Cumulative variable

[Marooz_Malik]

I have an eta distribution that I want to convert to a distribution of a new cumulative variable Chi(eta), so that the new distribution becomes flat.
I can’t figure out the block of code that can be used for cumulative functions.
Thank you.

ROOT Version: v6
Platform: ubuntu 20

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[couet]

Do you have some code already ? if yes can you post it ?
I guess @moneta may help you.

[Marooz_Malik]

I can only scale the histogram like this:

    TH1F *ratio11 = (TH1F*)h5->Clone()

    Float_t norm11 = 1;
   Float_t scaleeta11 = norm11/(ratio11->Integral());
   ratio11->Scale(scaleeta11);

I have no idea on how to use this function and also the integration limits.

[moneta]

Hi,

The function TH1::GetIntegral() is probably what you are looking for. See ROOT: TH1 Class Reference.

Lorenzo

[Marooz_Malik]

Thank you for the reply. How should I use GetIntegral() for the above formula?

[moneta]

TH1::GetIntegral() implement exactly the above formula.
if fEtaBin1 is your original histogram, you cumulative histogram is obtained as following:

auto ig = fEtaBin1->GetIntegral()
auto cumHist = new TH1D("cumHist","cumulative distribution",fEtaBin1->GetNbinsX(), fEtaBin1->GetXaxis()->GetXmin(),fEtaBin1->GetXaxis()->GetXmax());  
for (int i = 1; i <= cumHist->GetNbinsX(); i++)
   cumHist->SetBinContent(i, ig[i-1] ); 

cumHist->Draw(); 

[Marooz_Malik]

It worked. Does it look okay?

[moneta]

Hi,

I don’t think so. The cumulative distribution should be between 0 and 1. I see instead there a uniform distribution at ~ 35E6. Please post the full code, so we can understand what went wrong

Lorenzo