## main127

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    // main127.cc is a part of the PYTHIA event generator.
    // Copyright (C) 2026 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.

    // Keywords:
    //            Basic usage
    //            LHE file

    // This is a simple test program.
    // It illustrates how Les Houches Event File version 3.0 information
    // can be extracted from pythia.info.

    #include "Pythia8/Pythia.h"
    using namespace Pythia8;

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

    int main() {

      // Generator
      Pythia pythia;

      // Stick with default values, so do not bother with a separate file
      // for changes. However, do one change, to show readString in action.
      pythia.readString("PartonLevel:MPI = off");
      pythia.readString("HadronLevel:all = off");

      // Initialize Les Houches Event File run.
      pythia.readString("Beams:frameType = 4");
      pythia.readString("Beams:LHEF = wbj_lhef3.lhe");
      // If Pythia fails to initialize, exit with error.
      if (!pythia.init()) return 1;

      // Check if LHEF3 reader exists.
      bool hasRead = (pythia.info.LHEFversion() == 3);

      // Print header read from LHEF.
      cout << endl << "*****************************************************"
           << endl << "  PRINT HEADER OF LHE FILE" << endl;
      if (hasRead) cout << pythia.info.getHeaderBlock() << endl;
      cout << "*****************************************************" << endl;

      // Print extra LHEF v3 header information.
      cout << endl << "*****************************************************"
           << endl << "  RETRIEVE INITRWGT INFORMATION" << endl;
      if (hasRead) {
        const LHAinitrwgt* initrwgt = pythia.info.initrwgt;
        cout << endl << "Attributes: " << endl;
        for ( map<string,string>::const_iterator
          it = initrwgt->attributes.begin();
          it != initrwgt->attributes.end(); ++it )
          cout << "  Attribute: " << it->first << ".  ." << it->second
               << endl;
        cout << "Contents: " << initrwgt->contents << endl;

        cout << endl << endl << "  RETRIEVE WEIGHTGROUP INFORMATION" << endl;
        map<string,LHAweightgroup> weightgroups = initrwgt->weightgroups;
        for ( map<string,LHAweightgroup>::const_iterator
          it = weightgroups.begin();
          it != weightgroups.end(); ++it ) {
          cout << "  Weightgroup: " << it->first << endl;
          for ( map<string,string>::const_iterator
            it2 = it->second.attributes.begin();
            it2 != it->second.attributes.end(); ++it2 ) {
            cout << "  Attribute: " << it2->first << ".  ." << it2->second
                 << endl;
          }
          cout << endl << "  Retrieve weight information:" << endl;
          map<string,LHAweight> weights = it->second.weights;
          for ( map<string,LHAweight>::const_iterator
            it2 = weights.begin(); it2 != weights.end(); ++it2 ) {
            cout << "  Weight: " << it2->first << endl;
            for ( map<string,string>::const_iterator
              it3 = it2->second.attributes.begin();
              it3 != it2->second.attributes.end(); ++it3 ) {
              cout << "  Attribute: " << it3->first << ".  ." << it3->second
                   << endl;
            }
            cout << "  Contents: " << it2->second.contents << endl;
          }
        }
      }
      cout << "*****************************************************" << endl;

      // Print extra LHEF v3 initialization information.
      cout << endl << "*****************************************************"
           << endl << "  RETRIEVE GENERATOR INFORMATION" << endl;
      unsigned int ngen = 0;
      if (hasRead) ngen = pythia.info.generators->size();
      cout << "Number of generator tags " << ngen << endl;
      for (unsigned int igen = 0; igen < ngen; ++igen) {
        cout << ".  generator tag ." << igen << ". : ."
             << pythia.info.generators->at(igen).contents << ".\n";
        for ( map<string, string>::const_iterator
                it = pythia.info.generators->at(igen).attributes.begin();
              it != pythia.info.generators->at(igen).attributes.end(); ++it )
          cout << ". " << it->first << " ." << it->second;
        cout << "\n";
      }
      cout << "*****************************************************" << endl;

