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fix_nve_line.cpp
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Tue, Jun 11, 21:54

fix_nve_line.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 <stdio.h>
#include <string.h>
#include "fix_nve_line.h"
#include "atom.h"
#include "atom_vec_line.h"
#include "domain.h"
#include "math_const.h"
#include "error.h"
using namespace LAMMPS_NS;
using namespace FixConst;
using namespace MathConst;
#define INERTIA (1.0/12.0) // moment of inertia prefactor for line segment
/* ---------------------------------------------------------------------- */
FixNVELine::FixNVELine(LAMMPS *lmp, int narg, char **arg) :
FixNVE(lmp, narg, arg)
{
if (narg != 3) error->all(FLERR,"Illegal fix nve/line command");
time_integrate = 1;
MINUSPI = -MY_PI;
TWOPI = 2.0*MY_PI;
}
/* ---------------------------------------------------------------------- */
int FixNVELine::setmask()
{
int mask = 0;
mask |= INITIAL_INTEGRATE;
mask |= FINAL_INTEGRATE;
mask |= INITIAL_INTEGRATE_RESPA;
mask |= FINAL_INTEGRATE_RESPA;
return mask;
}
/* ---------------------------------------------------------------------- */
void FixNVELine::init()
{
// error checks
avec = (AtomVecLine *) atom->style_match("line");
if (!avec) error->all(FLERR,"Fix nve/line requires atom style line");
if (domain->dimension != 2)
error->all(FLERR,"Fix nve/line can only be used for 2d simulations");
// check that all particles are line segments
// no point particles allowed
int *line = atom->line;
int *mask = atom->mask;
int nlocal = atom->nlocal;
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
if (line[i] < 0) error->one(FLERR,"Fix nve/line requires line particles");
}
FixNVE::init();
}
/* ---------------------------------------------------------------------- */
void FixNVELine::initial_integrate(int vflag)
{
double dtfm,dtirotate,length,theta;
AtomVecLine::Bonus *bonus = avec->bonus;
int *line = atom->line;
double **x = atom->x;
double **v = atom->v;
double **f = atom->f;
double **omega = atom->omega;
double **torque = atom->torque;
double *rmass = atom->rmass;
int *mask = atom->mask;
int nlocal = atom->nlocal;
if (igroup == atom->firstgroup) nlocal = atom->nfirst;
// set timestep here since dt may have changed or come via rRESPA
double dtfrotate = dtf / INERTIA;
// update v,x,omega,theta for all particles
// d_omega/dt = torque / inertia
// bound theta by -PI to PI
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
dtfm = dtf / rmass[i];
v[i][0] += dtfm * f[i][0];
v[i][1] += dtfm * f[i][1];
x[i][0] += dtv * v[i][0];
x[i][1] += dtv * v[i][1];
length = bonus[line[i]].length;
theta = bonus[line[i]].theta;
dtirotate = dtfrotate / (length*length*rmass[i]);
omega[i][2] += dtirotate * torque[i][2];
theta += dtv * omega[i][2];
while (theta <= MINUSPI) theta += TWOPI;
while (theta > MY_PI) theta -= TWOPI;
bonus[line[i]].theta = theta;
}
}
/* ---------------------------------------------------------------------- */
void FixNVELine::final_integrate()
{
double dtfm,dtirotate,length;
AtomVecLine::Bonus *bonus = avec->bonus;
int *line = atom->line;
double **v = atom->v;
double **f = atom->f;
double **omega = atom->omega;
double **torque = atom->torque;
double *rmass = atom->rmass;
int *mask = atom->mask;
int nlocal = atom->nlocal;
if (igroup == atom->firstgroup) nlocal = atom->nfirst;
// set timestep here since dt may have changed or come via rRESPA
double dtfrotate = dtf / INERTIA;
// update v,omega for all particles
// d_omega/dt = torque / inertia
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
dtfm = dtf / rmass[i];
v[i][0] += dtfm * f[i][0];
v[i][1] += dtfm * f[i][1];
length = bonus[line[i]].length;
dtirotate = dtfrotate / (length*length*rmass[i]);
omega[i][2] += dtirotate * torque[i][2];
}
}

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