void Config()
{

  new AliGeant3("C++ Interface to Geant3");

  // Create the output file
  TFile *rootfile = new TFile("TRD_test.root","recreate");
  rootfile->SetCompressionLevel(2);

  // Define the monte carlo
  TGeant3 *geant3 = (TGeant3*) gMC;

  // Set external decayer
  AliDecayer* decayer = new AliDecayerPythia();
  decayer->SetForceDecay(all);
  decayer->Init();
  gMC->SetExternalDecayer(decayer);

  // ******* GEANT STEERING parameters FOR ALICE SIMULATION *******
  geant3->SetTRIG(1); // Number of events to be processed 
  geant3->SetSWIT(4,10);
  geant3->SetDEBU(0,0,1);
  //geant3->SetSWIT(2,2);
  geant3->SetDCAY(1);
  geant3->SetPAIR(1);
  geant3->SetCOMP(1);
  geant3->SetPHOT(1);
  geant3->SetPFIS(0);
  geant3->SetDRAY(0);
  geant3->SetANNI(1);
  geant3->SetBREM(1);
  geant3->SetMUNU(1);
  geant3->SetCKOV(1);
  geant3->SetHADR(1); // Select pure GEANH (HADR 1) or GEANH/NUCRIN (HADR 3)
  geant3->SetLOSS(2);
  geant3->SetMULS(1);
  geant3->SetRAYL(1);
  geant3->SetAUTO(1); // Select automatic STMIN etc... calc. (AUTO 1) or manual (AUTO 0)
  geant3->SetABAN(0); // Restore 3.16 behaviour for abandoned tracks
  geant3->SetOPTI(2); // Select optimisation level for GEANT geometry searches (0,1,2)
  geant3->SetERAN(5.e-7);

  Float_t cut    = 1.e-3; // 1MeV cut by default
  Float_t tofmax = 1.e10;
  //             GAM ELEC NHAD CHAD MUON EBREM MUHAB EDEL MUDEL MUPA TOFMAX
  geant3->SetCUTS(cut,cut, cut, cut, cut, cut,  cut,  cut, cut,  cut, tofmax);

  // ************* STEERING parameters FOR ALICE SIMULATION **************
  // --- Specify event type to be tracked through the ALICE setup
  // --- All positions are in cm, angles in degrees, and P and E in GeV
  //AliGenHIJINGpara *gener = new AliGenHIJINGpara(250);
  AliGenBox *gener = new AliGenBox(100);
  gener->SetMomentumRange(1.0,3.0);
  gener->SetPhiRange(80.0,100.0);
  gener->SetThetaRange(70.0,110.0);
  gener->SetPart(11);             // Only electrons 
  gener->SetOrigin(0,0,0);        // Vertex position
  gener->SetSigma(0,0,0);         // Sigma in (X,Y,Z) (cm) on IP position
  gener->Init();

  //Specify maximum magnetic field in Tesla (neg. ==> default field)
  gAlice->SetField(-999,2);    

  Int_t iMAG   = 1;
  Int_t iITS   = 1;
  Int_t iTPC   = 1;
  Int_t iTRD   = 1;
  Int_t iABSO  = 1;
  Int_t iDIPO  = 1;
  Int_t iHALL  = 1;
  Int_t iFRAME = 1;
  Int_t iSHIL  = 1;
  Int_t iPIPE  = 1;

  //=================== Alice BODY parameters =============================
  AliBODY *BODY = new AliBODY("BODY","Alice envelop");

  if (iMAG) {
    //=================== MAG parameters ============================
    // --- Start with Magnet since detector layouts may be depending ---
    // --- on the selected Magnet dimensions ---
    AliMAG *MAG  = new AliMAG("MAG","Magnet");
  }

  if (iABSO) { 
    //=================== ABSO parameters ============================
    AliABSO *ABSO  = new AliABSOv0("ABSO","Muon Absorber");
  }

  if (iDIPO) {
    //=================== DIPO parameters ============================
    AliDIPO *DIPO  = new AliDIPOv2("DIPO","Dipole version 2");
  }

  if (iHALL) {
    //=================== HALL parameters ============================
    AliHALL *HALL  = new AliHALL("HALL","Alice Hall");
  }

  if (iFRAME) {
    //=================== FRAME parameters ============================
    AliFRAME *FRAME  = new AliFRAMEv1("FRAME","Space Frame");
  }

  if (iSHIL) {
    //=================== SHIL parameters ============================
    AliSHIL *SHIL  = new AliSHILv0("SHIL","Shielding");
  }

  if (iPIPE) {
    //=================== PIPE parameters ============================
    AliPIPE *PIPE  = new AliPIPEv0("PIPE","Beam Pipe");
  }

  if (iITS) {
    //=================== ITS parameters ============================
    //
    // EUCLID is a flag to output (=1) both geometry and media to two ASCII files 
    // (called by default ITSgeometry.euc and ITSgeometry.tme) in a format
    // understandable to the CAD system EUCLID. The default (=0) means that you 
    // dont want to use this facility.
    //
    AliITS *ITS  = new AliITSv5("ITS","normal ITS");
    ITS->SetEUCLID(0);
  }

  if (iTPC) {
    //============================ TPC parameters ================================
    // --- This allows the user to specify sectors for the SLOW (TPC geometry 2)
    // --- Simulator. SecAL (SecAU) <0 means that ALL lower (upper)
    // --- sectors are specified, any value other than that requires at least one 
    // --- sector (lower or upper)to be specified!
    // --- Reminder: sectors 1-24 are lower sectors (1-12 -> z>0, 13-24 -> z<0)
    // ---           sectors 25-72 are the upper ones (25-48 -> z>0, 49-72 -> z<0)
    // --- SecLows - number of lower sectors specified (up to 6)
    // --- SecUps - number of upper sectors specified (up to 12)
    // --- Sens - sensitive strips for the Slow Simulator !!!
    // --- This does NOT work if all S or L-sectors are specified, i.e.
    // --- if SecAL or SecAU < 0
    //
    //
    //-----------------------------------------------------------------------------

    gROOT->LoadMacro("SetTPCParam.C");
    AliTPCParam *param = SetTPCParam();
    AliTPC *TPC  = new AliTPCv1("TPC","Default"); //v1 is default
    TPC->SetParam(param); // pass the parameter object to the TPC

    // set gas mixture
    TPC->SetGasMixt(2,20,10,-1,0.9,0.1,0.);
    TPC->SetSecAL(4);
    TPC->SetSecAU(4);
    TPC->SetSecLows(1,  2,  3, 19, 20, 21);
    TPC->SetSecUps(37, 38, 39, 37+18, 38+18, 39+18, -1, -1, -1, -1, -1, -1);
    TPC->SetSens(1);

    if (TPC->IsVersion()==1) param->Write(param->GetTitle());

  }

  if (iTRD) {
    //=================== TRD parameters ============================
  
    AliTRD *TRD  = new AliTRDv1("TRD","TRD slow simulator");
    TRD->SetSensChamber(2);
    TRD->SetSensSector(13);
  
    // Select the gas mixture (0: 97% Xe + 3% isobutane, 1: 90% Xe + 10% CO2)
    TRD->SetGasMix(1);

    // Set to detailed display
    TRD->SetDisplayType(1);

    // Switch on TR
    AliTRDsim *TRDsim = TRD->CreateTR();

  }
        
}