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nbin_standard.cpp
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Mon, Nov 18, 08:13

nbin_standard.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 "nbin_standard.h"
#include "neighbor.h"
#include "atom.h"
#include "group.h"
#include "domain.h"
#include "comm.h"
#include "update.h"
#include "error.h"
using namespace LAMMPS_NS;
enum{NSQ,BIN,MULTI}; // also in Neighbor
#define SMALL 1.0e-6
#define CUT2BIN_RATIO 100
/* ---------------------------------------------------------------------- */
NBinStandard::NBinStandard(LAMMPS *lmp) : NBin(lmp) {}
/* ----------------------------------------------------------------------
setup neighbor binning geometry
bin numbering in each dimension is global:
0 = 0.0 to binsize, 1 = binsize to 2*binsize, etc
nbin-1,nbin,etc = bbox-binsize to bbox, bbox to bbox+binsize, etc
-1,-2,etc = -binsize to 0.0, -2*binsize to -binsize, etc
code will work for any binsize
since next(xyz) and stencil extend as far as necessary
binsize = 1/2 of cutoff is roughly optimal
for orthogonal boxes:
a dim must be filled exactly by integer # of bins
in periodic, procs on both sides of PBC must see same bin boundary
in non-periodic, coord2bin() still assumes this by use of nbin xyz
for triclinic boxes:
tilted simulation box cannot contain integer # of bins
stencil & neigh list built differently to account for this
mbinlo = lowest global bin any of my ghost atoms could fall into
mbinhi = highest global bin any of my ghost atoms could fall into
mbin = number of bins I need in a dimension
------------------------------------------------------------------------- */
void NBinStandard::setup_bins(int style)
{
// bbox = size of bbox of entire domain
// bsubbox lo/hi = bounding box of my subdomain extended by comm->cutghost
// for triclinic:
// bbox bounds all 8 corners of tilted box
// subdomain is in lamda coords
// include dimension-dependent extension via comm->cutghost
// domain->bbox() converts lamda extent to box coords and computes bbox
double bbox[3],bsubboxlo[3],bsubboxhi[3];
double *cutghost = comm->cutghost;
if (triclinic == 0) {
bsubboxlo[0] = domain->sublo[0] - cutghost[0];
bsubboxlo[1] = domain->sublo[1] - cutghost[1];
bsubboxlo[2] = domain->sublo[2] - cutghost[2];
bsubboxhi[0] = domain->subhi[0] + cutghost[0];
bsubboxhi[1] = domain->subhi[1] + cutghost[1];
bsubboxhi[2] = domain->subhi[2] + cutghost[2];
} else {
double lo[3],hi[3];
lo[0] = domain->sublo_lamda[0] - cutghost[0];
lo[1] = domain->sublo_lamda[1] - cutghost[1];
lo[2] = domain->sublo_lamda[2] - cutghost[2];
hi[0] = domain->subhi_lamda[0] + cutghost[0];
hi[1] = domain->subhi_lamda[1] + cutghost[1];
hi[2] = domain->subhi_lamda[2] + cutghost[2];
domain->bbox(lo,hi,bsubboxlo,bsubboxhi);
}
bbox[0] = bboxhi[0] - bboxlo[0];
bbox[1] = bboxhi[1] - bboxlo[1];
bbox[2] = bboxhi[2] - bboxlo[2];
// optimal bin size is roughly 1/2 the cutoff
// for BIN style, binsize = 1/2 of max neighbor cutoff
// for MULTI style, binsize = 1/2 of min neighbor cutoff
// special case of all cutoffs = 0.0, binsize = box size
double binsize_optimal;
if (binsizeflag) binsize_optimal = binsize_user;
else if (style == BIN) binsize_optimal = 0.5*cutneighmax;
else binsize_optimal = 0.5*cutneighmin;
if (binsize_optimal == 0.0) binsize_optimal = bbox[0];
double binsizeinv = 1.0/binsize_optimal;
// test for too many global bins in any dimension due to huge global domain
if (bbox[0]*binsizeinv > MAXSMALLINT || bbox[1]*binsizeinv > MAXSMALLINT ||
bbox[2]*binsizeinv > MAXSMALLINT)
error->all(FLERR,"Domain too large for neighbor bins");
