GeneratorPythia8.cxx

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// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
// All rights not expressly granted are reserved.
//
// This software is distributed under the terms of the GNU General Public
// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
//
// In applying this license CERN does not waive the privileges and immunities
// granted to it by virtue of its status as an Intergovernmental Organization
// or submit itself to any jurisdiction.
 
 
#include "Generators/GeneratorPythia8.h"
#include "Generators/GeneratorPythia8Param.h"
#include "CommonUtils/ConfigurationMacroHelper.h"
#include <fairlogger/Logger.h>
#include "TParticle.h"
#include "TF1.h"
#include "TRandom.h"
#include "SimulationDataFormat/MCEventHeader.h"
#include "SimulationDataFormat/MCGenProperties.h"
#include "SimulationDataFormat/ParticleStatus.h"
#if PYTHIA_VERSION_INTEGER >= 8310
#include "Pythia8/HIInfo.h"
#else
#include "Pythia8/HIUserHooks.h"
#endif
#include "Pythia8Plugins/PowhegHooks.h"
#include "TString.h"
#include "TSystem.h"
#include "ZDCBase/FragmentParam.h"
#include <CommonUtils/ConfigurationMacroHelper.h>
#include <filesystem>
#include <CommonUtils/FileSystemUtils.h>
 
#include <iostream>
#include <unordered_map>
#include <numeric>
 
namespace o2
{
namespace eventgen
{
 
std::atomic<int> GeneratorPythia8::Pythia8InstanceCounter;
 
/*****************************************************************/
/*****************************************************************/
 
// the default construct uses the GeneratorPythia8Param singleton to extract a config and delegates
// to the proper constructor
GeneratorPythia8::GeneratorPythia8() : GeneratorPythia8(GeneratorPythia8Param::Instance().detach())
{
  LOG(info) << "GeneratorPythia8 constructed from GeneratorPythia8Param ConfigurableParam";
}
 
/*****************************************************************/
 
GeneratorPythia8::GeneratorPythia8(Pythia8GenConfig const& config) : Generator("ALICEo2", "ALICEo2 Pythia8 Generator")
{
  mThisPythia8InstanceID = GeneratorPythia8::Pythia8InstanceCounter;
  GeneratorPythia8::Pythia8InstanceCounter++;
 
  mInterface = reinterpret_cast<void*>(&mPythia);
  mInterfaceName = "pythia8";
 
  // Decrease Pythia8 verbosity when running in Hyperloop
  if (mIsHyperloop) {
    LOG(info) << "Simulation running in Hyperloop => reducing Pythia8 logs";
    mPythia.readString("Print:quiet on");
  }
 
  LOG(info) << "Instance \'Pythia8\' generator with following parameters";
  LOG(info) << "config: " << config.config;
  LOG(info) << "hooksFileName: " << config.hooksFileName;
  LOG(info) << "hooksFuncName: " << config.hooksFuncName;
 
  mGenConfig = config;
 
  setConfig(mGenConfig.config);
  setHooksFileName(mGenConfig.hooksFileName);
  setHooksFuncName(mGenConfig.hooksFuncName);
}
 
/*****************************************************************/
 
GeneratorPythia8::GeneratorPythia8(const Char_t* name, const Char_t* title) : Generator(name, title)
{
  mInterface = reinterpret_cast<void*>(&mPythia);
  mInterfaceName = "pythia8";
}
 
bool GeneratorPythia8::setInitialSeed(long seed)
{
  // check first of all if Init not yet called and seed not <0
  if (mIsInitialized) {
    return false;
  }
  if (seed < 0) {
    return false;
  }
  // sets the initial seed and applies the correct Pythia
  // range
  mInitialRNGSeed = seed % (MAX_SEED + 1);
  LOG(info) << "GeneratorPythia8: Setting initial seed to " << mInitialRNGSeed;
  return true;
}
 
/*****************************************************************/
void GeneratorPythia8::seedGenerator()
{
 
 
  auto seed = mInitialRNGSeed;
  if (seed == -1) {
    // Will use the mInitialRNGSeed if it was set.
    // Otherwise will seed the generator with the state of
    // TRandom::GetSeed. This is the seed that is influenced from
    // SimConfig --seed command line options options.
    seed = gRandom->TRandom::GetSeed(); // this uses the "original" seed
    // we advance the seed by one so that the next Pythia8 generator gets a different value
    if (mThisPythia8InstanceID > 0) {
      gRandom->Rndm();
      LOG(info) << "Multiple Pythia8 generator instances detected .. automatically adjusting seed further to avoid overlap ";
      seed = seed ^ gRandom->GetSeed(); // this uses the "current" seed
    }
    // apply max seed cuttof
    seed = seed % (MAX_SEED + 1);
    LOG(info) << "GeneratorPythia8: Using random seed from gRandom % 900000001: " << seed;
  }
  mPythia.readString("Random:setSeed on");
  mPythia.readString("Random:seed " + std::to_string(seed));
}
 
