#include <fstream>
#include <iostream>
#include <stdlib.h>
#include <string.h>

using namespace std;


void momentum() {

  Int_t n = 8;
  Float_t datax[] = {3.1025,3.1349,3.1665,3.1829,3.1989,3.2149,3.2309,3.2469};
  Float_t datay[] = {557,2285,5471,8197,7789,6915,4470,1280};
  Float_t dataex[] = {0,0,0,0,0,0,0,0};
  Float_t dataey[] = {2.997,10.530,16.636,61.685,61.815,90.740,61.804,52.636};

  TCanvas *c1 = new TCanvas("c1","55Ni momentum distribution",1);
  gr1 = new TGraphErrors(n,datax,datay,dataex,dataey);
  gr1->SetTitle("Momentum Distribution");
  gr1->SetMarkerStyle(21);
  gr1->SetMarkerColor(2);
  gr1->Draw("AP");

   Double_t par[5];
   TF1 *g1    = new TF1("g1","expo",3.0,3.172);
   TF1 *g2    = new TF1("g2","gaus",3.170,3.26);
   TF1 *total = new TF1("total","exp([0]+[1]*x)+[2]*exp(-0.5*((x-[3])/[4])^2)",3.0,3.26);
   total->SetLineColor(2);
   gr1->Fit(g1,"R");
   gr1->Fit(g2,"R+");
   g1->GetParameters(&par[0]);
   g2->GetParameters(&par[2]);

   total->SetParameters(par);
   //total->FixParameter(0,par[0]);
   //total->FixParameter(1,par[1]);
   //total->FixParameter(2,par[2]);
   //total->FixParameter(3,par[3]);
   //total->FixParameter(4,par[4]);

    gr1->Fit(total,"R+");
   

   Double_t chi2_gaus = g2->GetChisquare();
   cout << "chi2 for fit gaussian  " << chi2_gaus << endl;
   Double_t chi2_expo = g1->GetChisquare();
   cout << "chi2 for fit exponential  " << chi2_expo << endl;
   Double_t chi2_total = total->GetChisquare();
   cout << "chi2 for fit total  " << chi2_total << endl;

}