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root/OpenMD/trunk/src/parallel/ForceMatrixDecomposition.cpp
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branches/development/src/parallel/ForceDecomposition.cpp (file contents), Revision 1538 by chuckv, Tue Jan 11 18:58:12 2011 UTC vs.
branches/development/src/parallel/ForceMatrixDecomposition.cpp (file contents), Revision 1576 by gezelter, Wed Jun 8 16:05:07 2011 UTC

# Line 1 | Line 1
1 < /**
2 < * @file ForceDecomposition.cpp
3 < * @author Charles Vardeman <cvardema.at.nd.edu>
4 < * @date 08/18/2010
5 < * @time 11:56am
6 < * @version 1.0
1 > /*
2 > * Copyright (c) 2005 The University of Notre Dame. All Rights Reserved.
3   *
8 * @section LICENSE
9 * Copyright (c) 2010 The University of Notre Dame. All Rights Reserved.
10 *
4   * The University of Notre Dame grants you ("Licensee") a
5   * non-exclusive, royalty free, license to use, modify and
6   * redistribute this software in source and binary code form, provided
# Line 45 | Line 38
38   * [3]  Sun, Lin & Gezelter, J. Chem. Phys. 128, 24107 (2008).          
39   * [4]  Vardeman & Gezelter, in progress (2009).                        
40   */
41 + #include "parallel/ForceMatrixDecomposition.hpp"
42 + #include "math/SquareMatrix3.hpp"
43 + #include "nonbonded/NonBondedInteraction.hpp"
44 + #include "brains/SnapshotManager.hpp"
45 + #include "brains/PairList.hpp"
46  
47 + using namespace std;
48 + namespace OpenMD {
49  
50 +  /**
51 +   * distributeInitialData is essentially a copy of the older fortran
52 +   * SimulationSetup
53 +   */
54 +  
55 +  void ForceMatrixDecomposition::distributeInitialData() {
56 +    snap_ = sman_->getCurrentSnapshot();
57 +    storageLayout_ = sman_->getStorageLayout();
58 +    ff_ = info_->getForceField();
59 +    nLocal_ = snap_->getNumberOfAtoms();
60 +    nGroups_ = snap_->getNumberOfCutoffGroups();
61  
62 < /*  -*- c++ -*-  */
63 < #include "config.h"
64 < #include <stdlib.h>
62 >    // gather the information for atomtype IDs (atids):
63 >    identsLocal = info_->getIdentArray();
64 >    AtomLocalToGlobal = info_->getGlobalAtomIndices();
65 >    cgLocalToGlobal = info_->getGlobalGroupIndices();
66 >    vector<int> globalGroupMembership = info_->getGlobalGroupMembership();
67 >    vector<RealType> massFactorsLocal = info_->getMassFactors();
68 >    PairList excludes = info_->getExcludedInteractions();
69 >    PairList oneTwo = info_->getOneTwoInteractions();
70 >    PairList oneThree = info_->getOneThreeInteractions();
71 >    PairList oneFour = info_->getOneFourInteractions();
72 >
73   #ifdef IS_MPI
74 < #include <mpi.h>
75 < #endif
74 >
75 >    AtomCommIntRow = new Communicator<Row,int>(nLocal_);
76 >    AtomCommRealRow = new Communicator<Row,RealType>(nLocal_);
77 >    AtomCommVectorRow = new Communicator<Row,Vector3d>(nLocal_);
78 >    AtomCommMatrixRow = new Communicator<Row,Mat3x3d>(nLocal_);
79 >    AtomCommPotRow = new Communicator<Row,potVec>(nLocal_);
80  
81 < #include <iostream>
82 < #include <vector>
83 < #include <algorithm>
84 < #include <cmath>
85 < #include "parallel/ForceDecomposition.hpp"
81 >    AtomCommIntColumn = new Communicator<Column,int>(nLocal_);
82 >    AtomCommRealColumn = new Communicator<Column,RealType>(nLocal_);
83 >    AtomCommVectorColumn = new Communicator<Column,Vector3d>(nLocal_);
84 >    AtomCommMatrixColumn = new Communicator<Column,Mat3x3d>(nLocal_);
85 >    AtomCommPotColumn = new Communicator<Column,potVec>(nLocal_);
86  
87 +    cgCommIntRow = new Communicator<Row,int>(nGroups_);
88 +    cgCommVectorRow = new Communicator<Row,Vector3d>(nGroups_);
