Model.h

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/**
 *  \file IMP/Model.h
 *  \brief Storage of a model, its restraints, constraints and particles.
 *
 *  Copyright 2007-2022 IMP Inventors. All rights reserved.
 *
 */

#ifndef IMPKERNEL_MODEL_H
#define IMPKERNEL_MODEL_H

#include <IMP/kernel_config.h>
#include "ModelObject.h"
#include "ScoringFunction.h"
#include "Restraint.h"
#include "RestraintSet.h"
#include "ScoreState.h"
#include "container_macros.h"
#include "base_types.h"
//#include "Particle.h"
#include "Undecorator.h"
#include "internal/AttributeTable.h"
#include "internal/attribute_tables.h"
#include "internal/moved_particles_cache.h"
#include "internal/KeyVector.h"
#include <IMP/Object.h>
#include <IMP/Pointer.h>
#include <IMP/internal/IDGenerator.h>
#include <boost/unordered_map.hpp>
#include <boost/unordered_set.hpp>
#include <IMP/tuple_macros.h>
#include <boost/iterator/transform_iterator.hpp>
#include <boost/iterator/filter_iterator.hpp>
#include <cereal/access.hpp>
#include <cereal/types/polymorphic.hpp>

#include <limits>

IMPKERNEL_BEGIN_NAMESPACE

class ModelObject;
class Undecorator;
class Particle;

#if !defined(SWIG) && !defined(IMP_DOXYGEN)
namespace internal {
enum Stage {
  NOT_EVALUATING,
  BEFORE_EVALUATING,
  EVALUATING,
  AFTER_EVALUATING,
  COMPUTING_DEPENDENCIES
};
}
#endif

class Model;

#if !defined(SWIG) && !defined(IMP_DOXYGEN)
// This is needed as NodeInfo (below) needs to be showable, and Edges are not
inline std::ostream &operator<<(
              std::ostream &out, const std::set<ModelObject *> &) {
  out << "(set of ModelObject)";
  return out;
}
#endif

//! Class for storing model, its restraints, constraints, and particles.
/** The Model maintains a standard \imp container for each of Particle,
    ScoreState and Restraint object types.

    Each Float attribute has an associated range which reflects the
    range of values that it is expected to take on during optimization.
    The optimizer can use these ranges to make the optimization process
    more efficient. By default, the range estimates are simply the
    range of values for that attribute in the various particles, but
    it can be set to another value. For example, an attribute storing
    an angle could have the range set to (0,PI).

    The ranges are not enforced; they are just guidelines. In order to
    enforce ranges, see, for example,
    IMP::example::ExampleSingletonModifier.

    \headerfile Model.h "IMP/Model.h"
 */
class IMPKERNELEXPORT Model : public Object
#if !defined(SWIG) && !defined(IMP_DOXYGEN)
                              ,
                              public internal::Masks,
                              // The attribute tables provide fast access to
                              // e.g. particle attributes, etc.
                              public internal::FloatAttributeTable,
                              public internal::StringAttributeTable,
                              public internal::IntAttributeTable,
                              public internal::ObjectAttributeTable,
                              public internal::WeakObjectAttributeTable,
                              public internal::IntsAttributeTable,
                              public internal::FloatsAttributeTable,
                              public internal::ObjectsAttributeTable,
                              public internal::ParticleAttributeTable,
                              public internal::ParticlesAttributeTable,
                              public internal::SparseStringAttributeTable,
                              public internal::SparseIntAttributeTable,
                              public internal::SparseFloatAttributeTable,
                              public internal::SparseParticleAttributeTable
#endif
                              {
  typedef std::set<ModelObject *> Edges;
  // must be up top
  // we don't want any liveness checks
  IMP_NAMED_TUPLE_5(NodeInfo, NodeInfos, Edges, inputs, Edges, input_outputs,
                    Edges, outputs, Edges, readers, Edges, writers, );
  typedef boost::unordered_map<const ModelObject *, NodeInfo> DependencyGraph;
  DependencyGraph dependency_graph_;
  boost::unordered_set<const ModelObject *> no_dependencies_;
  boost::unordered_map<const ModelObject *, ScoreStatesTemp>
      required_score_states_;

  // basic representation
  boost::unordered_map<FloatKey, FloatRange> ranges_;

  ParticleIndexes free_particles_;
  IndexVector<ParticleIndexTag, Pointer<Particle> > particle_index_;
  IndexVector<ParticleIndexTag, Undecorators> undecorators_index_;

  internal::KeyVector<ModelKey, PointerMember<Object> > model_data_;