/*****************************************************************/
 
Bool_t GeneratorPythia8::Init()
{
  Generator::Init();
 
  seedGenerator();
 
  if (!mConfig.empty()) {
    std::stringstream ss(mConfig);
    std::string config;
    while (getline(ss, config, ' ')) {
      TString expandedConfig = config;
      gSystem->ExpandPathName(expandedConfig);
      config = expandedConfig.Data();
      LOG(info) << "Reading configuration from file: " << config;
      if (!mPythia.readFile(config, true)) {
        LOG(fatal) << "Failed to init \'Pythia8\': problems with configuration file "
                   << config;
        return false;
      }
    }
  }
 
  if (!mHooksFileName.empty()) {
    LOG(info) << "Applying \'Pythia8\' user hooks: " << mHooksFileName << " -> " << mHooksFuncName;
    auto hooks = o2::conf::GetFromMacro<Pythia8::UserHooks*>(mHooksFileName, mHooksFuncName, "Pythia8::UserHooks*", "pythia8_user_hooks");
    if (!hooks) {
      LOG(fatal) << "Failed to init \'Pythia8\': problem with user hooks configuration ";
      return false;
    }
    setUserHooks(hooks);
  }
 
#if PYTHIA_VERSION_INTEGER < 8300
  mPythia.readString("HadronLevel:Decay off");
#endif
  if (mPythia.settings.mode("Beams:frameType") == 4) {
    // Hook for POWHEG
    // Read in key POWHEG merging settings
    int vetoMode = mPythia.settings.mode("POWHEG:veto");
    int MPIvetoMode = mPythia.settings.mode("POWHEG:MPIveto");
    bool loadHooks = (vetoMode > 0 || MPIvetoMode > 0);
    // Add in user hooks for shower vetoing
    std::shared_ptr<Pythia8::PowhegHooks> powhegHooks;
    if (loadHooks) {
      // Set ISR and FSR to start at the kinematical limit
      if (vetoMode > 0) {
        mPythia.readString("SpaceShower:pTmaxMatch = 2");
        mPythia.readString("TimeShower:pTmaxMatch = 2");
      }
      // Set MPI to start at the kinematical limit
      if (MPIvetoMode > 0) {
        mPythia.readString("MultipartonInteractions:pTmaxMatch = 2");
      }
      powhegHooks = std::make_shared<Pythia8::PowhegHooks>();
      mPythia.setUserHooksPtr((Pythia8::UserHooksPtr)powhegHooks);
    }
  }
  mPythia.particleData.addParticle(1000100200, "20Ne", 6, 30, 0, 19.992440);
  if (!mPythia.init()) {
    LOG(fatal) << "Failed to init \'Pythia8\': init returned with error";
    return false;
  }
 
  initUserFilterCallback();
 
  mIsInitialized = true;
 
  return true;
}
 
/*****************************************************************/
void GeneratorPythia8::setUserHooks(Pythia8::UserHooks* hooks)
{
#if PYTHIA_VERSION_INTEGER < 8300
  mPythia.setUserHooksPtr(hooks);
#else
  mPythia.setUserHooksPtr(std::shared_ptr<Pythia8::UserHooks>(hooks));
#endif
}
 
/*****************************************************************/
 
Bool_t
  GeneratorPythia8::generateEvent()
{
  if (!mPythia.next()) {
    return false;
  }
 
#if PYTHIA_VERSION_INTEGER < 8300
  auto nParticles = mPythia.event.size();
  for (int iparticle = 0; iparticle < nParticles; iparticle++) {
    auto& aParticle = mPythia.event[iparticle];
    aParticle.xProd(0.);
    aParticle.yProd(0.);
    aParticle.zProd(0.);
    aParticle.tProd(0.);
  }
 
  if (!mPythia.moreDecays())
    return false;
#endif
 
  return true;
}
 
/*****************************************************************/
void GeneratorPythia8::investigateRelatives(Pythia8::Event& event,
                                            const std::vector<int>& old2New,
                                            size_t index,
                                            std::vector<bool>& done,
                                            GetRelatives getter,
                                            SetRelatives setter,
                                            FirstLastRelative firstLast,
                                            const std::string& what,
                                            const std::string& ind)
{
  // New index of this particle, or -1 if not kept. Index old2New directly:
  // it is event-sized, and this is a recursive function called once per
  // particle, so wrapping it in a by-value-capturing lambda copied the whole
  // vector on every call -- O(N^2) in the event multiplicity, which dominated
  // high-multiplicity PbPb generation.
  int newIdx = old2New[index];
  int hepmc = event[index].statusHepMC();
 
  LOG(debug) << ind
             << index << " -> "
             << newIdx << " (" << hepmc << ") ";
  if (done[index]) {
    LOG(debug) << ind << " already done";
    return;
  }
 
