Herwig6Hadronizer.cc

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#include <cstring>
#include <sstream>
#include <string>
#include <vector>
#include <memory>
#include <map>
#include <set>

#include <boost/shared_ptr.hpp>
#include <boost/algorithm/string/classification.hpp>
#include <boost/algorithm/string/split.hpp>

#include <HepMC/GenEvent.h>
#include <HepMC/GenParticle.h>
#include <HepMC/GenVertex.h>
#include <HepMC/PdfInfo.h>
#include <HepMC/HerwigWrapper6_4.h>
#include <HepMC/HEPEVT_Wrapper.h>
#include <HepMC/IO_HERWIG.h>
#include "HepPID/ParticleIDTranslations.hh"

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

#include "SimDataFormats/GeneratorProducts/interface/HepMCProduct.h"
#include "SimDataFormats/GeneratorProducts/interface/GenRunInfoProduct.h"

#include "SimDataFormats/GeneratorProducts/interface/LesHouches.h"
#include "SimDataFormats/GeneratorProducts/interface/LHECommonBlocks.h"

#include "GeneratorInterface/Core/interface/ParameterCollector.h"
#include "GeneratorInterface/Core/interface/BaseHadronizer.h"
#include "GeneratorInterface/Core/interface/GeneratorFilter.h"
#include "GeneratorInterface/Core/interface/HadronizerFilter.h"

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

#include "GeneratorInterface/Herwig6Interface/interface/Herwig6Instance.h"
#include "GeneratorInterface/Herwig6Interface/interface/herwig.h"

#include "DataFormats/Math/interface/LorentzVector.h"

extern "C" {
  void hwuidt_(int *iopt, int *ipdg, int *iwig, char nwig[8]);
  double hwualf_(int *mode, double* scale);
  double hwuaem_(double* scale);
}

// helpers
namespace {
    static inline bool call_hwmsct()
    {
        int result;
        hwmsct(&result);
        return result;
    }

    static int pdgToHerwig(int ipdg, char *nwig)
    {
        int iopt = 1;
        int iwig = 0;
        hwuidt_(&iopt, &ipdg, &iwig, nwig);
        return ipdg ? iwig : 0;
    }

    static bool markStable(int pdgId)
    {
        char nwig[9] = "        ";
        if (!pdgToHerwig(pdgId, nwig))
            return false;
        hwusta(nwig, 1);
        return true;
    }
}

class Herwig6Hadronizer : public gen::BaseHadronizer,
                          public gen::Herwig6Instance {
    public:
    Herwig6Hadronizer(const edm::ParameterSet &params);
    ~Herwig6Hadronizer();

    void setSLHAFromHeader(const std::vector<std::string> &lines);
    bool initialize(const lhef::HEPRUP *heprup);

    bool initializeForInternalPartons() { return initialize(0); }
    bool initializeForExternalPartons() { return initialize(lheRunInfo()->getHEPRUP()); }

    bool declareStableParticles( const std::vector<int> &pdgIds);
    bool declareSpecialSettings( const std::vector<std::string> );

    void statistics();


    bool generatePartonsAndHadronize() { return hadronize(); }
    bool hadronize();
    bool decay();
    bool residualDecay();
    void finalizeEvent();

    const char *classname() const { return "Herwig6Hadronizer"; }

    private:
    void clear();

    int pythiaStatusCode(const HepMC::GenParticle *p) const;
    void pythiaStatusCodes();

    virtual void upInit();
    virtual void upEvnt();

    HepMC::IO_HERWIG        conv;
    bool                needClear;
    bool                externalPartons;

    gen::ParameterCollector     parameters;
    int             herwigVerbosity;
    int             hepmcVerbosity;
    int             maxEventsToPrint;
    bool                printCards;
    bool                emulatePythiaStatusCodes;
    double              comEnergy;
    bool                useJimmy;
    bool                doMPInteraction;
    int             numTrials;
        bool                            fConvertToPDG;  // convert PIDs 

        bool                            readMCatNLOfile;

};

extern "C" {
    void hwwarn_(const char *method, int *id);
    void setherwpdf_(void);
    void mysetpdfpath_(const char *path);
} // extern "C"

