JetScapeWriterHepMC.cc

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/*******************************************************************************
 * Copyright (c) The JETSCAPE Collaboration, 2018
 *
 * Modular, task-based framework for simulating all aspects of heavy-ion collisions
 * 
 * For the list of contributors see AUTHORS.
 *
 * Report issues at https://github.com/JETSCAPE/JETSCAPE/issues
 *
 * or via email to bugs.jetscape@gmail.com
 *
 * Distributed under the GNU General Public License 3.0 (GPLv3 or later).
 * See COPYING for details.
 ******************************************************************************/

/*******************************************************************************
 * kk Sep 22, 2020:  Significant updates to status codes
 * to conform with Appendix A in https://arxiv.org/pdf/1912.08005.pdf
 * We will follow Pythia's example of preserving as much of the internal status code as possible
 * Specifically:
 - beam particles. We don't have those, yet. If they ever become part of initial
   state moduls, those module writers MUST set the status to 4, all we do here 
   is respect that code (for the future). 
   However, this particle won't be a parton, so we only check that for hadrons.
   In practice, this will probably require a revamp of the graph structure, both
   in the framework and in here. Then, probably also use GenEvent::add_beam_particle()
 - decayed particle. We don't have those either yet, but it's a feature that may 
   come pretty soon.
   Here, we use that exclusively to mean decayed unstable hadrons, 
   e.g. K0S -> pi pi 
   In this case, the module that produced the hadron list MUST ensure to set the 
   status of K0s to 2. The pions are final particles, see below.
 - Final hadrons will all be forced to status 1
 - Partons: By default, we will accept and use any code provided by the framework
            within 11<=status<=200 and use the absolute value.
   Parton exceptions: 
            1) If the code is not HepMC-legal (|status|<11 or >200, often 0), 
               we assign 12 to most and 11 to the final partons before hadronization
               (to mimic the 1, 2 scheme)
            2) If there are NO hadrons in the event, we assume the user would like to treat 
               the final partons (like 11 from above) as final particles and assign 1
 ******************************************************************************/


#include "JetScapeWriterHepMC.h"
#include "JetScapeLogger.h"
#include "HardProcess.h"
#include "JetScapeSignalManager.h"
#include "GTL/node.h"
#include <GTL/topsort.h>

using HepMC3::Units;

namespace Jetscape {

JetScapeWriterHepMC::~JetScapeWriterHepMC() {
  if (GetActive())
    Close();
}

void JetScapeWriterHepMC::WriteHeaderToFile() {
  // Create event here - not actually writing
  // TODO: GeV seems right, but I don't think we actually measure in mm
  // Should multiply all lengths by 1e-12 probably
  evt = GenEvent(Units::GEV, Units::MM);

  // Expects pb, pythia delivers mb
  auto xsec = make_shared<HepMC3::GenCrossSection>();
  xsec->set_cross_section(GetHeader().GetSigmaGen() * 1e9, 0);
  xsec->set_cross_section(GetHeader().GetSigmaGen() * 1e9,
                          GetHeader().GetSigmaErr() * 1e9);
  evt.set_cross_section(xsec);
  evt.weights().push_back(GetHeader().GetEventWeight());

  auto heavyion = make_shared<HepMC3::GenHeavyIon>();
  // see https://gitlab.cern.ch/hepmc/HepMC3/blob/master/include/HepMC/GenHeavyIon.h
  if (GetHeader().GetNpart() > -1) {
    // Not clear what the difference is...
    heavyion->Ncoll_hard = GetHeader().GetNcoll();
    heavyion->Ncoll = GetHeader().GetNcoll();
  }
  if (GetHeader().GetNcoll() > -1) {
    // Hepmc separates into target and projectile.
    // Set one? Which? Both? half to each? setting projectile for now.
    // setting both might lead to weird problems when they get added up
    heavyion->Npart_proj = GetHeader().GetNpart();
  }
  if (GetHeader().GetTotalEntropy() > -1) {
    // nothing good in the HepMC standard. Something related to mulitplicity would work
  }

  if (GetHeader().GetEventPlaneAngle() > -999) {
    heavyion->event_plane_angle = GetHeader().GetEventPlaneAngle();
  }

  evt.set_heavy_ion(heavyion);

  // also a good moment to initialize the hadron boolean
}

void JetScapeWriterHepMC::WriteEvent() {
  VERBOSE(1) << "Run JetScapeWriterHepMC: Write event # " << GetCurrentEvent();
  
  // Have collected all vertices now.
  // Add all vertices to the event
  for (auto v : vertices){
    evt.add_vertex(v);
  }

