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b51c50294e3d209eba33d7010591738ecff9d38c
lammps/src/min_linesearch.cpp
Axel Kohlmeyer 93c7b6928f remove dead code, silence compiler warnings
2021-12-23 01:32:31 -05:00

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// clang-format off
/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
https://www.lammps.org/, 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.
------------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
Contributing author: Aidan Thompson (SNL)
improved CG and backtrack ls, added quadratic ls
Contributing author: Asad Hasan (CMU)
added forcezero ls
Sources: Numerical Recipes frprmn routine
"Conjugate Gradient Method Without the Agonizing Pain" by
JR Shewchuk, https://www.cs.cmu.edu/~quake-papers/painless-conjugate-gradient.pdf
------------------------------------------------------------------------- */
#include "min_linesearch.h"
#include "atom.h"
#include "fix_minimize.h"
#include "modify.h"
#include "output.h"
#include "pair.h"
#include "thermo.h"
#include <cmath>
using namespace LAMMPS_NS;
// ALPHA_MAX = max alpha allowed to avoid long backtracks
// ALPHA_REDUCE = reduction ratio, should be in range [0.5,1)
// BACKTRACK_SLOPE, should be in range (0,0.5]
// QUADRATIC_TOL = tolerance on alpha0, should be in range [0.1,1)
// EMACH = machine accuracy limit of energy changes (1.0e-8)
// EPS_QUAD = tolerance for quadratic projection
#define ALPHA_MAX 1.0
#define ALPHA_REDUCE 0.5
#define BACKTRACK_SLOPE 0.4
#define QUADRATIC_TOL 0.1
//#define EMACH 1.0e-8
#define EMACH 1.0e-8
#define EPS_QUAD 1.0e-28
/* ---------------------------------------------------------------------- */
MinLineSearch::MinLineSearch(LAMMPS *lmp) : Min(lmp)
{
searchflag = 1;
gextra = hextra = nullptr;
x0extra_atom = gextra_atom = hextra_atom = nullptr;
}
/* ---------------------------------------------------------------------- */
MinLineSearch::~MinLineSearch()
{
delete [] gextra;
delete [] hextra;
delete [] x0extra_atom;
delete [] gextra_atom;
delete [] hextra_atom;
}
/* ---------------------------------------------------------------------- */
void MinLineSearch::init()
{
Min::init();
if (linestyle == 0) linemin = &MinLineSearch::linemin_backtrack;
else if (linestyle == 1) linemin = &MinLineSearch::linemin_quadratic;
else if (linestyle == 2) linemin = &MinLineSearch::linemin_forcezero;
delete [] gextra;
delete [] hextra;
gextra = hextra = nullptr;
delete [] x0extra_atom;
delete [] gextra_atom;
delete [] hextra_atom;
x0extra_atom = gextra_atom = hextra_atom = nullptr;
}
/* ---------------------------------------------------------------------- */
void MinLineSearch::setup_style()
{
// memory for x0,g,h for atomic dof
fix_minimize->add_vector(3);
fix_minimize->add_vector(3);
fix_minimize->add_vector(3);
// memory for g,h for extra global dof, fix stores x0
if (nextra_global) {
gextra = new double[nextra_global];
hextra = new double[nextra_global];
}
// memory for x0,g,h for extra per-atom dof
if (nextra_atom) {
x0extra_atom = new double*[nextra_atom];
gextra_atom = new double*[nextra_atom];
hextra_atom = new double*[nextra_atom];
for (int m = 0; m < nextra_atom; m++) {
fix_minimize->add_vector(extra_peratom[m]);
fix_minimize->add_vector(extra_peratom[m]);
fix_minimize->add_vector(extra_peratom[m]);
}
}
}
/* ----------------------------------------------------------------------
set current vector lengths and pointers
called after atoms have migrated
------------------------------------------------------------------------- */
void MinLineSearch::reset_vectors()
{
// atomic dof
nvec = 3 * atom->nlocal;
