IO_HERWIG.cc

// Matt.Dobbs@Cern.CH, October 2002
// Herwig 6.400 IO class

#include "HepMC/IO_HERWIG.h"
#include "HepMC/GenEvent.h"
#include <cstdio>       // needed for formatted output using sprintf 

namespace HepMC {

    IO_HERWIG::IO_HERWIG() : m_trust_mothers_before_daughters(false),
                             m_trust_both_mothers_and_daughters(true),
                             m_print_inconsistency_errors(true),
                             m_no_gaps_in_barcodes(true),
                             m_herwig_to_pdg_id(100,0)
    {
        // These arrays are copied from Lynn Garren's stdhep 5.01-5.06.
        //   see http://cepa.fnal.gov/psm/stdhep/
        // Translation from HERWIG particle ID's to PDG particle ID's.
        m_herwig_to_pdg_id[1] =1; 
        m_herwig_to_pdg_id[2] =2;
        m_herwig_to_pdg_id[3] =3;
        m_herwig_to_pdg_id[4] =4;
        m_herwig_to_pdg_id[5] =5;
        m_herwig_to_pdg_id[6] =6;
        m_herwig_to_pdg_id[7] =7;
        m_herwig_to_pdg_id[8] =8;
       
        m_herwig_to_pdg_id[11] =11;
        m_herwig_to_pdg_id[12] =12;
        m_herwig_to_pdg_id[13] =13;
        m_herwig_to_pdg_id[14] =14;
        m_herwig_to_pdg_id[15] =15;
        m_herwig_to_pdg_id[16] =16;
       
        m_herwig_to_pdg_id[21] =21;
        m_herwig_to_pdg_id[22] =22;
        m_herwig_to_pdg_id[23] =23;
        m_herwig_to_pdg_id[24] =24;
        m_herwig_to_pdg_id[25] =25;
        m_herwig_to_pdg_id[26] =51; // <-- H_L0 (redundant with h0(25))
       
        m_herwig_to_pdg_id[32] =32;
        m_herwig_to_pdg_id[35] =35;
        m_herwig_to_pdg_id[36] =36;
        m_herwig_to_pdg_id[37] =37;
        m_herwig_to_pdg_id[39] =39;
 
        m_herwig_to_pdg_id[40] =40; //Charybdis Black Hole
      
        m_herwig_to_pdg_id[81] =81;
        m_herwig_to_pdg_id[82] =82;
        m_herwig_to_pdg_id[83] =83;
        m_herwig_to_pdg_id[84] =84;
        m_herwig_to_pdg_id[85] =85;
        m_herwig_to_pdg_id[86] =86;
        m_herwig_to_pdg_id[87] =87;
        m_herwig_to_pdg_id[88] =88;
        m_herwig_to_pdg_id[89] =89;
        m_herwig_to_pdg_id[90] =90;
       
        m_herwig_to_pdg_id[91] =91;
        m_herwig_to_pdg_id[92] =92;
        m_herwig_to_pdg_id[93] =93;
        m_herwig_to_pdg_id[94] =94;
        m_herwig_to_pdg_id[95] =95;
        m_herwig_to_pdg_id[96] =96;
        m_herwig_to_pdg_id[97] =97;
        m_herwig_to_pdg_id[98] =9920022; // <-- remnant photon
        m_herwig_to_pdg_id[99] =9922212; // <-- remnant nucleon

        // These particle ID's have no antiparticle, so aren't allowed.
        m_no_antiparticles.insert(-21);
        m_no_antiparticles.insert(-22);
        m_no_antiparticles.insert(-23);
        m_no_antiparticles.insert(-25);
        m_no_antiparticles.insert(-51);
        m_no_antiparticles.insert(-35);
        m_no_antiparticles.insert(-36);
    }

    IO_HERWIG::~IO_HERWIG(){}

    void IO_HERWIG::print( std::ostream& ostr ) const { 
        ostr << "IO_HERWIG: reads an event from the FORTRAN Herwig HEPEVT "
             << "common block. \n" 
             << " trust_mothers_before_daughters = " 
             << m_trust_mothers_before_daughters
             << " trust_both_mothers_and_daughters = "
             << m_trust_both_mothers_and_daughters
             << " print_inconsistency_errors = " 
             << m_print_inconsistency_errors << std::endl;
    }

    bool IO_HERWIG::fill_next_event( GenEvent* evt ) {
        //
        // 0. Test that evt pointer is not null and set event number
        if ( !evt ) {
            std::cerr 
                << "IO_HERWIG::fill_next_event error - passed null event." 
                << std::endl;
            return false;
        }

