Pythia6Hadronizer.cc

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// -*- C++ -*-

#include "Pythia6Hadronizer.h"

#include "HepMC/GenEvent.h"
#include "HepMC/PdfInfo.h"
#include "HepMC/PythiaWrapper6_4.h"
#include "HepMC/HEPEVT_Wrapper.h"
#include "HepMC/IO_HEPEVT.h"

#include "FWCore/Concurrency/interface/SharedResourceNames.h"
#include "FWCore/MessageLogger/interface/MessageLogger.h"

#include "GeneratorInterface/Core/interface/FortranCallback.h"
#include "GeneratorInterface/Core/interface/FortranInstance.h"

#include "GeneratorInterface/LHEInterface/interface/LHERunInfo.h"

#include "SimDataFormats/GeneratorProducts/interface/LHEEventProduct.h"

#include "GeneratorInterface/PartonShowerVeto/interface/JetMatching.h"

 
HepMC::IO_HEPEVT conv;

#include "HepPID/ParticleIDTranslations.hh"

// NOTE: here a number of Pythia6 routines are declared,
// plus some functionalities to pass around Pythia6 params
//
#include "GeneratorInterface/Pythia6Interface/interface/Pythia6Service.h"
#include "GeneratorInterface/Pythia6Interface/interface/Pythia6Declarations.h"

#include <iomanip>

namespace gen
{

extern "C" {
   
   //
   // these two are NOT part of Pythi6 core code but are "custom" add-ons
   // we keep them interfaced here, rather than in GenExtensions, because
   // they tweak not at the ME level, but a step further, at the framgmentation
   //
   // stop-hadrons
   //
   void pystrhad_();   // init stop-hadrons (id's, names, charges...)
   void pystfr_(int&); // tweaks fragmentation, fragments the string near to a stop, 
                       // to form stop-hadron by producing a new q-qbar pair
   // gluino/r-hadrons
   void pyglrhad_();
   void pyglfr_();   // tweaks fragmentation, fragment the string near to a gluino,
                     // to form gluino-hadron, either by producing a new g-g pair,
             // or two new q-qbar ones


} // extern "C"

class Pythia6ServiceWithCallback : public Pythia6Service {
  public:
     Pythia6ServiceWithCallback( const edm::ParameterSet& ps ) : Pythia6Service(ps) {}

  private:
    void upInit() override
    { FortranCallback::getInstance()->fillHeader(); }

    void upEvnt() override
    {
      FortranCallback::getInstance()->fillEvent(); 
      if ( Pythia6Hadronizer::getJetMatching() )
        Pythia6Hadronizer::getJetMatching()->beforeHadronisationExec();    
    }

    bool upVeto() override
    { 
      if ( !Pythia6Hadronizer::getJetMatching() )
        return false;

      if ( !hepeup_.nup || Pythia6Hadronizer::getJetMatching()->isMatchingDone() )
         return true;

      bool retValue = Pythia6Hadronizer::getJetMatching()->match( nullptr, nullptr );
      // below is old code and a note of it
      // NOTE: I'm passing NULL pointers, instead of HepMC::GenEvent, etc.
      //retValur = Pythia6Hadronizer::getJetMatching()->match(0, 0, true);
      return retValue;


    }
};

static struct {
    int n, npad, k[5][pyjets_maxn];
    double p[5][pyjets_maxn], v[5][pyjets_maxn];
} pyjets_local;

JetMatching* Pythia6Hadronizer::fJetMatching = nullptr;

const std::vector<std::string> Pythia6Hadronizer::theSharedResources = { edm::SharedResourceNames::kPythia6,
                                                                         gen::FortranInstance::kFortranInstance };

Pythia6Hadronizer::Pythia6Hadronizer(edm::ParameterSet const& ps) 
   : BaseHadronizer(ps),
     fPy6Service( new Pythia6ServiceWithCallback(ps) ), // this will store py6 params for further settings
     fInitialState(PP),
     fCOMEnergy(ps.getParameter<double>("comEnergy")),
     fHepMCVerbosity(ps.getUntrackedParameter<bool>("pythiaHepMCVerbosity",false)),
     fMaxEventsToPrint(ps.getUntrackedParameter<int>("maxEventsToPrint", 0)),
     fPythiaListVerbosity(ps.getUntrackedParameter<int>("pythiaPylistVerbosity", 0)),
     fDisplayPythiaBanner(ps.getUntrackedParameter<bool>("displayPythiaBanner",false)),
     fDisplayPythiaCards(ps.getUntrackedParameter<bool>("displayPythiaCards",false))
{ 

