/data/refman/pasoursint/CMSSW_6_1_2_SLHC2_patch1/src/GeneratorInterface/Herwig6Interface/plugins/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/HerwigWrapper.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 readSettings( int );
        
        // bool initializeForInternalPartons() { return initialize(0); }
        // bool initializeForExternalPartons() { return initialize(lheRunInfo()->getHEPRUP()); }

        bool initializeForInternalPartons();
        bool initializeForExternalPartons() { return initializeForInternalPartons(); }

        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;

  // -------------------------------------------------------------------------------
        std::string                     particleSpecFileName; //Lars 20/Jul/2011
        bool                            readParticleSpecFile;
  // -------------------------------------------------------------------------------

};

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),

        // added to be able to read external particle spectrum file
        particleSpecFileName(params.getUntrackedParameter<std::string>("ParticleSpectrumFileName","")),
        readParticleSpecFile(params.getUntrackedParameter<bool>("readParticleSpecFile", 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:: readSettings( int key )
{

   clear();
   const lhef::HEPRUP* heprup = lheRunInfo()->getHEPRUP();
   externalPartons = ( heprup != 0 );
   
   if ( key == 0 && externalPartons ) return false;
   if ( key > 0 && !externalPartons ) return false;

   std::ostringstream info;
   info << "---------------------------------------------------\n"; 
   info << "Taking in settinsg for 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); // default init
   
   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);
        }

        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;


        //Lars: lower EFFMIN threshold, to continue execution of IPROC=4000, lambda'_211=0.01 at LM7,10
        if( readParticleSpecFile ) {
          openParticleSpecFile(particleSpecFileName.c_str());
          hwpram.EFFMIN = 1e-5;
        }
        

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

   return true;

}

bool Herwig6Hadronizer::initializeForInternalPartons()
{

   if (useJimmy) call(jimmin);
   
   call(hwuinc);

   // initialize HERWIG event generation
   call(hweini);

   if (useJimmy) call(jminit);

   return true;

}


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;

        //Lars: lower EFFMIN threshold, to continue execution of IPROC=4000, lambda'_211=0.01 at LM7,10
        if( readParticleSpecFile ) {
          openParticleSpecFile(particleSpecFileName.c_str());
          hwpram.EFFMIN = 1e-5;
        }
        
        // 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)
{
        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

        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);