        // 1. First we have to fix the HEPEVT input, which is all mucked up for
        //    herwig.
        repair_hepevt();

        evt->set_event_number( HEPEVT_Wrapper::event_number() );
        // Herwig units are GeV and mm
        // It would be nice to set the units right here,
        // but this could cause problems with existing code that 
        // might convert GeV to MeV without calling the appropriate HepMC method

        //
        // 2. create a particle instance for each HEPEVT entry and fill a map
        //    create a vector which maps from the HEPEVT particle index to the 
        //    GenParticle address
        //    (+1 in size accounts for hepevt_particle[0] which is unfilled)
        std::vector<GenParticle*> hepevt_particle( 
                                        HEPEVT_Wrapper::number_entries()+1 );
        hepevt_particle[0] = 0;
        for ( int i1 = 1; i1 <= HEPEVT_Wrapper::number_entries(); ++i1 ) {
            hepevt_particle[i1] = build_particle(i1);
        }
        std::set<GenVertex*> new_vertices;
        //
        // Here we assume that the first two particles in the list 
        // are the incoming beam particles.
        // Best make sure this is done before any rearranging...
        evt->set_beam_particles( hepevt_particle[1], hepevt_particle[2] );
        //
        // 3. We need to take special care with the hard process
        // vertex.  The problem we are trying to avoid is when the
        // partons entering the hard process also have daughters from
        // the parton shower. When this happens, each one can get its
        // own decay vertex, making it difficult to join them
        // later. We handle it by joining them together first, then
        // the other daughters get added on later.
        // Find the partons entering the hard vertex (status codes 121, 122).
        int index_121 = 0;
        int index_122 = 0;
        for ( int i = 1; i <=HEPEVT_Wrapper::number_entries(); i++ ) {
            if ( HEPEVT_Wrapper::status(i)==121 ) index_121=i;
            if ( HEPEVT_Wrapper::status(i)==122 ) index_122=i;
            if ( index_121!=0 && index_122!=0 ) break;
        }
        if ( index_121 && index_122 ) {
            GenVertex* hard_vtx = new GenVertex();
            hard_vtx->add_particle_in( hepevt_particle[index_121] );
            hard_vtx->add_particle_in( hepevt_particle[index_122] );
            // evt->add_vertex( hard_vtx ); // not necessary, its done in 
                                            // set_signal_process_vertex
            //BPK - Atlas -> index_hard retained if it is a boson
            int index_hard = 0;
            for ( int i = 1; i <=HEPEVT_Wrapper::number_entries(); i++ ) {
              if ( HEPEVT_Wrapper::status(i)==120 ) index_hard=i;
              if ( index_hard!=0 ) break;
            }
            
            if ( index_hard!=0) {
              hard_vtx->add_particle_out( hepevt_particle[index_hard] );
              GenVertex* hard_vtx2 = new GenVertex();
              hard_vtx2->add_particle_in( hepevt_particle[index_hard] );
                  for ( int i = 1; i <= HEPEVT_Wrapper::number_entries(); ++i ) {
                if (  HEPEVT_Wrapper::first_parent(i)==index_hard ) {
                  hard_vtx2->add_particle_out( hepevt_particle[i] );
                }
              }
              evt->set_signal_process_vertex( hard_vtx );
              evt->set_signal_process_vertex( hard_vtx2 );
            }
            else {
              evt->set_signal_process_vertex( hard_vtx );
            }
            //BPK - Atlas -<
        }
        //
        // 4. loop over HEPEVT particles AGAIN, this time creating vertices
        for ( int i = 1; i <= HEPEVT_Wrapper::number_entries(); ++i ) {
            // We go through and build EITHER the production or decay 
            // vertex for each entry in hepevt, depending on the switch
            // m_trust_mothers_before_daughters (new 2001-02-28)
            // Note: since the HEPEVT pointers are bi-directional, it is
            //
            // 3. Build the production_vertex (if necessary)
            if ( m_trust_mothers_before_daughters || 
                 m_trust_both_mothers_and_daughters ) {
                build_production_vertex( i, hepevt_particle, evt );
            }
            //
            // 4. Build the end_vertex (if necessary) 
            //    Identical steps as for production vertex
            if ( !m_trust_mothers_before_daughters || 
                 m_trust_both_mothers_and_daughters ) {
                build_end_vertex( i, hepevt_particle, evt );
            }
        }
        // 5.             01.02.2000
        // handle the case of particles in HEPEVT which come from nowhere -
        //  i.e. particles without mothers or daughters.
        //  These particles need to be attached to a vertex, or else they
        //  will never become part of the event. check for this situation.
        for ( int i3 = 1; i3 <= HEPEVT_Wrapper::number_entries(); ++i3 ) {
            // Herwig also has some non-physical entries in HEPEVT
            // like CMS, HARD, and CONE. These are flagged by
            // repair_hepevt by making their status and id zero. We
            // delete those particles here.
            if ( hepevt_particle[i3] && !hepevt_particle[i3]->parent_event()
                 && !hepevt_particle[i3]->pdg_id()
                 && !hepevt_particle[i3]->status() ) {
                //std::cout << "IO_HERWIG::fill_next_event is deleting null "
                //        << "particle" << std::endl;
                //hepevt_particle[i3]->print();
                delete hepevt_particle[i3];
            } else if ( hepevt_particle[i3] && 
                        !hepevt_particle[i3]->end_vertex() && 
                        !hepevt_particle[i3]->production_vertex() ) {
                GenVertex* prod_vtx = new GenVertex();
                prod_vtx->add_particle_out( hepevt_particle[i3] );
                evt->add_vertex( prod_vtx );
            }
        }
        return true;
    }

