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fix_com.cpp
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Mon, Jul 22, 19:25

fix_com.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
www.cs.sandia.gov/~sjplimp/lammps.html
Steve Plimpton, sjplimp@sandia.gov, Sandia National Laboratories
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 "stdlib.h"
#include "fix_com.h"
#include "atom.h"
#include "update.h"
#include "domain.h"
#include "group.h"
#include "error.h"
/* ---------------------------------------------------------------------- */
FixCOM::FixCOM(int narg, char **arg) : Fix(narg, arg)
{
if (narg != 5) error->all("Illegal fix com command");
nevery = atoi(arg[3]);
if (nevery <= 0) error->all("Illegal fix com command");
first = 1;
MPI_Comm_rank(world,&me);
if (me == 0) {
fp = fopen(arg[4],"w");
if (fp == NULL) {
char str[128];
sprintf(str,"Cannot open fix com file %s",arg[4]);
error->one(str);
}
}
if (me == 0) {
fprintf(fp,"Center-of-mass for group %s\n",group->names[igroup]);
fprintf(fp,"TimeStep x y z\n");
}
}
/* ---------------------------------------------------------------------- */
FixCOM::~FixCOM()
{
if (me == 0) fclose(fp);
}
/* ---------------------------------------------------------------------- */
int FixCOM::setmask()
{
int mask = 0;
mask |= END_OF_STEP;
return mask;
}
/* ---------------------------------------------------------------------- */
void FixCOM::init()
{
masstotal = group->mass(igroup);
}
/* ---------------------------------------------------------------------- */
void FixCOM::setup()
{
if (first) end_of_step();
first = 0;
}
/* ---------------------------------------------------------------------- */
void FixCOM::end_of_step()
{
double xcm[3];
group->xcm(igroup,masstotal,xcm);
if (me == 0) fprintf(fp,"%d %g %g %g\n",
update->ntimestep,xcm[0],xcm[1],xcm[2]);
}

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