  VERBOSE(1) << " found " << vertices.size() << " vertices in the list";

  // If there are no hadrons, promote final partons
  // The graph support of hepmc is a bit rudimentary.
  // easiest is to just check all childless particles
  // Note, one could just check for status==11,
  // but modules are allowed to assign that number to non-final partons
  if ( !hashadrons ) {
    VERBOSE(1) << " found no hadrons, promoting final partons to status 1";
    for ( auto p : evt.particles() ){
      if ( p->children().size() == 0 ){
        if ( p->status() !=11 ){
          JSWARN << "Found a final parton with status!=11 : status=" << p->status() << ". This should not happen";
        }
        p->set_status(1);
      }
    }
  }
  evt.set_event_number(GetCurrentEvent());
  write_event(evt);
  vertices.clear();
  hadronizationvertex = 0;
}

//This function dumps the particles in a specific parton shower to the event
void JetScapeWriterHepMC::Write(weak_ptr<PartonShower> ps) {
  shared_ptr<PartonShower> pShower = ps.lock();
  if (!pShower)
    return;

  // Need topological order, see
  // https://hepmc.web.cern.ch/hepmc/differences.html
  // That means if parton p1 comes into vertex v, and p2 goes out of v,
  // then p1 has to be created (bestowed an id) before p2
  // Take inspiration from hepmc3.0.0/interfaces/pythia8/src/Pythia8ToHepMC3.cc
  // But pythia showers are different from our existing graph structure,
  // So instead try to modify the first attempt to respect top. order
  // and don't create vertices and particles more than once

  // Using GTL's topsort
  // 1. Check that our graph is sane
  if (!pShower->is_acyclic())
    throw std::runtime_error(
        "PROBLEM in JetScapeWriterHepMC: Graph is not acyclic.");

  // 2.
  topsort topsortsearch;
  topsortsearch.scan_whole_graph(true);
  topsortsearch.start_node(); // defaults to first node
  topsortsearch.run(*pShower);
  auto nEnd =
      topsortsearch.top_order_end(); // this is a topsort::topsort_iterator

  // Need to keep track of already created ones
  map<int, GenParticlePtr> CreatedPartons;

  // probably unnecessary, used for consistency checks
  map<int, bool> vused;
  bool foundRoot = false;
  for (auto nIt = topsortsearch.top_order_begin(); nIt != nEnd; ++nIt) {
    // cout << *nIt << "  " << nIt->indeg() << "  " << nIt->outdeg() << endl;

    // Should be the only time we see this node.
    if (vused.find(nIt->id()) != vused.end()){
      throw std::runtime_error( "PROBLEM in JetScapeWriterHepMC: Reusing a vertex.");
    }
    vused[nIt->id()] = true;

    // 0. No incoming edges?
    // ---------------------
    // This is typically a shower initiator.
    // HepMC needs an incoming and outgoing particle for every vertex.
    // That could be a place to attach partons or ions.
    // We could also do both, but as of now, JETSCAPE actually attaches a dummy vertex
    // to the start of the initiator, that can safely go away.
    // Previously, we attached a dummy or clone of the outgoing one here.
    // Instead, we can just skip the vertex. Its outgoing edges will be picked up
    // as incomers in a later vertex.
    // Note that the [0]=>[1] connection in JETSCAPE
    // already uses a dummy node[0], and [1] is at time t=0; removing that seems correct.
    if (nIt->indeg() == 0)    continue;

    // 1. Create a new vertex.
    // --------------------------------------------
    auto v = castVtxToHepMC(pShower->GetVertex(*nIt));

    // 2. Incoming edges
    // -----------------
    //  In the current framework, it should only be one.
    //  So we will catch anything more but provide a mechanism that should work anyway.
    if (nIt->indeg() > 1) {
      JSWARN << "Found more than one mother parton! Should only happen if we "
        "added medium particles. "
             << "The code should work, but proceed with caution";
    }

    auto inIt = nIt->in_edges_begin();
    auto inEnd = nIt->in_edges_end();
    for (/* nop */; inIt != inEnd; ++inIt) {
      auto phepin = CreatedPartons.find(inIt->id());
      if (phepin != CreatedPartons.end()) {
        // We should already have one!
        v->add_particle_in(phepin->second);
      } else {
        // This indicates we skipped an earlier vertex without incomers.
        // JSWARN << "Incoming particle out of nowhere. This could maybe happen "
        //           "if we pick up medium particles "
        //        << " but is probably a topsort problem. Try using the code "
        //           "after this throw() but be very careful.";
        // throw std::runtime_error("PROBLEM in JetScapeWriterHepMC: Incoming "
        //                          "particle out of nowhere.");
        