   
   // J.Y.: the following 3 parameters are hacked "for a reason"
   //
   if ( ps.exists( "PPbarInitialState" ) )
   {
      if ( fInitialState == PP )
      {
         fInitialState = PPbar;
         edm::LogInfo("GeneratorInterface|Pythia6Interface")
     << "Pythia6 will be initialized for PROTON-ANTIPROTON INITIAL STATE. "
     << "This is a user-request change from the DEFAULT PROTON-PROTON initial state." << std::endl;
     std::cout << "Pythia6 will be initialized for PROTON-ANTIPROTON INITIAL STATE." << std::endl;
     std::cout << "This is a user-request change from the DEFAULT PROTON-PROTON initial state." << std::endl;
      }
      else
      {
         // probably need to throw on attempt to override ?
      }
   }
   else if ( ps.exists( "ElectronPositronInitialState" ) )
   {
      if ( fInitialState == PP )
      {
         fInitialState = ElectronPositron;
         edm::LogInfo("GeneratorInterface|Pythia6Interface")
     << "Pythia6 will be initialized for ELECTRON-POSITRON INITIAL STATE. "
     << "This is a user-request change from the DEFAULT PROTON-PROTON initial state." << std::endl;
     std::cout << "Pythia6 will be initialized for ELECTRON-POSITRON INITIAL STATE." << std::endl;
     std::cout << "This is a user-request change from the DEFAULT PROTON-PROTON initial state." << std::endl;
      }
      else
      {
         // probably need to throw on attempt to override ?
      }
   }
   else if ( ps.exists( "ElectronProtonInitialState" ) )
   {
      if ( fInitialState == PP )
      {
         fInitialState = ElectronProton;     
     fBeam1PZ = (ps.getParameter<edm::ParameterSet>("ElectronProtonInitialState")).getParameter<double>("electronMomentum");
     fBeam2PZ = (ps.getParameter<edm::ParameterSet>("ElectronProtonInitialState")).getParameter<double>("protonMomentum");
         edm::LogInfo("GeneratorInterface|Pythia6Interface")
     << "Pythia6 will be initialized for ELECTRON-PROTON INITIAL STATE. "
     << "This is a user-request change from the DEFAULT PROTON-PROTON initial state." << std::endl;
     std::cout << "Pythia6 will be initialized for ELECTRON-PROTON INITIAL STATE." << std::endl;
     std::cout << "This is a user-request change from the DEFAULT PROTON-PROTON initial state." << std::endl;
      }
      else
      {
         // probably need to throw on attempt to override ?
      }
   }
   else if ( ps.exists( "PositronProtonInitialState" ) )
   {
      if ( fInitialState == PP )
      {
         fInitialState = PositronProton;     
     fBeam1PZ = (ps.getParameter<edm::ParameterSet>("ElectronProtonInitialState")).getParameter<double>("positronMomentum");
     fBeam2PZ = (ps.getParameter<edm::ParameterSet>("ElectronProtonInitialState")).getParameter<double>("protonMomentum");
         edm::LogInfo("GeneratorInterface|Pythia6Interface")
     << "Pythia6 will be initialized for POSITRON-PROTON INITIAL STATE. "
     << "This is a user-request change from the DEFAULT PROTON-PROTON initial state." << std::endl;
     std::cout << "Pythia6 will be initialized for POSITRON-PROTON INITIAL STATE." << std::endl;
     std::cout << "This is a user-request change from the DEFAULT PROTON-PROTON initial state." << std::endl;
      }
      else
      {
         // throw on unknown initial state !
         throw edm::Exception(edm::errors::Configuration,"Pythia6Interface") 
             <<" UNKNOWN INITIAL STATE. \n The allowed initial states are: PP, PPbar, ElectronPositron, ElectronProton, and PositronProton \n";
      }
   }
   
   
   // J.Y.: the following 4 params are "hacked", in the sense 
   // that they're tracked but get in optionally;
   // this will be fixed once we update all applications
   //

   fStopHadronsEnabled = false;
   if ( ps.exists( "stopHadrons" ) )
      fStopHadronsEnabled = ps.getParameter<bool>("stopHadrons") ;

   fGluinoHadronsEnabled = false;
   if ( ps.exists( "gluinoHadrons" ) )
      fGluinoHadronsEnabled = ps.getParameter<bool>("gluinoHadrons");
   
   fImposeProperTime = false;
   if ( ps.exists( "imposeProperTime" ) )
   {
      fImposeProperTime = ps.getParameter<bool>("imposeProperTime");
   }
   
   fConvertToPDG = false;
   if ( ps.exists( "doPDGConvert" ) )
      fConvertToPDG = ps.getParameter<bool>("doPDGConvert");
   
   if ( ps.exists("jetMatching") )
   {
      edm::ParameterSet jmParams =
            ps.getUntrackedParameter<edm::ParameterSet>(
                                "jetMatching");

      fJetMatching = JetMatching::create(jmParams).release();
   }
   
   // first of all, silence Pythia6 banner printout, unless display requested
   //
   if ( !fDisplayPythiaBanner )
   {
      if (!call_pygive("MSTU(12)=12345")) 
      {
         throw edm::Exception(edm::errors::Configuration,"PythiaError") 
             <<" Pythia did not accept MSTU(12)=12345";
      }
   }
   