// create actual bins
// always have one bin even if cutoff > bbox
// for 2d, nbinz = 1
nbinx = static_cast<int> (bbox[0]*binsizeinv);
nbiny = static_cast<int> (bbox[1]*binsizeinv);
if (dimension == 3) nbinz = static_cast<int> (bbox[2]*binsizeinv);
else nbinz = 1;
if (nbinx == 0) nbinx = 1;
if (nbiny == 0) nbiny = 1;
if (nbinz == 0) nbinz = 1;
// compute actual bin size for nbins to fit into box exactly
// error if actual bin size << cutoff, since will create a zillion bins
// this happens when nbin = 1 and box size << cutoff
// typically due to non-periodic, flat system in a particular dim
// in that extreme case, should use NSQ not BIN neighbor style
binsizex = bbox[0]/nbinx;
binsizey = bbox[1]/nbiny;
binsizez = bbox[2]/nbinz;
bininvx = 1.0 / binsizex;
bininvy = 1.0 / binsizey;
bininvz = 1.0 / binsizez;
if (binsize_optimal*bininvx > CUT2BIN_RATIO ||
binsize_optimal*bininvy > CUT2BIN_RATIO ||
binsize_optimal*bininvz > CUT2BIN_RATIO)
error->all(FLERR,"Cannot use neighbor bins - box size << cutoff");
// mbinlo/hi = lowest and highest global bins my ghost atoms could be in
// coord = lowest and highest values of coords for my ghost atoms
// static_cast(-1.5) = -1, so subract additional -1
// add in SMALL for round-off safety
int mbinxhi,mbinyhi,mbinzhi;
double coord;
coord = bsubboxlo[0] - SMALL*bbox[0];
mbinxlo = static_cast<int> ((coord-bboxlo[0])*bininvx);
if (coord < bboxlo[0]) mbinxlo = mbinxlo - 1;
coord = bsubboxhi[0] + SMALL*bbox[0];
mbinxhi = static_cast<int> ((coord-bboxlo[0])*bininvx);
coord = bsubboxlo[1] - SMALL*bbox[1];
mbinylo = static_cast<int> ((coord-bboxlo[1])*bininvy);
if (coord < bboxlo[1]) mbinylo = mbinylo - 1;
coord = bsubboxhi[1] + SMALL*bbox[1];
mbinyhi = static_cast<int> ((coord-bboxlo[1])*bininvy);
if (dimension == 3) {
coord = bsubboxlo[2] - SMALL*bbox[2];
mbinzlo = static_cast<int> ((coord-bboxlo[2])*bininvz);
if (coord < bboxlo[2]) mbinzlo = mbinzlo - 1;
coord = bsubboxhi[2] + SMALL*bbox[2];
mbinzhi = static_cast<int> ((coord-bboxlo[2])*bininvz);
}
// extend bins by 1 to insure stencil extent is included
// for 2d, only 1 bin in z
mbinxlo = mbinxlo - 1;
mbinxhi = mbinxhi + 1;
mbinx = mbinxhi - mbinxlo + 1;
mbinylo = mbinylo - 1;
mbinyhi = mbinyhi + 1;
mbiny = mbinyhi - mbinylo + 1;
if (dimension == 3) {
mbinzlo = mbinzlo - 1;
mbinzhi = mbinzhi + 1;
} else mbinzlo = mbinzhi = 0;
mbinz = mbinzhi - mbinzlo + 1;
bigint bbin = ((bigint) mbinx) * ((bigint) mbiny) * ((bigint) mbinz) + 1;
if (bbin > MAXSMALLINT) error->one(FLERR,"Too many neighbor bins");
mbins = bbin;
}
/* ----------------------------------------------------------------------
bin owned and ghost atoms
------------------------------------------------------------------------- */
void NBinStandard::bin_atoms()
{
int i,ibin;
last_bin = update->ntimestep;
for (i = 0; i < mbins; i++) binhead[i] = -1;
// bin in reverse order so linked list will be in forward order
// also puts ghost atoms at end of list, which is necessary
double **x = atom->x;
int *mask = atom->mask;
int nlocal = atom->nlocal;
int nall = nlocal + atom->nghost;
if (includegroup) {
int bitmask = group->bitmask[includegroup];
for (i = nall-1; i >= nlocal; i--) {
if (mask[i] & bitmask) {
ibin = coord2bin(x[i]);
bins[i] = binhead[ibin];
binhead[ibin] = i;
}
}
for (i = atom->nfirst-1; i >= 0; i--) {
ibin = coord2bin(x[i]);
bins[i] = binhead[ibin];
binhead[ibin] = i;
}
} else {
for (i = nall-1; i >= 0; i--) {
ibin = coord2bin(x[i]);
bins[i] = binhead[ibin];
binhead[ibin] = i;
}
}
}

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