#if !defined(IMP_DOXYGEN)
  // Map unique ID to Model*
  class ModelMap {
    std::map<uint32_t, Model*> map_;
    internal::IDGenerator id_gen_;
  public:
    ModelMap() {}
    uint32_t add_new_model(Model *m);
    void add_model_with_id(Model *m, uint32_t id);
    void remove_model(Model *m);
    Model *get(uint32_t id) const;
  };

  static ModelMap model_map_;
  uint32_t unique_id_;
#endif

  void do_add_dependencies(const ModelObject *mo);
  void do_clear_required_score_states(ModelObject *mo);
  void do_check_required_score_states(const ModelObject *mo) const;
  void do_check_update_order(const ScoreState *ss) const;
  void do_check_inputs_and_outputs(const ModelObject *mo) const;
  void do_check_readers_and_writers(const ModelObject *mo) const;
  void do_check_not_in_readers_and_writers(const ModelObject *mo) const;
  void do_clear_dependencies(const ModelObject *mo);

  // used to track time when triggers are activated
  unsigned age_counter_;
  // all triggers
  Vector<unsigned> trigger_age_;
  // time when dependencies were last changed, or 0
  unsigned dependencies_age_;

  // allow skipping updating dependencies_age_ for temporary ModelObjects
  bool dependencies_saved_;
  unsigned saved_dependencies_age_;
  // We don't use ModelObjectsTemp here because these objects might get freed
  // under us, which would cause WeakPointer to raise an exception
  std::vector<ModelObject *> mos_added_since_save_, mos_removed_since_save_;

  // cache of restraints that are affected by each moved particle,
  // used for evaluate_moved() and related functions
  internal::MovedParticlesRestraintCache moved_particles_restraint_cache_;
  // cache of particles that are affected by each moved particle
  internal::MovedParticlesParticleCache moved_particles_particle_cache_;
  // time when moved_particles_*_cache_ were last updated, or 0
  unsigned moved_particles_cache_age_;

  void register_unique_id();

  friend class cereal::access;

  template<class Archive> void serialize(Archive &ar,
                                         std::uint32_t const version) {
    ar(cereal::base_class<Object>(this));
    // We need to get unique_id_ early on read, so that any ModelObjects
    // that reference it get correctly associated with this model
    ar(unique_id_);
    if (std::is_base_of<cereal::detail::InputArchiveBase, Archive>::value) {
      register_unique_id();
    }
    ar(cereal::base_class<internal::FloatAttributeTable>(this),
       cereal::base_class<internal::StringAttributeTable>(this),
       cereal::base_class<internal::IntAttributeTable>(this),
       cereal::base_class<internal::IntsAttributeTable>(this),
       cereal::base_class<internal::FloatsAttributeTable>(this),
       cereal::base_class<internal::ParticleAttributeTable>(this),
       cereal::base_class<internal::ParticlesAttributeTable>(this),
       cereal::base_class<internal::SparseStringAttributeTable>(this),
       cereal::base_class<internal::SparseIntAttributeTable>(this),
       cereal::base_class<internal::SparseFloatAttributeTable>(this),
       cereal::base_class<internal::SparseParticleAttributeTable>(this));

    if (std::is_base_of<cereal::detail::InputArchiveBase, Archive>::value) {
      size_t count;
      free_particles_.clear();
      ar(count);
      particle_index_.clear();
      while(count-- > 0) {
        std::string name;
        ar(name);
        add_particle(name);
      }
      ParticleIndexes to_free;
      ar(to_free);
      for (auto pi : to_free) {
        remove_particle(pi);
      }
    } else {
      size_t count = particle_index_.size();
      ar(count);
      for (size_t i = 0; i < count; ++i) {
        std::string name;
        if (get_has_particle(ParticleIndex(i))) {
          name = get_particle_name(ParticleIndex(i));
        }
        ar(name);
      }
      ar(free_particles_);
    }

    // Need particle info before anything that might refer to a particle
    // (ScoreState, or arbitrary Object)
    ar(cereal::base_class<internal::ObjectAttributeTable>(this),
       cereal::base_class<internal::ObjectsAttributeTable>(this),
       cereal::base_class<internal::WeakObjectAttributeTable>(this),
       model_data_, mutable_access_score_states());

    if (std::is_base_of<cereal::detail::InputArchiveBase, Archive>::value) {
      // clear caches
      age_counter_ = 1;
      trigger_age_.clear();
      dependencies_age_ = 0;
      saved_dependencies_age_ = 0;
      dependencies_saved_ = false;
      moved_particles_cache_age_ = 0;
    }
  }