    void IO_HERWIG::build_production_vertex(int i, 
                                            std::vector<GenParticle*>& 
                                            hepevt_particle,
                                            GenEvent* evt ) {
        GenParticle* p = hepevt_particle[i];
        // a. search to see if a production vertex already exists
        int mother = HEPEVT_Wrapper::first_parent(i);
        GenVertex* prod_vtx = p->production_vertex();
        while ( !prod_vtx && mother > 0 ) {
            prod_vtx = hepevt_particle[mother]->end_vertex();
            if ( prod_vtx ) prod_vtx->add_particle_out( p );
            // increment mother for next iteration
            if ( ++mother > HEPEVT_Wrapper::last_parent(i) ) mother = 0;
        }
        // b. if no suitable production vertex exists - and the particle
        // has atleast one mother or position information to store - 
        // make one
        FourVector prod_pos( HEPEVT_Wrapper::x(i), HEPEVT_Wrapper::y(i), 
                                   HEPEVT_Wrapper::z(i), HEPEVT_Wrapper::t(i) 
                                 ); 
        if ( !prod_vtx && (HEPEVT_Wrapper::number_parents(i)>0 
                           || prod_pos!=FourVector(0,0,0,0)) )
        {
            prod_vtx = new GenVertex();
            prod_vtx->add_particle_out( p );
            evt->add_vertex( prod_vtx ); 
        }
        // c. if prod_vtx doesn't already have position specified, fill it
        if ( prod_vtx && prod_vtx->position()==FourVector(0,0,0,0) ) {
            prod_vtx->set_position( prod_pos );
        }
        // d. loop over mothers to make sure their end_vertices are
        //     consistent
        mother = HEPEVT_Wrapper::first_parent(i);
        while ( prod_vtx && mother > 0 ) {
            if ( !hepevt_particle[mother]->end_vertex() ) {
                // if end vertex of the mother isn't specified, do it now
                prod_vtx->add_particle_in( hepevt_particle[mother] );
            } else if (hepevt_particle[mother]->end_vertex() != prod_vtx ) {
                // problem scenario --- the mother already has a decay
                // vertex which differs from the daughter's produciton 
                // vertex. This means there is internal
                // inconsistency in the HEPEVT event record. Print an
                // error
                // Note: we could provide a fix by joining the two 
                //       vertices with a dummy particle if the problem
                //       arrises often with any particular generator.
                if ( m_print_inconsistency_errors ) {
                  std::cerr
                    << "HepMC::IO_HERWIG: inconsistent mother/daugher "
                    << "information in HEPEVT event " 
                    << HEPEVT_Wrapper::event_number()
                    << ". \n I recommend you try "
                    << "inspecting the event first with "
                    << "\n\tHEPEVT_Wrapper::check_hepevt_consistency()"
                    << "\n This warning can be turned off with the "
                    << "IO_HERWIG::print_inconsistency_errors switch."
                    << std::endl;
                  hepevt_particle[mother]->print(std::cerr);
                  std::cerr
                    << "problem vertices are: (prod_vtx, mother)" << std::endl;
                  if ( prod_vtx ) prod_vtx->print(std::cerr);
                  hepevt_particle[mother]->end_vertex()->print(std::cerr);
                }
            }
            if ( ++mother > HEPEVT_Wrapper::last_parent(i) ) mother = 0;
        }
    }

