RIVET usage

RIVET is a toolkit for the validation of Monte Carlo event generators [Buc10]. It contains the results of many experimental analyses, so that generator output can easily be compared to data, as well as providing a framework to implement your own analyses. Although using PYTHIA with RIVET is not officially supported, some helpful hints are given below. The full RIVET manual is available online.

Using PYTHIA with RIVET

The following assumes that you already have RIVET installed. Instructions for this may be found here.

Events are passed from PYTHIA to RIVET using the HepMC format. PYTHIA must be compiled with HepMC support, using the same version of HepMC used when compiling RIVET. This is setup through the PYTHIA configure script e.g.

 
  ./configure --with-hepmc=/path/to/HepMC

The PYTHIA library itself does not need to be recompiled.

The examples/main42.cc sample program can then be used to generate events in HepMC format (which examples/main43.cc extends by allowing subruns). When in the examples directory, the main program can be built and used as follows

 
  make main42 
  ./main42 main42.cmnd main42.hepmc

The first argument is the input file which provides the options for event generation, while the second is the output file where the HepMC events should be written.

This HepMC file may now be read and processed by RIVET

 
  rivet --analysis=ANALYSIS_NAME main42.hepmc

where ANALYSIS_NAME is a built-in RIVET analysis, or one you have created yourself. The output of RIVET is in the form of .aida files, containing the histograms for the analysis, which can be processed further with RIVET (see the RIVET documentation for more details).

The above examples requires that (potentially large) HepMC events are stored to disk before being read by RIVET. It is possible, instead, to pass the events directly to RIVET as they are produced by using a FIFO pipe. This is done with the mkfifo command

 
  mkfifo my_fifo 
  ./main42.exe main42.cmnd my_fifo & 
  rivet --analysis=ANALYSIS_NAME my_fifo

Note that main42 is run in the background.

Compiling PYTHIA with RIVET

It is also possible to compile a PYTHIA main program together with the RIVET library. To facilitate this, there is a header file called Pythia8Plugins/Pythia8Rivet.h defining a helper class called Pythia8::Pythia8Rivet. To use this class, a main program needs to be modified as follows:

 
  #include "Pythia8/Pythia.h" 
 
  // Include the Pythia8Rivet header file. 
  #include "Pythia8Plugins/Pythia8Rivet.h" 
 
  int main() { 
 
    Pythia pythia; 
 
    // Setup the run by reading strings or a command file. 
 
    pythia.init(); 
 
    // Create a Pythia8Rivet object and add (one or several) analyses. 
 
    Pythia8Rivet rivet(pythia, "outputfile.yoda"); 
    rivet.addAnalysis("AnalysisName"); 
    rivet.addAnalysis("AnotherAnalysisName"); 
 
    for (int iEvent = 0; iEvent < 100; ++iEvent) { 
      if (!pythia.next()) continue; 
 
      // Push event to Rivet. 
      rivet(); 
 
      // Maybe do other non-Rivet analysis. 
    } 
 
    // Tell Rivet to finalise the run. 
    rivet.done(); 
 
  }

To compile the program, information about where Rivet and its dependencies are installed is needed. This information is available via the rivet-config script via the following.

 
  rivet-config --includedir --libdir --cppflags --libs

The example program main111.cc includes optional analysis with Pythia8::Pythia8Rivet. To use it configure Pythia with the option --with-rivet. This will automatically use the rivet-config script to determine all the necessary paths. If one wishes to pass a specific config script, use the option --with-rivet-config=CONFIG where CONFIG is the Rivet configuration script. Note, a RIVET configuration script must be available to compile the Rivet examples.

The most common user case (run PYTHIA with a run card, using one or several RIVET analyses) is implemented in the example main93. The sample command file main93.cmnd provides a good starting point. The lines:

 
    Main:runRivet = on 
    Main:analyses = ATLAS_2010_S8817804,ALICE_2010_S8625980,CMS_2011_S8957746 
    Main:writeHepMC = on

provides the switch to run RIVET, and gives the user the possibility to add any number of (installed) RIVET analyses to the run, as a comma separated list. The last line is the switch needed to write a HepMC file. The example is run with:

 
  ./main93 -c main93.cmnd

and a .yoda file (the RIVET output) is then written. There are several other useful command line options to main93. They are all displayed by running ./main93 -h.