if (nvec) xvec = atom->x[0];
if (nvec) fvec = atom->f[0];
x0 = fix_minimize->request_vector(0);
g = fix_minimize->request_vector(1);
h = fix_minimize->request_vector(2);
// extra per-atom dof
if (nextra_atom) {
int n = 3;
for (int m = 0; m < nextra_atom; m++) {
extra_nlen[m] = extra_peratom[m] * atom->nlocal;
requestor[m]->min_xf_pointers(m,&xextra_atom[m],&fextra_atom[m]);
x0extra_atom[m] = fix_minimize->request_vector(n++);
gextra_atom[m] = fix_minimize->request_vector(n++);
hextra_atom[m] = fix_minimize->request_vector(n++);
}
}
}
/* ----------------------------------------------------------------------
line minimization methods
find minimum-energy starting at x along h direction
input args: eoriginal = energy at initial x
input extra: n,x,x0,f,h for atomic, extra global, extra per-atom dof
output args: return 0 if successful move, non-zero alpha
return non-zero if failed
alpha = distance moved along h for x at min eng config
update neval counter of eng/force function evaluations
output extra: if fail, energy_force() of original x
if succeed, energy_force() at x + alpha*h
atom->x = coords at new configuration
atom->f = force at new configuration
ecurrent = energy of new configuration
------------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
linemin: backtracking line search (Proc 3.1, p 41 in Nocedal and Wright)
uses no gradient info, but should be very robust
start at maxdist, backtrack until energy decrease is sufficient
------------------------------------------------------------------------- */
int MinLineSearch::linemin_backtrack(double eoriginal, double &alpha)
{
int i,m,n;
double fdothall,fdothme,hme,hmax,hmaxall;
double de_ideal,de;
double *xatom,*x0atom,*fatom,*hatom;
// fdothall = projection of search dir along downhill gradient
// if search direction is not downhill, exit with error
fdothme = 0.0;
for (i = 0; i < nvec; i++) fdothme += fvec[i]*h[i];
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
fatom = fextra_atom[m];
hatom = hextra_atom[m];
n = extra_nlen[m];
for (i = 0; i < n; i++) fdothme += fatom[i]*hatom[i];
}
MPI_Allreduce(&fdothme,&fdothall,1,MPI_DOUBLE,MPI_SUM,world);
if (nextra_global)
for (i = 0; i < nextra_global; i++) fdothall += fextra[i]*hextra[i];
if (output->thermo->normflag) fdothall /= atom->natoms;
if (fdothall <= 0.0) return DOWNHILL;
// set alpha so no dof is changed by more than max allowed amount
// for atom coords, max amount = dmax
// for extra per-atom dof, max amount = extra_max[]
// for extra global dof, max amount is set by fix
// also insure alpha <= ALPHA_MAX
// else will have to backtrack from huge value when forces are tiny
// if all search dir components are already 0.0, exit with error
hme = 0.0;
for (i = 0; i < nvec; i++) hme = MAX(hme,fabs(h[i]));
MPI_Allreduce(&hme,&hmaxall,1,MPI_DOUBLE,MPI_MAX,world);
alpha = MIN(ALPHA_MAX,dmax/hmaxall);
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
hatom = hextra_atom[m];
n = extra_nlen[m];
hme = 0.0;
for (i = 0; i < n; i++) hme = MAX(hme,fabs(hatom[i]));
MPI_Allreduce(&hme,&hmax,1,MPI_DOUBLE,MPI_MAX,world);
alpha = MIN(alpha,extra_max[m]/hmax);
hmaxall = MAX(hmaxall,hmax);
}
if (nextra_global) {
double alpha_extra = modify->max_alpha(hextra);
alpha = MIN(alpha,alpha_extra);
for (i = 0; i < nextra_global; i++)
hmaxall = MAX(hmaxall,fabs(hextra[i]));
}
if (hmaxall == 0.0) return ZEROFORCE;
// store box and values of all dof at start of linesearch
fix_minimize->store_box();
for (i = 0; i < nvec; i++) x0[i] = xvec[i];
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
xatom = xextra_atom[m];
x0atom = x0extra_atom[m];
n = extra_nlen[m];
