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 // -*- C++ -*-
 #ifndef RIVET_Event_HH
 #define RIVET_Event_HH
 
 #include "Rivet/Config/RivetCommon.hh"
 #include "Rivet/Particle.hh"
 #include "Rivet/Projection.hh"
 
 namespace Rivet {
 
 
   /// @brief Representation of a HepMC event, and enabler of Projection caching
   ///
   /// Event is a concrete class representing an generated event in Rivet. It is
   /// constructed given a HepMC::GenEvent, a pointer to which is kept by the
   /// Event object throughout its lifetime. The user must therefore make sure
   /// that the corresponding HepMC::GenEvent will persist at least as long as
   /// the Event object.
   ///
   /// In addition to the HepMC::GenEvent object the Event also keeps track of
   /// all Projection objects which have been applied to the Event so far.
   class Event {
   public:
 
     /// @name Constructors and destructors.
     /// @{
 
     /// Constructor from a HepMC GenEvent pointer
     ///
     /// @note Although Rivet is an analysis system and should not modify the
     /// *physics* of provided events, it needs to ensure that the events are
     /// "sane" for analysis purposes, including fixing units and potentially
     /// orientations and unphysical graph structures. The passed event pointer
     /// is hence not const.
     Event(GenEvent* ge, const vector<size_t>& weightindices={}) //, bool strip=false)
       : _weightIndices(weightindices), _genevent(*ge)
     {
       if (!ge) throw UserError("User provided a null GenEvent pointer for analysis");
       // if (strip) _strip(_genevent);
       _fixGenEvent();
     }
 
     /// Constructor from a HepMC GenEvent reference
     ///
     /// @note See the pointer-based constructor for discussion of the
     /// non-constness of the passed GenEvent.
     ///
     /// @deprecated HepMC uses pointers, so we should talk to HepMC via pointers: no need to duplicate.
     Event(GenEvent& ge, const vector<size_t>& weightindices={}) //, bool strip=false)
       : _weightIndices(weightindices), _genevent(ge)
     {
       // if (strip) _strip(_genevent);
       _fixGenEvent();
     }
 
     /// Copy constructor
     Event(const Event& e)
       : _weightIndices(e._weightIndices),
         _genevent(e._genevent) {  }
 
     /// @}
 
 
     /// @name Major event properties
     /// @{
 
     /// The generated HepMC event obtained from an external event generator
     const GenEvent& hepmcEvent() const { return _genevent; }
     // /// @brief The generated HepMC event obtained from an external event generator
     // ///
     // /// Convenience alias for hepmcEventPtr()
     // const GenEvent& hepmc() const { return _genevent; }
 
     /// The generated HepMC event pointer obtained from an external event generator
     const GenEvent* hepmcEventPtr() const { return &_genevent; }
     /// @brief The generated HepMC event pointer obtained from an external event generator
     ///
     /// Backward-compatibility alias for hepmcEventPtr()
     const GenEvent* genEvent() const { return &_genevent; }
 
     /// Get the beam particles
     ParticlePair beams() const;
 
     /// Get the beam centre-of-mass energy
     double sqrtS() const;
 
     /// Get the beam centre-of-mass energy per nucleon
     double asqrtS() const;
 
     /// @}
 
 
     /// @name Access to event particles
     /// @{
 
     /// All the raw GenEvent particles, wrapped in Rivet::Particle objects
     const Particles& allParticles() const;
 
     /// @brief All the raw GenEvent particles, wrapped in Rivet::Particle objects, but with a Cut applied
     ///
     /// @note Due to the cut, this returns by value, i.e. involves an expensive copy
     inline Particles allParticles(const Cut& c) const {
       return select(allParticles(), c);
     }
 
     /// @brief All the raw GenEvent particles, wrapped in Rivet::Particle objects, but with a selection function applied
     ///
     /// @note Due to the cut, this returns by value, i.e. involves an expensive copy
     template <typename FN>
     inline Particles allParticles(const FN& f) const {
       return select(allParticles(), f);
     }
 
     /// @brief The generation weights associated with the event
     ///
     /// This vector contains only the weights selected by the AnalysisHandler,
     /// so is of constant length for all events.
     ///
     /// @note Excluded generation weights, and their associated weight names
     /// if set, can be accessed via the GenEvent pointer hepmcEventPtr().
     std::valarray<double> weights() const;
 
