lammps/src/compute_force_tally.cpp

/* ----------------------------------------------------------------------
   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_force_tally.h"
#include "atom.h"
#include "group.h"
#include "pair.h"
#include "update.h"
#include "memory.h"
#include "error.h"
#include "force.h"

using namespace LAMMPS_NS;

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

ComputeForceTally::ComputeForceTally(LAMMPS *lmp, int narg, char **arg) :
  Compute(lmp, narg, arg)
{
  if (narg < 4) error->all(FLERR,"Illegal compute force/tally command");

  igroup2 = group->find(arg[3]);
  if (igroup2 == -1)
    error->all(FLERR,"Could not find compute force/tally second group ID");
  groupbit2 = group->bitmask[igroup2];

  scalar_flag = 1;
  vector_flag = 0;
  peratom_flag = 1;
  timeflag = 1;

  comm_reverse = size_peratom_cols = 3;
  extscalar = 1;
  peflag = 1;                   // we need Pair::ev_tally() to be run

  nmax = -1;
  fatom = NULL;
  vector = new double[size_peratom_cols];
}

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

ComputeForceTally::~ComputeForceTally()
{
  if (force->pair) force->pair->del_tally_callback(this);
  delete[] vector;
}

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

void ComputeForceTally::init()
{
  if (force->pair == NULL)
    error->all(FLERR,"Trying to use compute force/tally with no pair style");
  else
    force->pair->add_tally_callback(this);

  did_compute = -1;
}


/* ---------------------------------------------------------------------- */
void ComputeForceTally::pair_tally_callback(int i, int j, int nlocal, int newton,
                                            double, double, double fpair,
                                            double dx, double dy, double dz)
{
  const int ntotal = atom->nlocal + atom->nghost;
  const int * const mask = atom->mask;

  // do setup work that needs to be done only once per timestep

  if (did_compute != update->ntimestep) {
    did_compute = update->ntimestep;
    
    // grow local force array if necessary
    // needs to be atom->nmax in length

    if (atom->nmax > nmax) {
      memory->destroy(fatom);
      nmax = atom->nmax;
      memory->create(fatom,nmax,size_peratom_cols,"force/tally:fatom");
      array_atom = fatom;
    }

    // clear storage as needed

    if (newton) {
      for (int i=0; i < ntotal; ++i)
        for (int j=0; j < size_peratom_cols; ++j)
          fatom[i][j] = 0.0;
    } else {
      for (int i=0; i < atom->nlocal; ++i)
        for (int j=0; j < size_peratom_cols; ++j)
          fatom[i][j] = 0.0;
    }

    for (int i=0; i < size_peratom_cols; ++i)
      vector[i] = ftotal[i] = 0.0;
  }

  if ( ((mask[i] & groupbit) && (mask[j] & groupbit2))
       || ((mask[i] & groupbit2) && (mask[j] & groupbit)) ) {

    if (newton || i < nlocal) {
      ftotal[0] += fpair*dx; fatom[i][0] += fpair*dx;
      ftotal[1] += fpair*dy; fatom[i][1] += fpair*dy;
      ftotal[2] += fpair*dz; fatom[i][2] += fpair*dz;
    }
    if (newton || j < nlocal) {
      ftotal[0] -= fpair*dx; fatom[i][0] -= fpair*dx;
      ftotal[1] -= fpair*dy; fatom[i][1] -= fpair*dy;
      ftotal[2] -= fpair*dz; fatom[i][2] -= fpair*dz;
    }
  }
}

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

int ComputeForceTally::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++] = fatom[i][0];
    buf[m++] = fatom[i][1];
    buf[m++] = fatom[i][2];
  }
  return m;
}

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

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

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

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

double ComputeForceTally::compute_scalar()
{
  invoked_scalar = update->ntimestep;
  if (update->eflag_global != invoked_scalar)
    error->all(FLERR,"Energy was not tallied on needed timestep");

  // sum accumulated forces across procs

  MPI_Allreduce(ftotal,vector,size_peratom_cols,MPI_DOUBLE,MPI_SUM,world);

  scalar = sqrt(vector[0]*vector[0]+vector[1]*vector[1]+vector[2]*vector[2]);
  return scalar;
}

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

void ComputeForceTally::compute_peratom()
{
  invoked_peratom = update->ntimestep;
  if (update->eflag_global != invoked_peratom)
    error->all(FLERR,"Energy was not tallied on needed timestep");

  // collect contributions from ghost atoms

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

    const int nall = atom->nlocal + atom->nghost;
    for (int i = atom->nlocal; i < nall; ++i)
      for (int j = 0; j < size_peratom_cols; ++j)
        fatom[i][j] = 0.0;
  }
}

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

double ComputeForceTally::memory_usage()
{
  double bytes = nmax*size_peratom_cols * sizeof(double);
  return bytes;
}