  // Our list of new relatives
  using IdList = std::pair<int, int>;
  constexpr int invalid = 0xFFFFFFF;
  IdList newRelatives = std::make_pair(invalid, -invalid);
 
  // Utility to add id
  auto addId = [](IdList& l, size_t id) {
    l.first = std::min(int(id), l.first);
    l.second = std::max(int(id), l.second);
  };
 
  // Get particle and relatives
  auto& particle = event[index];
  auto relatives = getter(particle);
 
  LOG(debug) << ind << " Check " << what << "s ["
             << std::setw(3) << firstLast(particle).first << ","
             << std::setw(3) << firstLast(particle).second << "] "
             << relatives.size();
 
  for (auto relativeIdx : relatives) {
    int newRelative = old2New[relativeIdx];
    if (newRelative >= 0) {
      // If this relative is to be kept, then append to list of new
      // relatives.
      LOG(debug) << ind << " "
                 << what << " "
                 << relativeIdx << " -> "
                 << newRelative << " to be kept" << std::endl;
      addId(newRelatives, newRelative);
      continue;
    }
    LOG(debug) << ind << " "
               << what << " "
               << relativeIdx << " not to be kept "
               << (done[relativeIdx] ? "already done" : "to be done")
               << std::endl;
 
    // Below is code for when the relative is not to be kept
    auto& relative = event[relativeIdx];
    if (not done[relativeIdx]) {
      // IF the relative hasn't been processed yet, do so now
      investigateRelatives(event,       // Event
                           old2New,     // Map from old to new
                           relativeIdx, // current particle index
                           done,        // cache flag
                           getter,      // get mother relatives
                           setter,      // set mother relatives
                           firstLast,   // get first and last
                           what,        // what we're looking at
                           ind + "  "); // Logging indent
    }
 
    // If this relative was already done, then get its relatives and
    // add them to the list of new relatives.
    auto grandRelatives = firstLast(relative);
    int grandRelative1 = grandRelatives.first;
    int grandRelative2 = grandRelatives.second;
    assert(grandRelative1 != invalid);
    assert(grandRelative2 != -invalid);
    if (grandRelative1 > 0) {
      addId(newRelatives, grandRelative1);
    }
    if (grandRelative2 > 0) {
      addId(newRelatives, grandRelative2);
    }
    LOG(debug) << ind << " "
               << what << " "
               << relativeIdx << " gave new relatives "
               << grandRelative1 << " -> " << grandRelative2;
  }
  LOG(debug) << ind << " Got "
             << (newRelatives.second - newRelatives.first + 1) << " new "
             << what << "s ";
 
  if (newRelatives.first != invalid) {
    // If the first relative is not invalid, then the second isn't
    // either (possibly the same though).
    int newRelative1 = newRelatives.first;
    int newRelative2 = newRelatives.second;
    setter(particle, newRelative1, newRelative2);
    LOG(debug) << ind << " " << what << "s: "
               << firstLast(particle).first << " ("
               << newRelative1 << "),"
               << firstLast(particle).second << " ("
               << newRelative2 << ")";
 
  } else {
    setter(particle, 0, 0);
  }
  done[index] = true;
}
 
/*****************************************************************/
void GeneratorPythia8::pruneEvent(Pythia8::Event& event, Select select)
{
  // Mapping from old to new index.
  std::vector<int> old2new(event.size(), -1);
 
  // Particle 0 is a system particle, and we will skip that in the
  // following.
  size_t newId = 0;
 
  // Loop over particles and store those we need
  for (size_t i = 1; i < event.size(); i++) {
    auto& particle = event[i];
    if (select(particle)) {
      ++newId;
      old2new[i] = newId;
    }
  }
 
  // First loop, investigate mothers - from the bottom
  auto getMothers = [](const Pythia8::Particle& particle) { return particle.motherList(); };
  auto setMothers = [](Pythia8::Particle& particle, int m1, int m2) { particle.mothers(m1, m2); };
  auto firstLastMothers = [](const Pythia8::Particle& particle) { return std::make_pair(particle.mother1(), particle.mother2()); };
 
  std::vector<bool> motherDone(event.size(), false);
  for (size_t i = 1; i < event.size(); ++i) {
    investigateRelatives(event,            // Event
                         old2new,          // Map from old to new
                         i,                // current particle index
                         motherDone,       // cache flag
                         getMothers,       // get mother relatives
                         setMothers,       // set mother relatives
                         firstLastMothers, // get first and last
                         "mother");        // what we're looking at
  }
 
