ImpactX
Gaussian.H
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1 /* Copyright 2022-2023 The Regents of the University of California, through Lawrence
2  * Berkeley National Laboratory (subject to receipt of any required
3  * approvals from the U.S. Dept. of Energy). All rights reserved.
4  *
5  * This file is part of ImpactX.
6  *
7  * Authors: Chad Mitchell, Axel Huebl
8  * License: BSD-3-Clause-LBNL
9  */
10 #ifndef IMPACTX_DISTRIBUTION_GAUSSIAN
11 #define IMPACTX_DISTRIBUTION_GAUSSIAN
12 
13 #include <AMReX_Random.H>
14 #include <AMReX_REAL.H>
15 
16 #include <cmath>
17 
18 
19 namespace impactx::distribution
20 {
21  struct Gaussian
22  {
32  Gaussian(amrex::ParticleReal const sigx, amrex::ParticleReal const sigy,
33  amrex::ParticleReal const sigt,amrex::ParticleReal const sigpx,
34  amrex::ParticleReal const sigpy,amrex::ParticleReal const sigpt,
35  amrex::ParticleReal const muxpx=0.0, amrex::ParticleReal const muypy=0.0,
36  amrex::ParticleReal const mutpt=0.0
37  )
38  : m_sigmaX(sigx),m_sigmaY(sigy),m_sigmaT(sigt),m_sigmaPx(sigpx),m_sigmaPy(sigpy),
39  m_sigmaPt(sigpt),m_muxpx(muxpx),m_muypy(muypy),m_mutpt(mutpt)
40  {
41  }
42 
55  amrex::ParticleReal & x,
56  amrex::ParticleReal & y,
57  amrex::ParticleReal & t,
58  amrex::ParticleReal & px,
59  amrex::ParticleReal & py,
60  amrex::ParticleReal & pt,
61  amrex::RandomEngine const& engine) const {
62 
63  using namespace amrex::literals;
64 
65  amrex::ParticleReal ln1,u1,u2;
66  amrex::ParticleReal root,a1,a2;
67 
68  constexpr amrex::ParticleReal pi = 3.14159265358979_prt;
69 
70  // Generate six standard normal random variables using Box-Muller:
71 
72  u1 = amrex::Random(engine);
73  u2 = amrex::Random(engine);
74  ln1 = sqrt(-2_prt*log(u1));
75  x = ln1*cos(2_prt*pi*u2);
76  px = ln1*sin(2_prt*pi*u2);
77 
78  u1 = amrex::Random(engine);
79  u2 = amrex::Random(engine);
80  ln1 = sqrt(-2_prt*log(u1));
81  y = ln1*cos(2_prt*pi*u2);
82  py = ln1*sin(2_prt*pi*u2);
83 
84  u1 = amrex::Random(engine);
85  u2 = amrex::Random(engine);
86  ln1 = sqrt(-2_prt*log(u1));
87  t = ln1*cos(2_prt*pi*u2);
88  pt = ln1*sin(2_prt*pi*u2);
89 
90  // Transform to produce the desired second moments/correlations:
91  root = sqrt(1.0_prt-m_muxpx*m_muxpx);
92  a1 = m_sigmaX*x/root;
93  a2 = m_sigmaPx*(-m_muxpx*x/root+px);
94  x = a1;
95  px = a2;
96  root = sqrt(1.0_prt-m_muypy*m_muypy);
97  a1 = m_sigmaY*y/root;
98  a2 = m_sigmaPy*(-m_muypy*y/root+py);
99  y = a1;
100  py = a2;
101  root = sqrt(1.0_prt-m_mutpt*m_mutpt);
102  a1 = m_sigmaT*t/root;
103  a2 = m_sigmaPt*(-m_mutpt*t/root+pt);
104  t = a1;
105  pt = a2;
106  }
107  private:
108  amrex::ParticleReal m_sigmaX,m_sigmaY,m_sigmaT;
109  amrex::ParticleReal m_sigmaPx,m_sigmaPy,m_sigmaPt;
110  amrex::ParticleReal m_muxpx,m_muypy,m_mutpt;
111  };
112 
113 } // namespace impactx::distribution
114 
115 #endif // IMPACTX_DISTRIBUTION_GAUSSIAN
#define AMREX_FORCE_INLINE
#define AMREX_GPU_HOST_DEVICE
constexpr std::enable_if_t< std::is_floating_point< T >::value, T > pi()
AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE GpuComplex< T > log(const GpuComplex< T > &a_z) noexcept
Real Random()
AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE GpuComplex< T > sqrt(const GpuComplex< T > &a_z) noexcept
Definition: All.H:26
Definition: Gaussian.H:22
AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE void operator()(amrex::ParticleReal &x, amrex::ParticleReal &y, amrex::ParticleReal &t, amrex::ParticleReal &px, amrex::ParticleReal &py, amrex::ParticleReal &pt, amrex::RandomEngine const &engine) const
Definition: Gaussian.H:54
amrex::ParticleReal m_sigmaPy
Definition: Gaussian.H:109
amrex::ParticleReal m_muypy
Definition: Gaussian.H:110
amrex::ParticleReal m_sigmaX
Definition: Gaussian.H:108
amrex::ParticleReal m_sigmaT
Definition: Gaussian.H:108
Gaussian(amrex::ParticleReal const sigx, amrex::ParticleReal const sigy, amrex::ParticleReal const sigt, amrex::ParticleReal const sigpx, amrex::ParticleReal const sigpy, amrex::ParticleReal const sigpt, amrex::ParticleReal const muxpx=0.0, amrex::ParticleReal const muypy=0.0, amrex::ParticleReal const mutpt=0.0)
Definition: Gaussian.H:32
amrex::ParticleReal m_sigmaY
Definition: Gaussian.H:108
amrex::ParticleReal m_muxpx
RMS momentum.
Definition: Gaussian.H:110
amrex::ParticleReal m_sigmaPt
Definition: Gaussian.H:109
amrex::ParticleReal m_sigmaPx
related RMS sizes (length)
Definition: Gaussian.H:109
amrex::ParticleReal m_mutpt
Definition: Gaussian.H:110