// silence printouts from PYGIVE, unless display requested
//
   if ( ! fDisplayPythiaCards )
   {
      if (!call_pygive("MSTU(13)=0")) 
      {
         throw edm::Exception(edm::errors::Configuration,"PythiaError") 
             <<" Pythia did not accept MSTU(13)=0";
      }
   }

   // tmp stuff to deal with EvtGen corrupting pyjets
   // NPartsBeforeDecays = 0;
   flushTmpStorage();
   
}

Pythia6Hadronizer::~Pythia6Hadronizer()
{
   if ( fPy6Service != nullptr ) delete fPy6Service;
   if ( fJetMatching != nullptr ) delete fJetMatching;
}

void Pythia6Hadronizer::doSetRandomEngine(CLHEP::HepRandomEngine* v)
{
   fPy6Service->setRandomEngine(v);
}

void Pythia6Hadronizer::flushTmpStorage()
{

   pyjets_local.n = 0 ;
   pyjets_local.npad = 0 ;
   for ( int ip=0; ip<pyjets_maxn; ip++ )
   {
      for ( int i=0; i<5; i++ )
      {
         pyjets_local.k[i][ip] = 0;
     pyjets_local.p[i][ip] = 0.;
     pyjets_local.v[i][ip] = 0.;
      }
   }
   return;

}

void Pythia6Hadronizer::fillTmpStorage()
{

   pyjets_local.n = pyjets.n;
   pyjets_local.npad = pyjets.npad;
   for ( int ip=0; ip<pyjets_maxn; ip++ )
   {
      for ( int i=0; i<5; i++ )
      {
         pyjets_local.k[i][ip] = pyjets.k[i][ip];
     pyjets_local.p[i][ip] = pyjets.p[i][ip];
     pyjets_local.v[i][ip] = pyjets.v[i][ip];
      }
   }
   
   return ;

}

void Pythia6Hadronizer::finalizeEvent()
{

   bool lhe = lheEvent() != nullptr;

   HepMC::PdfInfo pdf;

   // if we are in hadronizer mode, we can pass on information from
   // the LHE input
   if (lhe)
   {
      lheEvent()->fillEventInfo( event().get() );
      lheEvent()->fillPdfInfo( &pdf );
   }
   else
   {
      // filling in factorization "Q scale" now! pthat moved to binningValues()
      //
            
      if ( event()->signal_process_id() <= 0) event()->set_signal_process_id( pypars.msti[0] );
      if ( event()->event_scale() <=0 )       event()->set_event_scale( pypars.pari[22] );
      if ( event()->alphaQED() <= 0)          event()->set_alphaQED( pyint1.vint[56] );
      if ( event()->alphaQCD() <= 0)          event()->set_alphaQCD( pyint1.vint[57] );
   
      // get pdf info directly from Pythia6 and set it up into HepMC::GenEvent
      // S. Mrenna: Prefer vint block
      //
      if ( pdf.id1() <= 0)      pdf.set_id1( pyint1.mint[14] == 21 ? 0 : pyint1.mint[14] );
      if ( pdf.id2() <= 0)      pdf.set_id2( pyint1.mint[15] == 21 ? 0 : pyint1.mint[15] );
      if ( pdf.x1() <= 0)       pdf.set_x1( pyint1.vint[40] );
      if ( pdf.x2() <= 0)       pdf.set_x2( pyint1.vint[41] );
      if ( pdf.pdf1() <= 0)     pdf.set_pdf1( pyint1.vint[38] / pyint1.vint[40] );
      if ( pdf.pdf2() <= 0)     pdf.set_pdf2( pyint1.vint[39] / pyint1.vint[41] );
      if ( pdf.scalePDF() <= 0) pdf.set_scalePDF( pyint1.vint[50] );   
   }

/* 9/9/2010 - JVY: This is the old piece of code - I can't remember why we implemented it this way.
                   However, it's causing problems with pdf1 & pdf2 when processing LHE samples,
           specifically, because both are set to -1, it tries to fill with Py6 numbers that
           are NOT valid/right at this point !
           In general, for LHE/ME event processing we should implement the correct calculation
           of the pdf's, rather than using py6 ones.

   // filling in factorization "Q scale" now! pthat moved to binningValues()

   if (!lhe || event()->signal_process_id() < 0) event()->set_signal_process_id( pypars.msti[0] );
   if (!lhe || event()->event_scale() < 0)       event()->set_event_scale( pypars.pari[22] );
   if (!lhe || event()->alphaQED() < 0)          event()->set_alphaQED( pyint1.vint[56] );
   if (!lhe || event()->alphaQCD() < 0)          event()->set_alphaQCD( pyint1.vint[57] );
   
