Histogram Normalizationnb to single plot

Afzaal786 · July 13, 2020, 2:20am

Hi, I am quite new at ROOT and trying to normalize two histograms in single plot but don’t know how to do it. I have attached the two selected histograms that i want to normalize. Please suggest possible solutions.
Thanks for your time and consideration.
unnamed.pdf (14.6 KB)
h20.pdf (14.3 KB)

bellenot · July 13, 2020, 6:30am

Did you try to search the forum?

Afzaal786 · July 13, 2020, 7:17am

Yes, but I didn’t find any appropriate solution.

bellenot · July 13, 2020, 7:30am

Could you post the code producing the histograms?

Afzaal786 · July 13, 2020, 5:33am

Code?

bellenot · July 13, 2020, 10:54am

Yes, the source code producing those histograms. I.e. how did you generate those histograms?

Afzaal786 · July 13, 2020, 11:28am

I opened the histograms in ROOT TBrowser b;
/home/afzaal/PET/Geant4/geant4.10.06.p01/examples/extended/electromagnetic/TestEm5/build/acosta.root.

bellenot · July 13, 2020, 11:33am

Oh, OK, thanks. I’ll try to come with a working solution

Afzaal786 · July 13, 2020, 11:56am

Thanks. I am waiting…

bellenot · July 13, 2020, 1:11pm

In fact, do you really want to normalize them, or simply draw them both in the same canvas? If you just want to draw several histograms in the same canvas, simply use the SAME option of the TH1::Draw(), otherwise you should really try the different methods of normalizing histograms, as described in this topic, for example

Afzaal786 · July 20, 2020, 6:43pm

Could you please give me direct commands to draw both histograms in same canvas and to normalize them? As i can’t figure out it.
Thanks

bellenot · July 21, 2020, 6:33am

Something like this:

{
   // open the ROOT file
   TFile *f = TFile::Open("acosta.root");
   // check the validity of the file
   if ((!f) || f->IsZombie()) {
      std::cout << "Failed to open acosta.root!" << std::endl;
      return;
   }
   // create a canvas
   TCanvas *c1 = new TCanvas("c1", "c1");
   // get the first histogram from the file
   TH1F *h1 = (TH1F *)f->Get("h1");
   // get the second histogram from the file
   TH1F *h2 = (TH1F *)f->Get("h2");
   // display the first histogram
   h1->Draw();
   // display the second histogram with the option "SAME"
   h2->Draw("SAME");   
}

And change the file or histogram names following your needs. I would also suggest to start with the ROOT Primer and the tutorials

Afzaal786 · July 21, 2020, 12:17pm

Thanks for your response!
I tried by this program it opened histograms in a new canvas c1(see screenshot). How can I normalize them?
// create a canvas TCanvas *c1 = new TCanvas(“c1”, “c1”); // get the first histogram from the file TH1F *h1 = (TH1F *)f->Get(“h1”); // get the second histogram from the file TH1F *h2 = (TH1F *)f->Get(“h2”); // display the first histogram h1->Draw(); // display the second histogram with the option “SAME” h2->Draw(“SAME”);

bellenot · July 21, 2020, 12:20pm

Maybe @couet can explain how to normalize histograms…

moneta · July 21, 2020, 2:14pm

Hi,
To normalize histogram use TH1::Scale. For example, to normalise such that the sum of all bins is equal to 1, do:

histogram->Scale(1./histogram->Integral() );