for (i = 0; i < n; i++) x0atom[i] = xatom[i];
}
if (nextra_global) modify->min_store();
// // important diagnostic: test the gradient against energy
// double etmp;
// double alphatmp = alpha*1.0e-4;
// etmp = alpha_step(alphatmp,1);
// printf("alpha = %g dele = %g dele_force = %g err = %g\n",
// alphatmp,etmp-eoriginal,-alphatmp*fdothall,
// etmp-eoriginal+alphatmp*fdothall);
// alpha_step(0.0,1);
// backtrack with alpha until energy decrease is sufficient
while (true) {
ecurrent = alpha_step(alpha,1);
// if energy change is better than ideal, exit with success
de_ideal = -BACKTRACK_SLOPE*alpha*fdothall;
de = ecurrent - eoriginal;
if (de <= de_ideal) {
if (nextra_global) {
int itmp = modify->min_reset_ref();
if (itmp) ecurrent = energy_force(1);
}
return 0;
}
// reduce alpha
alpha *= ALPHA_REDUCE;
// backtracked too much
// reset to starting point
// if de is positive, exit with error
// if de is negative, exit with ETOL
if (alpha <= 0.0 || de_ideal >= -EMACH) {
ecurrent = alpha_step(0.0,0);
if (de < 0.0) return ETOL;
else return ZEROALPHA;
}
}
}
/* ----------------------------------------------------------------------
// linemin: quadratic line search (adapted from Dennis and Schnabel)
// The objective function is approximated by a quadratic
// function in alpha, for sufficiently small alpha.
// This idea is the same as that used in the well-known secant
// method. However, since the change in the objective function
// (difference of two finite numbers) is not known as accurately
// as the gradient (which is close to zero), all the expressions
// are written in terms of gradients. In this way, we can converge
// the LAMMPS forces much closer to zero.
//
// We know E,Eprev,fh,fhprev. The Taylor series about alpha_prev
// truncated at the quadratic term is:
//
// E = Eprev - del_alpha*fhprev + (1/2)del_alpha^2*Hprev
//
// and
//
// fh = fhprev - del_alpha*Hprev
//
// where del_alpha = alpha-alpha_prev
//
// We solve these two equations for Hprev and E=Esolve, giving:
//
// Esolve = Eprev - del_alpha*(f+fprev)/2
//
// We define relerr to be:
//
// relerr = |(Esolve-E)/Eprev|
// = |1.0 - (0.5*del_alpha*(f+fprev)+E)/Eprev|
//
// If this is accurate to within a reasonable tolerance, then
// we go ahead and use a secant step to fh = 0:
//
// alpha0 = alpha - (alpha-alphaprev)*fh/delfh;
//
------------------------------------------------------------------------- */
int MinLineSearch::linemin_quadratic(double eoriginal, double &alpha)
{
int i,m,n;
double fdothall,fdothme,hme,hmax,hmaxall;
double de_ideal,de;
double delfh,engprev,relerr,alphaprev,fhprev,fh,alpha0;
double dot[2],dotall[2];
double *xatom,*x0atom,*fatom,*hatom;
double alphamax;
// fdothall = projection of search dir along downhill gradient
// if search direction is not downhill, exit with error
fdothme = 0.0;
for (i = 0; i < nvec; i++) fdothme += fvec[i]*h[i];
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
fatom = fextra_atom[m];
hatom = hextra_atom[m];
n = extra_nlen[m];
for (i = 0; i < n; i++) fdothme += fatom[i]*hatom[i];
}
MPI_Allreduce(&fdothme,&fdothall,1,MPI_DOUBLE,MPI_SUM,world);
if (nextra_global)
for (i = 0; i < nextra_global; i++) fdothall += fextra[i]*hextra[i];
if (output->thermo->normflag) fdothall /= atom->natoms;
if (fdothall <= 0.0) return DOWNHILL;
// set alphamax so no dof is changed by more than max allowed amount
// for atom coords, max amount = dmax
// for extra per-atom dof, max amount = extra_max[]
// for extra global dof, max amount is set by fix
// also insure alphamax <= ALPHA_MAX
// else will have to backtrack from huge value when forces are tiny