Herwig6Hadronizer::Herwig6Hadronizer(const edm::ParameterSet &params) :
    BaseHadronizer(params),
    needClear(false),
    parameters(params.getParameter<edm::ParameterSet>("HerwigParameters")),
    herwigVerbosity(params.getUntrackedParameter<int>("herwigVerbosity", 0)),
    hepmcVerbosity(params.getUntrackedParameter<int>("hepmcVerbosity", 0)),
    maxEventsToPrint(params.getUntrackedParameter<int>("maxEventsToPrint", 0)),
    printCards(params.getUntrackedParameter<bool>("printCards", false)),
    emulatePythiaStatusCodes(params.getUntrackedParameter<bool>("emulatePythiaStatusCodes", false)),
    comEnergy(params.getParameter<double>("comEnergy")),
    useJimmy(params.getParameter<bool>("useJimmy")),
    doMPInteraction(params.getParameter<bool>("doMPInteraction")),
    numTrials(params.getUntrackedParameter<int>("numTrialsMPI", 100)),
    readMCatNLOfile(false)
{
  
  fConvertToPDG = false;
  if ( params.exists( "doPDGConvert" ) )
    fConvertToPDG = params.getParameter<bool>("doPDGConvert");
}

Herwig6Hadronizer::~Herwig6Hadronizer()
{
    clear();
}

void Herwig6Hadronizer::clear()
{
    if (!needClear)
        return;

    // teminate elementary process
    call(hwefin);
    if (useJimmy)
        call(jmefin);

    needClear = false;
}

void Herwig6Hadronizer::setSLHAFromHeader(
                const std::vector<std::string> &lines)
{
    std::set<std::string> blocks;
    std::string block;
    for(std::vector<std::string>::const_iterator iter = lines.begin();
        iter != lines.end(); ++iter) {
        std::string line = *iter;
        std::transform(line.begin(), line.end(),
                       line.begin(), (int(*)(int))std::toupper);
        std::string::size_type pos = line.find('#');
        if (pos != std::string::npos)
            line.resize(pos);

        if (line.empty())
            continue;

        if (!boost::algorithm::is_space()(line[0])) {
            std::vector<std::string> tokens;
            boost::split(tokens, line,
                         boost::algorithm::is_space(),
                         boost::token_compress_on);
            if (!tokens.size())
                continue;
            block.clear();
            if (tokens.size() < 2)
                continue;
            if (tokens[0] == "BLOCK")
                block = tokens[1];
            else if (tokens[0] == "DECAY")
                block = "DECAY";

            if (block.empty())
                continue;

            if (!blocks.count(block)) {
                blocks.insert(block);
                edm::LogWarning("Generator|Herwig6Hadronzier")
                    << "Unsupported SLHA block \"" << block
                    << "\".  It will be ignored."
                    << std::endl;
            }
        }
    }
}

bool Herwig6Hadronizer::initialize(const lhef::HEPRUP *heprup)
{
    clear();

    externalPartons = (heprup != 0);

    std::ostringstream info;
    info << "---------------------------------------------------\n"; 
    info << "Initializing Herwig6Hadronizer for "
         << (externalPartons ? "external" : "internal") << " partons\n";
    info << "---------------------------------------------------\n";

    info << "   Herwig verbosity level         = " << herwigVerbosity << "\n";
    info << "   HepMC verbosity                = " << hepmcVerbosity << "\n";
    info << "   Number of events to be printed = " << maxEventsToPrint << "\n";

    // Call hwudat to set up HERWIG block data
    hwudat();

    // Setting basic parameters
    if (externalPartons) {
        hwproc.PBEAM1 = heprup->EBMUP.first;
        hwproc.PBEAM2 = heprup->EBMUP.second;
        pdgToHerwig(heprup->IDBMUP.first, hwbmch.PART1);
        pdgToHerwig(heprup->IDBMUP.second, hwbmch.PART2);
    } else {
        hwproc.PBEAM1 = 0.5 * comEnergy;
        hwproc.PBEAM2 = 0.5 * comEnergy;
        pdgToHerwig(2212, hwbmch.PART1);
        pdgToHerwig(2212, hwbmch.PART2);
    }

    if (useJimmy) {
        info << "   HERWIG will be using JIMMY for UE/MI.\n";
        jmparm.MSFLAG = 1;
        if (doMPInteraction)
            info << "   JIMMY trying to generate multiple interactions.\n";
    }


