#include <TGraphErrors.h>
#include <TCanvas.h>
#include <TStyle.h>
#include <TMath.h>
#include <TF1.h>

//linear background function
Double_t background(Double_t *x, Double_t *par) {
   return par[0];
}

//Breit Wigner function
Double_t BreitWig(Double_t *x, Double_t *par) {
  return  par[0]*par[2]*par[2]/TMath::Max(1.e-10,(x[0]*x[0]-4*0.938272013*0.938272013)*((x[0]-par[1])*(x[0]-par[1])+.25*par[2]*par[2]));
}

// Sum of background and peak function
Double_t fitFunction(Double_t *x, Double_t *par) {
  return background(x,par) + BreitWig(x,&par[1]);
}

void test(){
	gStyle->SetOptFit();

        //Try a fit with simple breitwigner and background
        TF1 *fitsimple = new TF1("fitsimple",fitFunction,3.85,3.9,4);
        fitsimple->SetParNames("back","Constant","Mean","Width");
        fitsimple->SetParameters(30,150,3.872,120*1e-06);
        fitsimple->SetNpx(500);

        //Data Points
        Double_t stepsize = 0.00005;Double_t mass = 3.872;const int numberofscanpoints=20;
	Double_t x[numberofscanpoints];Double_t xerr1[numberofscanpoints];Double_t xerr2[numberofscanpoints];
        Double_t yerr[numberofscanpoints];
        Double_t y[] = {30,25,19,40,22,22,28,35,55,75,100,90,50,40,45,30,35,35,20,25};
        for(int i=0;i<numberofscanpoints;i++){
         xerr1[i] = 0.0001; xerr2[i] = 0.00001;
         x[i] = (mass-0.00001)+(i - numberofscanpoints/2.0)*stepsize;
         yerr[i] = TMath::Sqrt(y[i]);
        }
       
        

        //Create Graphs
	TGraphErrors* graph1 = new TGraphErrors(numberofscanpoints,x,y,xerr1,yerr);
	TGraphErrors* graph2 = new TGraphErrors(numberofscanpoints,x,y,xerr2,yerr);
	TCanvas* canvas = new TCanvas("canvas", "canvas", 800, 600);
	canvas->Divide(2,1);
	canvas->cd(1);
	graph1->Draw("APZ");
	graph1->Fit("gaus");
	canvas->cd(2);
	graph2->Draw("APZ");
	graph2->Fit("gaus");
}