// if all search dir components are already 0.0, exit with error
hme = 0.0;
for (i = 0; i < nvec; i++) hme = MAX(hme,fabs(h[i]));
MPI_Allreduce(&hme,&hmaxall,1,MPI_DOUBLE,MPI_MAX,world);
alphamax = MIN(ALPHA_MAX,dmax/hmaxall);
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
hatom = hextra_atom[m];
n = extra_nlen[m];
hme = 0.0;
for (i = 0; i < n; i++) hme = MAX(hme,fabs(hatom[i]));
MPI_Allreduce(&hme,&hmax,1,MPI_DOUBLE,MPI_MAX,world);
alphamax = MIN(alphamax,extra_max[m]/hmax);
hmaxall = MAX(hmaxall,hmax);
}
if (nextra_global) {
double alpha_extra = modify->max_alpha(hextra);
alphamax = MIN(alphamax,alpha_extra);
for (i = 0; i < nextra_global; i++)
hmaxall = MAX(hmaxall,fabs(hextra[i]));
}
if (hmaxall == 0.0) return ZEROFORCE;
// store box and values of all dof at start of linesearch
fix_minimize->store_box();
for (i = 0; i < nvec; i++) x0[i] = xvec[i];
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
xatom = xextra_atom[m];
x0atom = x0extra_atom[m];
n = extra_nlen[m];
for (i = 0; i < n; i++) x0atom[i] = xatom[i];
}
if (nextra_global) modify->min_store();
// backtrack with alpha until energy decrease is sufficient
// or until get to small energy change, then perform quadratic projection
alpha = alphamax;
fhprev = fdothall;
engprev = eoriginal;
alphaprev = 0.0;
// // important diagnostic: test the gradient against energy
// double etmp;
// double alphatmp = alphamax*1.0e-4;
// etmp = alpha_step(alphatmp,1);
// printf("alpha = %g dele = %g dele_force = %g err = %g\n",
// alphatmp,etmp-eoriginal,-alphatmp*fdothall,
// etmp-eoriginal+alphatmp*fdothall);
// alpha_step(0.0,1);
while (true) {
ecurrent = alpha_step(alpha,1);
// compute new fh, alpha, delfh
dot[0] = dot[1] = 0.0;
for (i = 0; i < nvec; i++) {
dot[0] += fvec[i]*fvec[i];
dot[1] += fvec[i]*h[i];
}
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
fatom = fextra_atom[m];
hatom = hextra_atom[m];
n = extra_nlen[m];
for (i = 0; i < n; i++) {
dot[0] += fatom[i]*fatom[i];
dot[1] += fatom[i]*hatom[i];
}
}
MPI_Allreduce(dot,dotall,2,MPI_DOUBLE,MPI_SUM,world);
if (nextra_global) {
for (i = 0; i < nextra_global; i++) {
dotall[0] += fextra[i]*fextra[i];
dotall[1] += fextra[i]*hextra[i];
}
}
fh = dotall[1];
if (output->thermo->normflag) fh /= atom->natoms;
delfh = fh - fhprev;
// if fh or delfh is epsilon, reset to starting point, exit with error
if (fabs(fh) < EPS_QUAD || fabs(delfh) < EPS_QUAD) {
ecurrent = alpha_step(0.0,0);
return ZEROQUAD;
}
// Check if ready for quadratic projection, equivalent to secant method
// alpha0 = projected alpha
relerr = fabs(1.0-(0.5*(alpha-alphaprev)*(fh+fhprev)+ecurrent)/engprev);
alpha0 = alpha - (alpha-alphaprev)*fh/delfh;
if (relerr <= QUADRATIC_TOL && alpha0 > 0.0 && alpha0 < alphamax) {
ecurrent = alpha_step(alpha0,1);
if (ecurrent - eoriginal < EMACH) {
if (nextra_global) {
int itmp = modify->min_reset_ref();
if (itmp) ecurrent = energy_force(1);
}
return 0;
}
}
// if backtracking energy change is better than ideal, exit with success
de_ideal = -BACKTRACK_SLOPE*alpha*fdothall;
de = ecurrent - eoriginal;
if (de <= de_ideal) {
if (nextra_global) {
int itmp = modify->min_reset_ref();
if (itmp) ecurrent = energy_force(1);
}
return 0;
}
// save previous state
fhprev = fh;
engprev = ecurrent;
alphaprev = alpha;
// reduce alpha
alpha *= ALPHA_REDUCE;
// backtracked all the way to 0.0
// reset to starting point, exit with error
if (alpha <= 0.0 || de_ideal >= -EMACH) {
ecurrent = alpha_step(0.0,0);
return ZEROALPHA;
}
}
}
/* ----------------------------------------------------------------------
forcezero linesearch method - seeks a zero of force in a robust manner.