      // Begin event loop; generate until none left in input file.
      for (int iEvent = 0; iEvent < 1000; ++iEvent) {

        cout << endl << "Read event # " << iEvent << endl;

        // Generate events, and check whether generation failed.
        if (!pythia.next()) {
          // If failure because reached end of file then exit event loop.
          if (pythia.info.atEndOfFile()) break;
          else continue;
        }

        // Print process-level event.
        pythia.process.list();

        // Print extra LHEF v3 event information.
        cout << endl << "Print event # " << iEvent << endl;

        cout << endl << "*****************************************************"
             << endl << "  RETRIEVE EVENT INFORMATION" << endl;
        if (hasRead) {
          const map <string,string>* eventAttributes =
            pythia.info.eventAttributes;
          cout << endl << "Attributes:" << endl;
          for ( map<string,string>::const_iterator it = eventAttributes->begin();
                it != eventAttributes->end(); ++it )
              cout << "  Attribute\t" << it->first << " = " << it->second
                   << endl;
        }
        cout << "*****************************************************" << endl;

        // Print extra LHEF v3 event weight information.
        cout << endl << "*****************************************************"
             << endl << "  RETRIEVE WEIGHTS (DETAILED FORMAT) INFORMATION" << endl;
        if (hasRead) {
          int nwgt = pythia.info.rwgt->size();
          cout << "Number of wgt tags " << nwgt << endl;
          const map<string,double>* weights = pythia.info.weights_detailed;
          for ( map<string,double>::const_iterator it = weights->begin();
            it != weights->end(); ++it ) {
            cout << it->first << " " << it->second << " " << endl;
          }
          cout << "Second option, from ordered vector:" << endl;
          for ( int i = 0; i < int(pythia.info.weights_detailed_vector.size());
                ++i ) {
            cout << "Weight " << i << " : "
                 << pythia.info.weights_detailed_vector.at(i) << endl;
          }
        }
        cout << "*****************************************************" << endl;

        // Print extra LHEF v3 compressed format event weight information.
        cout << endl << "*****************************************************"
             << endl << "  RETRIEVE WEIGHTS (COMPRESSED FORMAT) INFORMATION"
             << endl;
        if (hasRead) {
          int nweights = pythia.info.weights->size();
          cout << "Number of weights (only one tag!) " << nweights << endl;
          const LHAweights* weights = pythia.info.weights;
          cout << endl << "Attributes:" << endl;
          for ( map<string,string>::const_iterator
            it = weights->attributes.begin();
            it != weights->attributes.end(); ++it )
              cout << "  Attribute\t" << it->first << " = " << it->second << endl;
          cout << "Weights:" << endl;
          for ( int i = 0; i < int(weights->weights.size()); ++i)
            cout << "  Weight\t" << weights->weights[i] << endl;
          cout << endl << "Contents:" << weights->contents << endl;
          cout << "Second option, from stored vector:" << endl;
          for ( int i = 0; i < int(pythia.info.weights_compressed->size());
                ++i ) {
            cout << "Weight\t" << i << " : "
                 << pythia.info.weights_compressed->at(1) << endl;
          }
        }
        cout << "*****************************************************" << endl;

        // Print extra LHEF v3 scale information.
        cout << endl << "*****************************************************"
             << endl << "  RETRIEVE SCALES INFORMATION" << endl;
        if (hasRead) {
          const LHAscales* scales = pythia.info.scales;
          cout << endl << "Attributes:" << endl;
          for ( map<string,double>::const_iterator
            it = scales->attributes.begin(); it != scales->attributes.end(); ++it )
              cout << "  Attribute\t" << it->first << " = " << it->second << endl;
          cout << "Contents:" << scales->contents << endl;
        }
        cout << "*****************************************************" << endl;

        // Print event comments.
        cout << endl << "*****************************************************"
             << endl << "  RETRIEVE EVENT COMMENTS" << endl;
        if (hasRead) cout << pythia.info.getEventComments() << endl;
        cout << "*****************************************************" << endl;

      // End of event loop.
      }

      // Give statistics.
      pythia.stat();

      // Done.
      return 0;
    }