void analysis(const char *energy)
{
  gROOT->Reset();
  char name[128];

  sprintf(name,"%s GeV pions",energy);
  c1 = new TCanvas("c1",name,10,10,800,800);

  const Int_t nColumns = 25;
  const Int_t nRows = 25;

  TH2F *h_int = new TH2F("h_int","interaction",nRows,0,nRows,nColumns,0,nColumns);
  h_int->SetStats(0);
  h_int->SetBit(TH1::kCanRebin);

  char *Blacks[25] = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
		      "10", "11", "12", "13", "14", "15", "16", "17", "18", "19",
		      "20", "21", "22", "23", "24"};
  char *Whites[25] = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
		      "10", "11", "12", "13", "14", "15", "16", "17", "18", "19",
		      "20", "21", "22", "23", "24"};


  sprintf(name,"largePions_%sGeV.root",energy);
  cout << name << endl;
  TFile *f = new TFile(name);
  TTree *tree = (TTree*)f->Get("tree");

  TEventList *elInt_list = (TEventList*)gDirectory->Get("elInt_list");
  TEventList *inInt_list = (TEventList*)gDirectory->Get("inInt_list");

  TEventList *int_list = new TEventList(*elInt_list);
  int_list->Add(inInt_list);
  int_list->Sort();

  Event *event = new Event();
  TBranch *branch  = tree->GetBranch("event");
  branch->SetAddress(&event);
  TClonesArray *tracks = 0;
  Track *t = 0;
  Float_t beta;

  //int
  tree->SetEventList(int_list);
  Int_t nevent = (Int_t)int_list->GetN();
  cout << nevent << endl;
  for (Int_t i=0;i<nevent;i++) {
    tree->GetEntry(i);

    // pion vertex
    if(event->GetID() != 14 ) continue;

    Int_t nBlacks = 0;
    Int_t nWhites = 0;
    for(Int_t j = 0; j<event->GetNtrack(); ++j) {

      tracks = event->GetTracks();
      t = (Track*)tracks->At(j);
    
      if(is_charged(t->GetID())) {
  	beta = t->GetP()/t->GetEnergy();
  	if(beta<0.7) ++nBlacks;
  	else ++nWhites;
      }
    }

    h_int->Fill(Blacks[nBlacks], Whites[nWhites],1);
    event->Clear();
  }

  h_int->LabelsDeflate("X");
  h_int->LabelsDeflate("Y");
//    h_int->GetXaxis()->LabelsOption(">");
//    h_int->GetYaxis()->LabelsOption(">");
  h_int->GetXaxis()->SetTitle("Blacks");
  h_int->GetYaxis()->SetTitle("Whites");
  gPad->SetGrid();
  h_int->Draw("TEXT");

  sprintf(name,"largePions_%sGeV.ps",energy);
  c1->Print(name);
  // close root file
  f->Close();
}