HepMCEx01/data/example_MyPythia.cxx

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0026 /// \file example_MyPythia.cxx
0027 /// \brief Main program of the HepMCEx01/data example
0028
0029 // Matt.Dobbs@Cern.CH, December 1999
0030 // November 2000, updated to use Pythia 6.1
0031 // example of generating events with Pythia
0032 // using HepMC/PythiaWrapper.h
0033 // Events are read into the HepMC event record from the FORTRAN HEPEVT
0034 // common block using the IO_HEPEVT strategy and then output to file in
0035 // ascii format using the IO_Ascii strategy.
0036 //////////////////////////////////////////////////////////////////////////
0037 // To Compile: go to the HepMC directory and type:
0038 // gmake examples/example_MyPythia.exe
0039 //
0040 // In this example the precision and number of entries for the HEPEVT
0041 // fortran common block are explicitly defined to correspond to those
0042 // used in the Pythia version of the HEPEVT common block.
0043 //
0044 // If you get funny output from HEPEVT in your own code, probably you have
0045 // set these values incorrectly!
0046 //
0047
0048 #include <iostream>
0049 #include "HepMC/PythiaWrapper.h"
0050 #include "HepMC/IO_HEPEVT.h"
0051 #include "HepMC/IO_GenEvent.h"
0052 #include "HepMC/GenEvent.h"
0053
0054 int main() {
0055     //
0056     //........................................HEPEVT
0057     // Pythia 6.1 uses HEPEVT with 4000 entries and 8-byte floating point
0058     //  numbers. We need to explicitly pass this information to the
0059     //  HEPEVT_Wrapper.
0060     //
0061     HepMC::HEPEVT_Wrapper::set_max_number_entries(4000);
0062     HepMC::HEPEVT_Wrapper::set_sizeof_real(8);
0063     //
0064     //........................................PYTHIA INITIALIZATIONS
0065     // (Some platforms may require the initialization of pythia PYDATA block
0066     //  data as external - if you get pythia initialization errors try
0067     //  commenting in/out the below call to initpydata() )
0068     // initpydata();
0069     //
0070     // Select W+gamma process (process number 20)
0071     // (here we have to be careful of C/F77 differences: arrays in C
0072     //  start at 0, F77 at 1, so we need to subtract 1 from the process #)
0073     pysubs.msel=0;
0074     pysubs.msub[20-1] = 1;
0075     // set random number seed (mandatory!)
0076     pydatr.mrpy[0]=55122 ;
0077     // Tell Pythia not to write multiple copies of particles in event record.
0078     pypars.mstp[128-1] = 2;
0079     // Example of setting a Pythia parameter: set the top mass
0080     pydat2.pmas[1-1][6-1]= 175;
0081     //
0082     // Call pythia initialization
0083     call_pyinit( "CMS", "p", "p", 14000. );
0084
0085     //........................................HepMC INITIALIZATIONS
0086     //
0087     // Instantiate an IO strategy for reading from HEPEVT.
0088     HepMC::IO_HEPEVT hepevtio;
0089     //
0090     // Instantial an IO strategy to write the data to file - it uses the
0091     //  same ParticleDataTable
0092     HepMC::IO_GenEvent ascii_io("example_MyPythia.dat",std::ios::out);
0093     //
0094     //........................................EVENT LOOP
0095     for ( int i = 1; i <= 10; i++ ) {
0096     if ( i%50==1 ) std::cout << "Processing Event Number "
0097                  << i << std::endl;
0098     call_pyevnt();      // generate one event with Pythia
0099     // pythia pyhepc routine converts common PYJETS in common HEPEVT
0100     call_pyhepc( 1 );
0101     HepMC::GenEvent* evt = hepevtio.read_next_event();
0102     // add some information to the event
0103     evt->set_event_number(i);
0104     evt->set_signal_process_id(20);
0105     // write the event out to the ascii file
0106     ascii_io << evt;
0107     // we also need to delete the created event from memory
0108     delete evt;
0109     }
0110     //........................................TERMINATION
0111     // write out some information from Pythia to the screen
0112     call_pystat( 1 );
0113
0114     return 0;
0115 }