  // Second loop, investigate daughters - from the top
  auto getDaughters = [](const Pythia8::Particle& particle) {
    // In case of |status|==13 (diffractive), we cannot use
    // Pythia8::Particle::daughterList as it will give more than
    // just the immediate daughters. In that cae, we do it
    // ourselves.
    if (std::abs(particle.status()) == 13) {
      int d1 = particle.daughter1();
      int d2 = particle.daughter2();
      if (d1 == 0 and d2 == 0) {
        return std::vector<int>();
      }
      if (d2 == 0) {
        return std::vector<int>{d1};
      }
      if (d2 > d1) {
        std::vector<int> ret(d2-d1+1);
        std::iota(ret.begin(), ret.end(), d1);
        return ret;
      }
      return std::vector<int>{d2,d1};
    }
    return particle.daughterList(); };
  auto setDaughters = [](Pythia8::Particle& particle, int d1, int d2) { particle.daughters(d1, d2); };
  auto firstLastDaughters = [](const Pythia8::Particle& particle) { return std::make_pair(particle.daughter1(), particle.daughter2()); };
 
  std::vector<bool> daughterDone(event.size(), false);
  for (size_t i = event.size() - 1; i > 0; --i) {
    investigateRelatives(event,              // Event
                         old2new,            // Map from old to new
                         i,                  // current particle index
                         daughterDone,       // cache flag
                         getDaughters,       // get mother relatives
                         setDaughters,       // set mother relatives
                         firstLastDaughters, // get first and last
                         "daughter");        // what we're looking at
  }
 
  // Make a pruned event
  Pythia8::Event pruned;
  pruned.init("Pruned event", &mPythia.particleData);
  pruned.reset();
 
  for (size_t i = 1; i < event.size(); i++) {
    int newIdx = old2new[i];
    if (newIdx < 0) {
      continue;
    }
 
    auto particle = event[i];
    int realIdx = pruned.append(particle);
    assert(realIdx == newIdx);
  }
 
  // We may have that two or more mothers share some daughters, but
  // that one or more mothers have more daughters than the other
  // mothers, and hence not all daughters point back to all mothers.
  // This can happen, for example, if a beam particle radiates
  // on-shell particles before an interaction with any daughters
  // from the other mothers.  Thus, we need to take care of that or
  // the event record will be corrupted.
  //
  // What we do is that for all particles, we look up the daughters.
  // Then for each daughter, we check the mothers of those
  // daughters.  If this list of mothers include other mothers than
  // the currently investigated mother, we must change the mothers
  // of the currently investigated daughters.
  using IdList = std::pair<int, int>;
  // Utility to add id
  auto addId = [](IdList& l, size_t id) {
    l.first = std::min(int(id), l.first);
    l.second = std::max(int(id), l.second);
  };
  constexpr int invalid = 0xFFFFFFF;
 
  std::vector<bool> shareDone(pruned.size(), false);
  for (size_t i = 1; i < pruned.size(); i++) {
    if (shareDone[i]) {
      continue;
    }
 
    auto& particle = pruned[i];
    auto daughters = particle.daughterList();
    IdList allDaughters = std::make_pair(invalid, -invalid);
    IdList allMothers = std::make_pair(invalid, -invalid);
    addId(allMothers, i);
    for (auto daughterIdx : daughters) {
      // Add this daughter to set of all daughters
      addId(allDaughters, daughterIdx);
      auto& daughter = pruned[daughterIdx];
      auto otherMothers = daughter.motherList();
      for (auto otherMotherIdx : otherMothers) {
        // Add this mother to set of all mothers.  That is, take all
        // mothers of the current daughter of the current particle
        // and store that.  In this way, we register mothers that
        // share a daughter with the current particle.
        addId(allMothers, otherMotherIdx);
        // We also need to take all the daughters of this shared
        // mother and reister those.
        auto& otherMother = pruned[otherMotherIdx];
        int otherDaughter1 = otherMother.daughter1();
        int otherDaughter2 = otherMother.daughter2();
        if (otherDaughter1 > 0) {
          addId(allDaughters, otherDaughter1);
        }
        if (otherDaughter2 > 0) {
          addId(allDaughters, otherDaughter2);
        }
      }
      // At this point, we have added all mothers of current
      // daughter, and all daughters of those mothers.
    }
    // At this point, we have all mothers that share daughters with
    // the current particle, and we have all of the daughters
    // too.
    //
    // We can now update the daughter information on all mothers
    int minDaughter = allDaughters.first;
    int maxDaughter = allDaughters.second;
    int minMother = allMothers.first;
    int maxMother = allMothers.second;
    if (minMother != invalid) {
      // If first mother isn't invalid, then second isn't either
      for (size_t motherIdx = minMother; motherIdx <= maxMother; //
           motherIdx++) {
        shareDone[motherIdx] = true;
        if (minDaughter == invalid) {
          pruned[motherIdx].daughters(0, 0);
        } else {
          pruned[motherIdx].daughters(minDaughter, maxDaughter);
        }
      }
    }
    if (minDaughter != invalid) {
      // If least mother isn't invalid, then largest mother will not
      // be invalid either.
      for (size_t daughterIdx = minDaughter; daughterIdx <= maxDaughter; //
           daughterIdx++) {
        if (minMother == invalid) {
          pruned[daughterIdx].mothers(0, 0);
        } else {
          pruned[daughterIdx].mothers(minMother, maxMother);
        }
      }
    }
  }
  if (mGenConfig.verbose) {
    LOG(info) << "Pythia event was pruned from " << event.size()
              << " to " << pruned.size() << " particles";
  }
  // Assign our pruned event to the event passed in
  event = pruned;
}
 