(motivated by a line minimization routine of f77 DYNAMO code)
central idea:
In each linesearch we attempt to converge to a zero of force
(usual case) or reduces forces (worst case).
Energy does not play any role in the search procedure,
except we ensure that it doesn't increase.
pseudo code:
i) Fix an alpha max:
// also account for nextra atom & global
alpha_max <= dmax/hmaxall
ii) Initialize:
fhCurr = current_force.dot.search_direction
fhoriginal = fhCurr
// try decreasing the energy to 1/10 of initial
alpha_init = 0.1*fabs(eoriginal)/fhCurr;
// initial alpha is smaller than alpha_max
alpha_del = MIN(alpha_init, 0.5*alpha_max);
alpha = 0.0
iii) Loop:
backtrack = false
alpha += alpha_del
if (alpha > alpha_max):
// we have done enough in the search space
EXIT with success
Step with the new alpha
Compute:
current energy and 'fhCurr'
de = ecurrent - eprev
// ZERO_ENERGY = 1e-12, is max allowed energy increase
if (de > ZERO_ENERGY):
bactrack = true
// GRAD_TOL = 0.1
if ((not backtrack) && (fabs(fhCurr/fh0) <= GRAD_TOL)):
// forces sufficiently reduced without energy increase
EXIT with success
// projected force changed sign but didn't become small enough
if ( fhCurr < 0):
backtrack = true
if (bactrack):
// forces along search direction changed sign
if (fhCurr < 0):
Get alpha_del by solving for zero
of force (1D Newton's Method)
else:
// force didn't change sign but only energy increased,
// we overshot a minimum which is very close to a
// maximum (or there is an inflection point)
// New alpha_del should be much smaller
// ALPHA_FACT = 0.1
alpha_del *= ALPHA_FACT
// Check to see if new 'alpha_del' isn't too small
if (alpha_del < MIN_ALPHA):
EXIT with failure("linesearch alpha is zero")
Undo the step of alpha.
