void plot() {
  TFile *f = new TFile("input.root");
  f->ls();
  TCanvas *canvas = new TCanvas("canvas","proton range study",200,10,700,500);
  h2->Draw();
  int n;
  double x, y;
  double theta_appear_with[100], pcut_appear_with[100];
  double theta_appear_without[100], pcut_appear_without[100];
  double theta_track_with[100], pcut_track_with[100];
  double theta_track_without[100], pcut_track_without[100];

  ifstream input("pcut_appear_wcf.dat");
  if (!input) {
    cout << "could not open file\n";
    return 1;
  }
  n = 0;
  while (input >> x >> y) {
    // cout << n << ' ' << x << ' ' << y << ' ' << endl;
    theta_appear_with[n] = x;
    pcut_appear_with[n] = y/1000.;
    n++;
  }
  input.close();
  TGraph *grw = new TGraph(n, theta_appear_with, pcut_appear_with);
  grw->SetLineColor(2);
  grw->Draw();

  ifstream input("pcut_appear_wocf.dat");
  if (!input) {
    cout << "could not open file\n";
    return 1;
  }
  n = 0;
  while (input >> x >> y) {
    // cout << n << ' ' << x << ' ' << y << ' ' << endl;
    theta_appear_without[n] = x;
    pcut_appear_without[n] = y/1000.;
    n++;
  }
  input.close();
  TGraph *grwo = new TGraph(n, theta_appear_without, pcut_appear_without);
  grwo->SetLineColor(4);
  grwo->Draw();

  ifstream input("pcut_track_wcf.dat");
  if (!input) {
    cout << "could not open file\n";
    return 1;
  }
  n = 0;
  while (input >> x >> y) {
    // cout << n << ' ' << x << ' ' << y << ' ' << endl;
    theta_track_with[n] = x;
    pcut_track_with[n] = y/1000.;
    n++;
  }
  input.close();
  TGraph *grtw = new TGraph(n, theta_track_with, pcut_track_with);
  grtw->SetLineColor(1);
  grtw->Draw();

  ifstream input("pcut_track_wocf.dat");
  if (!input) {
    cout << "could not open file\n";
    return 1;
  }
  n = 0;
  while (input >> x >> y) {
    // cout << n << ' ' << x << ' ' << y << ' ' << endl;
    theta_track_without[n] = x;
    pcut_track_without[n] = y/1000.;
    n++;
  }
  input.close();
  TGraph *grtwo = new TGraph(n, theta_track_without, pcut_track_without);
  grtwo->SetLineColor(3);
  grtwo->Draw();

  canvas->Print("sc_study_cut.png", "png");

  TEfficiency* eff_appear_without =
    new TEfficiency("effawo","efficiency;theta;#epsilon",90,0,90);
  TEfficiency* eff_appear_with = 
    new TEfficiency("effaw","efficiency;theta;#epsilon",90,0,90);
  TEfficiency* eff_track_without =
    new TEfficiency("efftwo","efficiency;theta;#epsilon",90,0,90);
  TEfficiency* eff_track_with = 
    new TEfficiency("efftw","efficiency;theta;#epsilon",90,0,90);

  TH1F* h1pa = new TH1F("h1pa","proton polar angle",90,0,90);

  float thrange = theta_appear_without[n-1] - theta_appear_without[0];
  float thbin = thrange/(float)(n - 1);
  float thhalfbin = 0.5*thbin;
  float thmin = theta_appear_without[0] - thhalfbin;
  cout << "binning params: " << thrange << ' ' << thbin << endl;
  int ibin;
  bool pass;

  int nev = ntuple->GetEntries();
  float weight = 5./(double)nev;
  float theta0, ptot0;
  // define some counters
  int naw = 0, nawo = 0, ntw = 0, ntwo = 0;
  ntuple->SetBranchAddress("theta",&theta0);
  ntuple->SetBranchAddress("ptot",&ptot0);
  for (int i = 0; i < nev; i++) {
    ntuple->GetEntry(i);
    h1pa->Fill(theta0, weight);
    ibin = (int)((theta0-thmin)/thbin);
    if (i < 3) {
      cout << i << ' ' << theta0 << ' ' << ptot0 << endl;
      cout << "   " << ibin << ' ' << theta_appear_without[ibin] << ' '
	   << pcut_appear_without[ibin] << endl;
    }
    if (ptot0 >= pcut_appear_without[ibin]) {pass = true; nawo++;} else {pass = false;}
    eff_appear_without->Fill(pass, theta0);
    if (ptot0 >= pcut_appear_with[ibin]) {pass = true; naw++;} else {pass = false;}
    eff_appear_with->Fill(pass, theta0);
    if (ptot0 >= pcut_track_without[ibin]) {pass = true; ntwo++;} else {pass = false;}
    eff_track_without->Fill(pass, theta0);
    if (ptot0 >= pcut_track_with[ibin]) {pass = true; ntw++;} else {pass = false;}
    eff_track_with->Fill(pass, theta0);
  }
  eff_appear_without->SetMarkerColor(4);
  eff_appear_without->SetMarkerStyle(20);
  eff_appear_without->SetMarkerSize(1);
  eff_appear_without->Draw();
  eff_appear_with->SetMarkerColor(2);
  eff_appear_with->SetMarkerStyle(20);
  eff_appear_with->SetMarkerSize(1);
  eff_appear_with->Draw("same");
  eff_track_without->SetMarkerColor(3);
  eff_track_without->SetMarkerStyle(20);
  eff_track_without->SetMarkerSize(1);
  eff_track_without->Draw("same");
  eff_track_with->SetMarkerColor(1);
  eff_track_with->SetMarkerStyle(20);
  eff_track_with->SetMarkerSize(1);
  eff_track_with->Draw("same");

  h1pa->Draw("same");

  canvas->Print("sc_study_eff.png", "png");

  // overall efficiencies
  float fnev = (float)nev;
  float eaw = naw/fnev, eawo = nawo/fnev, etw = ntw/fnev , etwo = ntwo/fnev;
  cout << "overall efficiencies:"
       << " eawo = " << eawo
       << " eaw = " << eaw
       << " etwo = " << etwo
       << " etw = " << etw
       << endl;

}