/* ----------------------------------------------------------------------
   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_tersoff_omp.h"
#include "atom.h"
#include "comm.h"
#include "force.h"
#include "neighbor.h"
#include "neigh_list.h"

using namespace LAMMPS_NS;

/* ---------------------------------------------------------------------- */

PairTersoffOMP::PairTersoffOMP(LAMMPS *lmp) :
  PairTersoff(lmp), ThrOMP(lmp, PAIR)
{
  respa_enable = 0;
}

/* ---------------------------------------------------------------------- */

void PairTersoffOMP::compute(int eflag, int vflag)
{
  if (eflag || vflag) {
    ev_setup(eflag,vflag);
    ev_setup_thr(this);
  } else evflag = vflag_fdotr = vflag_atom = 0;

  const int nall = atom->nlocal + atom->nghost;
  const int nthreads = comm->nthreads;
  const int inum = list->inum;

#if defined(_OPENMP)
#pragma omp parallel default(shared)
#endif
  {
    int ifrom, ito, tid;
    double **f;

    f = loop_setup_thr(atom->f, ifrom, ito, tid, inum, nall, nthreads);

    if (evflag) {
      if (eflag) {
	if (vflag_atom) eval<1,1,1>(f, ifrom, ito, tid);
	else eval<1,1,0>(f, ifrom, ito, tid);
      } else {
	if (vflag_atom) eval<1,0,1>(f, ifrom, ito, tid);
	else eval<1,0,0>(f, ifrom, ito, tid);
      }
    } else eval<0,0,0>(f, ifrom, ito, tid);

    // reduce per thread forces into global force array.
    data_reduce_thr(&(atom->f[0][0]), nall, nthreads, 3, tid);
  } // end of omp parallel region

  // reduce per thread energy and virial, if requested.
  if (evflag) ev_reduce_thr(this);
  if (vflag_fdotr) virial_fdotr_compute();
}

template <int EVFLAG, int EFLAG, int VFLAG_ATOM>
void PairTersoffOMP::eval(double **f, int iifrom, int iito, int tid)
{
  int i,j,k,ii,jj,kk,jnum;
  int itag,jtag,itype,jtype,ktype,iparam_ij,iparam_ijk;
  double xtmp,ytmp,ztmp,delx,dely,delz,evdwl,fpair;
  double rsq,rsq1,rsq2;
  double delr1[3],delr2[3],fi[3],fj[3],fk[3];
  double zeta_ij,prefactor;
  int *ilist,*jlist,*numneigh,**firstneigh;

  evdwl = 0.0;

  double **x = atom->x;
  int *tag = atom->tag;
  int *type = atom->type;
  int nlocal = atom->nlocal;

  ilist = list->ilist;
  numneigh = list->numneigh;
  firstneigh = list->firstneigh;

  double fxtmp,fytmp,fztmp;

  // loop over full neighbor list of my atoms

  for (ii = iifrom; ii < iito; ++ii) {

    i = ilist[ii];
    itag = tag[i];
    itype = map[type[i]];
    xtmp = x[i][0];
    ytmp = x[i][1];
    ztmp = x[i][2];
    fxtmp = fytmp = fztmp = 0.0;

    // two-body interactions, skip half of them

    jlist = firstneigh[i];
    jnum = numneigh[i];

    for (jj = 0; jj < jnum; jj++) {
      j = jlist[jj];
      j &= NEIGHMASK;
      jtag = tag[j];

      if (itag > jtag) {
	if ((itag+jtag) % 2 == 0) continue;
      } else if (itag < jtag) {
	if ((itag+jtag) % 2 == 1) continue;
      } else {
	if (x[j][2] < ztmp) continue;
	if (x[j][2] == ztmp && x[j][1] < ytmp) continue;
	if (x[j][2] == ztmp && x[j][1] == ytmp && x[j][0] < xtmp) continue;
      }

      jtype = map[type[j]];

      delx = xtmp - x[j][0];
      dely = ytmp - x[j][1];
      delz = ztmp - x[j][2];
      rsq = delx*delx + dely*dely + delz*delz;

      iparam_ij = elem2param[itype][jtype][jtype];
      if (rsq > params[iparam_ij].cutsq) continue;

      repulsive(&params[iparam_ij],rsq,fpair,EFLAG,evdwl);

      fxtmp += delx*fpair;
      fytmp += dely*fpair;
      fztmp += delz*fpair;
      f[j][0] -= delx*fpair;
      f[j][1] -= dely*fpair;
      f[j][2] -= delz*fpair;

      if (EVFLAG) ev_tally_thr(this,i,j,nlocal,/* newton_pair */ 1,
			       evdwl,0.0,fpair,delx,dely,delz,tid);
    }

