## main114

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    // main114.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:
    //            Christian Bierlich

    // Keywords:
    //            Basic usage
    //            Plotting
    //            Yoda

    // This is a simple test program.
    // It illustrates how YODA2 histograms can be used through the Pythia8Yoda
    // simplified interface. This can be useful for more advanced statistical
    // treatments than the built-in histogram types allow, for example using
    // profile histograms or custom types, as shown below.

    #include "Pythia8/Pythia.h"
    #include "Pythia8Plugins/Pythia8Yoda.h"

    using namespace Pythia8;

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

    int main() {
      Pythia pythia;
      pythia.readString("Beams:eCM = 8000.");
      pythia.readString("SoftQCD:all = on");
      // If Pythia fails to initialize, exit with error.
      if (!pythia.init()) return 1;
      Pythia8Yoda p8y("MAIN114", "main114.yoda");
      // Booking of normal types, as defined in Pythia8Yoda.
      auto h1 = p8y.bookHisto1D(15, 0.5, 191.5, "charged-mult");
      auto h2 = p8y.bookProfile1D(15, 0.5, 191.5, "mean-pt");
      // Booking of custom YODA types. Two examples:
      // 1) a 1D histogram with discrete string binning, used
      // to count the number of pi, K and p per event, and
      // 2) a 1D Profile histogram with discrete string binning,
      // used to count <pT> of said particles.
      // First the types:
      using IntegerHisto1D = YODA::BinnedHisto1D<string>;
      using IntegerProfile1D = YODA::BinnedProfile1D<string>;
      // Then the desired axis binning.
      const auto pidAxis = YODA::Axis<string>({"211", "321", "2212"});
      // And finally the two histograms.
      auto h3 = p8y.book<IntegerHisto1D>(pidAxis,
        "/MAIN114/pid-mult", "pid-mult");
      auto h4 = p8y.book<IntegerProfile1D>(pidAxis,
        "/MAIN114/pid-mean-pt", "pid-mean-pt");

      // Begin event loop. Generate event. Skip if error. List first one.
      int nEvents = 10000;
      for (int iEvent = 0; iEvent < nEvents; ++iEvent) {
        if (!pythia.next()) continue;
        // Find number of all final charged particles and fill histogram.
        int nCharged = 0;
        double sumpT = 0.;
        for (auto p : pythia.event) {
          if (p.isFinal() && p.isHadron() && p.isCharged() &&
            abs(p.eta()) < 2.5) {
            ++nCharged;
            h3->fill(to_string(abs(p.id())));
            sumpT += p.pT();
            h4->fill(to_string(abs(p.id())), p.pT());
          }
        }
        if (nCharged > 0) {
          h1->fill(nCharged);
          h2->fill(nCharged, sumpT/double(nCharged));
        }
      // End of event loop. Statistics. Histogram. Done.
      }
      pythia.stat();
      // Normalize to number of events generated.
      h1->scaleW(1./double(nEvents));
      h3->scaleW(1./double(nEvents));

      // Write histograms to file.
      p8y.write();
      cout << "Histograms have been written. "
        "You can now plot them with e.g. rivet-mkhtml or Python.\n";

      // Done.
      return 0;
    }