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fix_momentum_kokkos.cpp
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Wed, Apr 2, 15:50

fix_momentum_kokkos.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
http://lammps.sandia.gov, Sandia National Laboratories
Steve Plimpton, sjplimp@sandia.gov
Copyright (2003) Sandia Corporation. Under the terms of Contract
DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
certain rights in this software. This software is distributed under
the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
#include <stdlib.h>
#include <string.h>
#include "fix_momentum_kokkos.h"
#include "atom_kokkos.h"
#include "atom_masks.h"
#include "domain.h"
#include "domain_kokkos.h"
#include "group.h"
#include "error.h"
#include "force.h"
#include "kokkos_few.h"
using namespace LAMMPS_NS;
using namespace FixConst;
/* ----------------------------------------------------------------------
Contributing author: Dan Ibanez (SNL)
------------------------------------------------------------------------- */
/* ---------------------------------------------------------------------- */
template<class DeviceType>
FixMomentumKokkos<DeviceType>::FixMomentumKokkos(LAMMPS *lmp, int narg, char **arg) :
FixMomentum(lmp, narg, arg)
{
kokkosable = 1;
atomKK = (AtomKokkos *) atom;
execution_space = ExecutionSpaceFromDevice<DeviceType>::space;
datamask_read = EMPTY_MASK;
datamask_modify = EMPTY_MASK;
}
/* ---------------------------------------------------------------------- */
template<class DeviceType>
static double get_kinetic_energy(
AtomKokkos* atomKK,
MPI_Comm world,
int groupbit,
int nlocal,
typename ArrayTypes<DeviceType>::t_v_array_randomread v,
typename ArrayTypes<DeviceType>::t_int_1d_randomread mask)
{
using AT = ArrayTypes<DeviceType>;
auto execution_space = ExecutionSpaceFromDevice<DeviceType>::space;
double ke=0.0;
if (atomKK->rmass) {
atomKK->sync(execution_space, RMASS_MASK);
typename AT::t_float_1d_randomread rmass = atomKK->k_rmass.view<DeviceType>();
Kokkos::parallel_reduce(nlocal, LAMMPS_LAMBDA(int i, double& update) {
if (mask(i) & groupbit)
update += rmass(i) *
(v(i,0)*v(i,0) + v(i,1)*v(i,1) + v(i,2)*v(i,2));
}, ke);
} else {
// D.I. : why is there no MASS_MASK ?
atomKK->sync(execution_space, TYPE_MASK);
typename AT::t_int_1d_randomread type = atomKK->k_type.view<DeviceType>();
typename AT::t_float_1d_randomread mass = atomKK->k_mass.view<DeviceType>();
Kokkos::parallel_reduce(nlocal, LAMMPS_LAMBDA(int i, double& update) {
if (mask(i) & groupbit)
update += mass(type(i)) *
(v(i,0)*v(i,0) + v(i,1)*v(i,1) + v(i,2)*v(i,2));
}, ke);
}
double ke_total;
MPI_Allreduce(&ke,&ke_total,1,MPI_DOUBLE,MPI_SUM,world);
return ke_total;
}
template<class DeviceType>
void FixMomentumKokkos<DeviceType>::end_of_step()
{
atomKK->sync(execution_space, V_MASK | MASK_MASK);
typename AT::t_v_array v = atomKK->k_v.view<DeviceType>();
typename AT::t_int_1d_randomread mask = atomKK->k_mask.view<DeviceType>();
const int nlocal = atom->nlocal;
double ekin_old,ekin_new;
ekin_old = ekin_new = 0.0;
if (dynamic)
masstotal = group->mass(igroup); // change once Group is ported to Kokkos
