HepMCEx01/data/example_MyPythia.cxx

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0027 //////////////////////////////////////////////////////////////////////////
0028 // Matt.Dobbs@Cern.CH, December 1999
0029 // November 2000, updated to use Pythia 6.1
0030 // example of generating events with Pythia
0031 // using HepMC/PythiaWrapper.h
0032 // Events are read into the HepMC event record from the FORTRAN HEPEVT
0033 // common block using the IO_HEPEVT strategy and then output to file in
0034 // ascii format using the IO_Ascii strategy.
0035 //////////////////////////////////////////////////////////////////////////
0036 // To Compile: go to the HepMC directory and type:
0037 // gmake examples/example_MyPythia.exe
0038 //
0039 // In this example the precision and number of entries for the HEPEVT
0040 // fortran common block are explicitly defined to correspond to those
0041 // used in the Pythia version of the HEPEVT common block.
0042 //
0043 // If you get funny output from HEPEVT in your own code, probably you have
0044 // set these values incorrectly!
0045 //
0046
0047 #include <iostream>
0048 #include "HepMC/PythiaWrapper.h"
0049 #include "HepMC/IO_HEPEVT.h"
0050 #include "HepMC/IO_GenEvent.h"
0051 #include "HepMC/GenEvent.h"
0052
0053 int main() {
0054     //
0055     //........................................HEPEVT
0056     // Pythia 6.1 uses HEPEVT with 4000 entries and 8-byte floating point
0057     //  numbers. We need to explicitly pass this information to the
0058     //  HEPEVT_Wrapper.
0059     //
0060     HepMC::HEPEVT_Wrapper::set_max_number_entries(4000);
0061     HepMC::HEPEVT_Wrapper::set_sizeof_real(8);
0062     //
0063     //........................................PYTHIA INITIALIZATIONS
0064     // (Some platforms may require the initialization of pythia PYDATA block
0065     //  data as external - if you get pythia initialization errors try
0066     //  commenting in/out the below call to initpydata() )
0067     // initpydata();
0068     //
0069     // Select W+gamma process (process number 20)
0070     // (here we have to be careful of C/F77 differences: arrays in C
0071     //  start at 0, F77 at 1, so we need to subtract 1 from the process #)
0072     pysubs.msel=0;
0073     pysubs.msub[20-1] = 1;
0074     // set random number seed (mandatory!)
0075     pydatr.mrpy[0]=55122 ;
0076     // Tell Pythia not to write multiple copies of particles in event record.
0077     pypars.mstp[128-1] = 2;
0078     // Example of setting a Pythia parameter: set the top mass
0079     pydat2.pmas[1-1][6-1]= 175;
0080     //
0081     // Call pythia initialization
0082     call_pyinit( "CMS", "p", "p", 14000. );
0083
0084     //........................................HepMC INITIALIZATIONS
0085     //
0086     // Instantiate an IO strategy for reading from HEPEVT.
0087     HepMC::IO_HEPEVT hepevtio;
0088     //
0089     // Instantial an IO strategy to write the data to file - it uses the
0090     //  same ParticleDataTable
0091     HepMC::IO_GenEvent ascii_io("example_MyPythia.dat",std::ios::out);
0092     //
0093     //........................................EVENT LOOP
0094     for ( int i = 1; i <= 10; i++ ) {
0095     if ( i%50==1 ) std::cout << "Processing Event Number "
0096                  << i << std::endl;
0097     call_pyevnt();      // generate one event with Pythia
0098     // pythia pyhepc routine converts common PYJETS in common HEPEVT
0099     call_pyhepc( 1 );
0100     HepMC::GenEvent* evt = hepevtio.read_next_event();
0101     // add some information to the event
0102     evt->set_event_number(i);
0103     evt->set_signal_process_id(20);
0104     // write the event out to the ascii file
0105     ascii_io << evt;
0106     // we also need to delete the created event from memory
0107     delete evt;
0108     }
0109     //........................................TERMINATION
0110     // write out some information from Pythia to the screen
0111     call_pystat( 1 );
0112
0113     return 0;
0114 }