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pair_dpd_omp.cpp
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Tue, Jul 30, 10:24

pair_dpd_omp.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
This software is distributed under the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
Contributing author: Axel Kohlmeyer (Temple U)
------------------------------------------------------------------------- */
#include <math.h>
#include "pair_dpd_omp.h"
#include "atom.h"
#include "comm.h"
#include "force.h"
#include "neighbor.h"
#include "neigh_list.h"
#include "update.h"
#include "random_mars.h"
#include "suffix.h"
using namespace LAMMPS_NS;
#define EPSILON 1.0e-10
/* ---------------------------------------------------------------------- */
PairDPDOMP::PairDPDOMP(LAMMPS *lmp) :
PairDPD(lmp), ThrOMP(lmp, THR_PAIR)
{
suffix_flag |= Suffix::OMP;
respa_enable = 0;
random_thr = NULL;
nthreads = 0;
}
/* ---------------------------------------------------------------------- */
PairDPDOMP::~PairDPDOMP()
{
if (random_thr) {
for (int i=1; i < nthreads; ++i)
delete random_thr[i];
delete[] random_thr;
random_thr = NULL;
}
}
/* ---------------------------------------------------------------------- */
void PairDPDOMP::compute(int eflag, int vflag)
{
if (eflag || vflag) {
ev_setup(eflag,vflag);
} else evflag = vflag_fdotr = 0;
const int nall = atom->nlocal + atom->nghost;
const int inum = list->inum;
// number of threads has changed. reallocate pool of pRNGs
if (nthreads != comm->nthreads) {
if (random_thr) {
for (int i=1; i < nthreads; ++i)
delete random_thr[i];
delete[] random_thr;
}
nthreads = comm->nthreads;
random_thr = new RanMars*[nthreads];
for (int i=1; i < nthreads; ++i)
random_thr[i] = NULL;
// to ensure full compatibility with the serial DPD style
// we use the serial random number generator instance for thread 0
random_thr[0] = random;
}
#if defined(_OPENMP)
#pragma omp parallel default(none) shared(eflag,vflag)
#endif
{
int ifrom, ito, tid;
loop_setup_thr(ifrom, ito, tid, inum, nthreads);
ThrData *thr = fix->get_thr(tid);
thr->timer(Timer::START);
ev_setup_thr(eflag, vflag, nall, eatom, vatom, thr);
// generate a random number generator instance for
// all threads != 0. make sure we use unique seeds.
if ((tid > 0) && (random_thr[tid] == NULL))
random_thr[tid] = new RanMars(Pair::lmp, seed + comm->me
+ comm->nprocs*tid);
if (evflag) {
if (eflag) {
if (force->newton_pair) eval<1,1,1>(ifrom, ito, thr);
else eval<1,1,0>(ifrom, ito, thr);
} else {
if (force->newton_pair) eval<1,0,1>(ifrom, ito, thr);
else eval<1,0,0>(ifrom, ito, thr);
}
} else {
if (force->newton_pair) eval<0,0,1>(ifrom, ito, thr);
else eval<0,0,0>(ifrom, ito, thr);
}
thr->timer(Timer::PAIR);
reduce_thr(this, eflag, vflag, thr);
} // end of omp parallel region
}
template <int EVFLAG, int EFLAG, int NEWTON_PAIR>
void PairDPDOMP::eval(int iifrom, int iito, ThrData * const thr)
{
int i,j,ii,jj,jnum,itype,jtype;
double xtmp,ytmp,ztmp,delx,dely,delz,evdwl,fpair;
double vxtmp,vytmp,vztmp,delvx,delvy,delvz;
double rsq,r,rinv,dot,wd,randnum,factor_dpd;
int *ilist,*jlist,*numneigh,**firstneigh;
evdwl = 0.0;
const dbl3_t * _noalias const x = (dbl3_t *) atom->x[0];
const dbl3_t * _noalias const v = (dbl3_t *) atom->v[0];
dbl3_t * _noalias const f = (dbl3_t *) thr->get_f()[0];
const int * _noalias const type = atom->type;
const int nlocal = atom->nlocal;
const double *special_lj = force->special_lj;
const double dtinvsqrt = 1.0/sqrt(update->dt);
double fxtmp,fytmp,fztmp;
RanMars &rng = *random_thr[thr->get_tid()];
ilist = list->ilist;
numneigh = list->numneigh;
firstneigh = list->firstneigh;
// loop over neighbors of my atoms
for (ii = iifrom; ii < iito; ++ii) {
i = ilist[ii];
xtmp = x[i].x;
ytmp = x[i].y;
ztmp = x[i].z;
vxtmp = v[i].x;
vytmp = v[i].y;
vztmp = v[i].z;
itype = type[i];
jlist = firstneigh[i];
jnum = numneigh[i];
fxtmp=fytmp=fztmp=0.0;
for (jj = 0; jj < jnum; jj++) {
j = jlist[jj];
factor_dpd = special_lj[sbmask(j)];
j &= NEIGHMASK;
delx = xtmp - x[j].x;
dely = ytmp - x[j].y;
delz = ztmp - x[j].z;
rsq = delx*delx + dely*dely + delz*delz;
jtype = type[j];
if (rsq < cutsq[itype][jtype]) {
r = sqrt(rsq);
if (r < EPSILON) continue; // r can be 0.0 in DPD systems
rinv = 1.0/r;
delvx = vxtmp - v[j].x;
delvy = vytmp - v[j].y;
delvz = vztmp - v[j].z;
dot = delx*delvx + dely*delvy + delz*delvz;
wd = 1.0 - r/cut[itype][jtype];
randnum = rng.gaussian();
// conservative force = a0 * wd
// drag force = -gamma * wd^2 * (delx dot delv) / r
// random force = sigma * wd * rnd * dtinvsqrt;
fpair = a0[itype][jtype]*wd;
fpair -= gamma[itype][jtype]*wd*wd*dot*rinv;
fpair += sigma[itype][jtype]*wd*randnum*dtinvsqrt;
fpair *= factor_dpd*rinv;
fxtmp += delx*fpair;
fytmp += dely*fpair;
fztmp += delz*fpair;
if (NEWTON_PAIR || j < nlocal) {
f[j].x -= delx*fpair;
f[j].y -= dely*fpair;
f[j].z -= delz*fpair;
}
if (EFLAG) {
// unshifted eng of conservative term:
// evdwl = -a0[itype][jtype]*r * (1.0-0.5*r/cut[itype][jtype]);
// eng shifted to 0.0 at cutoff
evdwl = 0.5*a0[itype][jtype]*cut[itype][jtype] * wd*wd;
evdwl *= factor_dpd;
}
if (EVFLAG) ev_tally_thr(this, i,j,nlocal,NEWTON_PAIR,
evdwl,0.0,fpair,delx,dely,delz,thr);
}
}
f[i].x += fxtmp;
f[i].y += fytmp;
f[i].z += fztmp;
}
}
/* ---------------------------------------------------------------------- */
double PairDPDOMP::memory_usage()
{
double bytes = memory_usage_thr();
bytes += PairDPD::memory_usage();
bytes += comm->nthreads * sizeof(RanMars*);
bytes += comm->nthreads * sizeof(RanMars);
return bytes;
}

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