    void IO_HERWIG::build_end_vertex
    ( int i, std::vector<GenParticle*>& hepevt_particle, GenEvent* evt ) 
    {
        //    Identical steps as for build_production_vertex
        GenParticle* p = hepevt_particle[i];
        // a.
        int daughter = HEPEVT_Wrapper::first_child(i);
        GenVertex* end_vtx = p->end_vertex();
        while ( !end_vtx && daughter > 0 ) {
            end_vtx = hepevt_particle[daughter]->production_vertex();
            if ( end_vtx ) end_vtx->add_particle_in( p );
            if ( ++daughter > HEPEVT_Wrapper::last_child(i) ) daughter = 0;
        }
        // b. (different from 3c. because HEPEVT particle can not know its
        //        decay position )
        if ( !end_vtx && HEPEVT_Wrapper::number_children(i)>0 ) {
            end_vtx = new GenVertex();
            end_vtx->add_particle_in( p );
            evt->add_vertex( end_vtx );
        }
        // c+d. loop over daughters to make sure their production vertices 
        //    point back to the current vertex.
        //    We get the vertex position from the daughter as well.
        daughter = HEPEVT_Wrapper::first_child(i);
        while ( end_vtx && daughter > 0 ) {
            if ( !hepevt_particle[daughter]->production_vertex() ) {
                // if end vertex of the mother isn't specified, do it now
                end_vtx->add_particle_out( hepevt_particle[daughter] );
                // 
                // 2001-03-29 M.Dobbs, fill vertex the position.
                if ( end_vtx->position()==FourVector(0,0,0,0) ) {
                    FourVector prod_pos( HEPEVT_Wrapper::x(daughter), 
                                               HEPEVT_Wrapper::y(daughter), 
                                               HEPEVT_Wrapper::z(daughter), 
                                               HEPEVT_Wrapper::t(daughter) 
                        );
                    if ( prod_pos != FourVector(0,0,0,0) ) {
                        end_vtx->set_position( prod_pos );
                    }
                }
            } else if (hepevt_particle[daughter]->production_vertex() 
                       != end_vtx){
                // problem scenario --- the daughter already has a prod
                // vertex which differs from the mother's end 
                // vertex. This means there is internal
                // inconsistency in the HEPEVT event record. Print an
                // error
                if ( m_print_inconsistency_errors ) std::cerr
                    << "HepMC::IO_HERWIG: inconsistent mother/daugher "
                    << "information in HEPEVT event " 
                    << HEPEVT_Wrapper::event_number()
                    << ". \n I recommend you try "
                    << "inspecting the event first with "
                    << "\n\tHEPEVT_Wrapper::check_hepevt_consistency()"
                    << "\n This warning can be turned off with the "
                    << "IO_HERWIG::print_inconsistency_errors switch."
                    << std::endl;
            }
            if ( ++daughter > HEPEVT_Wrapper::last_child(i) ) daughter = 0;
        }
        if ( !p->end_vertex() && !p->production_vertex() ) {
            // Added 2001-11-04, to try and handle Isajet problems.
            build_production_vertex( i, hepevt_particle, evt );
        }
    }

    GenParticle* IO_HERWIG::build_particle( int index ) {
        // 
        GenParticle* p 
            = new GenParticle( FourVector( HEPEVT_Wrapper::px(index), 
                                                 HEPEVT_Wrapper::py(index), 
                                                 HEPEVT_Wrapper::pz(index), 
                                                 HEPEVT_Wrapper::e(index) ),
                               HEPEVT_Wrapper::id(index), 
                               HEPEVT_Wrapper::status(index) );
        p->setGeneratedMass( HEPEVT_Wrapper::m(index) );
        p->suggest_barcode( index );
        return p;
    }

    int IO_HERWIG::find_in_map( const std::map<GenParticle*,int>& m, 
                                GenParticle* p) const {
        std::map<GenParticle*,int>::const_iterator iter = m.find(p);
        if ( iter == m.end() ) return 0;
        return iter->second;
    }

    void IO_HERWIG::repair_hepevt() const {

        // Make sure hepvt isn't empty.
        if ( HEPEVT_Wrapper::number_entries() <= 0 ) return;