  // update model age (can never be zero, even if it wraps)
  void increase_age() {
    age_counter_++;
    if (age_counter_ == 0) {
      age_counter_ = 1;
    }
  }

  template <class MOType, class MOVector>
  void do_get_dependent(ModelObject *mo, MOVector &ret) {
    const auto &node = dependency_graph_.find(mo);
    IMP_INTERNAL_CHECK(mo->get_has_dependencies(),
                       "Object " << mo->get_name()
                                 << " does not have dependencies.");
    IMP_INTERNAL_CHECK(node != dependency_graph_.end(),
                       "Node not in dependency_graph.");
    MOType *r = dynamic_cast<MOType *>(mo);
    if (r) {
      ret.push_back(r);
    }
    for (ModelObject *cur : node->second.get_outputs()) {
      do_get_dependent<MOType, MOVector>(cur, ret);
    }
    for (ModelObject *cur : node->second.get_readers()) {
      do_get_dependent<MOType, MOVector>(cur, ret);
    }
  }

#if !defined(IMP_DOXYGEN) && !defined(SWIG)
  // things the evaluate template functions need, can't be bothered with friends
 public:
#endif
  // check more things on the first call
  bool first_call_;
  // the stage of evaluation
  internal::Stage cur_stage_;

  //! Get all Restraints that depend on the given particle
  const std::set<Restraint *> &get_dependent_restraints(ParticleIndex pi) {
    return moved_particles_restraint_cache_.get_dependent_restraints(pi);
  }

  //! Get all particles that depend on the given particle
  const ParticleIndexes &get_dependent_particles(ParticleIndex pi) {
    return moved_particles_particle_cache_.get_dependent_particles(pi);
  }

  ModelObjectsTemp get_dependency_graph_inputs(const ModelObject *mo) const;
  ModelObjectsTemp get_dependency_graph_outputs(const ModelObject *mo) const;
  bool do_get_has_dependencies(const ModelObject *mo) const {
    return no_dependencies_.find(mo) == no_dependencies_.end();
  }
  void do_set_has_dependencies(const ModelObject *mo, bool tf);
  void do_set_has_all_dependencies(bool tf);

  void validate_computed_derivatives() const {}
  void set_has_all_dependencies(bool tf);
  bool get_has_all_dependencies() const;
  void check_dependency_invariants() const;
  void check_dependency_invariants(const ModelObject *mo) const;
  ScoreStatesTemp get_ancestor_score_states(const ModelObject *mo) const;
  ScoreStatesTemp get_descendent_score_states(const ModelObject *mo) const;

  void before_evaluate(const ScoreStatesTemp &states);
  void after_evaluate(const ScoreStatesTemp &states, bool calc_derivs);

  internal::Stage get_stage() const { return cur_stage_; }
  ParticleIndex add_particle_internal(Particle *p);
  static void do_remove_score_state(ScoreState *obj);
  void do_add_score_state(ScoreState *obj);
  void do_remove_particle(ParticleIndex pi);
  bool do_get_has_required_score_states(const ModelObject *mo) const;
  void do_set_has_required_score_states(ModelObject *mo, bool tf);
  const ScoreStatesTemp &do_get_required_score_states(const ModelObject *mo)
      const {
    IMP_USAGE_CHECK(do_get_has_required_score_states(mo),
                    "Doesn't have score states");
    return required_score_states_.find(mo)->second;
  }
  void do_add_model_object(ModelObject *mo);
  void do_remove_model_object(ModelObject *mo);

 public:
  //! Construct an empty model
  Model(std::string name = "Model %1%");

 public:
#if !defined(SWIG) && !defined(IMP_DOXYGEN)
  IMP_MODEL_IMPORT(internal::FloatAttributeTable);
  IMP_MODEL_IMPORT(internal::StringAttributeTable);
  IMP_MODEL_IMPORT(internal::IntAttributeTable);
  IMP_MODEL_IMPORT(internal::ObjectAttributeTable);
  IMP_MODEL_IMPORT(internal::WeakObjectAttributeTable);
  IMP_MODEL_IMPORT(internal::IntsAttributeTable);
  IMP_MODEL_IMPORT(internal::FloatsAttributeTable);
  IMP_MODEL_IMPORT(internal::ObjectsAttributeTable);
  IMP_MODEL_IMPORT(internal::ParticleAttributeTable);
  IMP_MODEL_IMPORT(internal::ParticlesAttributeTable);
  IMP_MODEL_SPARSE_IMPORT(internal::SparseStringAttributeTable);
  IMP_MODEL_SPARSE_IMPORT(internal::SparseIntAttributeTable);
  IMP_MODEL_SPARSE_IMPORT(internal::SparseFloatAttributeTable);
  IMP_MODEL_SPARSE_IMPORT(internal::SparseParticleAttributeTable);
#endif
  //! Clear all the cache attributes of a given particle.
  void clear_particle_caches(ParticleIndex pi);

