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 //------------------------------- -*- C++ -*- -------------------------------//
 // Copyright Celeritas contributors: see top-level COPYRIGHT file for details
 // SPDX-License-Identifier: (Apache-2.0 OR MIT)
 //---------------------------------------------------------------------------//
 //! \file celeritas/phys/PhysicsData.hh
 //---------------------------------------------------------------------------//
 #pragma once
 
 #include "corecel/cont/Array.hh"
 #include "corecel/data/Collection.hh"
 #include "corecel/data/CollectionBuilder.hh"
 #include "corecel/data/StackAllocatorData.hh"
 #include "celeritas/Quantities.hh"
 #include "celeritas/Types.hh"
 #include "celeritas/em/data/AtomicRelaxationData.hh"
 #include "celeritas/em/data/EPlusGGData.hh"
 #include "celeritas/em/data/LivermorePEData.hh"
 #include "celeritas/grid/XsGridData.hh"
 #include "celeritas/neutron/data/NeutronElasticData.hh"
 
 #include "Interaction.hh"
 #include "Secondary.hh"
 
 namespace celeritas
 {
 //---------------------------------------------------------------------------//
 // TYPES
 //---------------------------------------------------------------------------//
 //! Currently all value grids are cross section grids
 using ValueGrid = XsGridRecord;
 using ValueGridId = OpaqueId<XsGridRecord>;
 using ValueTableId = OpaqueId<struct ValueTable>;
 
 //---------------------------------------------------------------------------//
 // PARAMS
 //---------------------------------------------------------------------------//
 /*!
  * Set of value grids for all elements or materials.
  *
  * It is allowable for this to be "false" (i.e. no materials assigned)
  * indicating that the value table doesn't apply in the context -- for
  * example, an empty ValueTable macro_xs means that the process doesn't have a
  * discrete interaction.
  */
 struct ValueTable
 {
     ItemRange<ValueGridId> grids;  //!< Value grid by element or material index
 
     //! True if assigned
     explicit CELER_FUNCTION operator bool() const { return !grids.empty(); }
 };
 
 //---------------------------------------------------------------------------//
 /*!
  * Set of cross section CDF tables for a model.
  *
  * Each material has a set of value grids for its constituent elements; these
  * are used to sample an element from a material when required by a discrete
  * interaction. A null ValueTableId means the material only has a single
  * element, so no cross sections need to be stored. An empty ModelXsTable means
  * no element selection is required for the model.
  */
 struct ModelXsTable
 {
     ItemRange<ValueTableId> material;  //!< Value table by material index
 
     //! True if assigned
     explicit CELER_FUNCTION operator bool() const { return !material.empty(); }
 };
 
 //---------------------------------------------------------------------------//
 /*!
  * Energy-dependent model IDs for a single process and particle type.
  *
  * For a given particle type, a single process should be divided into multiple
  * models as a function of energy. The ModelGroup represents this with an
  * energy grid, and each cell of the grid corresponding to a particular
  * ModelId.
  */
 struct ModelGroup
 {
     using Energy = units::MevEnergy;
 
     ItemRange<real_type> energy;  //!< Energy grid bounds [MeV]
     ItemRange<ParticleModelId> model;  //!< Corresponding models
 
     //! True if assigned
     explicit CELER_FUNCTION operator bool() const
     {
         return (energy.size() >= 2) && (model.size() + 1 == energy.size());
     }
 };
 
 //---------------------------------------------------------------------------//
 /*!
  * Particle-process that uses MC integration to sample interaction length.
  *
  * This is needed for the integral approach for correctly sampling the discrete
  * interaction length after a particle loses energy along a step. An \c
  * IntegralXsProcess is stored for each particle-process. This will be "false"
  * (i.e. no energy_max assigned) if the particle associated with the process
  * does not have energy loss processes or if \c use_integral_xs is false.
  */
 struct IntegralXsProcess
 {
     ItemRange<real_type> energy_max_xs;  //!< Energy of the largest xs [mat]
 
     //! True if assigned
     explicit CELER_FUNCTION operator bool() const
     {
         return !energy_max_xs.empty();
     }
 };
 
