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/* Copyright 2020 Yinjian Zhao, David Grote
*
* This file is part of WarpX.
*
* License: BSD-3-Clause-LBNL
*/
#include "PairWiseCoulombCollision.H"
#include "ShuffleFisherYates.H"
#include "ElasticCollisionPerez.H"
#include "Utils/ParticleUtils.H"
#include "Utils/WarpXUtil.H"
#include "WarpX.H"
using namespace amrex::literals;
PairWiseCoulombCollision::PairWiseCoulombCollision (std::string const collision_name)
: CollisionBase(collision_name)
{
AMREX_ALWAYS_ASSERT_WITH_MESSAGE(m_species_names.size() == 2,
"Pair wise Coulomb must have exactly two species.");
amrex::ParmParse pp(collision_name);
// default Coulomb log, if < 0, will be computed automatically
m_CoulombLog = -1.0_rt;
queryWithParser(pp, "CoulombLog", m_CoulombLog);
if (m_species_names[0] == m_species_names[1])
m_isSameSpecies = true;
else
m_isSameSpecies = false;
}
void
PairWiseCoulombCollision::doCollisions (amrex::Real cur_time, MultiParticleContainer* mypc)
{
const amrex::Real dt = WarpX::GetInstance().getdt(0);
if ( int(std::floor(cur_time/dt)) % m_ndt != 0 ) return;
auto& species1 = mypc->GetParticleContainerFromName(m_species_names[0]);
auto& species2 = mypc->GetParticleContainerFromName(m_species_names[1]);
// Enable tiling
amrex::MFItInfo info;
if (amrex::Gpu::notInLaunchRegion()) info.EnableTiling(species1.tile_size);
// Loop over refinement levels
for (int lev = 0; lev <= species1.finestLevel(); ++lev){
// Loop over all grids/tiles at this level
#ifdef AMREX_USE_OMP
info.SetDynamic(true);
#pragma omp parallel if (amrex::Gpu::notInLaunchRegion())
#endif
for (amrex::MFIter mfi = species1.MakeMFIter(lev, info); mfi.isValid(); ++mfi){
doCoulombCollisionsWithinTile( lev, mfi, species1, species2 );
}
}
}
// Define shortcuts for frequently-used type names
using ParticleType = WarpXParticleContainer::ParticleType;
using ParticleTileType = WarpXParticleContainer::ParticleTileType;
using ParticleBins = amrex::DenseBins<ParticleType>;
using index_type = ParticleBins::index_type;
using namespace ParticleUtils;
/** Perform all binary collisions within a tile
*
* @param lev AMR level of the tile
* @param mfi iterator for multifab
* @param species1/2 pointer to species container
* @param ndt user input number of time stpes between collisions
*
*/
void PairWiseCoulombCollision::doCoulombCollisionsWithinTile
( int const lev, amrex::MFIter const& mfi,
WarpXParticleContainer& species_1,
WarpXParticleContainer& species_2)
{
int const ndt = m_ndt;
amrex::Real CoulombLog = m_CoulombLog;
if ( m_isSameSpecies ) // species_1 == species_2
{
// Extract particles in the tile that `mfi` points to
ParticleTileType& ptile_1 = species_1.ParticlesAt(lev, mfi);
// Find the particles that are in each cell of this tile
ParticleBins bins_1 = findParticlesInEachCell( lev, mfi, ptile_1 );
// Loop over cells, and collide the particles in each cell
// Extract low-level data
int const n_cells = bins_1.numBins();
// - Species 1
auto& soa_1 = ptile_1.GetStructOfArrays();
amrex::ParticleReal * const AMREX_RESTRICT ux_1 =
soa_1.GetRealData(PIdx::ux).data();
amrex::ParticleReal * const AMREX_RESTRICT uy_1 =
soa_1.GetRealData(PIdx::uy).data();
amrex::ParticleReal * const AMREX_RESTRICT uz_1 =
soa_1.GetRealData(PIdx::uz).data();
amrex::ParticleReal const * const AMREX_RESTRICT w_1 =
soa_1.GetRealData(PIdx::w).data();
index_type* indices_1 = bins_1.permutationPtr();
index_type const* cell_offsets_1 = bins_1.offsetsPtr();
amrex::Real q1 = species_1.getCharge();
amrex::Real m1 = species_1.getMass();
const amrex::Real dt = WarpX::GetInstance().getdt(lev);
amrex::Geometry const& geom = WarpX::GetInstance().Geom(lev);
amrex::Box const& cbx = mfi.tilebox(amrex::IntVect::TheZeroVector()); //Cell-centered box
const auto lo = lbound(cbx);
const auto hi = ubound(cbx);
int nz = hi.y-lo.y+1;
#if defined WARPX_DIM_XZ
auto dV = geom.CellSize(0) * geom.CellSize(1);
#elif defined WARPX_DIM_RZ
auto dr = geom.CellSize(0);
auto dz = geom.CellSize(1);
#elif (AMREX_SPACEDIM == 3)
auto dV = geom.CellSize(0) * geom.CellSize(1) * geom.CellSize(2);
#endif
// Loop over cells
amrex::ParallelForRNG( n_cells,
[=] AMREX_GPU_DEVICE (int i_cell, amrex::RandomEngine const& engine) noexcept
{
// The particles from species1 that are in the cell `i_cell` are
// given by the `indices_1[cell_start_1:cell_stop_1]`
