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compute_inertia.cpp
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Wed, Jul 17, 18:03

compute_inertia.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 "compute_inertia.h"
#include "update.h"
#include "group.h"
#include "error.h"
#include "math_extra.h"
using namespace LAMMPS_NS;
/* ---------------------------------------------------------------------- */
ComputeInertia::ComputeInertia(LAMMPS *lmp, int narg, char **arg) :
Compute(lmp, narg, arg)
{
if (narg != 3) error->all(FLERR,"Illegal compute inertia command");
vector_flag = 1;
size_vector = 3;
extvector = 0;
vector = new double[3];
}
/* ---------------------------------------------------------------------- */
void ComputeInertia::init()
{
masstotal = group->mass(igroup);
}
/* ---------------------------------------------------------------------- */
void ComputeInertia::compute_vector()
{
invoked_vector = update->ntimestep;
double xcm[3];
group->xcm(igroup,masstotal,xcm);
double itensor[3][3];
group->inertia(igroup,xcm,itensor);
double eigvect[3][3];
int ierror;
ierror = MathExtra::jacobi(itensor,vector,eigvect);
if (ierror)
error->warning(FLERR,
"Insufficient Jacobi rotations for principal moments of inertia");
// sort principal moments by size
double tmp;
if (vector[0] < vector[1]) {
tmp = vector[1];
vector[1] = vector[0];
vector[0] = tmp;
}
if (vector[0] < vector[2]) {
tmp = vector[2];
vector[2] = vector[0];
vector[0] = tmp;
}
if (vector[1] < vector[2]) {
tmp = vector[2];
vector[2] = vector[1];
vector[1] = tmp;
}
return;
}

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