     /// @brief The generation cross-sections associated with the event
     ///
     /// This vector contains only the cross-sections selected by the AnalysisHandler,
     /// so is of constant length for all events.
     ///
     /// @note Excluded cross-sections, and their associated names if set,
     /// can be accessed via the GenEvent pointer hepmcEventPtr().
     std::vector<std::pair<double, double>> crossSections() const;
 
     /// @}
 
     /// @name Projection running
     /// @{
 
     /// @brief Add a projection @a p to this Event.
     ///
     /// If an equivalent Projection has been applied before, the
     /// Projection::project(const Event&) of @a p is not called and a reference
     /// to the previous equivalent projection is returned. If no previous
     /// Projection was found, the Projection::project(const Event&) of @a p is
     /// called and a reference to @a p is returned.
     ///
     /// @todo Can make this non-templated, since only cares about ptr to Projection base class
     ///
     /// @note Comparisons here are by direct pointer comparison, because
     /// equivalence is guaranteed if pointers are equal, and inequivalence
     /// guaranteed if they aren't, thanks to the ProjectionHandler registry
     template <typename PROJ>
     const PROJ& applyProjection(PROJ& p) const {
       static bool docaching = getEnvParam("RIVET_CACHE_PROJECTIONS", true);
       if (docaching) {
         MSG_TRACE("Applying projection " << &p << " (" << p.name() << ") -> comparing to projections " << _projections);
         // First search for this projection *or an equivalent* in the already-executed list
         const Projection* cpp(&p);
         /// @note Currently using reint cast to integer type to bypass operator==(Proj*, Proj*)
         // std::set<const Projection*>::const_iterator old = _projections.find(cpp);
         std::set<const Projection*>::const_iterator old = std::begin(_projections);
         std::uintptr_t recpp = reinterpret_cast<std::uintptr_t>(cpp);
         for (; old != _projections.end(); ++old)
           if (reinterpret_cast<std::uintptr_t>(*old) == recpp) break;
         if (old != _projections.end()) {
           MSG_TRACE("Equivalent projection found -> returning already-run projection " << *old);
           const Projection& pRef = **old;
           return pcast<PROJ>(pRef);
         }
         MSG_TRACE("No equivalent projection in the already-run list -> projecting now");
       } else {
         MSG_TRACE("Applying projection " << &p << " (" << p.name() << ") WITHOUT projection caching & comparison");
       }
       // If this one hasn't been run yet on this event, run it and add to the list
       Projection* pp = const_cast<Projection*>(&p);
       pp->_isValid = true;
       pp->project(*this);
       if (docaching) _projections.insert(pp);
       return p;
     }
 
 
     /// @brief Add a projection @a p to this Event by pointer.
     template <typename PROJ>
     const PROJ& applyProjection(PROJ* pp) const {
       if (!pp) throw Error("Event::applyProjection(PROJ*): Projection pointer is null.");
       return applyProjection(*pp);
     }
 
     /// @}
 
 
   private:
 
     /// Tweak the GenEvent to Rivet's expected standards if necessary
     void _fixGenEvent();
 
     /// Get a Log object for Event
     Log& getLog() const;
 
 
     // /// @brief Remove uninteresting or unphysical particles in the
     // /// GenEvent to speed up searches
     // ///
     // /// @todo Remove!
     // void _strip(GenEvent& ge);
 
     // /// @brief Convert the GenEvent to use conventional alignment
     // ///
     // /// For example, FHerwig only produces DIS events in the unconventional
     // /// hadron-lepton orientation and has to be corrected for DIS analysis
     // /// portability.
     // void _geNormAlignment();
 
     /// @brief The indices of the selected weights, as instructed to the AnalysisHandler.
     ///
     /// The user can (de-)select weights and the AnalysisHandler knows about the subset
     /// that match the specifications.
     const std::vector<size_t> _weightIndices;
 
     /// The GenEvent used by Rivet analysis projections etc.
     const GenEvent& _genevent;
 
     /// All the GenEvent particles, wrapped as Rivet::Particles
     ///
     /// @note To be populated lazily, hence mutability
     mutable Particles _particles;
 
     /// The set of Projection objects applied so far
     mutable std::set<ConstProjectionPtr> _projections;
 
     /// A cached set of event weights (a single unit weight if the original weight vector was empty)
     mutable std::valarray<double> _weights;
 
     /// A cached set of event cross-section & errors (a pair of zeros if the original weight vector was empty)
     mutable std::vector<std::pair<double,double>> _xsecs;
   };
 
 
 }
 
 #endif

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