 //---------------------------------------------------------------------------//
 /*!
  * Processes for a single particle type.
  *
  * Each index should be accessed with type ParticleProcessId. \c macro_xs
  * stores the cross section tables for each process, while \c energy_loss and
  * \c range are the process-integrated dE/dx and range for the particle.  \c
  * integral_xs will only be assigned if the integral approach is used and the
  * particle has continuous-discrete processes.
  *
  * \todo If it's possible for a particle to have multiple at-rest processes, \c
  * at_rest should be the process with the smallest lifetime. This is used in \c
  * select_discrete_interaction to choose the at-rest process with the smallest
  * time to interaction if the particle is stopped and has a process that
  * applies at rest.
  */
 struct ProcessGroup
 {
     ItemRange<ProcessId> processes;  //!< Processes that apply [ppid]
     ItemRange<ModelGroup> models;  //!< Model applicability [ppid]
     ItemRange<IntegralXsProcess> integral_xs;  //!< [ppid]
     ItemRange<ValueTable> macro_xs;  //!< [ppid]
     ValueTableId energy_loss;  //!< Process-integrated energy loss
     ValueTableId range;  //!< Process-integrated range
     ValueTableId inverse_range;  //!< Inverse process-integrated range
     ParticleProcessId at_rest;  //!< ID of the particle's at-rest process
 
     //! True if assigned and valid
     explicit CELER_FUNCTION operator bool() const
     {
         return !processes.empty() && models.size() == processes.size();
     }
 
     //! Number of processes that apply
     CELER_FUNCTION ParticleProcessId::size_type size() const
     {
         return processes.size();
     }
 };
 
 //---------------------------------------------------------------------------//
 /*!
  * Model data for special hardwired cases (on-the-fly xs calculations).
  *
  * TODO: livermore/relaxation are owned by other classes, but
  * because we assign <host, value> -> { <host, cref> ; <device, value> ->
  * <device, cref> }
  */
 template<Ownership W, MemSpace M>
 struct HardwiredModels
 {
     //// DATA ////
 
     // Photoelectric effect
     ProcessId photoelectric;
     units::MevEnergy photoelectric_table_thresh;
     ModelId livermore_pe;
     LivermorePEData<W, M> livermore_pe_data;
     AtomicRelaxParamsData<W, M> relaxation_data;
 
     // Positron annihilation
     ProcessId positron_annihilation;
     ModelId eplusgg;
     EPlusGGData eplusgg_data;
 
     // Neutron elastic
     ProcessId neutron_elastic;
     ModelId chips;
     NeutronElasticData<W, M> chips_data;
 
     //// MEMBER FUNCTIONS ////
 
     //! Assign from another set of hardwired models
     template<Ownership W2, MemSpace M2>
     HardwiredModels& operator=(HardwiredModels<W2, M2> const& other)
     {
         // Note: don't require the other set of hardwired models to be assigned
         photoelectric = other.photoelectric;
         if (photoelectric)
         {
             // Only assign photoelectric data if that process is present
             photoelectric_table_thresh = other.photoelectric_table_thresh;
             livermore_pe = other.livermore_pe;
             livermore_pe_data = other.livermore_pe_data;
         }
         relaxation_data = other.relaxation_data;
         positron_annihilation = other.positron_annihilation;
         eplusgg = other.eplusgg;
         eplusgg_data = other.eplusgg_data;
 
         neutron_elastic = other.neutron_elastic;
         if (neutron_elastic)
         {
             // Only assign neutron_elastic data if that process is present
             chips = other.chips;
             chips_data = other.chips_data;
         }
 
         return *this;
     }
 };
 
 //---------------------------------------------------------------------------//
 /*!
  * User-configurable particle-dependent physics constants.
  *
  * These scalar quantities can have different values for electrons/positrons
  * and muons/hadrons. They are described in \c PhysicsParams .
  */
 struct ParticleScalars
 {
     using Energy = units::MevEnergy;
 
     // Energy loss/range options
     real_type min_range{};  //!< rho [len]
     real_type max_step_over_range{};  //!< alpha [unitless]
     Energy lowest_energy{};  //!< Lowest kinetic energy
 
     // Multiple scattering options
     bool displaced{};  //!< Whether lateral displacement is enabled
     real_type range_factor{};
     MscStepLimitAlgorithm step_limit_algorithm{MscStepLimitAlgorithm::size_};
 
     //! True if assigned
     explicit CELER_FUNCTION operator bool() const
     {
         return min_range > 0 && max_step_over_range > 0
                && lowest_energy > zero_quantity() && range_factor > 0
                && range_factor < 1
                && step_limit_algorithm != MscStepLimitAlgorithm::size_;
     }
 };
 
 //---------------------------------------------------------------------------//
 /*!
  * Scalar (no template needed) quantities used by physics.
  *
  * The user-configurable constants and multiple scattering options are
  * described in \c PhysicsParams .
  *
  * The \c model_to_action value corresponds to the \c ActionId for the first \c
  * ModelId . Additionally it implies (by construction in physics_params) the
  * action IDs of several other physics actions.
  */
 struct PhysicsParamsScalars
 {
     using Energy = units::MevEnergy;
 
