main221

// main221.cc is a part of the PYTHIA event generator.
// Copyright (C) 2024 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;
}