index_type const cell_start_1 = cell_offsets_1[i_cell];
index_type const cell_stop_1 = cell_offsets_1[i_cell+1];
index_type const cell_half_1 = (cell_start_1+cell_stop_1)/2;
// Do not collide if there is only one particle in the cell
if ( cell_stop_1 - cell_start_1 >= 2 )
{
// shuffle
ShuffleFisherYates(
indices_1, cell_start_1, cell_half_1, engine );
#if defined WARPX_DIM_RZ
int ri = (i_cell - i_cell%nz) / nz;
auto dV = MathConst::pi*(2.0_rt*ri+1.0_rt)*dr*dr*dz;
#else
amrex::ignore_unused(nz);
#endif
// Call the function in order to perform collisions
ElasticCollisionPerez(
cell_start_1, cell_half_1,
cell_half_1, cell_stop_1,
indices_1, indices_1,
ux_1, uy_1, uz_1, ux_1, uy_1, uz_1, w_1, w_1,
q1, q1, m1, m1, amrex::Real(-1.0), amrex::Real(-1.0),
dt*ndt, CoulombLog, dV, engine );
}
}
);
}
else // species_1 != species_2
{
// Extract particles in the tile that `mfi` points to
ParticleTileType& ptile_1 = species_1.ParticlesAt(lev, mfi);
ParticleTileType& ptile_2 = species_2.ParticlesAt(lev, mfi);
// Find the particles that are in each cell of this tile
ParticleBins bins_1 = findParticlesInEachCell( lev, mfi, ptile_1 );
ParticleBins bins_2 = findParticlesInEachCell( lev, mfi, ptile_2 );
// Loop over cells, and collide the particles in each cell
// Extract low-level data
int const n_cells = bins_1.numBins();
// - Species 1
auto& soa_1 = ptile_1.GetStructOfArrays();
amrex::ParticleReal * const AMREX_RESTRICT ux_1 =
soa_1.GetRealData(PIdx::ux).data();
amrex::ParticleReal * const AMREX_RESTRICT uy_1 =
soa_1.GetRealData(PIdx::uy).data();
amrex::ParticleReal * const AMREX_RESTRICT uz_1 =
soa_1.GetRealData(PIdx::uz).data();
amrex::ParticleReal const * const AMREX_RESTRICT w_1 =
soa_1.GetRealData(PIdx::w).data();
index_type* indices_1 = bins_1.permutationPtr();
index_type const* cell_offsets_1 = bins_1.offsetsPtr();
amrex::Real q1 = species_1.getCharge();
amrex::Real m1 = species_1.getMass();
// - Species 2
auto& soa_2 = ptile_2.GetStructOfArrays();
amrex::Real* ux_2 = soa_2.GetRealData(PIdx::ux).data();
amrex::Real* uy_2 = soa_2.GetRealData(PIdx::uy).data();
amrex::Real* uz_2 = soa_2.GetRealData(PIdx::uz).data();
amrex::Real* w_2 = soa_2.GetRealData(PIdx::w).data();
index_type* indices_2 = bins_2.permutationPtr();
index_type const* cell_offsets_2 = bins_2.offsetsPtr();
amrex::Real q2 = species_2.getCharge();
amrex::Real m2 = species_2.getMass();
const amrex::Real dt = WarpX::GetInstance().getdt(lev);
amrex::Geometry const& geom = WarpX::GetInstance().Geom(lev);
amrex::Box const& cbx = mfi.tilebox(amrex::IntVect::TheZeroVector()); //Cell-centered box
const auto lo = lbound(cbx);
const auto hi = ubound(cbx);
int nz = hi.y-lo.y+1;
#if defined WARPX_DIM_XZ
auto dV = geom.CellSize(0) * geom.CellSize(1);
#elif defined WARPX_DIM_RZ
auto dr = geom.CellSize(0);
auto dz = geom.CellSize(1);
#elif (AMREX_SPACEDIM == 3)
auto dV = geom.CellSize(0) * geom.CellSize(1) * geom.CellSize(2);
#endif
// Loop over cells
amrex::ParallelForRNG( n_cells,
[=] AMREX_GPU_DEVICE (int i_cell, amrex::RandomEngine const& engine) noexcept
{
// The particles from species1 that are in the cell `i_cell` are
// given by the `indices_1[cell_start_1:cell_stop_1]`
index_type const cell_start_1 = cell_offsets_1[i_cell];
index_type const cell_stop_1 = cell_offsets_1[i_cell+1];
// Same for species 2
index_type const cell_start_2 = cell_offsets_2[i_cell];
index_type const cell_stop_2 = cell_offsets_2[i_cell+1];
// ux from species1 can be accessed like this:
// ux_1[ indices_1[i] ], where i is between
// cell_start_1 (inclusive) and cell_start_2 (exclusive)
// Do not collide if one species is missing in the cell
if ( cell_stop_1 - cell_start_1 >= 1 &&
cell_stop_2 - cell_start_2 >= 1 )
{
// shuffle
ShuffleFisherYates(indices_1, cell_start_1, cell_stop_1, engine);
ShuffleFisherYates(indices_2, cell_start_2, cell_stop_2, engine);
#if defined WARPX_DIM_RZ
int ri = (i_cell - i_cell%nz) / nz;
auto dV = MathConst::pi*(2.0_rt*ri+1.0_rt)*dr*dr*dz;
#else
amrex::ignore_unused(nz);
#endif
// Call the function in order to perform collisions
ElasticCollisionPerez(
cell_start_1, cell_stop_1, cell_start_2, cell_stop_2,
indices_1, indices_2,
ux_1, uy_1, uz_1, ux_2, uy_2, uz_2, w_1, w_2,
q1, q2, m1, m2, amrex::Real(-1.0), amrex::Real(-1.0),
dt*ndt, CoulombLog, dV, engine );
}
}
);
} // end if ( m_isSameSpecies)
}
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