## main221

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    // main221.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.

    // Authors:
    //            Marius Utheim

    // Keywords:
    //            Parallelism

    // This is a simple test program to illustrate the usage of PythiaParallel.
    // The program is equivalent to main101, but in parallel.
    // This program is shortened to fit on a single slide.
    // See main222 for a more heavily commented version.

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

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

    int main() {
      // Use the PythiaParallel class for parallel generation.
      PythiaParallel pythia;
      pythia.readString("Beams:eCM = 8000.");
      pythia.readString("HardQCD:all = on");
      pythia.readString("PhaseSpace:pTHatMin = 20.");

      // If Pythia fails to initialize, exit with error.
      if (!pythia.init()) return 1;

      Hist mult("charged multiplicity", 100, -0.5, 799.5);
      // Use PythiaParallel::run to generate the specified number of events.
      pythia.run(10000, [&](Pythia* pythiaPtr) {
        // Find number of all final charged particles and fill histogram.
        int nCharged = 0;
        for (int i = 0; i < pythiaPtr->event.size(); ++i)
          if (pythiaPtr->event[i].isFinal() && pythiaPtr->event[i].isCharged())
            ++nCharged;
        mult.fill( nCharged );
        // End of event loop. Statistics. Histogram. Done.
      });
      pythia.stat();
      cout << mult;
      return 0;
    }