/*****************************************************************/
void GeneratorPythia8::initUserFilterCallback()
{
  mUserFilterFcn = [](Pythia8::Particle const&) -> bool { return true; };
 
  std::string filter = mGenConfig.particleFilter;
  if (filter.size() > 0) {
    LOG(info) << "Initializing the callback for user-based particle pruning " << filter;
    auto expandedFileName = o2::utils::expandShellVarsInFileName(filter);
    if (std::filesystem::exists(expandedFileName)) {
      // if the filter is in a file we will compile the hook on the fly
      mUserFilterFcn = o2::conf::GetFromMacro<UserFilterFcn>(expandedFileName, "filterPythia()", "o2::eventgen::GeneratorPythia8::UserFilterFcn", "o2mc_pythia8_userfilter_hook");
      LOG(info) << "Hook initialized from file " << expandedFileName;
    } else {
      // if it's not a file we interpret it as a C++ lambda string and JIT it directly;
      LOG(error) << "Did not find a file " << expandedFileName << " ; Will not execute hook";
    }
    mApplyPruning = true;
  }
}
 
/*****************************************************************/
 
Bool_t
  GeneratorPythia8::importParticles(Pythia8::Event& event)
{
  // The right moment to filter out unwanted stuff (like parton-level
  // event information) Here, we aim to filter out everything before
  // hadronization with the motivation to reduce the size of the MC
  // event record in the AOD.
 
  std::function<bool(const Pythia8::Particle&)> partonSelect = [](const Pythia8::Particle&) { return true; };
  bool includeParton = mGenConfig.includePartonEvent;
  if (not includeParton) {
 
    // Select pythia particles
    partonSelect = [](const Pythia8::Particle& particle) {
      switch (particle.statusHepMC()) {
        case 1: // Final st
        case 2: // Decayed
        case 4: // Beam
          return true;
      }
      // For example to keep diffractive particles
      // if (particle.id() == 9902210) return true;
      return false;
    };
    mApplyPruning = true;
  }
 
  if (mApplyPruning) {
    auto finalSelect = [partonSelect, this](const Pythia8::Particle& p) { return partonSelect(p) && mUserFilterFcn(p); };
    pruneEvent(event, finalSelect);
  }
 
  /* loop over particles */
  auto nParticles = event.size();
  for (Int_t iparticle = 1; iparticle < nParticles; iparticle++) {
    // first particle is system
    auto particle = event[iparticle];
    auto pdg = particle.id();
    auto st = o2::mcgenstatus::MCGenStatusEncoding(particle.statusHepMC(), //
                                                   particle.status())      //
                .fullEncoding;
    mParticles.push_back(TParticle(pdg,                      // Particle type
                                   st,                       // status
                                   particle.mother1() - 1,   // first mother
                                   particle.mother2() - 1,   // second mother
                                   particle.daughter1() - 1, // first daughter
                                   particle.daughter2() - 1, // second daughter
                                   particle.px(),            // X-momentum
                                   particle.py(),            // Y-momentum
                                   particle.pz(),            // Z-momentum
                                   particle.e(),             // Energy
                                   particle.xProd(),         // Production X
                                   particle.yProd(),         // Production Y
                                   particle.zProd(),         // Production Z
                                   particle.tProd()));       // Production t
    mParticles.back().SetBit(ParticleStatus::kToBeDone,      //
                             particle.statusHepMC() == 1);
  }
 
  return kTRUE;
}
 
/*****************************************************************/
 
void GeneratorPythia8::updateHeader(o2::dataformats::MCEventHeader* eventHeader)
{
  using Key = o2::dataformats::MCInfoKeys;
 
  eventHeader->putInfo<std::string>(Key::generator, "pythia8");
  eventHeader->putInfo<int>(Key::generatorVersion, PYTHIA_VERSION_INTEGER);
  eventHeader->putInfo<std::string>(Key::processName, mPythia.info.name());
  eventHeader->putInfo<int>(Key::processCode, mPythia.info.code());
  eventHeader->putInfo<float>(Key::weight, mPythia.info.weight());
 
  auto& info = mPythia.info;
 
  eventHeader->putInfo<int>(Key::acceptedEvents, info.nAccepted());
  eventHeader->putInfo<int>(Key::attemptedEvents, info.nTried());
 
