#include "TF1.h"
#include "TH1F.h"
#include "TCanvas.h"

TH1F* Calibrate(TH1F* h, TF1* f, int n, float fmin, float fmax) 
{
  // here, we draw a TH1F from the function, fit and compute the chi2.
  // we iterate to extract the "chi2 distribution".
  
  // this is for the result
  TH1F* chisqu = new TH1F("chisqu","chisqu",1000,0,10);

  // we clone the fit function. We will use it to fill pseudo-experiments
  TF1* ff = (TF1*)f->Clone("ff");
  ff->SetName("ff");

  // we clone the histogram. We will use it to have the right binning, etc.
  // we extract also the number of entries.
  //TH1F* h = new TH1F("histo","histo",1000,0,4096);
  int entries = h->GetEntries();
  TH1F* hh = (TH1F*)h->Clone("hh");


  for(int i = 0;i<n;++i) {
    hh->Clear();
    hh->Reset();
    hh->FillRandom("user",entries);
    hh->Fit("ff","LQ0","",fmin,fmax);
    chisqu->Fill(ff->GetChisquare()/ff->GetNDF());
  }

  new TCanvas;
  chisqu->Draw();

  return chisqu;
}