   // get pdf info directly from Pythia6 and set it up into HepMC::GenEvent
   // S. Mrenna: Prefer vint block
   //
   if (!lhe || pdf.id1() < 0)      pdf.set_id1( pyint1.mint[14] == 21 ? 0 : pyint1.mint[14] );
   if (!lhe || pdf.id2() < 0)      pdf.set_id2( pyint1.mint[15] == 21 ? 0 : pyint1.mint[15] );
   if (!lhe || pdf.x1() < 0)       pdf.set_x1( pyint1.vint[40] );
   if (!lhe || pdf.x2() < 0)       pdf.set_x2( pyint1.vint[41] );
   if (!lhe || pdf.pdf1() < 0)     pdf.set_pdf1( pyint1.vint[38] / pyint1.vint[40] );
   if (!lhe || pdf.pdf2() < 0)     pdf.set_pdf2( pyint1.vint[39] / pyint1.vint[41] );
   if (!lhe || pdf.scalePDF() < 0) pdf.set_scalePDF( pyint1.vint[50] );
*/

   event()->set_pdf_info( pdf ) ;

   HepMC::GenCrossSection xsec;
   double cs = pypars.pari[0]; // cross section in mb
   cs *= 1.0e9; // translate to pb
   double cserr = cs / sqrt(pypars.msti[4]);
   xsec.set_cross_section(cs, cserr);
   event()->set_cross_section(xsec);

   // this is "standard" Py6 event weight (corresponds to PYINT1/VINT(97)
   //
   if (lhe && std::abs(lheRunInfo()->getHEPRUP()->IDWTUP) == 4)
     // translate mb to pb (CMS/Gen "convention" as of May 2009)
     event()->weights().push_back( pyint1.vint[96] * 1.0e9 );
   else
     event()->weights().push_back( pyint1.vint[96] );
   //
   // this is event weight as 1./VINT(99) (PYINT1/VINT(99) is returned by the PYEVWT) 
   //
   event()->weights().push_back( 1./(pyint1.vint[98]) );

   // now create the GenEventInfo product from the GenEvent and fill
   // the missing pieces

   eventInfo().reset( new GenEventInfoProduct( event().get() ) );

   // in Pythia6 pthat is used to subdivide samples into different bins
   // in LHE mode the binning is done by the external ME generator
   // which is likely not pthat, so only filling it for Py6 internal mode
   if (!lhe)
   {
     eventInfo()->setBinningValues( std::vector<double>(1, pypars.pari[16]) );
   }

   // here we treat long-lived particles
   //
   if ( fImposeProperTime || pydat1.mstj[21]==3 || pydat1.mstj[21]==4 ) imposeProperTime();

   // convert particle IDs Py6->PDG, if requested
   if ( fConvertToPDG ) {
      for ( HepMC::GenEvent::particle_iterator part = event()->particles_begin(); 
                                               part != event()->particles_end(); ++part) {
         (*part)->set_pdg_id(HepPID::translatePythiatoPDT((*part)->pdg_id()));
      }
   }
   
   // service printouts, if requested
   //
   if (fMaxEventsToPrint > 0) 
   {
      fMaxEventsToPrint--;
      if (fPythiaListVerbosity) call_pylist(fPythiaListVerbosity);
      if (fHepMCVerbosity) 
      {
         std::cout << "Event process = " << pypars.msti[0] << std::endl 
          << "----------------------" << std::endl;
         event()->print();
      }
   }

   // dump of all settings after all initializations
   if ( fDisplayPythiaCards ) {
     fDisplayPythiaCards = false;
     call_pylist(12);
     call_pylist(13);
     std::cout << "\n PYPARS \n" << std::endl;
     std::cout << std::setw(5) << std::fixed << "I"
               << std::setw(10) << std::fixed << "MSTP(I)"
               << std::setw(16) << std::fixed << "PARP(I)"
               << std::setw(10) << std::fixed << "MSTI(I)"
               << std::setw(16) << std::fixed << "PARI(I)" << std::endl;
     for ( unsigned int ind=0; ind < 200; ind++ ) {
       std::cout << std::setw(5) << std::fixed << ind+1
                 << std::setw(10) << std::fixed << pypars.mstp[ind]
                 << std::setw(16) << std::fixed << pypars.parp[ind]
                 << std::setw(10) << std::fixed << pypars.msti[ind]
                 << std::setw(16) << std::fixed << pypars.pari[ind] << std::endl;
     }
   }
   
   return;
}

bool Pythia6Hadronizer::generatePartonsAndHadronize()
{
   Pythia6Service::InstanceWrapper guard(fPy6Service);  // grab Py6 instance

   FortranCallback::getInstance()->resetIterationsPerEvent();
      
   // generate event with Pythia6
   //
   
   if ( fStopHadronsEnabled || fGluinoHadronsEnabled )
   {
      // call_pygive("MSTJ(1)=-1");
      call_pygive("MSTJ(14)=-1");
   }
   
   call_pyevnt();
   
   if ( fStopHadronsEnabled || fGluinoHadronsEnabled )
   {
      // call_pygive("MSTJ(1)=1");
      call_pygive("MSTJ(14)=1");
      int ierr=0;
      if ( fStopHadronsEnabled ) 
      {
         pystfr_(ierr);
     if ( ierr != 0 ) // skip failed events
     {
        event().reset();
        return false;
     }
      }
      if ( fGluinoHadronsEnabled ) pyglfr_();
   }
   
   if ( pyint1.mint[50] != 0 ) // skip event if py6 considers it bad
   {
      event().reset();
      return false;
   }
   
   call_pyhepc(1);
   event().reset( conv.read_next_event() );
   