  //! Add particle to the model
  ParticleIndex add_particle(std::string name);

  //! Get the name of a particle
  std::string get_particle_name(ParticleIndex pi);

  //! Add the passed Undecorator to the particle.
  void add_undecorator(ParticleIndex pi, Undecorator *d);

#if !defined(IMP_DOXYGEN)
  RestraintsTemp get_dependent_restraints_uncached(ParticleIndex pi);

  ParticlesTemp get_dependent_particles_uncached(ParticleIndex pi);

  ScoreStatesTemp get_dependent_score_states_uncached(ParticleIndex pi);
#endif

  /** @name States

      ScoreStates maintain invariants in the Model (see ScoreState
      for more information.)

      ScoreStates do not need to be explicitly added to the Model, but they
      can be if desired in order to keep them alive as long as the model is
      alive.

      \advancedmethod
  */
  /**@{*/
  IMP_LIST_ACTION(public, ScoreState, ScoreStates, score_state, score_states,
                  ScoreState *, ScoreStates, do_add_score_state(obj), {},
                  do_remove_score_state(obj));
  /**@}*/

 public:
#ifndef SWIG
  using Object::clear_caches;
#endif

  //! Sometimes it is useful to be able to make sure the model is up to date
  /** This method updates all the state but does not necessarily compute the
      score. Use this to make sure that your containers and rigid bodies are
      up to date.
  */
  void update();

#ifdef IMP_DOXYGEN
  /** \name Accessing attributes
      \anchor model_attributes
      All the attribute data associated with each Particle are stored in the
      Model. For each type of attribute, there are the methods detailed below
      (where, eg, TypeKey is FloatKey or StringKey)
      @{
  */
  //! add particle attribute with the specified key and initial value
  /** \pre get_has_attribute(attribute_key, particle) is false*/
  void add_attribute(TypeKey attribute_key, ParticleIndex particle, Type value);

  //! remove particle attribute with the specified key
  /** \pre get_has_attribute(attribute_key, particle) is true*/
  void remove_attribute(TypeKey attribute_key, ParticleIndex particle);

  //! return true if particle has attribute with the specified key
  bool get_has_attribute(TypeKey attribute_key, ParticleIndex particle) const;

  //! set the value of particle attribute with the specified key
  /** \pre get_has_attribute(attribute_key, particle) is true*/
  void set_attribute(TypeKey attribute_key, ParticleIndex particle, Type value);

  //! get the value of the particle attribute with the specified key
  /** \pre get_has_attribute(attribute_key, particle) is true*/
  Type get_attribute(TypeKey attribute_key, ParticleIndex particle);

  /** Cache attributes, unlike normal attributes, can be added during
      evaluation. They are also cleared by the clear_cache_attributes() method.
      Cache attributes should be used when one is adding data to a particle
      to aid scoring (eg cache the rigid body collision acceleration structure).

      When some pertinent aspect of the particle changes, the clear method
      should
      be called (yes, this is a bit vague). Examples where it should be cleared
      include changing the set of members of a core::RigidBody or their
      coordinates, changing the members of an atom::Hierarchy.
  */
  void add_cache_attribute(TypeKey attribute_key, ParticleIndex particle,
                           Type value);

  //! Optimized attributes are the parameters of the model that are 
  //! allowed to be modified by samplers and optimizers
  void set_is_optimized(TypeKey attribute_key, ParticleIndex particle,
                        bool true_or_false);
/** @} */
#endif

#ifdef SWIG
#define IMP_MODEL_ATTRIBUTE_METHODS(Type, Value)                            \
  void add_attribute(Type##Key attribute_key, ParticleIndex particle,       \
                     Value value);                                          \
  void remove_attribute(Type##Key attribute_key, ParticleIndex particle);   \
  bool get_has_attribute(Type##Key attribute_key,                           \
                         ParticleIndex particle) const;                     \
  void set_attribute(Type##Key attribute_key, ParticleIndex particle,       \
                     Value value);                                          \
  Value get_attribute(Type##Key attribute_key, ParticleIndex particle);     \
  void add_cache_attribute(Type##Key attribute_key, ParticleIndex particle, \
                           Value value)

