#if !defined(__CINT__) || defined(__MAKECINT__)
#include <TH1.h>
#include <TF1.h>
#endif

	// Gausian background function
	Double_t background(Double_t *x, Double_t *par) {
   	return par[0] + par[1]*x[0] + par[2]*x[0]*x[0];
	}


	// Lorenzian Peak function
	Double_t lorentzianPeak(Double_t *x, Double_t *par) {
  		return  (0.5*par[0]*par[1]/TMath::Pi()) / 
          TMath::Max( 1.e-10,
                      (x[0]-par[2])*(x[0]-par[2]) + .25*par[1]*par[1]
                    );
	}

	// Sum of background and peak function
	Double_t fitFunction(Double_t *x, Double_t *par) {
  		return background(x,par) + lorentzianPeak(x,&par[3]);
	}



	
  	void Demo()
	{
	const int nBins = 60;
  
  	Stat_t data[nBins] = { 6, 1,10,12, 6,13,23,22,15,21,
                        23,26,36,25,27,35,40,44,66,81,
                        75,57,48,45,46,41,35,36,53,32,
                        40,37,38,31,36,44,42,37,32,32,
                        43,44,35,33,33,39,29,41,32,44,
                        26,39,29,35,32,21,21,15,25,15};
	TH1F *histo = new TH1F("example_9_1","Lorentzian Peak on Quadratic Background",60,0,3);
  
  	for(int i=0; i < nBins;  i++) {
    	histo->SetBinContent(i+1,data[i]);
    	histo->SetBinError(i+1,TMath::Sqrt(data[i]));
  	}

  	histo->Draw(); 

  	// create a FT1 with the range from 0 to 3 and 6 parameters
  	TF1 *fitFcn = new TF1("fitFcn",fitFunction,0,3,6);
  

  	// first try
	histo->Fit("fitFcn");


  	// second try: set start values for some parameters
  	fitFcn->SetParameter(4,0.2);
  	fitFcn->SetParameter(5,1);

  	histo->Fit("fitFcn");


  	// improve the picture:
  	TF1 *backFcn = new TF1("backFcn",background,0,3,3);
  	TF1 *signalFcn = new TF1("signalFcn",lorentzianPeak,0,3,3);
  	Double_t par[6];
 
  	fitFcn->GetParameters(par);
  	backFcn->SetParameters(par);
  	backFcn->Draw("same");

  	signalFcn->SetParameters(&par[3]);
  	signalFcn->Draw("same");
}