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fix_viscous.cpp
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Fri, Jul 4, 04:47

fix_viscous.cpp
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/* ----------------------------------------------------------------------
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 "math.h"
#include "stdlib.h"
#include "string.h"
#include "fix_viscous.h"
#include "atom.h"
#include "update.h"
#include "respa.h"
#include "error.h"
using namespace LAMMPS_NS;
/* ---------------------------------------------------------------------- */
FixViscous::FixViscous(LAMMPS *lmp, int narg, char **arg) :
Fix(lmp, narg, arg)
{
if (narg < 4) error->all("Illegal fix viscous command");
double gamma_one = atof(arg[3]);
gamma = new double[atom->ntypes+1];
for (int i = 1; i <= atom->ntypes; i++) gamma[i] = gamma_one;
// optional args
int iarg = 4;
while (iarg < narg) {
if (strcmp(arg[iarg],"scale") == 0) {
if (iarg+3 > narg) error->all("Illegal fix viscous command");
int itype = atoi(arg[iarg+1]);
double scale = atof(arg[iarg+2]);
if (itype <= 0 || itype > atom->ntypes)
error->all("Illegal fix viscous command");
gamma[itype] = gamma_one * scale;
iarg += 3;
} else error->all("Illegal fix viscous command");
}
}
/* ---------------------------------------------------------------------- */
FixViscous::~FixViscous()
{
delete [] gamma;
}
/* ---------------------------------------------------------------------- */
int FixViscous::setmask()
{
int mask = 0;
mask |= POST_FORCE;
mask |= POST_FORCE_RESPA;
return mask;
}
/* ---------------------------------------------------------------------- */
void FixViscous::init()
{
if (strcmp(update->integrate_style,"respa") == 0)
nlevels_respa = ((Respa *) update->integrate)->nlevels;
}
/* ---------------------------------------------------------------------- */
void FixViscous::setup()
{
if (strcmp(update->integrate_style,"verlet") == 0)
post_force(1);
else {
((Respa *) update->integrate)->copy_flevel_f(nlevels_respa-1);
post_force_respa(1,nlevels_respa-1,0);
((Respa *) update->integrate)->copy_f_flevel(nlevels_respa-1);
}
}
/* ---------------------------------------------------------------------- */
void FixViscous::post_force(int vflag)
{
// apply drag force to atoms in group
// direction is opposed to velocity vector
// magnitude depends on atom type
double **v = atom->v;
double **f = atom->f;
int *mask = atom->mask;
int *type = atom->type;
int nlocal = atom->nlocal;
double drag;
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
drag = gamma[type[i]];
f[i][0] -= drag*v[i][0];
f[i][1] -= drag*v[i][1];
f[i][2] -= drag*v[i][2];
}
}
/* ---------------------------------------------------------------------- */
void FixViscous::post_force_respa(int vflag, int ilevel, int iloop)
{
if (ilevel == nlevels_respa-1) post_force(vflag);
}

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