   // this is to deal with post-gen tools & residualDecay() that may reuse PYJETS
   //
   flushTmpStorage();
   fillTmpStorage();
      
   return true;
}

bool Pythia6Hadronizer::hadronize()
{
   Pythia6Service::InstanceWrapper guard(fPy6Service);  // grab Py6 instance

   FortranCallback::getInstance()->setLHEEvent( lheEvent() );
   FortranCallback::getInstance()->resetIterationsPerEvent();
   if ( fJetMatching )
   {
      fJetMatching->resetMatchingStatus() ;
      fJetMatching->beforeHadronisation( lheEvent() );
   }

   // generate event with Pythia6
   //
   if ( fStopHadronsEnabled || fGluinoHadronsEnabled )
   {
      call_pygive("MSTJ(1)=-1");
      call_pygive("MSTJ(14)=-1");
   }

   call_pyevnt();
   
   if ( FortranCallback::getInstance()->getIterationsPerEvent() > 1 || 
        hepeup_.nup <= 0 || pypars.msti[0] == 1 )
   {
      // update LHE matching statistics
      lheEvent()->count( lhef::LHERunInfo::kSelected );

      event().reset();
      return false;
   }

   // update LHE matching statistics
   //
   lheEvent()->count( lhef::LHERunInfo::kAccepted );

   if ( fStopHadronsEnabled || fGluinoHadronsEnabled )
   {
      call_pygive("MSTJ(1)=1");
      call_pygive("MSTJ(14)=1");
      int ierr = 0;
      if ( fStopHadronsEnabled ) 
      {
         pystfr_(ierr);
     if ( ierr != 0 ) // skip failed events
     {
        event().reset();
        return false;
     }
      }
            
      if ( fGluinoHadronsEnabled ) pyglfr_();
   }

   if ( pyint1.mint[50] != 0 ) // skip event if py6 considers it bad
   {
      event().reset();
      return false;
   }
   
   call_pyhepc(1);
   event().reset( conv.read_next_event() );
   
   // this is to deal with post-gen tools and/or residualDecay(), that may reuse PYJETS
   //
   flushTmpStorage();
   fillTmpStorage();
      
   return true;
}

bool Pythia6Hadronizer::decay()
{
   return true;
}

bool Pythia6Hadronizer::residualDecay()
{
   
   // event().get()->print();
   
   Pythia6Service::InstanceWrapper guard(fPy6Service);  // grab Py6 instance
   
   // int nDocLines = pypars.msti[3];
      
   int NPartsBeforeDecays = pyjets_local.n ;
   int NPartsAfterDecays = event().get()->particles_size();
   int barcode = NPartsAfterDecays;
      
   // JVY: well, in principle, it's not a 100% fair to go up to NPartsBeforeDecays,
   // because Photos will attach gamma's to existing vertexes, i.e. in the middle
   // of the event rather than at the end; but this will only shift poiters down,
   // so we'll be going again over a few "original" particle...
   // in the alternative, we may go all the way up to the beginning of the event
   // and re-check if anything remains to decay, that's fine even if it'll take
   // some extra CPU...
   
   for ( int ipart=NPartsAfterDecays; ipart>NPartsBeforeDecays; ipart-- )
   {
      HepMC::GenParticle* part = event().get()->barcode_to_particle( ipart );
      int status = part->status();
      if ( status != 1 ) continue; // check only "stable" particles, 
                                   // as some undecayed may still be marked as such
      int pdgid  = part->pdg_id();
      int py6ptr = pycomp_( pdgid );
      if ( pydat3.mdcy[0][py6ptr-1] != 1 ) continue; // particle is not expected to decay
      int py6id = HepPID::translatePDTtoPythia( pdgid );
      //
      // first, will need to zero out, then fill up PYJETS
      // I better do it directly (by hands) rather than via py1ent 
      // - to avoid (additional) mass smearing
      //
      if ( part->momentum().t() <= part->generated_mass() )
      {
         continue ; // e==m --> 0-momentum, nothing to decay...
      }
      else
      {
         pyjets.n = 0;
     for ( int i=0; i<5; i++ )
         {
            pyjets.k[i][0] = 0;
        pyjets.p[i][0] = 0.;
        pyjets.v[i][0] = 0.;
         }
         pyjets.k[0][0] = 1;
         pyjets.k[1][0] = py6id;
         pyjets.p[4][0] = part->generated_mass();
         pyjets.p[3][0] = part->momentum().t();
     pyjets.p[0][0] = part->momentum().x();
     pyjets.p[1][0] = part->momentum().y();
     pyjets.p[2][0] = part->momentum().z();
     HepMC::GenVertex* prod_vtx = part->production_vertex();
     if ( !prod_vtx ) continue; // in principle, should never happen but...
     pyjets.v[0][0] = prod_vtx->position().x();
     pyjets.v[1][0] = prod_vtx->position().y();
     pyjets.v[2][0] = prod_vtx->position().z();
     pyjets.v[3][0] = prod_vtx->position().t();
     pyjets.v[4][0] = 0.;
     pyjets.n = 1;
     pyjets.npad = pyjets_local.npad;
      }
      