        auto in = pShower->GetParton(*inIt);
        auto hepin = castPartonToHepMC(in);
        auto status = std::abs(hepin->status());
        if ( status < 11 || status > 200) {
          // incoming edge can't be final
          status = 12;
        }
        hepin->set_status(status);
        CreatedPartons[inIt->id()] = hepin;
        v->add_particle_in(hepin);
        
        if ( nIt->outdeg() == 0 ) {
          // However, motherless AND childless particles do exist
          // I.e., a shower initiator that never actually showers
          // For this, we need an out going clone, much like 3) below
          auto hepout = castPartonToHepMC(in);
          // Since the status information is preserved in the incomer, we'll force 11
          // Note: if we later see in WriteEvent() that there are no hadrons, this will be overwritten to 1
          hepout->set_status( 11 );
          // Note that we do not register this particle. Since it's pointing nowhere it can never be reused.
          v->add_particle_out(hepout);
        } 
      }
    }

    // 3. Outgoing edges?
    // --------------------------------------------
    // 3.1: No. Need to create one.
    // We'll use this opportunity to copy the incomer but give it a final code
    if (nIt->outdeg() == 0) {
      if (nIt->indeg() != 1) {
        // This won't work with multiple incomers (but that's pretty unphysical)
        throw std::runtime_error("PROBLEM in JetScapeWriterHepMC: Need exactly "
                                 "one parent to clone final state partons.");
      }
      auto in = pShower->GetParton(*(nIt->in_edges_begin()));
      auto hepout = castPartonToHepMC(in);
      // an outgoing edge without terminator is "final"
      // Since the status information is preserved in the incomer, we'll force 11
      // Note: if we later see in WriteEvent() that there are no hadrons, this will be overwritten to 1
      hepout->set_status( 11 );
      v->add_particle_out(hepout);
      // Note that we do not register this particle. Since it's pointing nowhere it can never be reused.
    }

    // 3.2: Otherwise use and register the outgoing edge
    if (nIt->outdeg() > 0) {
      auto outIt = nIt->out_edges_begin();
      auto outEnd = nIt->out_edges_end();
      for (/* nop */; outIt != outEnd; ++outIt) {
        if (CreatedPartons.find(outIt->id()) != CreatedPartons.end()) {
          throw std::runtime_error("PROBLEM in JetScapeWriterHepMC: Trying to "
                                   "recreate a preexisting GenParticle.");
        }
        auto out = pShower->GetParton(*outIt);
        auto hepout = castPartonToHepMC(out);
        if ( !hepout->status()) {
          // incoming and outgoing -> status 12
          hepout->set_status(12);
        }
        
        CreatedPartons[outIt->id()] = hepout;
        v->add_particle_out(hepout);
      }
    }
    
    vertices.push_back(v);
  }
}

void JetScapeWriterHepMC::Write(weak_ptr<Hadron> h) {
  auto hadron = h.lock();
  if (!hadron)
    return;

  // No clear source for most hadrons
  // Also, a graph with e.g. recombination hadrons would have loops,
  // (though the direction should still make it acyclic?)
  // Not sure how this is supposed to be done in HepMC3
  // Our solution: Attach all hadrons to one dedicated hadronization vertex.
  // Future option: Have separate shower and bulk vertices?

  // Create if it doesn't exist yet
  if (!hadronizationvertex) {
    // dummy position
    HepMC3::FourVector vtxPosition(0, 0, 0, 100); // set it to a late time...
    hadronizationvertex = make_shared<GenVertex>(vtxPosition);

    // dummy mother -- could also maybe use the first/hardest shower initiator
    HepMC3::FourVector pmom(0, 0, 0, 0);
    make_shared<GenParticle>(pmom, 0, 0);
    hadronizationvertex->add_particle_in(make_shared<GenParticle>(pmom, 0, 0));

    vertices.push_back(hadronizationvertex);
    hashadrons=true;
  }

  // now attach
  auto hepmc = castHadronToHepMC(hadron);
  if ( !hepmc->status() ) {
    // unless otherwise specified, all hadrons get status 1
    // TODO: Need to better account for short-lived hadrons
    hepmc->set_status(1);
  }
  hadronizationvertex->add_particle_out(hepmc);
}

void JetScapeWriterHepMC::Init() {
  if (GetActive()) {
    JSINFO << "JetScape HepMC Writer initialized with output file = "
           << GetOutputFileName();
  }
}

void JetScapeWriterHepMC::Exec() {
  // Nothing to do
}
} // end namespace Jetscape