hepmc - Rev 65

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//////////////////////////////////////////////////////////////////////////
// Matt.Dobbs@Cern.CH, December 1999
// November 2000, updated to use Pythia 6.1
// example of generating events with Pythia
// using HepMC/PythiaWrapper.h
// Events are read into the HepMC event record from the FORTRAN HEPEVT
// common block using the IO_HEPEVT strategy and then output to file in
// ascii format using the IO_Ascii strategy.
//////////////////////////////////////////////////////////////////////////
/// To Compile: go to the HepMC directory and type:
/// gmake examples/example_MyPythia.exe
///
/// In this example the precision and number of entries for the HEPEVT
/// fortran common block are explicitly defined to correspond to those
/// used in the Pythia version of the HEPEVT common block.
///
/// If you get funny output from HEPEVT in your own code, probably you have
/// set these values incorrectly!
///

#include <iostream>
#include "HepMC/PythiaWrapper.h"
#include "HepMC/IO_HEPEVT.h"
#include "HepMC/IO_Ascii.h"
#include "HepMC/GenEvent.h"
   
int main() {
    //
    //........................................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
    // (Some platforms may require the initialization of pythia PYDATA block
    //  data as external - if you get pythia initialization errors try
    //  commenting in/out the below call to initpydata() )
    // initpydata();
    //
    // Select W+gamma process (process number 20)
    // (here we have to be careful of C/F77 differences: arrays in C
    //  start at 0, F77 at 1, so we need to subtract 1 from the process #)
    pysubs.msel=0;
    pysubs.msub[20-1] = 1;
    // set random number seed (mandatory!)
    pydatr.mrpy[0]=55122 ;
    // Tell Pythia not to write multiple copies of particles in event record.
    pypars.mstp[128-1] = 2;
    // Example of setting a Pythia parameter: set the top mass
    pydat2.pmas[1-1][6-1]= 175;  
    //
    // Call pythia initialization
    call_pyinit( "CMS", "p", "p", 14000. );

    //........................................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_Ascii 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();
            // 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

    return 0;
}