run_sim(Int_t nEvents=5000, Int_t pid=13, Float_t p1=1.0, Float_t p2=-1){
  //2212 proton
  TStopwatch timer;
  timer.Start();
  gDebug=0;
  // Load basic libraries
  // If it does not work,  please check the path of the libs and put it by hands
  gROOT->LoadMacro("$VMCWORKDIR/gconfig/rootlogon.C");
  rootlogon();
  
  TString digiFile = "all.par";
  TString parFile = "params.root";
  
  FairRunSim *fRun = new FairRunSim();

  // set the MC version used
  // ------------------------

  fRun->SetName("TGeant3");
  //fRun->SetName("TGeant4");

  fRun->SetOutputFile("points.root");

  // Set Material file Name
  //-----------------------
  fRun->SetMaterials("media_pnd.geo");

  // Create and add detectors
  //-------------------------
  FairModule *Cave= new PndCave("CAVE");
  Cave->SetGeometryFileName("pndcave.geo");
  fRun->AddModule(Cave); 
	
  FairDetector *Fts= new PndFts("FTS", kTRUE);
  Fts->SetGeometryFileName("fts.geo");
  fRun->AddModule(Fts);  // Create and Set Event Generator
  //-------------------------------

  FairPrimaryGenerator* primGen = new FairPrimaryGenerator();
  fRun->SetGenerator(primGen);

   // Box Generator
  FairBoxGenerator* boxGen = new FairBoxGenerator(pid, 1); // 13 = muon; 1 = multipl.
  if (p2<0.) p2 = p1;
  boxGen->SetPRange(p1,p2); // GeV/c
  boxGen->SetPhiRange(0., 360.); // Azimuth angle range [degree]
  boxGen->SetThetaRange(1., 5.); // Polar angle in lab system range [degree]
  boxGen->SetXYZ(0., 0., 0.); // cm 
  primGen->AddGenerator(boxGen); 


  //fRun->SetStoreTraj(kTRUE); // to store particle trajectories  

  // Create and Set Magnetic Field
  //-------------------------------
  fRun->SetBeamMom(15);
  PndMultiField *fField= new PndMultiField("FULL");
  fRun->SetField(fField);

  // Set the parameters
  //-------------------------------
  
  TString allDigiFile = gSystem->Getenv("VMCWORKDIR");
  allDigiFile += "/macro/params/";
  allDigiFile += digiFile;

 
  FairRuntimeDb* rtdb = fRun->GetRuntimeDb();
  FairParAsciiFileIo* parIo1 = new FairParAsciiFileIo();
  parIo1->open(allDigiFile.Data(),"in");
  rtdb->setFirstInput(parIo1);        
  Bool_t kParameterMerged=kTRUE;
	
  FairParRootFileIo* output=new FairParRootFileIo(kParameterMerged);
  output->open(parFile);
  rtdb->setOutput(output);
  
  /**Initialize the session*/
  fRun->Init();
  
  rtdb->setOutput(output);
  rtdb->saveOutput();
  rtdb->print();

  // Transport nEvents
  // -----------------
  fRun->Run(nEvents);



    Int_t nEvents = 10;
    fRun->Run(nEvents);


  timer.Stop();

  Double_t rtime = timer.RealTime();
  Double_t ctime = timer.CpuTime();
  printf("RealTime=%f seconds, CpuTime=%f seconds\n",rtime,ctime);

}