    // set the IPROC already here... needed for VB pairs

    bool iprocFound=false;
    
    for(gen::ParameterCollector::const_iterator line = parameters.begin();
        line != parameters.end(); ++line) {
      if(!strcmp((line->substr(0,5)).c_str(),"IPROC")) {
        if (!give(*line))
          throw edm::Exception(edm::errors::Configuration)
        << "Herwig 6 did not accept the following: \""
        << *line << "\"." << std::endl;
        else iprocFound=true;
      }
    }
    
    if (!iprocFound && !externalPartons)
      throw edm::Exception(edm::errors::Configuration)
        << "You have to define the process with IPROC."  << std::endl;

    // initialize other common blocks ...
    call(hwigin);
    hwevnt.MAXER = 100000000;   // O(inf)
    hwpram.LWSUD = 0;       // don't write Sudakov form factors
    hwdspn.LWDEC = 0;       // don't write three/four body decays
                    // (no fort.77 and fort.88 ...)

    // init LHAPDF glue

    std::memset(hwprch.AUTPDF, ' ', sizeof hwprch.AUTPDF);
    for(unsigned int i = 0; i < 2; i++) {
        hwpram.MODPDF[i] = -111;
        std::memcpy(hwprch.AUTPDF[i], "HWLHAPDF", 8);
    }

    if (useJimmy)
        call(jimmin);

    hwevnt.MAXPR = maxEventsToPrint;
    hwpram.IPRINT = herwigVerbosity;
//  hwprop.RMASS[6] = 175.0;    //FIXME

    if (printCards) {
        info << "\n";
        info << "------------------------------------\n";
        info << "Reading HERWIG parameters\n";
        info << "------------------------------------\n";
    
    }
    for(gen::ParameterCollector::const_iterator line = parameters.begin();
        line != parameters.end(); ++line) {
        if (printCards)
            info << "   " << *line << "\n";
        if (!give(*line))
            throw edm::Exception(edm::errors::Configuration)
                << "Herwig 6 did not accept the following: \""
                << *line << "\"." << std::endl;
    }

    if (printCards)
        info << "\n";

    if (externalPartons) {
        std::vector<std::string> slha =
                lheRunInfo()->findHeader("slha");
        if (!slha.empty())
            setSLHAFromHeader(slha);
    }

    needClear = true;

    std::pair<int, int> pdfs(-1, -1);
    if (externalPartons)
        pdfs = lheRunInfo()->pdfSetTranslation();

    if (hwpram.MODPDF[0] != -111 || hwpram.MODPDF[1] != -111) {
        for(unsigned int i = 0; i < 2; i++)
            if (hwpram.MODPDF[i] == -111)
                hwpram.MODPDF[i] = -1;

        if (pdfs.first != -1 || pdfs.second != -1)
            edm::LogError("Generator|Herwig6Hadronzier")
                << "Both external Les Houches event and "
                       "config file specify a PDF set.  "
                   "User PDF will override external one."
                << std::endl;

        pdfs.first = hwpram.MODPDF[0] != -111 ? hwpram.MODPDF[0] : -1;
        pdfs.second = hwpram.MODPDF[1] != -111 ? hwpram.MODPDF[1] : -1;
    }

    hwpram.MODPDF[0] = pdfs.first;
    hwpram.MODPDF[1] = pdfs.second;

    if (externalPartons)
        hwproc.IPROC = -1;

    // HERWIG preparations ...
    call(hwuinc);
    markStable(13);          // MU+
    markStable(-13);     // MU-
    markStable(3112);    // SIGMA+
    markStable(-3112);   // SIGMABAR+
    markStable(3222);    // SIGMA-
    markStable(-3222);   // SIGMABAR-
    markStable(3122);    // LAMBDA0
    markStable(-3122);   // LAMBDABAR0
    markStable(3312);    // XI-
    markStable(-3312);   // XIBAR+
    markStable(3322);    // XI0
    markStable(-3322);   // XI0BAR
    markStable(3334);    // OMEGA-
    markStable(-3334);   // OMEGABAR+
    markStable(211);     // PI+
    markStable(-211);    // PI-
    markStable(321);     // K+
    markStable(-321);    // K-
    markStable(310);     // K_S0
    markStable(130);     // K_L0

    // better: merge with declareStableParticles
    // and get the list from configuration / Geant4 / Core somewhere

