main89

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// main89.cc is a part of the PYTHIA event generator.
// Copyright (C) 2021 Torbjorn Sjostrand.
// PYTHIA is licenced under the GNU GPL v2 or later, see COPYING for details.
// Please respect the MCnet Guidelines, see GUIDELINES for details.

// Authors:
//            Stefan Prestel

// Keywords:
//            Matching
//            Merging
//            Leading order
//            NLO
//            Powheg
//            Madgraph
//            aMC@NLO
//            CKKW‑L
//            UMEPS
//            NL3
//            UNLOPS
//            FxFx
//            MLM
//            Userhooks
//            LHE file
//            Hepmc

// This program illustrates how to do run PYTHIA with LHEF input, allowing a
// sample-by-sample generation of
// a) Non-matched/non-merged events
// b) MLM jet-matched events (kT-MLM, shower-kT, FxFx)
// c) CKKW-L and UMEPS-merged events
// d) UNLOPS NLO merged events
// see the respective sections in the online manual for details.
//
// An example command is
//     ./main89 main89ckkwl.cmnd hepmcout89.dat
// where main89.cmnd supplies the commands and hepmcout89.dat is the
// output file. This example requires HepMC2 or HepMC3.

#include "Pythia8/Pythia.h"
#ifndef HEPMC2
#include "Pythia8Plugins/HepMC3.h"
#else
#include "Pythia8Plugins/HepMC2.h"
#endif

// Include UserHooks for Jet Matching.
#include "Pythia8Plugins/CombineMatchingInput.h"
// Include UserHooks for randomly choosing between integrated and
// non-integrated treatment for unitarised merging.
#include "Pythia8Plugins/aMCatNLOHooks.h"

using namespace Pythia8;

//==========================================================================

// Example main programm to illustrate merging.

int main( int argc, char* argv[] ){

  // Check that correct number of command-line arguments
  if (argc != 3) {
    cerr << " Unexpected number of command-line arguments ("< matching;

  // Allow to set the number of addtional partons dynamically.
  shared_ptr setting;
  if ( doMerge ) {
    // Store merging scheme.
    int scheme = ( pythia.settings.flag("Merging:doUMEPSTree")
                || pythia.settings.flag("Merging:doUMEPSSubt")) ?
                1 :
                 ( ( pythia.settings.flag("Merging:doUNLOPSTree")
                || pythia.settings.flag("Merging:doUNLOPSSubt")
                || pythia.settings.flag("Merging:doUNLOPSLoop")
                || pythia.settings.flag("Merging:doUNLOPSSubtNLO")) ?
                2 :
                0 );
    setting = make_shared(scheme);
    pythia.setUserHooksPtr(setting);
  }

  // For jet matching, initialise the respective user hooks code.
  CombineMatchingInput combined;
  if (doMatch) combined.setHook(pythia);

  vector xss;

  // Allow usage also for non-matched configuration.
  if(!doMatchMerge) {
    // Loop over subruns with varying number of jets.
    for (int iMerge = 0; iMerge < nMerge; ++iMerge) {
      // Read in file for current subrun and initialize.
      pythia.readFile(argv[1], iMerge);
      // Initialise.
      pythia.init();
      // Start generation loop
      while( pythia.info.nSelected() < nEvent ){
        // Generate next event
        if( !pythia.next() ) {
          if ( pythia.info.atEndOfFile() ) break;
          else continue;
        }
      } // end loop over events to generate.
      // print cross section, errors
      pythia.stat();
      xss.push_back(pythia.info.sigmaGen());
    }
    pythia.info.weightContainerPtr->clearTotal();
  }

  // Allow abort of run if many errors.
  int  nAbort  = pythia.mode("Main:timesAllowErrors");
  int  iAbort  = 0;
  bool doAbort = false;

  cout << endl << endl << endl;
  cout << "Start generating events" << endl;

  // Loop over subruns with varying number of jets.
  for (int iMerge = 0; iMerge < nMerge; ++iMerge) {

    // Read in name of LHE file for current subrun and initialize.
    pythia.readFile(argv[1], iMerge);

    // Initialise.
    pythia.init();

    // Get the inclusive x-section by summing over all process x-sections.
    double xs = 0.;
    for (int i=0; i < pythia.info.nProcessesLHEF(); ++i)
      xs += pythia.info.sigmaLHEF(i);

    if (!doMatchMerge) xs = xss[iMerge];

    // Start generation loop
    while( pythia.info.nSelected() < nEvent ){

      // Generate next event
      if( !pythia.next() ) {
        if ( pythia.info.atEndOfFile() ) break;
        else if (++iAbort > nAbort) {doAbort = true; break;}
        else continue;
      }

      // Get event weight(s).
      // Additional weight due to random choice of reclustered/non-reclustered
      // treatment. Also contains additional sign for subtractive samples.
      double evtweight = pythia.info.weightValueByIndex();

      // Do not print zero-weight events.
      if ( evtweight == 0. ) continue;

      // Do not print broken / empty events
      if (pythia.event.size() < 3) continue;

      // Work with weighted (LHA strategy=-4) events.
      double norm = 1.;
      if (abs(pythia.info.lhaStrategy()) == 4)
        norm = 1. / double(1e9*nEvent);
      // Work with unweighted events.
      else
        norm = xs / double(1e9*nEvent);

      pythia.info.weightContainerPtr->accumulateXsec(norm);

      // Copy the weight names to HepMC.
      toHepMC.setWeightNames(pythia.info.weightNameVector());

      // Fill HepMC event.
      toHepMC.writeNextEvent( pythia );


    } // end loop over events to generate.

    if (doAbort) break;

    // Print cross section, errors.
    pythia.stat();

    // Get cross section statistics for sample.
    double sigmaSample = pythia.info.weightContainerPtr->getSampleXsec()[0];
    double errorSample = pythia.info.weightContainerPtr->getSampleXsecErr()[0];

    cout << endl << " Contribution of sample " << iMerge
         << " to the inclusive cross section : "
         << scientific << setprecision(8)
         << sigmaSample << "  +-  " << errorSample  << endl;
  }
  cout << endl << endl << endl;

  // Get cross section statistics for total run.
  double sigmaTotal = pythia.info.weightContainerPtr->getTotalXsec()[0];
  double errorTotal = pythia.info.weightContainerPtr->getSampleXsecErr()[0];
  if (doAbort)
    cout << " Run was not completed owing to too many aborted events" << endl;
  else
    cout << "Inclusive cross section: " << scientific << setprecision(8)
         << sigmaTotal << "  +-  " << errorTotal << " mb " << endl;
  cout << endl << endl << endl;

  // Done
  return 0;

}