/* ----------------------------------------------------------------------
   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 "mpi.h"
#include "string.h"
#include "compute_pair.h"
#include "update.h"
#include "force.h"
#include "pair.h"
#include "error.h"

using namespace LAMMPS_NS;

enum{EPAIR,EVDWL,ECOUL};

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

ComputePair::ComputePair(LAMMPS *lmp, int narg, char **arg) : 
  Compute(lmp, narg, arg)
{
  if (narg < 4 || narg > 5) error->all("Illegal compute pair command");
  if (igroup) error->all("Compute pair must use group all");

  scalar_flag = 1;
  extscalar = 1;
  peflag = 1;
  timeflag = 1;

  int n = strlen(arg[3]) + 1;
  pstyle = new char[n];
  strcpy(pstyle,arg[3]);

  if (narg == 5) {
    if (strcmp(arg[4],"epair") == 0) evalue = EPAIR;
    if (strcmp(arg[4],"evdwl") == 0) evalue = EVDWL;
    if (strcmp(arg[4],"ecoul") == 0) evalue = ECOUL;
  } else evalue = EPAIR;

  pair = force->pair_match(pstyle,1);
  if (!pair) error->all("Unrecognized pair style in compute pair command");
  npair = pair->nextra;

  if (npair) {
    vector_flag = 1;
    size_vector = npair;
    extvector = 1;
    one = new double[npair];
    vector = new double[npair];
  } else one = vector = NULL;
}

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

ComputePair::~ComputePair()
{
  delete [] pstyle;
  delete [] one;
  delete [] vector;
}

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

void ComputePair::init()
{
  // recheck for pair style in case it has been deleted

  pair = force->pair_match(pstyle,1);
  if (!pair) error->all("Unrecognized pair style in compute pair command");
}

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

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

  double eng;
  if (evalue == EPAIR) eng = pair->eng_vdwl + pair->eng_coul;
  else if (evalue == EVDWL) eng = pair->eng_vdwl;
  else if (evalue == ECOUL) eng = pair->eng_coul;

  MPI_Allreduce(&eng,&scalar,1,MPI_DOUBLE,MPI_SUM,world);
  return scalar;
}

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

void ComputePair::compute_vector()
{
  invoked_vector = update->ntimestep;
  if (update->eflag_global != invoked_vector)
    error->all("Energy was not tallied on needed timestep");

  for (int i = 0; i < npair; i++)
    one[i] = pair->pvector[i];
  MPI_Allreduce(one,vector,npair,MPI_DOUBLE,MPI_SUM,world);
}