// continue the loop with a new alpha_del
else:
Get new alpha_del by linearizing force and solving for its zero
---------------------------------------------------------------------- */
int MinLineSearch::linemin_forcezero(double eoriginal, double &alpha)
{
int i,m,n;
double fdothall,fdothme,hme,hmax,hmaxall;
double de;
double *xatom,*x0atom,*fatom,*hatom;
double alpha_max, alpha_init, alpha_del;
// projection of: force on itself, current force on search direction,
double ffCurr, fhCurr;
// previous force on search direction, initial force on search direction
double fhPrev, fhoriginal;
// current energy, previous energy
double engCurr, engPrev;
bool backtrack;
// hardcoded constants
// factor by which alpha is reduced when backtracking
double ALPHA_FACT = 0.1;
// maximum amount by which we'll permit energy increase
double ZERO_ENERGY = 1e-12;
// fraction to which we want to reduce the directional derivative
double GRAD_TOL = 0.1;
// largest alpha increment which will trigger a failed_linesearch
double MIN_ALPHA_FAC = 1e-14;
double LIMIT_BOOST = 4.0;
// fdothall = projection of search dir along downhill gradient
// if search direction is not downhill, exit with error
fdothme = 0.0;
for (i = 0; i < nvec; i++) fdothme += fvec[i]*h[i];
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
fatom = fextra_atom[m];
hatom = hextra_atom[m];
n = extra_nlen[m];
for (i = 0; i < n; i++)
fdothme += fatom[i]*hatom[i];
}
MPI_Allreduce(&fdothme,&fdothall,1,MPI_DOUBLE,MPI_SUM,world);
if (nextra_global)
for (i = 0; i < nextra_global; i++)
fdothall += fextra[i]*hextra[i];
if (output->thermo->normflag) fdothall /= atom->natoms;
if (fdothall <= 0.0) return DOWNHILL;
// set alpha so no dof is changed by more than max allowed amount
// for atom coords, max amount = dmax
// for extra per-atom dof, max amount = extra_max[]
// for extra global dof, max amount is set by fix
// also insure alpha <= ALPHA_MAX else will have
// to backtrack from huge value when forces are tiny
// if all search dir components are already 0.0, exit with error
hme = 0.0;
for (i = 0; i < nvec; i++)
hme = MAX(hme,fabs(h[i]));
MPI_Allreduce(&hme,&hmaxall,1,MPI_DOUBLE,MPI_MAX,world);
alpha_max = dmax/hmaxall;
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
hatom = hextra_atom[m];
n = extra_nlen[m];
hme = 0.0;
for (i = 0; i < n; i++) hme = MAX(hme,fabs(hatom[i]));
MPI_Allreduce(&hme,&hmax,1,MPI_DOUBLE,MPI_MAX,world);
alpha_max = MIN(alpha_max,extra_max[m]/hmax);
hmaxall = MAX(hmaxall,hmax);
}
if (nextra_global) {
double alpha_extra = modify->max_alpha(hextra);
alpha_max = MIN(alpha_max, alpha_extra);
for (i = 0; i < nextra_global; i++)
hmaxall = MAX(hmaxall,fabs(hextra[i]));
}
if (hmaxall == 0.0) return ZEROFORCE;
// store box and values of all dof at start of linesearch
fix_minimize->store_box();
for (i = 0; i < nvec; i++) x0[i] = xvec[i];
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
xatom = xextra_atom[m];
x0atom = x0extra_atom[m];
n = extra_nlen[m];
for (i = 0; i < n; i++) x0atom[i] = xatom[i];
}
if (nextra_global) modify->min_store();
// initialize important variables before main linesearch loop
ffCurr = 0.0;
fhCurr = fdothall;
fhoriginal = fhCurr;
engCurr = eoriginal;
// stores energy difference due to the current move
de = 0.0;
// choosing the initial alpha that we'll use
// rough estimate that'll decrease energy to 1/10
alpha_init = 0.1*fabs(eoriginal)/fdothall;
// initialize aplha to 0.0
alpha = 0.0;
// compute increment to alpha, ensure that we
// don't take the largest allowed alpha
// first alpha that will actually apply
alpha_del = MIN(alpha_init,0.5*alpha_max);
// main linesearch loop
while (true) {
backtrack = false;
fhPrev = fhCurr;
engPrev = engCurr;
// apply the increment to alpha, but first
// check whether we are still in allowed search space
alpha += alpha_del;
if (alpha > alpha_max) {
// undo the increment
alpha -= alpha_del;
if (nextra_global) {
int itmp = modify->min_reset_ref();
if (itmp) ecurrent = energy_force(1);
}
// exit linesearch with success: have done
// enough in allowed search space
return 0;
}
// move the system
// '1' updates coordinates of atoms which cross PBC
engCurr = alpha_step(alpha,1);
ecurrent = engCurr;
// compute the new directional derivative and also f_dot_f
fhCurr = compute_dir_deriv(ffCurr);
// energy change
de = engCurr - engPrev;
// if the function value increases measurably,
// then we have to reduce alpha
if (de >= ZERO_ENERGY)
backtrack = true;
// check if the directional derivative has sufficiently decreased
// NOTE: the fabs is essential here
if ((!backtrack) && (fabs(fhCurr/fhoriginal) <= GRAD_TOL)) {
if (nextra_global) {
int itmp = modify->min_reset_ref();
if (itmp) ecurrent = energy_force(1);
}
// we are done
return 0;
}
// check if the directional derivative changed sign
// but it's not small: we overshot the minima -- BACKTRACK
if (fhCurr < 0.0)
backtrack = true;
// backtrack by undoing step and choosing a new alpha
if (backtrack) {
// move back
alpha -= alpha_del;
// choose new alpha
// if the force changed sign, linearize force and
// solve for new alpha_del
if (fhCurr < 0.0)
alpha_del *= fhPrev/(fhPrev - fhCurr);
else
// force didn't change sign but only energy increased,
// we overshot a minimum which is very close to a maxima
// (or there is an inflection point)
// new alpha_del should be much smaller
alpha_del *= ALPHA_FACT;
// since we moved back ...