  // Set PDF information
  eventHeader->putInfo<int>(Key::pdfParton1Id, info.id1pdf());
  eventHeader->putInfo<int>(Key::pdfParton2Id, info.id2pdf());
  eventHeader->putInfo<float>(Key::pdfX1, info.x1pdf());
  eventHeader->putInfo<float>(Key::pdfX2, info.x2pdf());
  eventHeader->putInfo<float>(Key::pdfScale, info.QFac());
  eventHeader->putInfo<float>(Key::pdfXF1, info.pdf1());
  eventHeader->putInfo<float>(Key::pdfXF2, info.pdf2());
 
  // Set cross section
  eventHeader->putInfo<float>(Key::xSection, info.sigmaGen() * 1e9);
  eventHeader->putInfo<float>(Key::xSectionError, info.sigmaErr() * 1e9);
 
  // Set event scale and nMPI
  eventHeader->putInfo<float>(Key::eventScale, info.QRen());
  eventHeader->putInfo<int>(Key::mpi, info.nMPI());
 
  // Set weights (overrides cross-section for each weight)
  size_t iw = 0;
  auto xsecErr = info.weightContainerPtr->getTotalXsecErr();
  for (auto w : info.weightContainerPtr->getTotalXsec()) {
    std::string post = (iw == 0 ? "" : "_" + std::to_string(iw));
    eventHeader->putInfo<float>(Key::weight + post, info.weightValueByIndex(iw));
    eventHeader->putInfo<float>(Key::xSection + post, w * 1e9);
    eventHeader->putInfo<float>(Key::xSectionError + post, xsecErr[iw] * 1e9);
    iw++;
  }
 
#if PYTHIA_VERSION_INTEGER < 8300
  auto hiinfo = mPythia.info.hiinfo;
#else
  auto hiinfo = mPythia.info.hiInfo;
#endif
 
  if (hiinfo) {
    eventHeader->SetB(hiinfo->b());
    eventHeader->putInfo<double>(Key::impactParameter, hiinfo->b());
#if PYTHIA_VERSION_INTEGER >= 8310
    eventHeader->putInfo<double>(Key::planeAngle, hiinfo->phi());
#endif
    auto bImp = hiinfo->b();
    int nColl, nPart;
    int nPartProtonProj, nPartNeutronProj, nPartProtonTarg, nPartNeutronTarg;
    int nRemnProtonProj, nRemnNeutronProj, nRemnProtonTarg, nRemnNeutronTarg;
    int nFreeNeutronProj, nFreeProtonProj, nFreeNeutronTarg, nFreeProtonTarg;
    getNcoll(nColl);
    getNpart(nPart);
    getNpart(nPartProtonProj, nPartNeutronProj, nPartProtonTarg, nPartNeutronTarg);
    getNremn(nRemnProtonProj, nRemnNeutronProj, nRemnProtonTarg, nRemnNeutronTarg);
    getNfreeSpec(nFreeNeutronProj, nFreeProtonProj, nFreeNeutronTarg, nFreeProtonTarg);
    eventHeader->putInfo<int>(Key::nColl, nColl);
    // These are all non-HepMC3 fields - of limited use
    eventHeader->putInfo<int>("Npart", nPart);
    eventHeader->putInfo<int>("Npart_proj_p", nPartProtonProj);
    eventHeader->putInfo<int>("Npart_proj_n", nPartNeutronProj);
    eventHeader->putInfo<int>("Npart_targ_p", nPartProtonTarg);
    eventHeader->putInfo<int>("Npart_targ_n", nPartNeutronTarg);
    eventHeader->putInfo<int>("Nremn_proj_p", nRemnProtonProj);
    eventHeader->putInfo<int>("Nremn_proj_n", nRemnNeutronProj);
    eventHeader->putInfo<int>("Nremn_targ_p", nRemnProtonTarg);
    eventHeader->putInfo<int>("Nremn_targ_n", nRemnNeutronTarg);
    eventHeader->putInfo<int>("Nfree_proj_n", nFreeNeutronProj);
    eventHeader->putInfo<int>("Nfree_proj_p", nFreeProtonProj);
    eventHeader->putInfo<int>("Nfree_targ_n", nFreeNeutronTarg);
    eventHeader->putInfo<int>("Nfree_targ_p", nFreeProtonTarg);
 
    // --- HepMC3 conforming information ---
    // This is how the Pythia authors define Ncoll
    // eventHeader->putInfo<int>(Key::nColl,
    //                           hiinfo->nAbsProj() + hiinfo->nDiffProj() +
    //                           hiinfo->nAbsTarg() + hiinfo->nDiffTarg() -
    //                           hiiinfo->nCollND() - hiinfo->nCollDD());
    eventHeader->putInfo<int>(Key::nPartProjectile,
                              hiinfo->nAbsProj() + hiinfo->nDiffProj());
    eventHeader->putInfo<int>(Key::nPartTarget,
                              hiinfo->nAbsTarg() + hiinfo->nDiffTarg());
#if PYTHIA_VERSION_INTEGER >= 8313
    eventHeader->putInfo<int>(Key::nCollHard, hiinfo->nCollND());
#else
    eventHeader->putInfo<int>(Key::nCollHard, hiinfo->nCollNDTot());
#endif
  }
}
 
