void graphkhi2(double chi2min=32.27)
{

   double lamdaalpha[255];
   double lamdabeta[255];
   double khi2[255],k[255], I[255],J[255];

   ifstream f("val.txt");
 
   TH2D *h = new TH2D("h","h",15,0.05,1.55,15,0.05,1.55);


   for(int i=0; i<255; i++){
      f>>k[i]>>I[i]>>J[i]>>lamdaalpha[i]>>lamdabeta[i]>>khi2[i];
      h->Fill(lamdaalpha[i],lamdabeta[i],khi2[i]);//remplissage de hitogramme
   }

   TCanvas *c1=new TCanvas("c1","c1",800,600);
   c1->SetGridx();
   c1->SetGridy();

   Double_t contours[4];
   contours[0] = chi2min+0.1;
   contours[1] = chi2min+0.5;
   contours[2] = chi2min+1.;
   contours[3] = chi2min+2.;

   h->GetXaxis()->SetTitle("#lambda_{#alpha}");
   h->GetYaxis()->SetTitle("#lambda_{#beta}");
   h->SetContour(4,contours);
   

   h->Draw("CONT3");
   
   TMarker *m = new TMarker(0.55,0.59,20);
   m->SetMarkerColor(kRed);
   m->Draw();

}