     //! Highest number of processes for any particle type
     ProcessId::size_type max_particle_processes{};
     //! Offset to create an ActionId from a ModelId
     ActionId::size_type model_to_action{};
     //! Number of physics models
     ModelId::size_type num_models{};
 
     // User-configurable constants
     real_type min_eprime_over_e{};  //!< xi [unitless]
     real_type linear_loss_limit{};  //!< For scaled range calculation
     real_type fixed_step_limiter{};  //!< Global charged step size limit [len]
 
     // User-configurable multiple scattering options
     real_type lambda_limit{};  //!< lambda limit
     real_type safety_factor{};  //!< safety factor
 
     // Particle-dependent user-configurable constants
     ParticleScalars light;
     ParticleScalars heavy;
 
     real_type secondary_stack_factor = 3;  //!< Secondary storage per state
                                            //!< size
     // When fixed step limiter is used, this is the corresponding action ID
     ActionId fixed_step_action{};
 
     //! True if assigned
     explicit CELER_FUNCTION operator bool() const
     {
         return max_particle_processes > 0 && model_to_action >= 4
                && num_models > 0 && min_eprime_over_e > 0
                && linear_loss_limit > 0 && secondary_stack_factor > 0
                && ((fixed_step_limiter > 0)
                    == static_cast<bool>(fixed_step_action))
                && lambda_limit > 0 && safety_factor >= 0.1 && light && heavy;
     }
 
     //! Stop early due to MSC limitation
     CELER_FORCEINLINE_FUNCTION ActionId msc_action() const
     {
         return ActionId{model_to_action - 4};
     }
 
     //! Stop early due to range limitation
     CELER_FORCEINLINE_FUNCTION ActionId range_action() const
     {
         return ActionId{model_to_action - 3};
     }
 
     //! Undergo a discrete interaction
     CELER_FORCEINLINE_FUNCTION ActionId discrete_action() const
     {
         return ActionId{model_to_action - 2};
     }
 
     //! Indicate a discrete interaction was rejected by the integral method
     CELER_FORCEINLINE_FUNCTION ActionId integral_rejection_action() const
     {
         return ActionId{model_to_action - 1};
     }
 
     //! Indicate an interaction failed to allocate memory
     CELER_FORCEINLINE_FUNCTION ActionId failure_action() const
     {
         return ActionId{model_to_action + num_models};
     }
 };
 
 //---------------------------------------------------------------------------//
 /*!
  * Persistent shared physics data.
  *
  * This includes macroscopic cross section tables ordered by
  * [particle][process][material][energy] and process-integrated energy loss and
  * range tables ordered by [particle][material][energy].
  *
  * So the first applicable process (ProcessId{0}) for an arbitrary particle
  * (ParticleId{1}) in material 2 (PhysMatId{2}) will have the following
  * ID and cross section grid: \code
    ProcessId proc_id = params.particle[1].processes[0];
    const UniformGridData& grid
        = params.particle[1].macro_xs[0].material[2].log_energy;
  * \endcode
  *
  * \todo Energy loss, range, and model xs grids should use \c UniformGridRecord
  * instead of \c XsGridRecord because they have no scaled values.
  */
 template<Ownership W, MemSpace M>
 struct PhysicsParamsData
 {
     //// TYPES ////
 
     template<class T>
     using Items = Collection<T, W, M>;
     template<class T>
     using ParticleItems = Collection<T, W, M, ParticleId>;
     template<class T>
     using ParticleModelItems = Collection<T, W, M, ParticleModelId>;
 
     //// DATA ////
 
     // Backend storage
     Items<real_type> reals;
     Items<ParticleModelId> pmodel_ids;
     Items<ValueGrid> value_grids;
     Items<ValueGridId> value_grid_ids;
     Items<ProcessId> process_ids;
     Items<ValueTable> value_tables;
     Items<ValueTableId> value_table_ids;
     Items<IntegralXsProcess> integral_xs;
     Items<ModelGroup> model_groups;
     ParticleItems<ProcessGroup> process_groups;
     ParticleModelItems<ModelId> model_ids;
     ParticleModelItems<ModelXsTable> model_xs;
 
     // Special data
     HardwiredModels<W, M> hardwired;
 
     // Non-templated data
     PhysicsParamsScalars scalars;
 
     //// METHODS ////
 
     //! True if assigned
     explicit CELER_FUNCTION operator bool() const
     {
         return !process_groups.empty() && !model_ids.empty() && scalars;
     }
 