#define IMP_MODEL_SPARSE_ATTRIBUTE_METHODS(Type, Value)                     \
  void add_attribute(Type##Key attribute_key, ParticleIndex particle,       \
                     Value value);                                          \
  void remove_attribute(Type##Key attribute_key, ParticleIndex particle);   \
  bool get_has_attribute(Type##Key attribute_key,                           \
                         ParticleIndex particle) const;                     \
  void set_attribute(Type##Key attribute_key, ParticleIndex particle,       \
                     Value value);                                          \
  Value get_attribute(Type##Key attribute_key, ParticleIndex particle)

  IMP_MODEL_ATTRIBUTE_METHODS(Float, Float);
  IMP_MODEL_ATTRIBUTE_METHODS(Int, Int);
  IMP_MODEL_ATTRIBUTE_METHODS(Floats, Floats);
  IMP_MODEL_ATTRIBUTE_METHODS(Ints, Ints);
  IMP_MODEL_ATTRIBUTE_METHODS(String, String);
  IMP_MODEL_ATTRIBUTE_METHODS(ParticleIndexes, ParticleIndexes);
  IMP_MODEL_ATTRIBUTE_METHODS(ParticleIndex, ParticleIndex);
  IMP_MODEL_ATTRIBUTE_METHODS(Object, Object *);
  IMP_MODEL_ATTRIBUTE_METHODS(WeakObject, Object *);
  IMP_MODEL_SPARSE_ATTRIBUTE_METHODS(SparseString, String);
  IMP_MODEL_SPARSE_ATTRIBUTE_METHODS(SparseInt, Int);
  IMP_MODEL_SPARSE_ATTRIBUTE_METHODS(SparseFloat, Float);
  IMP_MODEL_SPARSE_ATTRIBUTE_METHODS(SparseParticleIndex, ParticleIndex);
  void set_is_optimized(FloatKey, ParticleIndex, bool);
  void add_to_derivative(FloatKey k, ParticleIndex particle, double v,
                         const DerivativeAccumulator &da);
#endif

  //! Get the particle from an index.
  Particle *get_particle(ParticleIndex p) const {
    IMP_USAGE_CHECK(get_has_particle(p), "Invalid particle requested");
    return particle_index_[p];
  }

  //! Check whether a given particle index exists.
  bool get_has_particle(ParticleIndex p) const {
    if (particle_index_.size() <= get_as_unsigned_int(p)) return false;
    return particle_index_[p];
  }

  //! Get all particle indexes
  ParticleIndexes get_particle_indexes();

  //! Get all the ModelObjects associated with this Model.
  ModelObjectsTemp get_model_objects() const;

  //! Remove a particle from the Model.
  /** The particle will then be inactive and cannot be used for anything
      and all data stored in the particle is lost.
   */
  void remove_particle(ParticleIndex pi);

  /** \name Storing data in the model

      One can store data associated with the model. This is used, for example,
      to keep a central ScoreState to normalize rigid body rotational variables.
      @{ */
  //! Store a piece of data in the model referenced by the key.
  void add_data(ModelKey mk, Object *o);
  //! Get back some data stored in the model.
  Object *get_data(ModelKey mk) const;
  //! Remove data stored in the model.
  void remove_data(ModelKey mk);
  //! Check if the model has a certain piece of data attached.
  bool get_has_data(ModelKey mk) const;
  /** @} */

  /** \name Model triggers

      Triggers can be used to track when to clear and rebuild caches
      of derived model properties. For example, a Restraint may restrain
      two particles as a function of the number of chemical bonds between
      them. To speed up this restraint, the bond graph can be cached; however,
      this graph needs to be rebuilt if bonds are created or removed. This
      can be achieved by checking that the model time (see get_age()) of the
      cache matches the time when the 'bond added/removed' Trigger was last
      updated (see get_trigger_last_updated()), either when the Restraint is
      evaluated or in an associated ScoreState.

      Triggers are intended for events that are rare during a typical
      optimization. Triggers can be created by any IMP module in either C++
      or Python by creating a new TriggerKey, much as model attributes
      are handled. To avoid name collisions, it is recommended to prepend
      the module and/or class name to the trigger, e.g. "atom.Bond.changed".

