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File indexing completed on 2025-09-17 08:53:45
0001 //------------------------------- -*- C++ -*- -------------------------------// 0002 // Copyright Celeritas contributors: see top-level COPYRIGHT file for details 0003 // SPDX-License-Identifier: (Apache-2.0 OR MIT) 0004 //---------------------------------------------------------------------------// 0005 //! \file celeritas/phys/FourVector.hh 0006 //---------------------------------------------------------------------------// 0007 #pragma once 0008 0009 #include <cmath> 0010 0011 #include "corecel/cont/Array.hh" 0012 #include "corecel/math/Algorithms.hh" 0013 #include "corecel/math/ArrayOperators.hh" 0014 #include "corecel/math/ArrayUtils.hh" 0015 #include "geocel/Types.hh" 0016 #include "celeritas/Quantities.hh" 0017 #include "celeritas/Types.hh" 0018 0019 namespace celeritas 0020 { 0021 //---------------------------------------------------------------------------// 0022 // STRUCTS 0023 //---------------------------------------------------------------------------// 0024 /*! 0025 * The momentum-energy four-vector (Lorentz vector). 0026 * 0027 * The units of this class are implicit: momentum is \c MevMomentum 0028 * and energy is \c MevEnergy. 0029 */ 0030 struct FourVector 0031 { 0032 using Energy = units::MevEnergy; 0033 using Momentum = units::MevMomentum; 0034 using Mass = units::MevMass; 0035 0036 Real3 mom{0, 0, 0}; //!< Particle momentum 0037 real_type energy{0}; //!< Particle total energy (\f$\sqrt{p^2 + m^2}\f$) 0038 0039 // Construct from a particle and direction 0040 template<class PTV> 0041 static inline CELER_FUNCTION FourVector 0042 from_particle(PTV const& particle, Real3 const& direction); 0043 0044 // Construct from momentum, rest mass, direction 0045 static inline CELER_FUNCTION FourVector 0046 from_mass_momentum(Mass m, Momentum p, Real3 const& direction); 0047 0048 //! In-place addition 0049 CELER_FUNCTION FourVector& operator+=(FourVector const& v) 0050 { 0051 mom += v.mom; 0052 energy += v.energy; 0053 return *this; 0054 } 0055 }; 0056 0057 //---------------------------------------------------------------------------// 0058 // INLINE UTILITY FUNCTIONS 0059 //---------------------------------------------------------------------------// 0060 /*! 0061 * Construct from rest mass, momentum, direction. 0062 * 0063 * Note that this could be improved by using \c std::hypot which yields more 0064 * accurate answers if the magnitudes of the momentum and mass are very 0065 * different. However, differences in the implementation of that function can 0066 * lead to differences across platforms, compilers, and architectures, so for 0067 * now we use a naive sqrt+ipow. 0068 */ 0069 CELER_FUNCTION FourVector FourVector::from_mass_momentum(Mass m, 0070 Momentum p, 0071 Real3 const& direction) 0072 { 0073 return {p.value() * direction, 0074 std::sqrt(ipow<2>(p.value()) + ipow<2>(m.value()))}; 0075 } 0076 0077 //---------------------------------------------------------------------------// 0078 /*! 0079 * Construct from a particle and direction. 0080 */ 0081 template<class PTV> 0082 CELER_FUNCTION FourVector FourVector::from_particle(PTV const& particle, 0083 Real3 const& direction) 0084 { 0085 return {direction * value_as<Momentum>(particle.momentum()), 0086 value_as<Energy>(particle.total_energy())}; 0087 } 0088 0089 //---------------------------------------------------------------------------// 0090 /*! 0091 * Add two four-vectors. 0092 */ 0093 inline CELER_FUNCTION FourVector operator+(FourVector const& lhs, 0094 FourVector const& rhs) 0095 { 0096 FourVector result = lhs; 0097 return result += rhs; 0098 } 0099 0100 //---------------------------------------------------------------------------// 0101 /*! 0102 * Get the boost vector (\f$ \frac{\vec{mom}}/{energy} \f$) of a four-vector. 0103 */ 0104 inline CELER_FUNCTION Real3 boost_vector(FourVector const& p) 0105 { 0106 CELER_EXPECT(p.energy > 0); 0107 return (real_type{1} / p.energy) * p.mom; 0108 } 0109 0110 //---------------------------------------------------------------------------// 0111 /*! 0112 * Perform the Lorentz transformation along a boost vector. 0113 * 0114 * The transformation (\f$ \Lambda^{\alpha}_{\beta} \f$) along 0115 * the boost vector (\f$ \vec{v} \f$) for a four-vector \f$ p^{\beta} \f$ is: 0116 * 0117 * \f[ p^{\prime \beta} = \Lambda^{\alpha}_{\beta} (\vec{v}) p^{\beta} \f]. 0118 * 0119 * \todo Define a boost function that takes a second FourVector for reduced 0120 * register usage 0121 */ 0122 inline CELER_FUNCTION void boost(Real3 const& v, FourVector* p) 0123 { 0124 real_type const v_sq = dot_product(v, v); 0125 CELER_EXPECT(v_sq < real_type{1}); 0126 0127 real_type const vp = dot_product(v, p->mom); 0128 real_type const gamma = real_type{1} / std::sqrt(1 - v_sq); 0129 real_type const lambda = (v_sq > 0 ? (gamma - 1) * vp / v_sq : 0) 0130 + gamma * p->energy; 0131 0132 axpy(lambda, v, &(p->mom)); 0133 p->energy = gamma * (p->energy + vp); 0134 } 0135 0136 //---------------------------------------------------------------------------// 0137 /*! 0138 * Calculate the magnitude of a four vector. 0139 */ 0140 inline CELER_FUNCTION real_type norm(FourVector const& a) 0141 { 0142 return std::sqrt(std::fabs(ipow<2>(a.energy) - dot_product(a.mom, a.mom))); 0143 } 0144 0145 //---------------------------------------------------------------------------// 0146 } // namespace celeritas
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