## main153

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    // main153.cc is a part of the PYTHIA event generator.
    // Copyright (C) 2025 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:
    //            Philip Ilten

    // Keywords:
    //            Matching
    //            Madgraph
    //            aMC@NLO

    // An example where the hard process (p p -> mu+ mu-) is automatically
    // produced externally with MadGraph 5, read in, and the remainder of
    // the event is then produced by Pythia (MPI, showers, hadronization,
    // and decays). A comparison is made between events produced with
    // Pythia at LO, MadGraph 5 at LO, and aMC@NLO at NLO.

    // For this example to run, MadGraph 5 must be installed and the
    // command "exe" (set by default as "mg5_aMC") must be available via
    // the command line. Additionally, GZIP support must be enabled via
    // the "--with-gzip" configuration option(s). Note that this example has
    // only been tested with MadGraph 5 version 2.3.3; due to rapid
    // MadGraph development, this example may not work with other
    // versions. For more details on the LHAMadgraph class see the
    // comments of Pythia8Plugins/LHAMadgraph.h.

    #include "Pythia8/Pythia.h"
    #include "Pythia8Plugins/LHAMadgraph.h"

    using namespace Pythia8;

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

    // A simple method to run Pythia, analyze the events, and fill a histogram.

    bool run(Pythia& pythia, Hist& hist, int nEvent) {
      pythia.readString("Random:setSeed = on");
      pythia.readString("Random:seed = 1");

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

      for (int iEvent = 0; iEvent < nEvent; ++iEvent) {
        if (!pythia.next()) continue;
        int iMu1(0), iMu2(0);
        for (int i = 0; i < pythia.event.size(); ++i) {
          if (!iMu1 && pythia.event[i].id() == 13)  iMu1 = i;
          if (!iMu2 && pythia.event[i].id() == -13) iMu2 = i;
          if (iMu1 && iMu2) {
            iMu1 = pythia.event[iMu1].iBotCopyId();
            iMu2 = pythia.event[iMu2].iBotCopyId();
            hist.fill((pythia.event[iMu1].p() + pythia.event[iMu2].p()).pT());
            break;
          }
        }
      }
      pythia.stat();
      return true;
    }

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

    int main() {

      // The name of the MadGraph5_aMC@NLO executable.
      // You must prepend this string with the path to the executable
      // on your local installation, or otherwise make it available.
      string exe("mg5_aMC");

      // Create the histograms.
      Hist pyPtZ("Pythia dN/dpTZ", 100, 0., 100.);
      Hist mgPtZ("MadGraph dN/dpTZ", 100, 0., 100.);
      Hist amPtZ("aMC@NLO dN/dpTZ", 100, 0., 100.);

      // Produce leading-order events with Pythia.
      {
        Pythia pythia;
        pythia.readString("Beams:eCM = 13000.");
        pythia.readString("WeakSingleBoson:ffbar2gmZ = on");
        pythia.readString("23:onMode = off");
        pythia.readString("23:onIfMatch = -13 13");
        pythia.readString("PhaseSpace:mHatMin = 80.");
        // If initialization fails, return with error.
        if (!run(pythia, pyPtZ, 1000)) return 1;
      }

      // Produce leading-order events with MadGraph 5.
      {
        Pythia pythia;
        shared_ptr<LHAupMadgraph> madgraph = make_shared<LHAupMadgraph>(&pythia,
          true, "madgraphrun", exe);
        madgraph->readString("generate p p > mu+ mu-");
        // Note the need for a blank character before "set".
        madgraph->readString(" set ebeam1 6500");
        madgraph->readString(" set ebeam2 6500");
        madgraph->readString(" set mmll 80");
        pythia.setLHAupPtr((LHAupPtr)madgraph);
        // If initialization fails, return with error.
        if (!run(pythia, mgPtZ, 1000)) return 1;
      }

      // Produce next-to-leading-order events with aMC@NLO.
      {
        Pythia pythia;
        shared_ptr<LHAupMadgraph> amcatnlo = make_shared<LHAupMadgraph>(&pythia,
          true, "amcatnlorun", exe);
        amcatnlo->readString("generate p p > mu+ mu- [QCD]");
        // Note the need for a blank character before "set".
        amcatnlo->readString(" set ebeam1 6500");
        amcatnlo->readString(" set ebeam2 6500");
        amcatnlo->readString(" set mll 80");
        pythia.setLHAupPtr((LHAupPtr)amcatnlo);
        // If initialization fails, return with error.
        if (!run(pythia, amPtZ, 1000)) return 1;
      }

      // Print the histograms.
      cout << pyPtZ;
      cout << mgPtZ;
      cout << amPtZ;
      return 0;
    }