/*****************************************************************/
 
void GeneratorPythia8::selectFromAncestor(int ancestor, Pythia8::Event& inputEvent, Pythia8::Event& outputEvent)
{
 
  // recursive selection via lambda function
  std::set<int> selected;
  std::function<void(int)> select;
  select = [&](int i) {
    selected.insert(i);
    auto dl = inputEvent[i].daughterList();
    for (auto j : dl) {
      select(j);
    }
  };
  select(ancestor);
 
  // map selected particle index to output index
  std::map<int, int> indexMap;
  int index = outputEvent.size();
  for (auto i : selected) {
    indexMap[i] = index++;
  }
 
  // adjust mother/daughter indices and append to output event
  for (auto i : selected) {
    auto p = mPythia.event[i];
    auto m1 = indexMap[p.mother1()];
    auto m2 = indexMap[p.mother2()];
    auto d1 = indexMap[p.daughter1()];
    auto d2 = indexMap[p.daughter2()];
    p.mothers(m1, m2);
    p.daughters(d1, d2);
 
    outputEvent.append(p);
  }
}
 
/*****************************************************************/
 
void GeneratorPythia8::getNcoll(const Pythia8::Info& info, int& nColl)
{
 
#if PYTHIA_VERSION_INTEGER < 8300
  auto hiinfo = info.hiinfo;
#else
  auto hiinfo = info.hiInfo;
#endif
  nColl = 0;
  if (!hiinfo) {
    LOG(warn) << "No heavy-ion information from Pythia";
    return;
  }
 
  // This is how the Pythia authors define Ncoll
  nColl = (hiinfo->nAbsProj() + hiinfo->nDiffProj() +
           hiinfo->nAbsTarg() + hiinfo->nDiffTarg() -
           hiinfo->nCollND() - hiinfo->nCollDD());
 
  if (not hiinfo->subCollisionsPtr()) {
#if PYTHIA_VERSION_INTEGER < 8310
    LOG(fatal) << "No sub-collision pointer from Pythia";
#endif
    return;
  }
 
  // loop over sub-collisions
  auto scptr = hiinfo->subCollisionsPtr();
  for (auto sc : *scptr) {
 
    // wounded nucleon flag in projectile/target
    auto pW = sc.proj->status() == Pythia8::Nucleon::ABS; // according to C.Bierlich this should be == Nucleon::ABS
    auto tW = sc.targ->status() == Pythia8::Nucleon::ABS;
 
    // increase number of collisions if both are wounded
    if (pW && tW) {
      nColl++;
    }
  }
}
 
/*****************************************************************/
 
void GeneratorPythia8::getNpart(const Pythia8::Info& info, int& nPart)
{
 
#if PYTHIA_VERSION_INTEGER < 8300
  auto hiinfo = info.hiinfo;
#else
  auto hiinfo = info.hiInfo;
#endif
  nPart = 0;
  if (not hiinfo) {
    return;
  }
 
  // This is how the Pythia authors calculate Npart
  nPart = (hiinfo->nAbsProj() + hiinfo->nDiffProj() +
           hiinfo->nAbsTarg() + hiinfo->nDiffTarg());
  if (not hiinfo->subCollisionsPtr()) {
    return;
  }
 
  int nProtonProj, nNeutronProj, nProtonTarg, nNeutronTarg;
  getNpart(info, nProtonProj, nNeutronProj, nProtonTarg, nNeutronTarg);
  nPart = nProtonProj + nNeutronProj + nProtonTarg + nNeutronTarg;
}
 
/*****************************************************************/
 
void GeneratorPythia8::getNpart(const Pythia8::Info& info, int& nProtonProj, int& nNeutronProj, int& nProtonTarg, int& nNeutronTarg)
{
 
#if PYTHIA_VERSION_INTEGER < 8300
  auto hiinfo = info.hiinfo;
#else
  auto hiinfo = info.hiInfo;
#endif
 
  nProtonProj = nNeutronProj = nProtonTarg = nNeutronTarg = 0;
  if (!hiinfo) {
    return;
  }
 
  nProtonProj = hiinfo->nAbsProj() + hiinfo->nDiffProj();
  nProtonTarg = hiinfo->nAbsTarg() + hiinfo->nDiffTarg();
  if (not hiinfo->subCollisionsPtr()) {
#if PYTHIA_VERSION_INTEGER < 8310
    LOG(fatal) << "No sub-collision pointer from Pythia";
#endif
    return;
  }
 
  // keep track of wounded nucleons
  std::vector<Pythia8::Nucleon*> projW;
  std::vector<Pythia8::Nucleon*> targW;
 
