#include "TCanvas.h"
#include "TStyle.h"
#include "TGraphErrors.h"
#include "TBackCompFitter.h"
#include "TMatrixD.h"
#include "TMath.h"


void test() { 
   gStyle->SetOptFit(1111); 
   const Int_t N = 9; 
   Float_t logE[N]; 
   Float_t logEffi[N]; 
   Float_t elogEffi[N]; 
   Float_t j[N] = {352.05,609.35,1120.44,1238.32,1764.58,463.15,727.38,795.00,911.27}; 
   Float_t k[N] = {8.59E-02,5.89E-02,3.88E-02,3.62E-02,2.84E-02,4.77E-02,4.09E-02,3.97E-02,3.79E-02}; 
   Float_t n[N] = {8.62E-04,6.04E-04,1.12E-03,2.82E-03,8.64E-04,1.85E-03,1.11E-03,1.45E-03,3.86E-04}; 

   for(int m =0; m < 9; m++ ) 
   { logE[m] = TMath::Log(j[m]); 
      logEffi[m] = TMath::Log(k[m]); 
// elogEffi[m] = n[m]*logEffi[m]; 
      elogEffi[m] = n[m]/k[m]; 
      cout << logE[m] << " " << logEffi[m] << " " << elogEffi[m] << endl; 
   } 
   TCanvas *myc = new TCanvas("myc","Fitting linear function"); 
   myc->SetFillColor(42); 
   myc->SetGrid(); 
// TGraph *gre3 = new TGraph(m,logE,logEffi); 
// gre3->Draw("a*"); 

   TGraphErrors *gre2 = new TGraphErrors(N,logE,logEffi,0,elogEffi); 
   gre2->SetTitle("Linear Fitting of U238 and Th232"); 
   gre2->Draw("E1A*"); 
//Fit the graph with the predefined "pol1" function 
   gre2->Fit("pol1"); 

   TMatrixD cov(2,2,TVirtualFitter::GetFitter()->GetCovarianceMatrix() ); 
   cov.Print();


}