/* ----------------------------------------------------------------------
   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 "string.h"
#include "compute_stress_atom.h"
#include "atom.h"
#include "neighbor.h"
#include "modify.h"
#include "comm.h"
#include "update.h"
#include "force.h"
#include "pair.h"
#include "memory.h"
#include "error.h"

using namespace LAMMPS_NS;

#define MIN(a,b) ((a) < (b) ? (a) : (b))
#define MAX(a,b) ((a) > (b) ? (a) : (b))

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

ComputeStressAtom::ComputeStressAtom(LAMMPS *lmp, int narg, char **arg) :
  Compute(lmp, narg, arg)
{
  if (narg != 3) error->all("Illegal compute stress/atom command");

  peratom_flag = 1;
  size_peratom = 6;
  comm_reverse = 6;
  neigh_half_once = 1;

  nmax = 0;
  stress = NULL;
}

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

ComputeStressAtom::~ComputeStressAtom()
{
  memory->destroy_2d_double_array(stress);
}

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

void ComputeStressAtom::init()
{
  if (force->pair == NULL || force->pair->single_enable == 0)
    error->all("Pair style does not support computing per-atom stress");

  int count = 0;
  for (int i = 0; i < modify->ncompute; i++)
    if (strcmp(modify->compute[i]->style,"stress/atom") == 0) count++;
  if (count > 1 && comm->me == 0)
    error->warning("More than one compute stress/atom defined");
}

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

void ComputeStressAtom::compute_peratom()
{
  int i,j,k,n,itype,jtype,numneigh;
  double xtmp,ytmp,ztmp,delx,dely,delz,rsq;
  double factor_coul,factor_lj,fforce,rmass;
  int *neighs;
  Pair::One one;

  // grow stress array if necessary

  if (atom->nmax > nmax) {
    memory->destroy_2d_double_array(stress);
    nmax = atom->nmax;
    stress =
      memory->create_2d_double_array(nmax,6,"compute/stress/atom:stress");
    vector_atom = stress;
  }

  // clear stress array
  // n includes ghosts only if newton_pair flag is set

  if (force->newton_pair) n = atom->nlocal + atom->nghost;
  else n = atom->nlocal;

  for (i = 0; i < n; i++) {
    stress[i][0] = 0.0;
    stress[i][1] = 0.0;
    stress[i][2] = 0.0;
    stress[i][3] = 0.0;
    stress[i][4] = 0.0;
    stress[i][5] = 0.0;
  }

  // if needed, build a half neighbor list

  if (!neighbor->half_every) neighbor->build_half();

  // compute pairwise stress for all atoms via pair->single()
  // use half neighbor list

  double *special_coul = force->special_coul;
  double *special_lj = force->special_lj;
  double **cutsq = force->pair->cutsq;

  double **x = atom->x;
  int *type = atom->type;
  int nlocal = atom->nlocal;
  int nall = atom->nlocal + atom->nghost;

  for (i = 0; i < nlocal; i++) {
    xtmp = x[i][0];
    ytmp = x[i][1];
    ztmp = x[i][2];
    itype = type[i];
    neighs = neighbor->firstneigh[i];
    numneigh = neighbor->numneigh[i];
    
    for (k = 0; k < numneigh; k++) {
      j = neighs[k];

      if (j < nall) factor_coul = factor_lj = 1.0;
      else {
	factor_coul = special_coul[j/nall];
	factor_lj = special_lj[j/nall];
	j %= nall;
      }

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

      if (rsq < cutsq[itype][jtype]) {
	force->pair->single(i,j,itype,jtype,rsq,factor_coul,factor_lj,0,one);
	fforce = one.fforce;

	stress[i][0] -= delx*delx*fforce;
	stress[i][1] -= dely*dely*fforce;
	stress[i][2] -= delz*delz*fforce;
	stress[i][3] -= delx*dely*fforce;
	stress[i][4] -= delx*delz*fforce;
	stress[i][5] -= dely*delz*fforce;
	if (force->newton_pair || j < nlocal) {
	  stress[j][0] -= delx*delx*fforce;
	  stress[j][1] -= dely*dely*fforce;
	  stress[j][2] -= delz*delz*fforce;
	  stress[j][3] -= delx*dely*fforce;
	  stress[j][4] -= delx*delz*fforce;
	  stress[j][5] -= dely*delz*fforce;
	}
      }
    }
  }

  // communicate stress between neighbor procs

  if (force->newton_pair) comm->reverse_comm_compute(this);

  // remove double counting of per-atom stress

  for (i = 0; i < nlocal; i++) {
    stress[i][0] *= 0.5;
    stress[i][1] *= 0.5;
    stress[i][2] *= 0.5;
    stress[i][3] *= 0.5;
    stress[i][4] *= 0.5;
    stress[i][5] *= 0.5;
  }

  // include kinetic energy term for each atom
  // mvv2e converts mv^2 to energy

  double **v = atom->v;
  double *mass = atom->mass;
  double mvv2e = force->mvv2e;

  for (i = 0; i < nlocal; i++) {
    rmass = mvv2e * mass[type[i]];
    stress[i][0] -= rmass*v[i][0]*v[i][0];
    stress[i][1] -= rmass*v[i][1]*v[i][1];
    stress[i][2] -= rmass*v[i][2]*v[i][2];
    stress[i][3] -= rmass*v[i][0]*v[i][1];
    stress[i][4] -= rmass*v[i][0]*v[i][2];
    stress[i][5] -= rmass*v[i][1]*v[i][2];
  }

  // convert to pressure units (actually stress/volume = pressure)

  double nktv2p = force->nktv2p;
  for (i = 0; i < nlocal; i++) {
    stress[i][0] *= nktv2p;
    stress[i][1] *= nktv2p;
    stress[i][2] *= nktv2p;
    stress[i][3] *= nktv2p;
    stress[i][4] *= nktv2p;
    stress[i][5] *= nktv2p;
  }
}

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

int ComputeStressAtom::pack_reverse_comm(int n, int first, double *buf)
{
  int i,m,last;

  m = 0;
  last = first + n;
  for (i = first; i < last; i++) {
    buf[m++] = stress[i][0];
    buf[m++] = stress[i][1];
    buf[m++] = stress[i][2];
    buf[m++] = stress[i][3];
    buf[m++] = stress[i][4];
    buf[m++] = stress[i][5];
  }
  return 6;
}

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

void ComputeStressAtom::unpack_reverse_comm(int n, int *list, double *buf)
{
  int i,j,m;

  m = 0;
  for (i = 0; i < n; i++) {
    j = list[i];
    stress[j][0] += buf[m++];
    stress[j][1] += buf[m++];
    stress[j][2] += buf[m++];
    stress[j][3] += buf[m++];
    stress[j][4] += buf[m++];
    stress[j][5] += buf[m++];
  }
}

/* ----------------------------------------------------------------------
   memory usage of local atom-based array
------------------------------------------------------------------------- */

int ComputeStressAtom::memory_usage()
{
  int bytes = nmax*6 * sizeof(double);
  return bytes;
}