    // three-body interactions
    // skip immediately if I-J is not within cutoff
    double fjxtmp,fjytmp,fjztmp;

    for (jj = 0; jj < jnum; jj++) {
      j = jlist[jj];
      j &= NEIGHMASK;
      jtype = map[type[j]];
      iparam_ij = elem2param[itype][jtype][jtype];

      delr1[0] = x[j][0] - xtmp;
      delr1[1] = x[j][1] - ytmp;
      delr1[2] = x[j][2] - ztmp;
      rsq1 = delr1[0]*delr1[0] + delr1[1]*delr1[1] + delr1[2]*delr1[2];
      if (rsq1 > params[iparam_ij].cutsq) continue;

      // accumulate bondorder zeta for each i-j interaction via loop over k

      fjxtmp = fjytmp = fjztmp = 0.0;
      zeta_ij = 0.0;

      for (kk = 0; kk < jnum; kk++) {
	if (jj == kk) continue;
	k = jlist[kk];
	k &= NEIGHMASK;
	ktype = map[type[k]];
	iparam_ijk = elem2param[itype][jtype][ktype];

	delr2[0] = x[k][0] - xtmp;
	delr2[1] = x[k][1] - ytmp;
	delr2[2] = x[k][2] - ztmp;
	rsq2 = delr2[0]*delr2[0] + delr2[1]*delr2[1] + delr2[2]*delr2[2];
	if (rsq2 > params[iparam_ijk].cutsq) continue;

	zeta_ij += zeta(&params[iparam_ijk],rsq1,rsq2,delr1,delr2);
      }

      // pairwise force due to zeta

      force_zeta(&params[iparam_ij],rsq1,zeta_ij,fpair,prefactor,EFLAG,evdwl);

      fxtmp += delr1[0]*fpair;
      fytmp += delr1[1]*fpair;
      fztmp += delr1[2]*fpair;
      fjxtmp -= delr1[0]*fpair;
      fjytmp -= delr1[1]*fpair;
      fjztmp -= delr1[2]*fpair;

      if (EVFLAG) ev_tally_thr(this,i,j,nlocal,/* newton_pair */ 1,evdwl,0.0,
			       -fpair,-delr1[0],-delr1[1],-delr1[2],tid);

      // attractive term via loop over k

      for (kk = 0; kk < jnum; kk++) {
	if (jj == kk) continue;
	k = jlist[kk];
	k &= NEIGHMASK;
	ktype = map[type[k]];
	iparam_ijk = elem2param[itype][jtype][ktype];

	delr2[0] = x[k][0] - xtmp;
	delr2[1] = x[k][1] - ytmp;
	delr2[2] = x[k][2] - ztmp;
	rsq2 = delr2[0]*delr2[0] + delr2[1]*delr2[1] + delr2[2]*delr2[2];
	if (rsq2 > params[iparam_ijk].cutsq) continue;

	attractive(&params[iparam_ijk],prefactor,
		   rsq1,rsq2,delr1,delr2,fi,fj,fk);

	fxtmp += fi[0];
	fytmp += fi[1];
	fztmp += fi[2];
	fjxtmp += fj[0];
	fjytmp += fj[1];
	fjztmp += fj[2];
	f[k][0] += fk[0];
	f[k][1] += fk[1];
	f[k][2] += fk[2];

	if (VFLAG_ATOM) v_tally3_thr(i,j,k,fj,fk,delr1,delr2,tid);
      }
      f[j][0] += fjxtmp;
      f[j][1] += fjytmp;
      f[j][2] += fjztmp;
    }
    f[i][0] += fxtmp;
    f[i][1] += fytmp;
    f[i][2] += fztmp;
  }
}

/* ---------------------------------------------------------------------- */

double PairTersoffOMP::memory_usage()
{
  double bytes = memory_usage_thr();
  bytes += PairTersoff::memory_usage();

  return bytes;
}