HepMC Reference Documentation HepMC

fio/example_MyPythia.cc

example to generate events and write output example to generate events and perform simple event selection example to read the file written by pythia_out example to generate events, write them, and read them back

// Matt.Dobbs@Cern.CH, December 1999
// November 2000, updated to use Pythia 6.1
// 


#include <iostream>
#include "HepMC/PythiaWrapper.h"
#include "HepMC/IO_HEPEVT.h"
#include "HepMC/IO_GenEvent.h"
#include "HepMC/IO_AsciiParticles.h"
#include "HepMC/GenEvent.h"
#include "PythiaHelper.h"


class IsGoodEventMyPythia {
public:
    bool operator()( const HepMC::GenEvent* evt ) { 
        for ( HepMC::GenEvent::particle_const_iterator p 
                  = evt->particles_begin(); p != evt->particles_end(); ++p ){
            if ( (*p)->pdg_id() == 22 && (*p)->momentum().perp() > 25. ) {
                //std::cout << "Event " << evt->event_number()
                //     << " is a good event." << std::endl;
                //(*p)->print();
                return 1;
            }
        }
        return 0;
    }
};
    

void pythia_out();
void pythia_in();
void pythia_in_out();
void event_selection();
void pythia_particle_out();

int main() { 
    // example to generate events and write output
    pythia_out();
    // example to generate events and perform simple event selection
    event_selection();
    // example to read the file written by pythia_out
    pythia_in();
    // example to generate events, write them, and read them back
    pythia_in_out();

    return 0;
}


void pythia_out()
{
    std::cout << std::endl;
    std::cout << "Begin pythia_out()" << std::endl;
   //........................................HEPEVT
    // Pythia 6.1 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);
    //
    //........................................PYTHIA INITIALIZATIONS
    initPythia();

    //........................................HepMC INITIALIZATIONS
    //
    // Instantiate an IO strategy for reading from HEPEVT.
    HepMC::IO_HEPEVT hepevtio;
    //
    { // begin scope of ascii_io
        // Instantiate an IO strategy to write the data to file 
        HepMC::IO_GenEvent ascii_io("example_MyPythia.dat",std::ios::out);
        //
        //........................................EVENT LOOP
        for ( int i = 1; i <= 100; i++ ) {
            if ( i%50==1 ) std::cout << "Processing Event Number " 
                                     << i << std::endl;
            call_pyevnt();      // generate one event with Pythia
            // pythia pyhepc routine converts common PYJETS in common HEPEVT
            call_pyhepc( 1 );
            HepMC::GenEvent* evt = hepevtio.read_next_event();
            // define the units (Pythia uses GeV and mm)
            evt->use_units(HepMC::Units::GEV, HepMC::Units::MM);
            // add some information to the event
            evt->set_event_number(i);
            evt->set_signal_process_id(20);
            // set number of multi parton interactions
            evt->set_mpi( pypars.msti[31-1] );
            // set cross section information
            evt->set_cross_section( HepMC::getPythiaCrossSection() );
            // write the event out to the ascii files
            ascii_io << evt;
            // we also need to delete the created event from memory
            delete evt;
        }
        //........................................TERMINATION
        // write out some information from Pythia to the screen
        call_pystat( 1 );    
    } // end scope of ascii_io
}

 
void event_selection()
{
    std::cout << std::endl;
    std::cout << "Begin event_selection()" << std::endl;
    //........................................HEPEVT
    // Pythia 6.1 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);
    //  
    //........................................PYTHIA INITIALIZATIONS
    initPythia();
    //
    //........................................HepMC INITIALIZATIONS
    // Instantiate an IO strategy for reading from HEPEVT.
    HepMC::IO_HEPEVT hepevtio;
    // declare an instance of the event selection predicate
    IsGoodEventMyPythia is_good_event;
    //........................................EVENT LOOP
    int icount=0;
    int num_good_events=0;
    for ( int i = 1; i <= 100; i++ ) {
        icount++;
        if ( i%50==1 ) std::cout << "Processing Event Number " 
                                 << i << std::endl;
        call_pyevnt(); // generate one event with Pythia
        // pythia pyhepc routine convert common PYJETS in common HEPEVT
        call_pyhepc( 1 );
        HepMC::GenEvent* evt = hepevtio.read_next_event();
        // define the units (Pythia uses GeV and mm)
        evt->use_units(HepMC::Units::GEV, HepMC::Units::MM);
        // set number of multi parton interactions
        evt->set_mpi( pypars.msti[31-1] );
        // set cross section information
        evt->set_cross_section( HepMC::getPythiaCrossSection() );
        // do event selection
        if ( is_good_event(evt) ) {
            std::cout << "Good Event Number " << i << std::endl;
            ++num_good_events;
        }
        // we also need to delete the created event from memory
        delete evt;
    }
    //........................................TERMINATION
    // write out some information from Pythia to the screen
    call_pystat( 1 );    
    //........................................PRINT RESULTS
    std::cout << num_good_events << " out of " << icount 
              << " processed events passed the cuts. Finished." << std::endl;
}