      For an example, see IMP::score_functor::OrientedSoap, which uses
      a cache built from the molecular hierarchy, which is cleared when the
      IMP::core::Hierarchy::get_changed_key() trigger is updated.

      @{ */

  //! Get the current 'model time'.
  /** This is a number 1 or more that tracks the 'age' of the model;
      it is incremented every time before_evaluate() is called.
      It may wrap (and so should not be assumed to always increase)
      but will never be 0. */
  unsigned get_age() { return age_counter_; }

  //! Get the time when the given trigger was last updated, or 0.
  /** Return the 'model time' (as given by get_age()) when the given
      trigger was last updated on this model, or 0 if never. */
  unsigned get_trigger_last_updated(TriggerKey tk) {
    if (trigger_age_.size() > tk.get_index()) {
      return trigger_age_[tk.get_index()];
    } else {
      return 0;
    }
  }

  //! Update the given trigger
  void set_trigger_updated(TriggerKey tk) {
    if (tk.get_index() >= trigger_age_.size()) {
      trigger_age_.resize(tk.get_index() + 1, 0);
    }
    trigger_age_[tk.get_index()] = age_counter_;
  }
  /** @} */

  //! Get the model age when ModelObject dependencies were last changed, or 0.
  /** This gives the Model age (see get_age()) when Particles, Restraints,
      or ScoreStates were last added or removed. It is typically used to
      help maintain caches that depend on the model's dependency graph. */
  unsigned get_dependencies_updated() { return dependencies_age_; }

  //! Mark a 'restore point' for ModelObject dependencies.
  /** \see restore_dependencies() */
  void save_dependencies() {
    dependencies_saved_ = true;
    saved_dependencies_age_ = dependencies_age_;
    IMP_IF_CHECK(USAGE_AND_INTERNAL) {
      mos_added_since_save_.clear();
      mos_removed_since_save_.clear();
    }
  }

  //! Restore ModelObject dependencies to previous restore point.
  /** This method, when paired with save_dependencies(), can be used to
      avoid triggering a model dependency update due to a temporary change
      in the model dependency graph, for example due to adding a temporary
      restraint, evaluating it, then removing that same restraint. It should
      only be called in cases where it is known that the dependency graph
      is the same as when save_dependencies() was called (this is only checked
      in debug mode). Save/restore call pairs cannot be nested, although it
      is OK to skip the call to restore_dependencies(), e.g. if an exception
      occurs.

      \see get_dependencies_updated()
      \see save_dependencies()
   */
  void restore_dependencies() {
    if (dependencies_saved_) {
      dependencies_saved_ = false;
      dependencies_age_ = saved_dependencies_age_;
      IMP_IF_CHECK(USAGE_AND_INTERNAL) {
        // Need to sort pointers since we may not add/remove in the same order
        std::sort(mos_added_since_save_.begin(), mos_added_since_save_.end());
        std::sort(mos_removed_since_save_.begin(),
                  mos_removed_since_save_.end());
        IMP_INTERNAL_CHECK(mos_added_since_save_ == mos_removed_since_save_,
                           "ModelObjects added do not match those removed");
      }
    }
  }

  //! Get an upper bound on the number of particles in the Model.
  /** This value is guaranteed to be at least the number of particles in
      the model (there may be fewer particles if any have been removed)
      and every ParticleIndex will be smaller than this value. */
  unsigned get_particles_size() const { return particle_index_.size(); }

  //! Get the unique ID of this Model.
  /** When multiple Models exist simultaneously, each has a different unique ID.
    */
  uint32_t get_unique_id() const {
    return unique_id_;
  }

  //! Return the Model with the given unique ID.
  /** If no Model with this ID exists, nullptr is returned. */
  static Model* get_by_unique_id(uint32_t id) {
    return model_map_.get(id);
  }

  IMP_OBJECT_METHODS(Model);

 public:
#if !defined(IMP_DOXYGEN)
  virtual void do_destroy() override;
#endif
};

IMPKERNEL_END_NAMESPACE

CEREAL_SPECIALIZE_FOR_ALL_ARCHIVES(
            IMP::Model, cereal::specialization::member_serialize);

CEREAL_CLASS_VERSION(IMP::Model, 1);

// This is needed for per cpp compilations, a not even sure why
// (perhaps cause Model returns ParticleIterator here and there?)
// - Feel free to remove if you *really* know what you're doing
#include "IMP/Particle.h"

#endif /* IMPKERNEL_MODEL_H */