engCurr = engPrev;
ecurrent = engCurr;
fhCurr = fhPrev;
// if new move is too small then we have failed;
// exit with 'failed_linesearch'
if (hmaxall*alpha_del <= MIN_ALPHA_FAC) {
// undo all line minization moves
engCurr = alpha_step(0.0,1);
ecurrent= engCurr;
return ZEROALPHA;
}
} else {
// get a new alpha by linearizing force and start over
double boostFactor = LIMIT_BOOST;
// avoids problems near an energy inflection point
if (fhPrev > fhCurr)
boostFactor = fhCurr/(fhPrev - fhCurr);
// don't want to boost too much
boostFactor = MIN(boostFactor, LIMIT_BOOST);
alpha_del *= boostFactor;
}
}
}
/* ---------------------------------------------------------------------- */
double MinLineSearch::alpha_step(double alpha, int resetflag)
{
int i,n,m;
double *xatom,*x0atom,*hatom;
// reset to starting point
if (nextra_global) modify->min_step(0.0,hextra);
for (i = 0; i < nvec; i++) xvec[i] = x0[i];
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
xatom = xextra_atom[m];
x0atom = x0extra_atom[m];
n = extra_nlen[m];
for (i = 0; i < n; i++) xatom[i] = x0atom[i];
requestor[m]->min_x_set(m);
}
// step forward along h
if (alpha > 0.0) {
if (nextra_global) modify->min_step(alpha,hextra);
for (i = 0; i < nvec; i++) xvec[i] += alpha*h[i];
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
xatom = xextra_atom[m];
hatom = hextra_atom[m];
n = extra_nlen[m];
for (i = 0; i < n; i++) xatom[i] += alpha*hatom[i];
requestor[m]->min_x_set(m);
}
}
// compute and return new energy
neval++;
return energy_force(resetflag);
}
/* ---------------------------------------------------------------------- */
// compute projection of force on: itself and the search direction
double MinLineSearch::compute_dir_deriv(double &ff)
{
int i,m,n;
double *hatom, *fatom;
double dot[2],dotall[2];
double fh;
// compute new fh, alpha, delfh
dot[0] = dot[1] = 0.0;
for (i = 0; i < nvec; i++) {
dot[0] += fvec[i]*fvec[i];
dot[1] += fvec[i]*h[i];
}
if (nextra_atom)
for (m = 0; m < nextra_atom; m++) {
fatom = fextra_atom[m];
hatom = hextra_atom[m];
n = extra_nlen[m];
for (i = 0; i < n; i++) {
dot[0] += fatom[i]*fatom[i];
dot[1] += fatom[i]*hatom[i];
}
}
MPI_Allreduce(dot,dotall,2,MPI_DOUBLE,MPI_SUM,world);
if (nextra_global) {
for (i = 0; i < nextra_global; i++) {
dotall[0] += fextra[i]*fextra[i];
dotall[1] += fextra[i]*hextra[i];
}
}
ff = dotall[0];
fh = dotall[1];
if (output->thermo->normflag) {
ff /= atom->natoms;
fh /= atom->natoms;
}
return fh;
}
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