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min_fire.cpp
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Mon, Nov 11, 08:49

min_fire.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 "min_fire.h"
#include "universe.h"
#include "atom.h"
#include "force.h"
#include "update.h"
#include "output.h"
#include "timer.h"
#include "error.h"
using namespace LAMMPS_NS;
// EPS_ENERGY = minimum normalization for energy tolerance
#define EPS_ENERGY 1.0e-8
// same as in other min classes
enum{MAXITER,MAXEVAL,ETOL,FTOL,DOWNHILL,ZEROALPHA,ZEROFORCE,ZEROQUAD};
#define DELAYSTEP 5
#define DT_GROW 1.1
#define DT_SHRINK 0.5
#define ALPHA0 0.1
#define ALPHA_SHRINK 0.99
#define TMAX 10.0
/* ---------------------------------------------------------------------- */
MinFire::MinFire(LAMMPS *lmp) : Min(lmp) {}
/* ---------------------------------------------------------------------- */
void MinFire::init()
{
Min::init();
dt = update->dt;
dtmax = TMAX * dt;
alpha = ALPHA0;
last_negative = update->ntimestep;
}
/* ---------------------------------------------------------------------- */
void MinFire::setup_style()
{
double **v = atom->v;
int nlocal = atom->nlocal;
for (int i = 0; i < nlocal; i++)
v[i][0] = v[i][1] = v[i][2] = 0.0;
}
/* ----------------------------------------------------------------------
set current vector lengths and pointers
called after atoms have migrated
------------------------------------------------------------------------- */
void MinFire::reset_vectors()
{
// atomic dof
nvec = 3 * atom->nlocal;
if (nvec) xvec = atom->x[0];
if (nvec) fvec = atom->f[0];
}
/* ---------------------------------------------------------------------- */
int MinFire::iterate(int maxiter)
{
bigint ntimestep;
double vmax,vdotf,vdotfall,vdotv,vdotvall,fdotf,fdotfall;
double scale1,scale2;
double dtvone,dtv,dtf,dtfm;
int flag,flagall;
alpha_final = 0.0;
for (int iter = 0; iter < maxiter; iter++) {
ntimestep = ++update->ntimestep;
niter++;
// vdotfall = v dot f
double **v = atom->v;
double **f = atom->f;
int nlocal = atom->nlocal;
vdotf = 0.0;
for (int i = 0; i < nlocal; i++)
vdotf += v[i][0]*f[i][0] + v[i][1]*f[i][1] + v[i][2]*f[i][2];
MPI_Allreduce(&vdotf,&vdotfall,1,MPI_DOUBLE,MPI_SUM,world);
// sum vdotf over replicas, if necessary
// this communicator would be invalid for multiprocess replicas
if (update->multireplica == 1) {
vdotf = vdotfall;
MPI_Allreduce(&vdotf,&vdotfall,1,MPI_DOUBLE,MPI_SUM,universe->uworld);
}
// if (v dot f) > 0:
// v = (1-alpha) v + alpha |v| Fhat
// |v| = length of v, Fhat = unit f
// if more than DELAYSTEP since v dot f was negative:
// increase timestep and decrease alpha
if (vdotfall > 0.0) {
vdotv = 0.0;
for (int i = 0; i < nlocal; i++)
vdotv += v[i][0]*v[i][0] + v[i][1]*v[i][1] + v[i][2]*v[i][2];
MPI_Allreduce(&vdotv,&vdotvall,1,MPI_DOUBLE,MPI_SUM,world);
// sum vdotv over replicas, if necessary
// this communicator would be invalid for multiprocess replicas
if (update->multireplica == 1) {
vdotv = vdotvall;
MPI_Allreduce(&vdotv,&vdotvall,1,MPI_DOUBLE,MPI_SUM,universe->uworld);
}
fdotf = 0.0;
for (int i = 0; i < nlocal; i++)
fdotf += f[i][0]*f[i][0] + f[i][1]*f[i][1] + f[i][2]*f[i][2];
MPI_Allreduce(&fdotf,&fdotfall,1,MPI_DOUBLE,MPI_SUM,world);