      // now call Py6 decay routine
      //
      int parent = 1; // since we always pass to Py6 a single particle
      pydecy_( parent );
      
      // now attach decay products to mother
      //
      for ( int iprt1=1; iprt1<pyjets.n; iprt1++ )
      {
     part->set_status( 2 );
     
     HepMC::GenVertex* DecVtx = new HepMC::GenVertex( HepMC::FourVector(pyjets.v[0][iprt1],
                                                                        pyjets.v[1][iprt1],
                                                pyjets.v[2][iprt1],
                                        pyjets.v[3][iprt1]) );
     DecVtx->add_particle_in( part ); // this will cleanup end_vertex if exists, replace with the new one
                          // I presume (vtx) barcode will be given automatically
     
     HepMC::FourVector  pmom(pyjets.p[0][iprt1],pyjets.p[1][iprt1],
                             pyjets.p[2][iprt1],pyjets.p[3][iprt1] );
     
     int dstatus = 0;
     if ( pyjets.k[0][iprt1] >= 1 && pyjets.k[0][iprt1] <= 10 )  
     {
           dstatus = 1;
     }
     else if ( pyjets.k[0][iprt1] >= 11 && pyjets.k[0][iprt1] <= 20 ) 
     {
           dstatus = 2;
     }
     else if ( pyjets.k[0][iprt1] >= 21 && pyjets.k[0][iprt1] <= 30 ) 
     {
           dstatus = 3;
     }
     else if ( pyjets.k[0][iprt1] >= 31 && pyjets.k[0][iprt1] <= 100 )
     {
           dstatus = pyjets.k[0][iprt1];
     }
     HepMC::GenParticle* daughter = new HepMC::GenParticle(pmom,
                                    HepPID::translatePythiatoPDT( pyjets.k[1][iprt1] ),
                        dstatus);
     barcode++;
     daughter->suggest_barcode( barcode ); 
     DecVtx->add_particle_out( daughter );

     int iprt2;
     for ( iprt2=iprt1+1; iprt2<pyjets.n; iprt2++ ) // the pointer is shifted by -1, c++ style
     {
           if ( pyjets.k[2][iprt2] != parent ) 
           {
              parent = pyjets.k[2][iprt2];
          break; // another parent particle; reset & break the loop
           }
           
           HepMC::FourVector  pmomN(pyjets.p[0][iprt2],pyjets.p[1][iprt2],
                                    pyjets.p[2][iprt2],pyjets.p[3][iprt2] );
           
           dstatus = 0;
           if ( pyjets.k[0][iprt2] >= 1 && pyjets.k[0][iprt2] <= 10 )  
           {
              dstatus = 1;
           }
           else if ( pyjets.k[0][iprt2] >= 11 && pyjets.k[0][iprt2] <= 20 ) 
           {
              dstatus = 2;
           }
           else if ( pyjets.k[0][iprt2] >= 21 && pyjets.k[0][iprt2] <= 30 ) 
           {
              dstatus = 3;
           }
           else if ( pyjets.k[0][iprt2] >= 31 && pyjets.k[0][iprt2] <= 100 )
           {
              dstatus = pyjets.k[0][iprt2];
           }
           HepMC::GenParticle* daughterN = new HepMC::GenParticle(pmomN,
                                           HepPID::translatePythiatoPDT( pyjets.k[1][iprt2] ),
                               dstatus);
           barcode++;
           daughterN->suggest_barcode( barcode ); 
           DecVtx->add_particle_out( daughterN );        
     }
     
     iprt1 = iprt2-1; // reset counter such that it doesn't go over the same child more than once
                      // don't forget to offset back into c++ counting, as it's already +1 forward

     event().get()->add_vertex( DecVtx );
      
      }

   }
   
   // now restore the very original Py6 event record 
   //
   if ( pyjets_local.n != pyjets.n )
   {
      // restore pyjets to its state as it was before external decays -
      // might have been jammed by action above or by py1ent calls in EvtGen
      pyjets.n = pyjets_local.n;
      pyjets.npad = pyjets_local.npad;
      for ( int ip=0; ip<pyjets_local.n; ip++ )
      {
         for ( int i=0; i<5; i++ )
     {
        pyjets.k[i][ip] = pyjets_local.k[i][ip];
        pyjets.p[i][ip] = pyjets_local.p[i][ip];
        pyjets.v[i][ip] = pyjets_local.v[i][ip];
     }
      }
   }  
         
   return true;
}

bool Pythia6Hadronizer::readSettings( int key )
{

   Pythia6Service::InstanceWrapper guard(fPy6Service);  // grab Py6 instance
    
   fPy6Service->setGeneralParams();   
   if ( key == 0 ) fPy6Service->setCSAParams();
   fPy6Service->setSLHAParams();

   return true;

}

bool Pythia6Hadronizer::initializeForExternalPartons()
{
   Pythia6Service::InstanceWrapper guard(fPy6Service);  // grab Py6 instance

   // note: CSA mode is NOT supposed to work with external partons !!!
   