        // Find the index of the beam-beam collision and of the hard subprocess
        // Later we will assume that 
        //              101 ---> 121 \. 
        //                             X  Hard subprocess
        //              102 ---> 122 /
        // 
        int index_collision = 0;
        int index_hard = 0;
        int index_101 = 0;
        int index_102 = 0;
        int index_121 = 0;
        int index_122 = 0;

        for ( int i = 1; i <=HEPEVT_Wrapper::number_entries(); i++ ) {
            if ( HEPEVT_Wrapper::status(i)==101 ) index_101=i;
            if ( HEPEVT_Wrapper::status(i)==102 ) index_102=i;
            if ( HEPEVT_Wrapper::status(i)==103 ) index_collision=i;
            if ( HEPEVT_Wrapper::status(i)==120 ) index_hard=i;
            if ( HEPEVT_Wrapper::status(i)==121 ) index_121=i;
            if ( HEPEVT_Wrapper::status(i)==122 ) index_122=i;
            if ( index_collision!=0 && index_hard!=0 && index_101!=0 && 
                 index_102!=0 && index_121!=0 && index_122!=0 ) break;
        }

        // The mother daughter information for the hard subprocess entry (120)
        // IS correct, whereas the information for the particles participating
        // in the hard subprocess contains instead the color flow relationships
        // Transfer the hard subprocess info onto the other particles
        // in the hard subprocess.
        //
        // We cannot specify daughters of the incoming hard process particles
        // because they have some daughters (their showered versions) which 
        // are not adjacent in the particle record, so we cannot properly 
        // set the daughter indices in hepevt.
        //
        if (index_121) HEPEVT_Wrapper::set_parents(index_121, index_101, 0 );
        if (index_121) HEPEVT_Wrapper::set_children( index_121, 0, 0 );
        if (index_122) HEPEVT_Wrapper::set_parents(index_122, index_102, 0 );
        if (index_122) HEPEVT_Wrapper::set_children( index_122, 0, 0 );

        for ( int i = HEPEVT_Wrapper::first_child(index_hard);
              i <= HEPEVT_Wrapper::last_child(index_hard); i++ ) {
            //BPK - Atlas ->
            if (index_hard && HEPEVT_Wrapper::id(index_hard) == 0 ) {
              HEPEVT_Wrapper::set_parents( 
                  i, HEPEVT_Wrapper::first_parent(index_hard), 
                  HEPEVT_Wrapper::last_parent(index_hard) );
            //BPK -> inconsistency in HWHGUP, desc from hard vert should point to it.
            } else if (  HEPEVT_Wrapper::first_parent(i)!=index_hard) {
              HEPEVT_Wrapper::set_parents(i,index_hard,HEPEVT_Wrapper::last_parent(i) );
            }
            //BPK - Atlas -<

            // When the direct descendants of the hard process are hadrons,
            // then the 2nd child contains color flow information, and so
            // we zero it.
            // However, if the direct descendant is status=195, then it is
            // a non-hadron, and so the 2nd child does contain real mother
            // daughter relationships. ( particularly relevant for H->WW,
            //                           April 18, 2003 )
            // BPK - part of the inconsistency in HWHGUP problem
            if ( HEPEVT_Wrapper::status(i) != 195 && HEPEVT_Wrapper::status(i) != 155 ) {
              HEPEVT_Wrapper::set_children(i,HEPEVT_Wrapper::first_child(i),0);
            }
        }

        // now zero the collision and hard entries.
        //BPK - Atlas ->
        if (index_hard && HEPEVT_Wrapper::id(index_hard) == 0 ) zero_hepevt_entry(index_hard);
        if (index_hard && HEPEVT_Wrapper::id(index_collision) == 0  ) zero_hepevt_entry(index_collision);
        //BPK - Atlas -<

        //     Loop over the particles individually and handle oddities
        for ( int i=1; i <=HEPEVT_Wrapper::number_entries(); i++ ) {

            //       ----------- Fix ID codes ----------
            //       particles with ID=94 are mirror images of their mothers:
            if ( HEPEVT_Wrapper::id(i)==94 ) {
                HEPEVT_Wrapper::set_id( 
                    i, HEPEVT_Wrapper::id( HEPEVT_Wrapper::first_parent(i) ) );
            }

            //     ----------- fix STATUS codes ------
            //     status=100 particles are "cones" which carry only color info
            //     throw them away
            if ( HEPEVT_Wrapper::status(i)==100 ) zero_hepevt_entry(i);


            // NOTE: status 101,102 particles are the beam particles.
            //       status 121,129 particles are the hard subprocess particles
            // we choose to allow the herwig particles to have herwig
            // specific codes, and so we don't bother to change these
            // to status =3.




