impactx::distribution::SpinvMF Struct Reference

#include <SpinvMF.H>

Public Member Functions
	SpinvMF (amrex::ParticleReal mux, amrex::ParticleReal muy, amrex::ParticleReal muz)
AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE void	operator() (amrex::ParticleReal &AMREX_RESTRICT sx, amrex::ParticleReal &AMREX_RESTRICT sy, amrex::ParticleReal &AMREX_RESTRICT sz, amrex::RandomEngine const &engine) const

Static Public Member Functions
AMREX_GPU_HOST static AMREX_FORCE_INLINE amrex::ParticleReal	inverse_Langevin (amrex::ParticleReal pmag)

Public Attributes
amrex::ParticleReal	m_muX
amrex::ParticleReal	m_muY
amrex::ParticleReal	m_muZ
amrex::ParticleReal	m_kappa
	components of a unit vector specifying the mean direction

Constructor & Destructor Documentation

SpinvMF()

impactx::distribution::SpinvMF::SpinvMF ( amrex::ParticleReal mux, amrex::ParticleReal muy, amrex::ParticleReal muz )

inline

A von Mises-Fisher (vMF) distribution on the unit 2-sphere.

This is used for initializing particle spin. There is a natural bijective correspondence between vMF distributions and mean (polarization) vectors.

The algorithm used here is a simplification of the algorithm described in: C. Pinzon and K. Jung, "Fast Python sampler of the von Mises Fisher distribution", in the special case of the 2-sphere. Additional references used include:

K. V. Mardia and P. E. Jupp, Directional Statistics, Wiley, 1999; S. Kang and H-S. Oh, "Novel sampling method for the von Mises-Fisher distribution", Stat. and Comput. 34, 106 (2024), https://doi.org/10.1007/s11222-024-10419-3.

Return sampling from a vMF distribution.

Parameters

mux,muy,muz

components of a unit vector specifying the mean direction

Member Function Documentation

inverse_Langevin()

AMREX_GPU_HOST static AMREX_FORCE_INLINE amrex::ParticleReal impactx::distribution::SpinvMF::inverse_Langevin ( amrex::ParticleReal pmag )

inlinestatic

This function evaluates the inverse Langevin function, in order to return the value of concentration (kappa) required to produce a given polarization magnitude. It is used to prepare for spin sampling using the vMF distribution.

Here, we use an approximate expression due to R. Petrosyan. See: R. Petrosyan, Rheologica Acta 56, 21-26, 2016; doi:10.1007/s00397-016-0977-9 R. Jedynak, Mathematics and Mechanics of Solids 24, 1-25, 2018; doi:10.1177/1081286518811395

Parameters

pmag	polarization magnitude

Returns

required value of concentration kappa

operator()()

AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE void impactx::distribution::SpinvMF::operator() ( amrex::ParticleReal &AMREX_RESTRICT sx, amrex::ParticleReal &AMREX_RESTRICT sy, amrex::ParticleReal &AMREX_RESTRICT sz, amrex::RandomEngine const & engine ) const

inline

Return 1 3D spin (unit) vector

Parameters

sx	particle spin component in x
sy	particle spin component in y
sz	particle spin component in z
engine	a random number engine (with associated state)

Member Data Documentation

m_kappa

amrex::ParticleReal impactx::distribution::SpinvMF::m_kappa

components of a unit vector specifying the mean direction

m_muX

amrex::ParticleReal impactx::distribution::SpinvMF::m_muX

m_muY

amrex::ParticleReal impactx::distribution::SpinvMF::m_muY

m_muZ

amrex::ParticleReal impactx::distribution::SpinvMF::m_muZ

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The documentation for this struct was generated from the following file:

• /home/docs/checkouts/readthedocs.org/user_builds/impactx/checkouts/1402/src/particles/distribution/SpinvMF.H