.3,7.53,3.43,0.60};
   Double_t ex1[] = {0,0,0,0,0,0,0,0};
   Double_t ey1[] = {6.4,3.6,3.0,2.1,1.3,0.72,0.33,0.06};
   TGraphErrors *gr1 = new TGraphErrors(n1,px1,py1,ex1,ey1);
   gr1->SetMarkerColor(kBlue);
   gr1->SetMarkerStyle(21);
   gr1->Draw("AP");

   gPad->Modified(); gPad->Update(); // see @Wile_E_Coyote reply

   TFile*f =new TFile("example.root");
   TTree*tree;
   f->GetObject("tree",tree);
   tree->Draw("event.Q2", "", "HIST SAME");
}
1 Like

@couet The "HIST SAME" options misbehave in TTree::Draw here. The automatically created "htemp" histogram has “xmin = 0” and “xmax = 1” (without "SAME" you would get “xmax = 10.8” here).

In order to overcome it here, one needs to use (note: when "SAME" is present, the "htemp" x-axis limits will then be inherited from the pad):
gr1->Draw("AP"); gPad->Modified(); gPad->Update();

1 Like

Thank you so much for your help. I am getting the output. I think due to the large variation in the data, one of the plots is around zero. Anyway, this is of great help.