    // initialize HERWIG event generation
    call(hweini);

    if (useJimmy)
        call(jminit);

    edm::LogInfo(info.str());

    return true;
}

bool Herwig6Hadronizer::declareStableParticles(const std::vector<int> &pdgIds)
{
    for(std::vector<int>::const_iterator iter = pdgIds.begin();
        iter != pdgIds.end(); ++iter)
        if (!markStable(*iter))
            return false;
    return true;
}

bool Herwig6Hadronizer::declareSpecialSettings( const std::vector<std::string> )
{
   return true;
}

void Herwig6Hadronizer::statistics()
{
    if (!runInfo().internalXSec()) {
      // not set via LHE, so get it from HERWIG
      // the reason is that HERWIG doesn't compute the xsec
      // in all LHE modes

      double RNWGT = 1. / hwevnt.NWGTS;
      double AVWGT = hwevnt.WGTSUM * RNWGT;

      double xsec = 1.0e3 * AVWGT;

      runInfo().setInternalXSec(xsec);
    }
}

bool Herwig6Hadronizer::hadronize()
{
    // hard process generation, parton shower, hadron formation

    InstanceWrapper wrapper(this);  // safe guard

    event().reset();

    // call herwig routines to create HEPEVT

    hwuine();   // initialize event
    
    if (callWithTimeout(10, hwepro)) { // process event and PS
      // We hung for more than 10 seconds
      int error = 199;
      hwwarn_("HWHGUP", &error);
    }
    
    hwbgen();   // parton cascades

    // call jimmy ... only if event is not killed yet by HERWIG
    if (useJimmy && doMPInteraction && !hwevnt.IERROR && call_hwmsct()) {
      if (lheEvent()) lheEvent()->count(lhef::LHERunInfo::kKilled);
      return false;
        }
    
    hwdhob();   // heavy quark decays
    hwcfor();   // cluster formation
    hwcdec();   // cluster decays
    
    // if event *not* killed by HERWIG, return true
    if (hwevnt.IERROR) {
      hwufne(); // finalize event, to keep system clean
      if (lheEvent()) lheEvent()->count(lhef::LHERunInfo::kKilled);
      return false;
    }

    if (lheEvent()) lheEvent()->count(lhef::LHERunInfo::kAccepted);
    return true;
}

void Herwig6Hadronizer::finalizeEvent()
{
  lhef::LHEEvent::fixHepMCEventTimeOrdering(event().get());
  
  HepMC::PdfInfo pdfInfo;
  if(externalPartons) {
    lheEvent()->fillEventInfo( event().get() );
    lheEvent()->fillPdfInfo( &pdfInfo );

    // for MC@NLO: IDWRUP is not filled...
    if(event()->signal_process_id()==0)
      event()->set_signal_process_id( abs(hwproc.IPROC) );

  }
    
  HepMC::GenParticle* incomingParton = NULL;
  HepMC::GenParticle* targetParton = NULL;
  
  HepMC::GenParticle* incomingProton = NULL;
  HepMC::GenParticle* targetProton = NULL;
  
  // find incoming parton (first entry with IST=121)
  for(HepMC::GenEvent::particle_const_iterator it = event()->particles_begin(); 
      (it != event()->particles_end() && incomingParton==NULL); it++)
    if((*it)->status()==121) incomingParton = (*it);
  
  // find target parton (first entry with IST=122)
  for(HepMC::GenEvent::particle_const_iterator it = event()->particles_begin(); 
      (it != event()->particles_end() && targetParton==NULL); it++)
    if((*it)->status()==122) targetParton = (*it);
  
  // find incoming Proton (first entry ID=2212, IST=101)
  for(HepMC::GenEvent::particle_const_iterator it = event()->particles_begin(); 
      (it != event()->particles_end() && incomingProton==NULL); it++)
    if((*it)->status()==101 && (*it)->pdg_id()==2212) incomingProton = (*it);
  
  // find target Proton (first entry ID=2212, IST=102)
  for(HepMC::GenEvent::particle_const_iterator it = event()->particles_begin(); 
      (it != event()->particles_end() && targetProton==NULL); it++)
    if((*it)->status()==102 && (*it)->pdg_id()==2212) targetProton = (*it);
  
  // find hard scale Q (computed from colliding partons)
  if( incomingParton && targetParton ) {
    math::XYZTLorentzVector totMomentum(0,0,0,0);
    totMomentum+=incomingParton->momentum();
    totMomentum+=targetParton->momentum();
    double evScale = totMomentum.mass(); 
    double evScale2 = evScale*evScale; 
    
