void run_sim(Int_t nEvents=1000)
{
  TStopwatch timer;
  timer.Start();
  gDebug=0;

  // Use non default gconfig and geometry directories
  TString dir = getenv("VMCWORKDIR");
  TString tutdir = dir + "/example";

  TString tut_geomdir = tutdir + "/geometry";
  gSystem->Setenv("GEOMPATH",tut_geomdir.Data());

  TString tut_configdir = tutdir + "/gconfig";
  gSystem->Setenv("CONFIG_DIR",tut_configdir.Data());

 // ----  Load libraries   -------------------------------------------------
   gROOT->LoadMacro("$VMCWORKDIR/example/gconfig/basiclibs.C");
   basiclibs();
   gSystem->Load("libFairTools");
   gSystem->Load("libFairDB");
   gSystem->Load("libGeoBase");
   gSystem->Load("libParBase");
   gSystem->Load("libBase");
   gSystem->Load("libMCStack");
   gSystem->Load("libGen");
   gSystem->Load("libPassive");
   gSystem->Load("libFairTestDetector.so");

  // create Instance of Run Manager class
  FairRunSim *fRun = new FairRunSim();
  


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

  fRun->SetName("TGeant3");
  // Choose the Geant Navigation System
  // fRun->SetGeoModel("G3Native");
  
  fRun->SetOutputFile("data/testrun.root");


  // -----   Magnetic field   -------------------------------------------
  // Constant Field
  FairConstField *fMagField = new FairConstField();
  fMagField->SetField(0., 10. ,0. ); // values are in kG
  fMagField->SetFieldRegion(-50, 50,-50, 50, 350, 450);// values are in cm (xmin,xmax,ymin,ymax,zmin,zmax)
  fRun->SetField(fMagField);
  // --------------------------------------------------------------------

 
  // Set Material file Name
  //-----------------------
  fRun->SetMaterials("media.geo");
  
  // Create and add detectors
  //-------------------------
  FairModule *Cave= new FairCave("CAVE");
  Cave->SetGeometryFileName("cave.geo");
  fRun->AddModule(Cave);

  FairModule *Magnet= new FairMagnet("MAGNET");
  Magnet->SetGeometryFileName("magnet.geo");
  fRun->AddModule(Magnet);

  FairDetector *Torino= new FairTestDetector("TORINO", kTRUE);
  Torino->SetGeometryFileName("torino.geo");
  fRun->AddModule(Torino);

  // Create and Set Event Generator
  //-------------------------------

  FairPrimaryGenerator* primGen = new FairPrimaryGenerator();
  fRun->SetGenerator(primGen);
  
  // Box Generator
  FairBoxGenerator* boxGen = new FairBoxGenerator(2212, 3); // 13 = muon; 1 = multipl.
  boxGen->SetPRange(2., 2.); // GeV/c //setPRange vs setPtRange
  boxGen->SetPhiRange(0, 360); // Azimuth angle range [degree]
  boxGen->SetThetaRange(3, 10); // Polar angle in lab system range [degree]
  boxGen->SetCosTheta();//uniform generation on all the solid angle(default)

  // boxGen->SetXYZ(0., 0.37, 0.); 
  primGen->AddGenerator(boxGen);
  
  fRun->SetStoreTraj(kTRUE);
  
  fRun->Init();


 // -Trajectories Visualization (TGeoManager Only )
 // -----------------------------------------------

 // Set cuts for storing the trajectpries
  /* FairTrajFilter* trajFilter = FairTrajFilter::Instance();
     trajFilter->SetStepSizeCut(0.01); // 1 cm
     trajFilter->SetVertexCut(-2000., -2000., 4., 2000., 2000., 100.);
     trajFilter->SetMomentumCutP(10e-3); // p_lab > 10 MeV
     trajFilter->SetEnergyCut(0., 1.02); // 0 < Etot < 1.04 GeV
     trajFilter->SetStorePrimaries(kTRUE);
     trajFilter->SetStoreSecondaries(kTRUE);
   */


  // Fill the Parameter containers for this run
  //-------------------------------------------

  FairRuntimeDb *rtdb=fRun->GetRuntimeDb();
  Bool_t kParameterMerged=kTRUE;
  FairParRootFileIo* output=new FairParRootFileIo(kParameterMerged);
  output->open("data/testparams.root");
  rtdb->setOutput(output);

  rtdb->saveOutput();
  rtdb->print();

  // Transport nEvents
  // -----------------

  //  Int_t nEvents = 1;
  fRun->Run(nEvents);

  fRun->CreateGeometryFile("data/geofile_full.root");


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