Fit multiple histograms at once

ROOT
1

Hi,

I do have 64 histograms of the same type. They are all 2D histograms, I can fit them individually using fit2d.C. I tried to make it at once by following code

{
#include "Riostream.h"

  Double_t par[3];
  TFile file("Scatter.root"); 
  Fit = new TF1("Fit", "pol2", -0.4, 0);

  // Create file to write output information.
  ofstream OutFile;
  OutFile.open("ScatterFitOut.txt",ios::out);
 
  for (Int_t i=0; i<64; i++)
    {
      TCanvas *Canvas1 = new TCanvas("Canvas1","Scatter Plot");
      TCanvas *Canvas2 = new TCanvas("Canvas2","Fit to Plot");
      Canvas1->Divide(1,1);
      Canvas1->cd(1);
      h20[i]->Draw();
      Canvas2->Divide(1,1);
      Canvas2->cd(1);
      
      //use a TProfile to convert the 2-d to 1-d problem
      TProfile *Profile = h20[i]->ProfileX();
      Profile->Fit(Fit,"R");
      Fit->GetParameters(&par[0]);
      OutFile  << i << " " << par[0] << " " << -par[1] << " " << +par[2] << endl;
    }    
}

It gives me the following error.

Error: Symbol h20[i] is not defined in current scope  FitAll.C:21:
Error: Failed to evaluate h20[i]->Draw()

How can I resolve this?

Thanks.

2

Where do you declare and fill your array h20?
The error message seems to be very clear!

Rene

3

Hi,

It is defined in Scatter.root file. So it should be fine. I can read individually not in a loop.

Thanks

4

These objects are may be in your ROOT file, but I do not see any code creating the array h20 in memory. When you have a ROOT file containg histograms named “h1”,“h2”, etc , “h20” in the ROOT file, you need code like

TFile *f = new TFile("myfile.root"); TH1 *h20[20]; for (int i=0;i<20;i++) { h20[i] = (TH1*)f->Get(Form("h%d",i+1)); }
Rene

5

I see. I modified part of your code and worked. Thanks a lot!