    // find alpha_QED & alpha_QCD     
    int one=1;
    double alphaQCD=hwualf_(&one,&evScale);
    double alphaQED=hwuaem_(&evScale2);
    
    if(!externalPartons || event()->event_scale() < 0) event()->set_event_scale(evScale);
    if(!externalPartons || event()->alphaQCD() < 0)    event()->set_alphaQCD(alphaQCD);
    if(!externalPartons || event()->alphaQED() < 0)    event()->set_alphaQED(alphaQED);
    
    if(!externalPartons || pdfInfo.x1() < 0) {
      // get the PDF information
      pdfInfo.set_id1( incomingParton->pdg_id()==21 ? 0 : incomingParton->pdg_id());
      pdfInfo.set_id2( targetParton->pdg_id()==21 ? 0 : targetParton->pdg_id());
      if( incomingProton && targetProton ) {
    double x1 = incomingParton->momentum().pz()/incomingProton->momentum().pz();
    double x2 = targetParton->momentum().pz()/targetProton->momentum().pz();    
    pdfInfo.set_x1(x1);
    pdfInfo.set_x2(x2);     
      }
      // we do not fill pdf1 & pdf2, since they are not easily available (what are they needed for anyways???)
      pdfInfo.set_scalePDF(evScale); // the same as Q above... does this make sense?
    } 
    
    if(!externalPartons || event()->signal_process_id() < 0) event()->set_signal_process_id( abs(hwproc.IPROC) );
    event()->set_pdf_info( pdfInfo );
  }
  
  // add event weight & PDF information
  if (lheRunInfo() != 0 && std::abs(lheRunInfo()->getHEPRUP()->IDWTUP) == 4)
    // in LHE weighting mode 4 the weight is an xsec, so convert form HERWIG
    // to standard CMS unit "picobarn"
    event()->weights().push_back( 1.0e3 * hwevnt.EVWGT );
  else
    event()->weights().push_back( hwevnt.EVWGT );

    
  // find final parton (first entry with IST=123)
  HepMC::GenParticle* finalParton = NULL;
  for(HepMC::GenEvent::particle_const_iterator it = event()->particles_begin(); 
      (it != event()->particles_end() && finalParton==NULL); it++)
    if((*it)->status()==123) finalParton = (*it);
  
  
  // add GenEventInfo & binning Values
  eventInfo().reset(new GenEventInfoProduct(event().get()));    
  if(finalParton) {
    double thisPt=finalParton->momentum().perp();
    eventInfo()->setBinningValues(std::vector<double>(1, thisPt));
  }
  
  // emulate PY6 status codes, if switched on...
  if (emulatePythiaStatusCodes)
    pythiaStatusCodes();          
  
}


bool Herwig6Hadronizer::decay()
{
    // hadron decays

    InstanceWrapper wrapper(this);  // safe guard

    hwdhad();   // unstable particle decays
    hwdhvy();   // heavy flavour decays
    hwmevt();   // soft underlying event

    hwufne();   // finalize event

    if (hwevnt.IERROR)
        return false;

    event().reset(new HepMC::GenEvent);
    if (!conv.fill_next_event(event().get()))
        throw cms::Exception("Herwig6Error")
            << "HepMC Conversion problems in event." << std::endl;

        // do particle ID conversion Herwig->PDG, if requested
        if ( fConvertToPDG ) {
           for ( HepMC::GenEvent::particle_iterator part = event()->particles_begin(); part != event()->particles_end(); ++part) {
             if ((*part)->pdg_id() != HepPID::translateHerwigtoPDT((*part)->pdg_id()))
               (*part)->set_pdg_id(HepPID::translateHerwigtoPDT((*part)->pdg_id()));
           }
        }

    return true;
}

bool Herwig6Hadronizer::residualDecay()
{
    return true;
}

void Herwig6Hadronizer::upInit()
{
    lhef::CommonBlocks::fillHEPRUP(lheRunInfo()->getHEPRUP());
    heprup_.pdfgup[0] = heprup_.pdfgup[1] = -1;
    heprup_.pdfsup[0] = heprup_.pdfsup[1] = -1;
    // we set up the PDFs ourselves
    
