ActsFatras/Kernel/ContinuousProcess.hpp

0001 // This file is part of the ACTS project.
0002 //
0003 // Copyright (C) 2016 CERN for the benefit of the ACTS project
0004 //
0005 // This Source Code Form is subject to the terms of the Mozilla Public
0006 // License, v. 2.0. If a copy of the MPL was not distributed with this
0007 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
0008
0009 #pragma once
0010
0011 #include "Acts/Material/MaterialSlab.hpp"
0012 #include "ActsFatras/EventData/Particle.hpp"
0013 #include "ActsFatras/Kernel/InteractionList.hpp"
0014
0015 namespace ActsFatras {
0016
0017 /// A continuous simulation process based on a physics model plus selectors.
0018 ///
0019 /// @tparam physics_t is the physics model type
0020 /// @tparam input_particle_selector_t is the input particle selector
0021 /// @tparam output_particle_selector_t is the output particle selector
0022 /// @tparam child_particle_selector_t is the child particle selector
0023 ///
0024 /// The physics model type **must** provide a call operator with the following
0025 /// signature
0026 ///
0027 ///     <Particle Container>
0028 ///     operator()(
0029 ///         generator_t& generator,
0030 ///         const Acts::MaterialSlab& slab,
0031 ///         Particle& particle) const
0032 ///
0033 /// The return type can be any `Container` with `Particle` elements.
0034 ///
0035 /// The input selector defines whether the process is applied while the
0036 /// output selector defines a break condition, i.e. whether to continue
0037 /// simulating the particle propagation. The child selector is used to
0038 /// filter the generated child particles.
0039 ///
0040 /// @note The output and child particle selectors are identical unless the
0041 ///       child particle selector is explicitly specified.
0042 template <detail::ContinuousProcessConcept physics_t,
0043           typename input_particle_selector_t,
0044           typename output_particle_selector_t,
0045           typename child_particle_selector_t = output_particle_selector_t>
0046 struct ContinuousProcess {
0047   /// The physics interactions implementation.
0048   physics_t physics;
0049   /// Input selection: if this process applies to this particle.
0050   input_particle_selector_t selectInputParticle;
0051   /// Output selection: if the particle is still valid after the interaction.
0052   output_particle_selector_t selectOutputParticle;
0053   /// Child selection: if a generated child particle should be kept.
0054   child_particle_selector_t selectChildParticle;
0055
0056   /// Execute the physics process considering the configured selectors.
0057   ///
0058   /// @param[in]     generator is the random number generator
0059   /// @param[in]     slab      is the passed material
0060   /// @param[in,out] particle  is the particle being updated
0061   /// @param[out]    generated is the container of generated particles
0062   /// @return Break condition, i.e. whether this process stops the propagation
0063   ///
0064   /// @tparam generator_t must be a RandomNumberEngine
0065   template <typename generator_t>
0066   bool operator()(generator_t &generator, const Acts::MaterialSlab &slab,
0067                   Particle &particle, std::vector<Particle> &generated) const {
0068     // not selecting this process is not a break condition
0069     if (!selectInputParticle(particle)) {
0070       return false;
0071     }
0072     // modify particle according to the physics process
0073     auto children = physics(generator, slab, particle);
0074     // move selected child particles to the output container
0075     std::copy_if(std::begin(children), std::end(children),
0076                  std::back_inserter(generated), selectChildParticle);
0077     // break condition is defined by whether the output particle is still valid
0078     // or not e.g. because it has fallen below a momentum threshold.
0079     return !selectOutputParticle(particle);
0080   }
0081 };
0082
0083 }  // namespace ActsFatras