Normalizing counts into yield %

[Karl007]

Hi,

Consider the attached histogram. How would one go about normalising the Y-axis into yield%. I guess I want to divide the data points on Y-axis by the total number of counts (entries). But is there a way to do it in ROOT?

Thanks!

Edit: Sorry, here is the a snip:

Capture

[couet]

@Karl007

Consider the attached histogram

nothing is attached …

[Karl007]

Just added it. Thanks for letting me know.

[Wile_E_Coyote]

Different ways of normalizing histograms

Hi everyone, I’m a new user of both ROOT and RootTalk so please pardon my ignorance. I’ve been trying to normalize several histograms, and when I search in RootTalk, a multitude of ways comes up. How do I know which one is “right”? What is the difference between the following methods? Here are the 4 methods I tried: Method 1: Double_t num = h->GetBinContent(i); Double_t den = h->GetBinWidth(i); Double_t value = 0; if (den!=0) { value = num/den; h->SetBinContent(i,value); } Met…

[Karl007]

Thanks, but I don’t seem to find a way to put everything together. Here’s my code:

{TFile *file = new TFile("myFile.root");
    TTree *myBranch= (TTree *) file->Get("myBranch");
    myBranch->Draw("myBranch>>h")
}

This will only give the attached photo, so how to link normalisation method to it?
P.S. I want to normalise to 100 (percentage).

[Wile_E_Coyote]

{
  // warning: due to a long-standing known bug in ROOT 6, all variables
  // need to be defined right in the beginning of an "unnamed macro"
  TFile *f;
  TTree *t;
  TH1D *h;
  Double_t integral;
  f = TFile::Open("myFile.root");
  if ((!f) || f->IsZombie()) {delete f; return;} // just a precaution
  f->GetObject("myTree", t);
  if (!t) {delete f; return;} // just a precaution
  gROOT->cd(); // all newly created histograms should be placed here
  h = new TH1D("h", "number of particles;n;yield [%]", 110, 0., 55.);
  h->Sumw2(kTRUE);
  t->Project("h", "nParticles");
  delete f; // no longer needed (automatically deletes "t", too)
  integral = h->Integral();
  if (integral != 0) h->Scale(100. / integral); // "normalize" to 100
  h->Draw();
}

[Karl007]

Thank you. It is working well. And here is the result:

[Karl007]

If you don’t mind, I have one more question. If you want to rescale Y-axis to a certain value, how would you approach that? For instance, I want to know the percentage of every mass number (0-55). Mathematically, it should be:

                      counts * 100 / total counts.

Counts: each counts reading on Y-axis.

[Wile_E_Coyote]

Not sure what you mean. Isn’t it what this line does?
if (integral != 0) h->Scale(100. / integral);

[Karl007]

Oh yes indeed. I confused it with another histogram I have. It all right thank you again.