// sum fdotf over replicas, if necessary
// this communicator would be invalid for multiprocess replicas
if (update->multireplica == 1) {
fdotf = fdotfall;
MPI_Allreduce(&fdotf,&fdotfall,1,MPI_DOUBLE,MPI_SUM,universe->uworld);
}
scale1 = 1.0 - alpha;
if (fdotfall == 0.0) scale2 = 0.0;
else scale2 = alpha * sqrt(vdotvall/fdotfall);
for (int i = 0; i < nlocal; i++) {
v[i][0] = scale1*v[i][0] + scale2*f[i][0];
v[i][1] = scale1*v[i][1] + scale2*f[i][1];
v[i][2] = scale1*v[i][2] + scale2*f[i][2];
}
if (ntimestep - last_negative > DELAYSTEP) {
dt = MIN(dt*DT_GROW,dtmax);
alpha *= ALPHA_SHRINK;
}
// else (v dot f) <= 0:
// decrease timestep, reset alpha, set v = 0
} else {
last_negative = ntimestep;
dt *= DT_SHRINK;
alpha = ALPHA0;
for (int i = 0; i < nlocal; i++)
v[i][0] = v[i][1] = v[i][2] = 0.0;
}
// limit timestep so no particle moves further than dmax
double *rmass = atom->rmass;
double *mass = atom->mass;
int *type = atom->type;
dtvone = dt;
for (int i = 0; i < nlocal; i++) {
vmax = MAX(fabs(v[i][0]),fabs(v[i][1]));
vmax = MAX(vmax,fabs(v[i][2]));
if (dtvone*vmax > dmax) dtvone = dmax/vmax;
}
MPI_Allreduce(&dtvone,&dtv,1,MPI_DOUBLE,MPI_MIN,world);
// min dtv over replicas, if necessary
// this communicator would be invalid for multiprocess replicas
if (update->multireplica == 1) {
dtvone = dtv;
MPI_Allreduce(&dtvone,&dtv,1,MPI_DOUBLE,MPI_MIN,universe->uworld);
}
dtf = dtv * force->ftm2v;
// Euler integration step
double **x = atom->x;
if (rmass) {
for (int i = 0; i < nlocal; i++) {
dtfm = dtf / rmass[i];
x[i][0] += dtv * v[i][0];
x[i][1] += dtv * v[i][1];
x[i][2] += dtv * v[i][2];
v[i][0] += dtfm * f[i][0];
v[i][1] += dtfm * f[i][1];
v[i][2] += dtfm * f[i][2];
}
} else {
for (int i = 0; i < nlocal; i++) {
dtfm = dtf / mass[type[i]];
x[i][0] += dtv * v[i][0];
x[i][1] += dtv * v[i][1];
x[i][2] += dtv * v[i][2];
v[i][0] += dtfm * f[i][0];
v[i][1] += dtfm * f[i][1];
v[i][2] += dtfm * f[i][2];
}
}
eprevious = ecurrent;
ecurrent = energy_force(0);
neval++;
// energy tolerance criterion
// only check after DELAYSTEP elapsed since velocties reset to 0
// sync across replicas if running multi-replica minimization
if (update->etol > 0.0 && ntimestep-last_negative > DELAYSTEP) {
if (update->multireplica == 0) {
if (fabs(ecurrent-eprevious) <
update->etol * 0.5*(fabs(ecurrent) + fabs(eprevious) + EPS_ENERGY))
return ETOL;
} else {
if (fabs(ecurrent-eprevious) <
update->etol * 0.5*(fabs(ecurrent) + fabs(eprevious) + EPS_ENERGY))
flag = 0;
else flag = 1;
MPI_Allreduce(&flag,&flagall,1,MPI_INT,MPI_SUM,universe->uworld);
if (flagall == 0) return ETOL;
}
}
// force tolerance criterion
// sync across replicas if running multi-replica minimization
if (update->ftol > 0.0) {
fdotf = fnorm_sqr();
if (update->multireplica == 0) {
if (fdotf < update->ftol*update->ftol) return FTOL;
} else {
if (fdotf < update->ftol*update->ftol) flag = 0;
else flag = 1;
MPI_Allreduce(&flag,&flagall,1,MPI_INT,MPI_SUM,universe->uworld);
if (flagall == 0) return FTOL;
}
}
// output for thermo, dump, restart files
if (output->next == ntimestep) {
timer->stamp();
output->write(ntimestep);
timer->stamp(Timer::OUTPUT);
}
}
return MAXITER;
}

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