    // pass HERWIG paramaters fomr header (if present)
    std::string mcnloHeader="herwig6header";
    std::vector<lhef::LHERunInfo::Header> headers=lheRunInfo()->getHeaders();
    for(std::vector<lhef::LHERunInfo::Header>::const_iterator hIter=headers.begin();hIter!=headers.end(); ++hIter) {
      if(hIter->tag()==mcnloHeader){
        readMCatNLOfile=true;
        for(lhef::LHERunInfo::Header::const_iterator lIter=hIter->begin(); lIter != hIter->end(); ++lIter) {
          if((lIter->c_str())[0]!='#' && (lIter->c_str())[0]!='\n') {   // it's not a comment) 
        if (!give(*lIter))
          throw edm::Exception(edm::errors::Configuration)
            << "Herwig 6 did not accept the following: \""
            << *lIter << "\"." << std::endl;
          }
        }
      }
    }
}

void Herwig6Hadronizer::upEvnt()
{
    lhef::CommonBlocks::fillHEPEUP(lheEvent()->getHEPEUP());

    // if MCatNLO external file is read, read comment & pass IHPRO to HERWIG
    if(readMCatNLOfile) {
      for(std::vector<std::string>::const_iterator iter=lheEvent()->getComments().begin();
          iter!=lheEvent()->getComments().end(); ++iter) {
        std::string toParse(iter->substr(1));
        if (!give(toParse))
          throw edm::Exception(edm::errors::Configuration)
            << "Herwig 6 did not accept the following: \""
            << toParse << "\"." << std::endl;
      }
    }
    
}

int Herwig6Hadronizer::pythiaStatusCode(const HepMC::GenParticle *p) const
{
    int status = p->status();

    // weird 9922212 particles...
    if (status == 3 && !p->end_vertex())
        return 2;

    if (status >= 1 && status <= 3)
        return status;

    if (!p->end_vertex())
        return 1;

    // let's prevent particles having status 3, if the identical
    // particle downstream is a better status 3 candidate
    int currentId = p->pdg_id();
    int orig = status;
    if (status == 123 || status == 124 ||
        status == 155 || status == 156 || status == 160 ||
        (status >= 195 && status <= 197)) {
        for(const HepMC::GenParticle *q = p;;) {
            const HepMC::GenVertex *vtx = q->end_vertex();
            if (!vtx)
                break;

            HepMC::GenVertex::particles_out_const_iterator iter;
            for(iter = vtx->particles_out_const_begin();
                iter != vtx->particles_out_const_end(); ++iter)
                if ((*iter)->pdg_id() == currentId)
                    break;

            if (iter == vtx->particles_out_const_end())
                break;

            q = *iter;
            if (q->status() == 3 ||
                ((status == 120 || status == 123 ||
                  status == 124) && orig > 124))
                return 4;
        }
    }

    int nesting = 0;
    for(;;) {
        if ((status >= 120 && status <= 122) || status == 3) {
            // avoid flagging status 3 if there is a
            // better status 3 candidate upstream
            if (externalPartons)
                return ((orig >= 121 && orig <= 124) ||
                        orig == 3) ? 3 : 4;
            else
                return (nesting ||
                        (status != 3 && orig <= 124)) ? 3 : 4;
        }

        // check whether we are leaving the hard process
        // including heavy resonance decays
        if (!(status == 4 || status == 123 || status == 124 ||
              status == 155 || status == 156 || status == 160 ||
              (status >= 195 && status <= 197)))
            break;

        const HepMC::GenVertex *vtx = p->production_vertex();
        if (!vtx || !vtx->particles_in_size())
            break;

        p = *vtx->particles_in_const_begin();
        status = p->status();

        int newId = p->pdg_id();

        if (!newId)
            break;

        // nesting increases if we move to the next-best mother
        if (newId != currentId) {
            if (++nesting > 1 && externalPartons)
                break;
            currentId = newId;
        }
    }

    return 2; 
}

void Herwig6Hadronizer::pythiaStatusCodes()
{
    for(HepMC::GenEvent::particle_iterator iter =
                            event()->particles_begin();
        iter != event()->particles_end(); iter++)
        (*iter)->set_status(pythiaStatusCode(*iter));

    for(HepMC::GenEvent::particle_iterator iter =
                            event()->particles_begin();
        iter != event()->particles_end(); iter++)
        if ((*iter)->status() == 4)
            (*iter)->set_status(2);
}

#include "GeneratorInterface/ExternalDecays/interface/ExternalDecayDriver.h"

typedef edm::GeneratorFilter<Herwig6Hadronizer, gen::ExternalDecayDriver> Herwig6GeneratorFilter;
DEFINE_FWK_MODULE(Herwig6GeneratorFilter);

typedef edm::HadronizerFilter<Herwig6Hadronizer, gen::ExternalDecayDriver> Herwig6HadronizerFilter;
DEFINE_FWK_MODULE(Herwig6HadronizerFilter);