// do nothing if group is empty, i.e. mass is zero;
if (masstotal == 0.0) return;
// compute kinetic energy before momentum removal, if needed
if (rescale) {
ekin_old = get_kinetic_energy<DeviceType>(atomKK, world, groupbit, nlocal, v, mask);
}
auto groupbit2 = groupbit;
if (linear) {
/* this is needed because Group is not Kokkos-aware ! */
atomKK->sync(ExecutionSpaceFromDevice<LMPHostType>::space,
V_MASK | MASK_MASK | TYPE_MASK | RMASS_MASK);
Few<double, 3> vcm;
group->vcm(igroup,masstotal,&vcm[0]);
// adjust velocities by vcm to zero linear momentum
// only adjust a component if flag is set
auto xflag2 = xflag;
auto yflag2 = yflag;
auto zflag2 = zflag;
Kokkos::parallel_for(nlocal, LAMMPS_LAMBDA(int i) {
if (mask(i) & groupbit2) {
if (xflag2) v(i,0) -= vcm[0];
if (yflag2) v(i,1) -= vcm[1];
if (zflag2) v(i,2) -= vcm[2];
}
});
atomKK->modified(execution_space, V_MASK);
}
if (angular) {
Few<double, 3> xcm, angmom, omega;
double inertia[3][3];
/* syncs for each Kokkos-unaware Group method */
atomKK->sync(ExecutionSpaceFromDevice<LMPHostType>::space,
X_MASK | MASK_MASK | TYPE_MASK | IMAGE_MASK | RMASS_MASK);
group->xcm(igroup,masstotal,&xcm[0]);
atomKK->sync(ExecutionSpaceFromDevice<LMPHostType>::space,
X_MASK | V_MASK | MASK_MASK | TYPE_MASK | IMAGE_MASK | RMASS_MASK);
group->angmom(igroup,&xcm[0],&angmom[0]);
atomKK->sync(ExecutionSpaceFromDevice<LMPHostType>::space,
X_MASK | MASK_MASK | TYPE_MASK | IMAGE_MASK | RMASS_MASK);
group->inertia(igroup,&xcm[0],inertia);
group->omega(&angmom[0],inertia,&omega[0]);
// adjust velocities to zero omega
// vnew_i = v_i - w x r_i
// must use unwrapped coords to compute r_i correctly
atomKK->sync(execution_space, X_MASK | IMAGE_MASK);
typename AT::t_x_array_randomread x = atomKK->k_x.view<DeviceType>();
typename AT::t_imageint_1d_randomread image = atomKK->k_image.view<DeviceType>();
int nlocal = atom->nlocal;
auto prd = Few<double,3>(domain->prd);
auto h = Few<double,6>(domain->h);
auto triclinic = domain->triclinic;
Kokkos::parallel_for(nlocal, LAMMPS_LAMBDA(int i) {
if (mask[i] & groupbit2) {
Few<double,3> x_i;
x_i[0] = x(i,0);
x_i[1] = x(i,1);
x_i[2] = x(i,2);
auto unwrap = DomainKokkos::unmap(prd,h,triclinic,x_i,image(i));
auto dx = unwrap[0] - xcm[0];
auto dy = unwrap[1] - xcm[1];
auto dz = unwrap[2] - xcm[2];
v(i,0) -= omega[1]*dz - omega[2]*dy;
v(i,1) -= omega[2]*dx - omega[0]*dz;
v(i,2) -= omega[0]*dy - omega[1]*dx;
}
});
atomKK->modified(execution_space, V_MASK);
}
// compute kinetic energy after momentum removal, if needed
if (rescale) {
ekin_new = get_kinetic_energy<DeviceType>(atomKK, world, groupbit, nlocal, v, mask);
double factor = 1.0;
if (ekin_new != 0.0) factor = sqrt(ekin_old/ekin_new);
Kokkos::parallel_for(nlocal, LAMMPS_LAMBDA(int i) {
if (mask(i) & groupbit2) {
v(i,0) *= factor;
v(i,1) *= factor;
v(i,2) *= factor;
}
});
atomKK->modified(execution_space, V_MASK);
}
}
namespace LAMMPS_NS {
template class FixMomentumKokkos<LMPDeviceType>;
#ifdef KOKKOS_HAVE_CUDA
template class FixMomentumKokkos<LMPHostType>;
#endif
}

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