            //  ----------- fix some MOTHER/DAUGHTER relationships
            //  Whenever the mother points to the hard process, it is referring
            //  to a color flow, so we zero it.
            if ( HEPEVT_Wrapper::last_parent(i)==index_hard ) {
                HEPEVT_Wrapper::set_parents( 
                    i, HEPEVT_Wrapper::first_parent(i), 0 );
            }

            // It makes no sense to have a mother that is younger than you are!

            if ( HEPEVT_Wrapper::first_parent(i) >= i ) {
                HEPEVT_Wrapper::set_parents( i, 0, 0 );
            }
            if ( HEPEVT_Wrapper::last_parent(i) >= i ) {
                HEPEVT_Wrapper::set_parents( 
                    i, HEPEVT_Wrapper::first_parent(i), 0 );
            }

            // Whenever the second mother/daughter has a lower index than the
            // first, it means the second mother/daughter contains color
            // info. Purge it.
            if ( HEPEVT_Wrapper::last_parent(i) <= 
                 HEPEVT_Wrapper::first_parent(i) ) {
                HEPEVT_Wrapper::set_parents( 
                    i, HEPEVT_Wrapper::first_parent(i), 0 );
            }

            if ( HEPEVT_Wrapper::last_child(i) <= 
                 HEPEVT_Wrapper::first_child(i) ) {
                HEPEVT_Wrapper::set_children(
                    i, HEPEVT_Wrapper::first_child(i), 0 );
            }

            // The mothers & daughters of a soft centre of mass (stat=170) seem
            // to be correct, but they are out of sequence. The information is
            // elsewhere in the event record, so zero it.
            //
            if ( HEPEVT_Wrapper::status(i) == 170 ) {
                HEPEVT_Wrapper::set_parents( i, 0, 0 );
                HEPEVT_Wrapper::set_children( i, 0, 0 );
            }

            // Recognise clusters.
            // Case 1: cluster has particle parents.  
            // Clusters normally DO point to its two
            // correct mothers, but those 2 mothers are rarely adjacent in the
            // event record ... so the mother information might say something
            // like 123,48 where index123 and index48 really are the correct
            // mothers... however the hepevt standard states that the mother
            // pointers should give the index range. So we would have to
            // reorder the event record and add entries if we wanted to use
            // it. Instead we just zero the mothers, since all of that
            // information is contained in the daughter information of the
            // mothers.
            // Case 2: cluster has a soft process centre of mass (stat=170)
            // as parent. This is ok, keep it.
            //
            // Note if we were going directly to HepMC, then we could 
            //  use this information properly!

            if ( HEPEVT_Wrapper::id(i)==91 ) {
                // if the cluster comes from a SOFT (id=0,stat=170)
                if ( HEPEVT_Wrapper::status(HEPEVT_Wrapper::first_parent(i)) 
                     == 170 ) {
                    ; // In this case the mothers are ok
                } else {
                    HEPEVT_Wrapper::set_parents( i, 0, 0 );
                }
            }
        }
        
        //     ---------- Loop over the particles individually and look 
        //                for mother/daughter inconsistencies.
        // We consider a mother daughter relationship to be valid
        // ONLy when the mother points to the daughter AND the
        // daughter points back (true valid bidirectional
        // pointers) OR when a one thing points to the other, but
        // the other points to zero. If this isn't true, we zero
        // the offending relationship.

        for ( int i=1; i <=HEPEVT_Wrapper::number_entries(); i++ ) {
            // loop over parents
            int ifirst = HEPEVT_Wrapper::first_parent(i);
            int ilast = HEPEVT_Wrapper::last_parent(i);
            if ( ilast == 0 ) ilast = HEPEVT_Wrapper::first_parent(i);
            bool first_is_acceptable = true;
            bool last_is_acceptable = true;
            // check for out of range.
            if ( ifirst>=i || ifirst<0 ) first_is_acceptable = false;
            if ( ilast>=i || ilast<ifirst || ilast<0 )last_is_acceptable=false;
            if ( first_is_acceptable ) {
                for ( int j = ifirst; j<=ilast; j++ ) {
                    // these are the acceptable outcomes
                    if ( HEPEVT_Wrapper::first_child(j)==i ) {;} 
                    // watch out
                    else if ( HEPEVT_Wrapper::first_child(j) <=i && 
                              HEPEVT_Wrapper::last_child(j) >=i ) {;}
                    else if ( HEPEVT_Wrapper::first_child(j) ==0 && 
                              HEPEVT_Wrapper::last_child(j) ==0 ) {;}

