#include "TH1.h"
#include "TF1.h"

#include "Fit/Chi2FCN.h"
#include "HFitInterface.h"
#include "Math/WrappedMultiTF1.h"
#include "Math/DistFunc.h"
#include <iostream>

// chi2 comparison  histogram-function
void testChi2FuncTest() { 

   TH1 * h1 = new TH1D("h1","h1",100,-3,3); 

   TF1 * f1 = new TF1("f1","gaus");
   int n = 100000;

   f1->SetParameters(n,0,1);

   h1->FillRandom("f1",n);

   ROOT::Fit::BinData data; 
   ROOT::Fit::FillData(data, h1);
   ROOT::Math::WrappedMultiTF1 wf(*f1);
   ROOT::Fit::Chi2Function chi2(data, wf); 
   // evaluate at parameter values
   f1->SetParameter(0, h1->GetMaximum() ); // fix constant to match histogram
   double val = chi2( f1->GetParameters() );
   int ndf  = chi2.NPoints() - chi2.NDim(); 
   double prob = ROOT::Math::chisquared_cdf_c( val, ndf);
   std::cout << " chi2 value = " << val <<  " ndf = " << ndf << std::endl;
   std::cout << " chi2 probability = " << prob << std::endl;

}