void plot_links(){
  double p[7]={0.5,1.0,1.5,2.0,2.5,3.0,3.5};
  double links4[7]={1472,1507,1098,953,942,805,712};
  double links3[7]={1734,510,589,643,671,671,706};
  double links2[7]={286,78,138,171,217,231,276};
  double links1[7]={21,5,14,28,29,26,40};
  double events[7],bevents[7];
  double frac1[7],frac2[7],frac3[7],frac4[7];
  double bfrac1[7],bfrac2[7],bfrac3[7],bfrac4[7];
  double blinks4[7]={1575,1749,1428,1336,1364,1290,1214};
  double blinks3[7]={1661,320,354,399,421,385,437};
  double blinks2[7]={248,24,55,47,66,54,77};
  double blinks1[7]={19,3,4,5,8,5,8};

  for (int i=0;i<7;i++){
    events[i]=links4[i]+links3[i]+links2[i]+links1[i];
    frac1[i]=links1[i]/events[i];
    frac2[i]=links2[i]/events[i];
    frac3[i]=links3[i]/events[i];
    frac4[i]=links4[i]/events[i]; 
    bevents[i]=blinks4[i]+blinks3[i]+blinks2[i]+blinks1[i];
    bfrac1[i]=blinks1[i]/bevents[i];
    bfrac2[i]=blinks2[i]/bevents[i];
    bfrac3[i]=blinks3[i]/bevents[i];
    bfrac4[i]=blinks4[i]/bevents[i];
  }

  TH2F *hr13 = new TH2F("hr13","Track linking efficiency",
                        2,0,4.,2,0,1.0);
  hr13->SetXTitle("p (GeV/c)");
  hr13->SetYTitle("Efficiency");
  hr13->Draw();

  TGraph *g0=new TGraph(7,p,frac4); 
  g0->SetMarkerStyle(kFullCircle);
  g0->SetMarkerColor(1);
  g0->SetLineColor(1);

  //  g0->Draw("p");  

  TGraph *g1=new TGraph(7,p,frac3); 
  g1->SetMarkerStyle(kOpenCircle);
  g1->SetMarkerColor(1);
  g1->SetLineColor(1);

  //g1->Draw("p"); 

  TGraph *g2=new TGraph(7,p,frac2); 
  g2->SetMarkerStyle(kFullSquare);
  g2->SetMarkerColor(1);
  g2->SetLineColor(1);

  //g2->Draw("p"); 

  TGraph *g3=new TGraph(7,p,frac1); 
  g3->SetMarkerStyle(kOpenSquare);
  g3->SetMarkerColor(1);
  g3->SetLineColor(1);

  //g3->Draw("p");

  TGraph *g4=new TGraph(7,p,bfrac4); 
  g4->SetMarkerStyle(kFullCircle);
  g4->SetMarkerColor(2);
  g4->SetLineColor(2);

  g4->Draw("p");  

  TGraph *g5=new TGraph(7,p,bfrac3); 
  g5->SetMarkerStyle(kOpenCircle);
  g5->SetMarkerColor(2);
  g5->SetLineColor(2);

  g5->Draw("p"); 

  TGraph *g6=new TGraph(7,p,bfrac2); 
  g6->SetMarkerStyle(kFullSquare);
  g6->SetMarkerColor(2);
  g6->SetLineColor(2);

  g6->Draw("p"); 

  TGraph *g7=new TGraph(7,p,bfrac1); 
  g7->SetMarkerStyle(kOpenSquare);
  g7->SetMarkerColor(2);
  g7->SetLineColor(2);

  g7->Draw("p");
 
  TLegend *legend=new TLegend(0.35,0.75,0.85,0.95);
  legend->AddEntry(g4,"4/4 segments linked","p");
  legend->AddEntry(g5,"3/4 segments linked","p");
  legend->AddEntry(g6,"2/4 segments linked","p");
  legend->AddEntry(g7,"No segments linked","p");
  legend->Draw();


}