  // loop over sub-collisions
  auto scptr = hiinfo->subCollisionsPtr();
  for (auto sc : *scptr) {
 
    // wounded nucleon flag in projectile/target
    auto pW = sc.proj->status() == Pythia8::Nucleon::ABS || sc.proj->status() == Pythia8::Nucleon::DIFF; // according to C.Bierlich this should be == Nucleon::ABS || Nucleon::DIFF
    auto tW = sc.targ->status() == Pythia8::Nucleon::ABS || sc.targ->status() == Pythia8::Nucleon::DIFF;
 
    // increase number of wounded projectile nucleons if not yet in the wounded vector
    if (pW && std::find(projW.begin(), projW.end(), sc.proj) == projW.end()) {
      projW.push_back(sc.proj);
      if (sc.proj->id() == 2212) {
        nProtonProj++;
      } else if (sc.proj->id() == 2112) {
        nNeutronProj++;
      }
    }
 
    // increase number of wounded target nucleons if not yet in the wounded vector
    if (tW && std::find(targW.begin(), targW.end(), sc.targ) == targW.end()) {
      targW.push_back(sc.targ);
      if (sc.targ->id() == 2212) {
        nProtonTarg++;
      } else if (sc.targ->id() == 2112) {
        nNeutronTarg++;
      }
    }
  }
}
 
/*****************************************************************/
 
void GeneratorPythia8::getNremn(const Pythia8::Event& event, int& nProtonProj, int& nNeutronProj, int& nProtonTarg, int& nNeutronTarg)
{
 
  // reset
  nProtonProj = nNeutronProj = nProtonTarg = nNeutronTarg = 0;
  auto nNucRem = 0;
 
  // particle loop
  auto nparticles = event.size();
  for (int ipa = 0; ipa < nparticles; ++ipa) {
    const auto particle = event[ipa];
    auto pdg = particle.id();
 
    // nuclear remnants have pdg code = ±10LZZZAAA9
    if (pdg < 1000000000) {
      continue; // must be nucleus
    }
    if (pdg % 10 != 9) {
      continue; // first digit must be 9
    }
    nNucRem++;
 
    // extract A, Z and L from pdg code
    pdg /= 10;
    auto A = pdg % 1000;
    pdg /= 1000;
    auto Z = pdg % 1000;
    pdg /= 1000;
    auto L = pdg % 10;
 
    if (particle.pz() > 0.) {
      nProtonProj = Z;
      nNeutronProj = A - Z;
    }
    if (particle.pz() < 0.) {
      nProtonTarg = Z;
      nNeutronTarg = A - Z;
    }
 
  } // end of particle loop
 
  if (nNucRem > 2) {
    LOG(warning) << " GeneratorPythia8: found more than two nuclear remnants (weird)";
  }
}
/*****************************************************************/
 
/*****************************************************************/
 
void GeneratorPythia8::getNfreeSpec(const Pythia8::Info& info, int& nFreenProj, int& nFreepProj, int& nFreenTarg, int& nFreepTarg)
{
#if PYTHIA_VERSION_INTEGER < 8300
  auto hiinfo = info.hiinfo;
#else
  auto hiinfo = info.hiInfo;
#endif
 
  if (!hiinfo) {
    return;
  }
 
  double b = hiinfo->b();
 
  static o2::zdc::FragmentParam frag; // data-driven model to get free spectators given impact parameter
 
  TF1 const& fneutrons = frag.getfNeutrons();
  TF1 const& fsigman = frag.getsigmaNeutrons();
  TF1 const& fprotons = frag.getfProtons();
  TF1 const& fsigmap = frag.getsigmaProtons();
 
  // Calculating no. of free spectators from parametrization
  int nneu[2] = {0, 0};
  for (int i = 0; i < 2; i++) {
    float nave = fneutrons.Eval(b);
    float sigman = fsigman.Eval(b);
    float nfree = gRandom->Gaus(nave, 0.68 * sigman * nave);
    nneu[i] = (int)nfree;
    if (nave < 0 || nneu[i] < 0) {
      nneu[i] = 0;
    }
    if (nneu[i] > 126) {
      nneu[i] = 126;
    }
  }
  //
  int npro[2] = {0, 0};
  for (int i = 0; i < 2; i++) {
    float pave = fprotons.Eval(b);
    float sigmap = fsigman.Eval(b);
    float pfree = gRandom->Gaus(pave, 0.68 * sigmap * pave) / 0.7;
    npro[i] = (int)pfree;
    if (pave < 0 || npro[i] < 0) {
      npro[i] = 0;
    }
    if (npro[i] > 82) {
      npro[i] = 82;
    }
  }
 
  nFreenProj = nneu[0];
  nFreenTarg = nneu[1];
  nFreepProj = npro[0];
  nFreepTarg = npro[1];
  /*****************************************************************/
}
 
} /* namespace eventgen */
} /* namespace o2 */