                    // Error Condition:
                    // modified by MADobbs@lbl.gov April 21, 2003
                    // we distinguish between the first parent and all parents
                    //  being incorrect
                    else if (j==ifirst) { first_is_acceptable = false; break; }
                    else { last_is_acceptable = false; break; }
                }
            }
            // if any one of the mothers gave a bad outcome, zero all mothers
            //BPK - Atlas ->
            // do not disconnect photons (most probably from photos)
            if ( HEPEVT_Wrapper::id(i) == 22 && HEPEVT_Wrapper::status(i) == 1 )
              { first_is_acceptable = true; }
            //BPK - Atlas -<
            if ( !first_is_acceptable ) {
              HEPEVT_Wrapper::set_parents( i, 0, 0 );
            } else if ( !last_is_acceptable ) {
              HEPEVT_Wrapper::set_parents(i,HEPEVT_Wrapper::first_parent(i),0);
            }
        }
        // Note: it's important to finish the mother loop, before
        // starting the daughter loop ... since many mother relations
        // will be zero'd which will validate the daughters.... i.e.,
        // we want relationships like:
        //      IHEP    ID      IDPDG IST MO1 MO2 DA1 DA2
        //        27 TQRK           6   3  26  26  30  30
        //        30 TQRK           6 155  26  11  31  32
        // to come out right.

        for ( int i=1; i <=HEPEVT_Wrapper::number_entries(); i++ ) {
            // loop over daughters
            int ifirst = HEPEVT_Wrapper::first_child(i);
            int ilast = HEPEVT_Wrapper::last_child(i);
            if ( ilast==0 ) ilast = HEPEVT_Wrapper::first_child(i);
            bool is_acceptable = true;
            // check for out of range.
            if ( ifirst<=i || ifirst<0 ) is_acceptable = false;
            if ( ilast<=i || ilast<ifirst || ilast<0 ) is_acceptable = false;
            if ( is_acceptable ) {
                for ( int j = ifirst; j<=ilast; j++ ) {
                    // these are the acceptable outcomes
                    if ( HEPEVT_Wrapper::first_parent(j)==i ) {;} 
                    else if ( HEPEVT_Wrapper::first_parent(j) <=i && 
                              HEPEVT_Wrapper::last_parent(j) >=i ) {;}
                    else if ( HEPEVT_Wrapper::first_parent(j) ==0 && 
                              HEPEVT_Wrapper::last_parent(j) ==0 ) {;}
                    else { is_acceptable = false; } // error condition 
                }
            }
            // if any one of the children gave a bad outcome, zero all children
            if ( !is_acceptable ) HEPEVT_Wrapper::set_children( i, 0, 0 );
        }

        // fixme

        for ( int i=1; i <=HEPEVT_Wrapper::number_entries(); i++ ) {
            HEPEVT_Wrapper::set_id(
                i, translate_herwig_to_pdg_id(HEPEVT_Wrapper::id(i)) );
        }


        if ( m_no_gaps_in_barcodes ) remove_gaps_in_hepevt();
    }

    void IO_HERWIG::remove_gaps_in_hepevt() const {
        std::vector<int> mymap(HEPEVT_Wrapper::number_entries()+1,0);
        int ilast = 0;
        for ( int i=1; i <=HEPEVT_Wrapper::number_entries(); i++ ) {
            if (HEPEVT_Wrapper::status(i)==0 && HEPEVT_Wrapper::id(i)==0) {
                // we remove all entries for which stat=0, id=0
                mymap[i]=0;
            } else {
                ilast += 1;
                if ( ilast != i ) {
                    HEPEVT_Wrapper::set_status(ilast, 
                                               HEPEVT_Wrapper::status(i) );
                    HEPEVT_Wrapper::set_id(ilast, HEPEVT_Wrapper::id(i) );
                    HEPEVT_Wrapper::set_parents(
                        ilast, 
                        HEPEVT_Wrapper::first_parent(i),
                        HEPEVT_Wrapper::last_parent(i) );
                    HEPEVT_Wrapper::set_children(
                        ilast, 
                        HEPEVT_Wrapper::first_child(i),
                        HEPEVT_Wrapper::last_child(i) );
                    HEPEVT_Wrapper::set_momentum(
                        ilast, 
                        HEPEVT_Wrapper::px(i), HEPEVT_Wrapper::py(i),
                        HEPEVT_Wrapper::pz(i), HEPEVT_Wrapper::e(i)  );
                    HEPEVT_Wrapper::set_mass(ilast, HEPEVT_Wrapper::m(i) );
                    HEPEVT_Wrapper::set_position(
                        ilast, HEPEVT_Wrapper::x(i),HEPEVT_Wrapper::y(i),
                        HEPEVT_Wrapper::z(i),HEPEVT_Wrapper::t(i) );
                }
                mymap[i]=ilast;
            }
        }