void pythia_in()
{
    std::cout << std::endl;
    std::cout << "Begin pythia_in()" << std::endl;
    std::cout << "reading example_MyPythia.dat" << std::endl;
    //........................................define an input scope
    {
        // open input stream
        std::ifstream istr( "example_MyPythia.dat" );
        if( !istr ) {
          std::cerr << "example_ReadMyPythia: cannot open example_MyPythia.dat" << std::endl;
          exit(-1);
        }
        HepMC::IO_GenEvent ascii_in(istr);
        // open output stream (alternate method)
        HepMC::IO_GenEvent ascii_out("example_MyPythia2.dat",std::ios::out);
        // now read the file
        int icount=0;
        HepMC::GenEvent* evt = ascii_in.read_next_event();
        while ( evt ) {
            icount++;
            if ( icount%50==1 ) std::cout << "Processing Event Number " << icount
                                          << " its # " << evt->event_number() 
                                          << std::endl;
            // write the event out to the ascii file
            ascii_out << evt;
            delete evt;
            ascii_in >> evt;
        }
        //........................................PRINT RESULT
        std::cout << icount << " events found. Finished." << std::endl;
    } // ascii_out and istr destructors are called here
}

void pythia_in_out()
{
    std::cout << std::endl;
    std::cout << "Begin pythia_in_out()" << std::endl;
    //........................................HEPEVT
    // Pythia 6.3 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);
    //
    //........................................PYTHIA INITIALIZATIONS
    initPythia();

    //........................................HepMC INITIALIZATIONS
    //
    // Instantiate an IO strategy for reading from HEPEVT.
    HepMC::IO_HEPEVT hepevtio;
    //
    //........................................define the output scope
    {
        // Instantial an IO strategy to write the data to file
        HepMC::IO_GenEvent ascii_io("example_MyPythiaRead.dat",std::ios::out);
        //
        //........................................EVENT LOOP
        for ( int i = 1; i <= 100; i++ ) {
            if ( i%50==1 ) std::cout << "Processing Event Number " 
                                     << i << std::endl;
            call_pyevnt();      // generate one event with Pythia
            // pythia pyhepc routine converts common PYJETS in common HEPEVT
            call_pyhepc( 1 );
            HepMC::GenEvent* evt = hepevtio.read_next_event();
            // define the units (Pythia uses GeV and mm)
            evt->use_units(HepMC::Units::GEV, HepMC::Units::MM);
            // set cross section information
            evt->set_cross_section( HepMC::getPythiaCrossSection() );
            // add some information to the event
            evt->set_event_number(i);
            evt->set_signal_process_id(20);
            // write the event out to the ascii file
            ascii_io << evt;
            // we also need to delete the created event from memory
            delete evt;
        }
        //........................................TERMINATION
        // write out some information from Pythia to the screen
        call_pystat( 1 );    
    }  // ascii_io destructor is called here
    //
    //........................................define an input scope
    {
        // now read the file we wrote
        HepMC::IO_GenEvent ascii_in("example_MyPythiaRead.dat",std::ios::in);
        HepMC::IO_GenEvent ascii_io2("example_MyPythiaRead2.dat",std::ios::out);
        int icount=0;
        HepMC::GenEvent* evt = ascii_in.read_next_event();
        while ( evt ) {
            icount++;
            if ( icount%50==1 ) std::cout << "Processing Event Number " << icount
                                          << " its # " << evt->event_number() 
                                          << std::endl;
            // write the event out to the ascii file
            ascii_io2 << evt;
            delete evt;
            ascii_in >> evt;
        }
        //........................................PRINT RESULT
        std::cout << icount << " events found. Finished." << std::endl;
    } // ascii_io2 and ascii_in destructors are called here
}

void pythia_particle_out()
{
    std::cout << std::endl;
    std::cout << "Begin pythia_particle_out()" << std::endl;
    //........................................HEPEVT
    // Pythia 6.1 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);
    //
    //........................................PYTHIA INITIALIZATIONS
    initPythia();

    //........................................HepMC INITIALIZATIONS
    //
    // Instantiate an IO strategy for reading from HEPEVT.
    HepMC::IO_HEPEVT hepevtio;
    //
    { // begin scope of ascii_io
        // Instantiate an IO strategy to write the data to file 
        HepMC::IO_AsciiParticles ascii_io("example_PythiaParticle.dat",std::ios::out);
        //
        //........................................EVENT LOOP
        for ( int i = 1; i <= 100; i++ ) {
            if ( i%50==1 ) std::cout << "Processing Event Number " 
                                     << i << std::endl;
            call_pyevnt();      // generate one event with Pythia
            // pythia pyhepc routine converts common PYJETS in common HEPEVT
            call_pyhepc( 1 );
            HepMC::GenEvent* evt = hepevtio.read_next_event();
            // define the units (Pythia uses GeV and mm)
            evt->use_units(HepMC::Units::GEV, HepMC::Units::MM);
            // set cross section information
            evt->set_cross_section( HepMC::getPythiaCrossSection() );
            // add some information to the event
            evt->set_event_number(i);
            evt->set_signal_process_id(20);
            // write the event out to the ascii file
            ascii_io << evt;
            // we also need to delete the created event from memory
            delete evt;
        }
        //........................................TERMINATION
        // write out some information from Pythia to the screen
        call_pystat( 1 );    
    } // end scope of ascii_io
}

---