HepMC Reference Documentation HepMC

fio/example_MyHerwig.cc

// Matt.Dobbs@Cern.CH, October 2002
// example of generating events with Herwig using HepMC/HerwigWrapper.h 
// Events are read into the HepMC event record from the FORTRAN HEPEVT 
// common block using the IO_HERWIG strategy.

#include <iostream>
#include "HepMC/HerwigWrapper.h"
#include "HepMC/IO_HERWIG.h"
#include "HepMC/IO_GenEvent.h"
#include "HepMC/GenEvent.h"
#include "HepMC/HEPEVT_Wrapper.h"

int main() { 
    //
    //........................................HEPEVT
    // Herwig 6.4 uses HEPEVT with 4000 entries and 8-byte floating point
    //  numbers. We need to explicitly pass this information to the 
    //  HEPEVT_Wrapper.
    //
    HepMC::HEPEVT_Wrapper::set_max_number_entries(4000);
    HepMC::HEPEVT_Wrapper::set_sizeof_real(8);
    //
    //.......................................INITIALIZATIONS

    hwproc.PBEAM1 = 7000.; // energy of beam1
    hwproc.PBEAM2 = 7000.; // energy of beam2
    // 1610 = gg->H--> WW, 1706 = qq-->ttbar, 2510 = ttH -> ttWW
    hwproc.IPROC = 1706; // qq -> ttbar production 
    hwproc.MAXEV = 100; // number of events
    // tell it what the beam particles are:
    for ( unsigned int i = 0; i < 8; ++i ) {
        hwbmch.PART1[i] = (i < 1) ? 'P' : ' ';
        hwbmch.PART2[i] = (i < 1) ? 'P' : ' ';
    }
    hwigin();    // INITIALISE OTHER COMMON BLOCKS
    hwevnt.MAXPR = 1; // number of events to print
    hwuinc(); // compute parameter-dependent constants
    hweini(); // initialise elementary process

    //........................................HepMC INITIALIZATIONS
    //
    // Instantiate an IO strategy for reading from HEPEVT.
    HepMC::IO_HERWIG hepevtio;
    // Instantiate an IO strategy to write the data to file 
    HepMC::IO_GenEvent ascii_io("example_MyHerwig.dat",std::ios::out);
    //
    //........................................EVENT LOOP
    for ( int i = 1; i <= hwproc.MAXEV; i++ ) {
        if ( i%50==1 ) std::cout << "Processing Event Number " 
                                 << i << std::endl;
        // initialise event
        hwuine();
        // generate hard subprocess
        hwepro();
        // generate parton cascades
        hwbgen();
        // do heavy object decays
        hwdhob();
        // do cluster formation
        hwcfor();
        // do cluster decays
        hwcdec();
        // do unstable particle decays
        hwdhad();
        // do heavy flavour hadron decays
        hwdhvy();
        // add soft underlying event if needed
        hwmevt();
        // finish event
        hwufne();
        HepMC::GenEvent* evt = hepevtio.read_next_event();
        // define the units (Herwig uses GeV and mm)
        evt->use_units(HepMC::Units::GEV, HepMC::Units::MM);
        // set cross section information
        evt->set_cross_section( HepMC::getHerwigCrossSection(i) );
        // add some information to the event
        evt->set_event_number(i);
        evt->set_signal_process_id(20);
        if (i<=hwevnt.MAXPR) {
            std::cout << "\n\n This is the FIXED version of HEPEVT as "
                      << "coded in IO_HERWIG " << std::endl;
            HepMC::HEPEVT_Wrapper::print_hepevt();
            evt->print();
        }
        // write the event to the ascii file
        ascii_io << evt;

        // we also need to delete the created event from memory
        delete evt;
    }
    //........................................TERMINATION
    hwefin();

    return 0;
}

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