        // M. Dobbs (from Borut) - April 26, to fix tauolo/herwig past
        // the end problem with daughter pointers: 
        // HEPEVT_Wrapper::set_number_entries( ilast );

        // Finally we need to re-map the mother/daughter pointers.      
        for ( int i=1; i <=ilast; i++ ) {

            HEPEVT_Wrapper::set_parents(
                i, 
                mymap[HEPEVT_Wrapper::first_parent(i)],
                mymap[HEPEVT_Wrapper::last_parent(i)] );
            HEPEVT_Wrapper::set_children(
                i, 
                mymap[HEPEVT_Wrapper::first_child(i)],
                mymap[HEPEVT_Wrapper::last_child(i)] );
        }
        // M. Dobbs (from Borut, part B) - April 26, to fix tauolo/herwig past
        // the end problem with daughter pointers: 
        HEPEVT_Wrapper::set_number_entries( ilast );
    }

    void IO_HERWIG::zero_hepevt_entry( int i ) const {
      if ( i <=0 || i > HepMC::HEPEVT_Wrapper::max_number_entries() ) return;
      HEPEVT_Wrapper::set_status( i, 0 );
      HEPEVT_Wrapper::set_id( i, 0 );
      HEPEVT_Wrapper::set_parents( i, 0, 0 );
      HEPEVT_Wrapper::set_children( i, 0, 0 );
      HEPEVT_Wrapper::set_momentum( i, 0, 0, 0, 0 );
      HEPEVT_Wrapper::set_mass( i, 0 );
      HEPEVT_Wrapper::set_position( i, 0, 0, 0, 0 );
    }

    int IO_HERWIG::translate_herwig_to_pdg_id( int id ) const {
 
                                               // example -9922212
        int hwtran = id;                       //         -9922212
        int ida    = abs(id);                  //          9922212
        int j1     = ida%10;                   //                2
        int i1     = (ida/10)%10;              //               1
        int i2     = (ida/100)%10;             //              2
        int i3     = (ida/1000)%10;            //             2
        //int i4     =(ida/10000)%10;          //            2
        //int i5     =(ida/100000)%10;         //           9
        //int k99    = (ida/100000)%100;       //          9
        int ksusy  = (ida/1000000)%10;         //         0
        //int ku     = (ida/10000000)%10;      //        0
        int kqn    = (ida/1000000000)%10;      //       0

        if ( kqn==1 ) {
            //  ions not recognized
            hwtran=0;
            if ( m_print_inconsistency_errors ) {
                std::cerr << "IO_HERWIG::translate_herwig_to_pdg_id " << id
                          << "nonallowed ion" << std::endl;
            }
        } 
        else if (ida < 100) {
            // Higgs, etc.
            hwtran = m_herwig_to_pdg_id[ida];
            if ( id < 0 ) hwtran *= -1;
            // check for illegal antiparticles
            if ( id < 0 ) {
                if ( hwtran>=-99 && hwtran<=-81) hwtran=0;
                if ( m_no_antiparticles.count(hwtran) ) hwtran=0;
            }
        }
        else if ( ksusy==1 || ksusy==2 ) { ; }
        //  SUSY
        else if ( i1!=0 && i3!=0 && j1==2 ) {;}
        // spin 1/2 baryons
        else if ( i1!=0 && i3!=0 && j1==4 ) {;}
        // spin 3/2 baryons
        else if ( i1!=0 && i2!=0 && i3==0 ) {
            // mesons 
            // check for illegal antiparticles
            if ( i1==i2 && id<0) hwtran=0;
        } 
        else if ( i2!=0 && i3!=0 && i1==0 ) {;}
        // diquarks
        else {
            // undefined
            hwtran=0;
        }

        // check for illegal anti KS, KL
        if ( id==-130 || id==-310 ) hwtran=0;

        if ( hwtran==0 && ida!=0 && m_print_inconsistency_errors ) {
            std::cerr 
                << "IO_HERWIG::translate_herwig_to_pdg_id HERWIG particle " 
                << id << " translates to zero." << std::endl;
        }

        return hwtran;
    }

} // HepMC