     //! Assign from another set of data
     template<Ownership W2, MemSpace M2>
     PhysicsParamsData& operator=(PhysicsParamsData<W2, M2> const& other)
     {
         CELER_EXPECT(other);
 
         reals = other.reals;
         pmodel_ids = other.pmodel_ids;
         value_grids = other.value_grids;
         value_grid_ids = other.value_grid_ids;
         process_ids = other.process_ids;
         value_tables = other.value_tables;
         value_table_ids = other.value_table_ids;
         integral_xs = other.integral_xs;
         model_groups = other.model_groups;
         process_groups = other.process_groups;
         model_ids = other.model_ids;
         model_xs = other.model_xs;
 
         hardwired = other.hardwired;
 
         scalars = other.scalars;
 
         return *this;
     }
 };
 
 //---------------------------------------------------------------------------//
 // STATE
 //---------------------------------------------------------------------------//
 /*!
  * Physics state data for a single track.
  *
  * State that's persistent across steps:
  * - Remaining number of mean free paths to the next discrete interaction
  *
  * State that is reset at every step:
  * - Current macroscopic cross section
  * - Within-step energy deposition
  * - Within-step energy loss range
  * - Secondaries emitted from an interaction
  * - Discrete process element selection
  */
 struct PhysicsTrackState
 {
     real_type interaction_mfp;  //!< Remaining MFP to interaction
 
     // TEMPORARY STATE
     real_type macro_xs;  //!< Total cross section for discrete interactions
     real_type energy_deposition;  //!< Local energy deposition in a step [MeV]
     real_type dedx_range;  //!< Local energy loss range [len]
     MscRange msc_range;  //!< Range properties for multiple scattering
     Span<Secondary> secondaries;  //!< Emitted secondaries
     ElementComponentId element;  //!< Element sampled for interaction
 };
 
 //---------------------------------------------------------------------------//
 /*!
  * Initialize a physics track state.
  *
  * Currently no data is required at initialization -- it all must be evaluated
  * by the physics kernels itself.
  */
 struct PhysicsTrackInitializer
 {
 };
 
 //---------------------------------------------------------------------------//
 /*!
  * Dynamic physics (models, processes) state data.
  *
  * The "xs scratch space" is a 2D array of reals, indexed with
  * [track_id][el_component_id], where the fast-moving dimension has the
  * greatest number of element components of any material in the problem. This
  * can be used for the physics to calculate microscopic cross sections.
  */
 template<Ownership W, MemSpace M>
 struct PhysicsStateData
 {
     //// TYPES ////
 
     template<class T>
     using StateItems = celeritas::StateCollection<T, W, M>;
     template<class T>
     using Items = celeritas::Collection<T, W, M>;
 
     //// DATA ////
 
     StateItems<PhysicsTrackState> state;  //!< Track state [track]
     StateItems<MscStep> msc_step;  //!< Internal MSC data [track]
 
     Items<real_type> per_process_xs;  //!< XS [track][particle process]
 
     AtomicRelaxStateData<W, M> relaxation;  //!< Scratch data
     StackAllocatorData<Secondary, W, M> secondaries;  //!< Secondary stack
 
     //// METHODS ////
 
     //! True if assigned
     explicit CELER_FUNCTION operator bool() const
     {
         return !state.empty() && secondaries;
     }
 
     //! State size
     CELER_FUNCTION size_type size() const { return state.size(); }
 
     //! Assign from another set of states
     template<Ownership W2, MemSpace M2>
     PhysicsStateData& operator=(PhysicsStateData<W2, M2>& other)
     {
         CELER_EXPECT(other);
         state = other.state;
         msc_step = other.msc_step;
 
         per_process_xs = other.per_process_xs;
 
         relaxation = other.relaxation;
         secondaries = other.secondaries;
 
         return *this;
     }
 };
 
 //---------------------------------------------------------------------------//
 /*!
  * Resize the state in host code.
  */
 template<MemSpace M>
 inline void resize(PhysicsStateData<Ownership::value, M>* state,
                    HostCRef<PhysicsParamsData> const& params,
                    size_type size)
 {
     CELER_EXPECT(size > 0);
     CELER_EXPECT(params.scalars.max_particle_processes > 0);
     resize(&state->state, size);
     resize(&state->msc_step, size);
     resize(&state->per_process_xs,
            size * params.scalars.max_particle_processes);
     resize(&state->relaxation, params.hardwired.relaxation_data, size);
     resize(
         &state->secondaries,
         static_cast<size_type>(size * params.scalars.secondary_stack_factor));
 }
 
 //---------------------------------------------------------------------------//
 }  // namespace celeritas

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