   // fPy6Service->setGeneralParams();
   
   fPy6Service->setPYUPDAParams(false);

   FortranCallback::getInstance()->setLHERunInfo( lheRunInfo() );

   if ( fStopHadronsEnabled )
   {
      // overwrite mstp(111), no matter what
      call_pygive("MSTP(111)=0");
      pystrhad_();
      call_pygive("MWID(302)=0");   // I don't know if this is specific to processing ME/LHE only,
      call_pygive("MDCY(302,1)=0"); // or this should also be the case for full event...
                                    // anyway, this comes from experience of processing MG events
   }
   
   if ( fGluinoHadronsEnabled )
   {
      // overwrite mstp(111), no matter what
      call_pygive("MSTP(111)=0");
      pyglrhad_();
      //call_pygive("MWID(309)=0");   
      //call_pygive("MDCY(309,1)=0"); 
   }
   
   call_pyinit("USER", "", "", 0.0);

   fPy6Service->setPYUPDAParams(true);

   std::vector<std::string> slha = lheRunInfo()->findHeader("slha");
   if (!slha.empty()) {
        edm::LogInfo("Generator|LHEInterface")
            << "Pythia6 hadronisation found an SLHA header, "
            << "will be passed on to Pythia." << std::endl;
      fPy6Service->setSLHAFromHeader(slha);   
      fPy6Service->closeSLHA();
   }

   if ( fJetMatching )
   {
      fJetMatching->init( lheRunInfo() );
// FIXME: the jet matching routine might not be interested in PS callback
      call_pygive("MSTP(143)=1");
   }

   return true;
}

bool Pythia6Hadronizer::initializeForInternalPartons()
{

   Pythia6Service::InstanceWrapper guard(fPy6Service);  // grab Py6 instance
   
   fPy6Service->setPYUPDAParams(false);
   
   if ( fStopHadronsEnabled )
   {
      // overwrite mstp(111), no matter what
      call_pygive("MSTP(111)=0");
      pystrhad_();
   }
   
   if ( fGluinoHadronsEnabled )
   {
      // overwrite mstp(111), no matter what
      call_pygive("MSTP(111)=0");
      pyglrhad_();
   }

   if ( fInitialState == PP ) // default
   {
      call_pyinit("CMS", "p", "p", fCOMEnergy);
   }
   else if ( fInitialState == PPbar )
   {
      call_pyinit( "CMS", "p", "pbar", fCOMEnergy);
   }
   else if ( fInitialState == ElectronPositron )
   {
      call_pyinit( "CMS", "e+", "e-", fCOMEnergy );
   }
   else if ( fInitialState == ElectronProton)
   {
      // set p(1,i) & p(2,i) for the beams in pyjets !
      pyjets.p[0][0] = 0.;
      pyjets.p[1][0] = 0.;
      pyjets.p[2][0] = fBeam1PZ;
      pyjets.p[0][1] = 0.;
      pyjets.p[1][1] = 0.;
      pyjets.p[2][1] = fBeam2PZ;
      // call "3mon" frame & 0.0 win
      call_pyinit( "3mom", "e-", "p", 0.0 );
   }
   else if ( fInitialState == PositronProton)
   {
      // set p(1,i) & p(2,i) for the beams in pyjets !
      pyjets.p[0][0] = 0.;
      pyjets.p[1][0] = 0.;
      pyjets.p[2][0] = fBeam1PZ;
      pyjets.p[0][1] = 0.;
      pyjets.p[1][1] = 0.;
      pyjets.p[2][1] = fBeam2PZ;
      // call "3mon" frame & 0.0 win
      call_pyinit( "3mom", "e+", "p", 0.0 );
   }
   else
   {
      // throw on unknown initial state !
      throw edm::Exception(edm::errors::Configuration,"Pythia6Interface") 
             <<" UNKNOWN INITIAL STATE. \n The allowed initial states are: PP, PPbar, ElectronPositron, ElectronProton, and PositronProton \n";
   }
   

   fPy6Service->setPYUPDAParams(true);
   
   fPy6Service->closeSLHA();
   
   return true;
}

bool Pythia6Hadronizer::declareStableParticles( const std::vector<int>& pdg )
{
   
   for ( unsigned int i=0; i<pdg.size(); i++ )
   {
      int PyID = HepPID::translatePDTtoPythia( pdg[i] );
      // int PyID = pdg[i]; 
      int pyCode = pycomp_( PyID );
      if ( pyCode > 0 )
      {
         std::ostringstream pyCard ;
         pyCard << "MDCY(" << pyCode << ",1)=0";
/* this is a test printout... 
         std::cout << "pdg= " << pdg[i] << " " << pyCard.str() << std::endl; 
*/
         call_pygive( pyCard.str() );
      }
   }
      
