/* ----------------------------------------------------------------------
   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_erotate_sphere_atom.h"
#include "atom.h"
#include "update.h"
#include "modify.h"
#include "comm.h"
#include "force.h"
#include "memory.h"
#include "error.h"

using namespace LAMMPS_NS;

#define INERTIA 0.4          // moment of inertia prefactor for sphere

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

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

  peratom_flag = 1;
  size_peratom_cols = 0;

  // error check

  if (!atom->sphere_flag)
    error->all(FLERR,"Compute erotate/sphere/atom requires atom style sphere");

  nmax = 0;
  erot = NULL;
}

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

ComputeErotateSphereAtom::~ComputeErotateSphereAtom()
{
  memory->destroy(erot);
}

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

void ComputeErotateSphereAtom::init()
{
  int count = 0;
  for (int i = 0; i < modify->ncompute; i++)
    if (strcmp(modify->compute[i]->style,"erotate/sphere/atom") == 0) count++;
  if (count > 1 && comm->me == 0)
    error->warning(FLERR,"More than one compute erotate/sphere/atom");

  pfactor = 0.5 * force->mvv2e * INERTIA;
}

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

void ComputeErotateSphereAtom::compute_peratom()
{
  invoked_peratom = update->ntimestep;

  // grow erot array if necessary

  if (atom->nlocal > nmax) {
    memory->destroy(erot);
    nmax = atom->nmax;
    memory->create(erot,nmax,"erotate/sphere/atom:erot");
    vector_atom = erot;
  }

  // compute rotational kinetic energy for each atom in group
  // point particles will have erot = 0.0, due to radius = 0.0

  double **omega = atom->omega;
  double *radius = atom->radius;
  double *rmass = atom->rmass;
  int *mask = atom->mask;
  int nlocal = atom->nlocal;

  for (int i = 0; i < nlocal; i++) {
    if (mask[i] & groupbit) {
      erot[i] = (omega[i][0]*omega[i][0] + omega[i][1]*omega[i][1] +
                 omega[i][2]*omega[i][2]) * radius[i]*radius[i]*rmass[i];
      erot[i] *= pfactor;
    } else erot[i] = 0.0;
  }
}

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

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