   return true;
}

bool Pythia6Hadronizer::declareSpecialSettings( const std::vector<std::string>& settings )
{
   
   for ( unsigned int iss=0; iss<settings.size(); iss++ )
   {
      if ( settings[iss].find("QED-brem-off") == std::string::npos ) continue;
      size_t fnd1 = settings[iss].find(":");
      if ( fnd1 == std::string::npos ) continue;
      
      std::string value = settings[iss].substr (fnd1+1);
      
      if ( value == "all" ) 
      {
         call_pygive( "MSTJ(41)=3" );
      }
      else
      {
         int number = atoi(value.c_str());
         int PyID = HepPID::translatePDTtoPythia( number );
     int pyCode = pycomp_( PyID );
         if ( pyCode > 0 )
         {
            
        // first of all, check if mstj(39) is 0 or if we're trying to override user's setting
        // if so, throw an exception and stop, because otherwise the user will get behaviour
        // that's different from what she/he expects !
        if ( pydat1_.mstj[38] > 0 && pydat1_.mstj[38] != pyCode )
        {
               throw edm::Exception(edm::errors::Configuration,"Pythia6Interface") 
                   << " Fatal conflict: \n mandatory internal directive to set MSTJ(39)=" << pyCode 
           << " overrides user setting MSTJ(39)=" << pydat1_.mstj[38] << " - user will not get expected behaviour \n";         
        }
        std::ostringstream pyCard ;
            pyCard << "MSTJ(39)=" << pyCode ;
        call_pygive( pyCard.str() );
     }
      }
   }
   
   return true;

}

void Pythia6Hadronizer::imposeProperTime()
{

   // this is practically a copy/paste of the original code by J.Alcaraz, 
   // taken directly from PythiaSource
    
   int dumm=0;
   HepMC::GenEvent::vertex_const_iterator vbegin = event()->vertices_begin();
   HepMC::GenEvent::vertex_const_iterator vend = event()->vertices_end();
   HepMC::GenEvent::vertex_const_iterator vitr = vbegin;
   for (; vitr != vend; ++vitr ) 
   {
      HepMC::GenVertex::particle_iterator pbegin = (*vitr)->particles_begin(HepMC::children);
      HepMC::GenVertex::particle_iterator pend = (*vitr)->particles_end(HepMC::children);
      HepMC::GenVertex::particle_iterator pitr = pbegin;
      for (; pitr != pend; ++pitr) 
      {
         if ((*pitr)->end_vertex()) continue;
         if ((*pitr)->status()!=1) continue;
         
     int pdgcode= abs((*pitr)->pdg_id());
         // Do nothing if the particle is not expected to decay
         if ( pydat3.mdcy[0][pycomp_(pdgcode)-1] !=1 ) continue;

         double ctau = pydat2.pmas[3][pycomp_(pdgcode)-1];
         HepMC::FourVector mom = (*pitr)->momentum();
         HepMC::FourVector vin = (*vitr)->position();
         double x = 0.;
         double y = 0.;
         double z = 0.;
         double t = 0.;
         bool decayInRange = false;
         while (!decayInRange) 
     {
            double unif_rand = fPy6Service->call(pyr_, &dumm);
            // Value of 0 is excluded, so following line is OK
            double proper_length = - ctau * log(unif_rand);
            double factor = proper_length/mom.m();
            x = vin.x() + factor * mom.px();
            y = vin.y() + factor * mom.py();
            z = vin.z() + factor * mom.pz();
            t = vin.t() + factor * mom.e();
            // Decay must be happen outside a cylindrical region
            if (pydat1.mstj[21]==4) {
               if (std::sqrt(x*x+y*y)>pydat1.parj[72] || fabs(z)>pydat1.parj[73]) decayInRange = true;
               // Decay must be happen outside a given sphere
               } 
           else if (pydat1.mstj[21]==3) {
                  if (std::sqrt(x*x+y*y+z*z)>pydat1.parj[71]) decayInRange = true;
               } 
               // Decay is always OK otherwise
           else {
                  decayInRange = true;
               }
         }
                  
         HepMC::GenVertex* vdec = new HepMC::GenVertex(HepMC::FourVector(x,y,z,t));
         event()->add_vertex(vdec);
         vdec->add_particle_in((*pitr));
      }
   }   

   return;
   
}

void Pythia6Hadronizer::statistics()
{

  if ( !runInfo().internalXSec() )
  {
     // set xsec if not already done (e.g. from LHE cross section collector)
     double cs = pypars.pari[0]; // cross section in mb
     cs *= 1.0e9; // translate to pb (CMS/Gen "convention" as of May 2009)
     runInfo().setInternalXSec( cs );
// FIXME: can we get the xsec statistical error somewhere?
  }

  call_pystat(1);
  
  return;

}

const char* Pythia6Hadronizer::classname() const
{
   return "gen::Pythia6Hadronizer";
}

} // namespace gen