89 +    cgCommIntColumn = new Communicator<Column,int>(nGroups_);
90 +    cgCommVectorColumn = new Communicator<Column,Vector3d>(nGroups_);
91  
92 < using namespace std;
93 < using namespace OpenMD;
92 >    nAtomsInRow_ = AtomCommIntRow->getSize();
93 >    nAtomsInCol_ = AtomCommIntColumn->getSize();
94 >    nGroupsInRow_ = cgCommIntRow->getSize();
95 >    nGroupsInCol_ = cgCommIntColumn->getSize();
96  
97 < //__static
98 < #ifdef IS_MPI
99 < static vector<MPI:Comm> communictors;
100 < #endif
97 >    // Modify the data storage objects with the correct layouts and sizes:
98 >    atomRowData.resize(nAtomsInRow_);
99 >    atomRowData.setStorageLayout(storageLayout_);
100 >    atomColData.resize(nAtomsInCol_);
101 >    atomColData.setStorageLayout(storageLayout_);
102 >    cgRowData.resize(nGroupsInRow_);
103 >    cgRowData.setStorageLayout(DataStorage::dslPosition);
104 >    cgColData.resize(nGroupsInCol_);
105 >    cgColData.setStorageLayout(DataStorage::dslPosition);
106 >        
107 >    identsRow.reserve(nAtomsInRow_);
108 >    identsCol.reserve(nAtomsInCol_);
109 >    
110 >    AtomCommIntRow->gather(identsLocal, identsRow);
111 >    AtomCommIntColumn->gather(identsLocal, identsCol);
112 >    
113 >    AtomCommIntRow->gather(AtomLocalToGlobal, AtomRowToGlobal);
114 >    AtomCommIntColumn->gather(AtomLocalToGlobal, AtomColToGlobal);
115 >    
116 >    cgCommIntRow->gather(cgLocalToGlobal, cgRowToGlobal);
117 >    cgCommIntColumn->gather(cgLocalToGlobal, cgColToGlobal);
118  
119 < //____ MPITypeTraits
120 < template<typename T>
75 < struct MPITypeTraits;
119 >    AtomCommRealRow->gather(massFactorsLocal, massFactorsRow);
120 >    AtomCommRealColumn->gather(massFactorsLocal, massFactorsCol);
121  
122 < #ifdef IS_MPI
123 < template<>
124 < struct MPITypeTraits<RealType> {
125 <  static const MPI::Datatype datatype;
126 < };
127 < const MPI_Datatype MPITypeTraits<RealType>::datatype = MY_MPI_REAL;
122 >    groupListRow_.clear();
123 >    groupListRow_.reserve(nGroupsInRow_);
124 >    for (int i = 0; i < nGroupsInRow_; i++) {
125 >      int gid = cgRowToGlobal[i];
126 >      for (int j = 0; j < nAtomsInRow_; j++) {
127 >        int aid = AtomRowToGlobal[j];
128 >        if (globalGroupMembership[aid] == gid)
129 >          groupListRow_[i].push_back(j);
130 >      }      
131 >    }
132  
133 < template<>
134 < struct MPITypeTraits<int> {
135 <  static const MPI::Datatype datatype;
136 < };
137 < const MPI::Datatype MPITypeTraits<int>::datatype = MPI_INT;
138 < #endif
133 >    groupListCol_.clear();
134 >    groupListCol_.reserve(nGroupsInCol_);
135 >    for (int i = 0; i < nGroupsInCol_; i++) {
136 >      int gid = cgColToGlobal[i];
137 >      for (int j = 0; j < nAtomsInCol_; j++) {
138 >        int aid = AtomColToGlobal[j];
139 >        if (globalGroupMembership[aid] == gid)
140 >          groupListCol_[i].push_back(j);
141 >      }      
142 >    }
143  
144 < /**
145 < * Constructor for ForceDecomposition Parallel Decomposition Method
146 < * Will try to construct a symmetric grid of processors. Ideally, the
147 < * number of processors will be a square ex: 4, 9, 16, 25.
148 < *
149 < */
144 >    skipsForRowAtom.clear();
145 >    skipsForRowAtom.reserve(nAtomsInRow_);
146 >    for (int i = 0; i < nAtomsInRow_; i++) {
147 >      int iglob = AtomRowToGlobal[i];
148 >      for (int j = 0; j < nAtomsInCol_; j++) {
149 >        int jglob = AtomColToGlobal[j];        
150 >        if (excludes.hasPair(iglob, jglob))
151 >          skipsForRowAtom[i].push_back(j);      
152 >      }      
153 >    }
154  
155 < ForceDecomposition::ForceDecomposition() {
155 >    toposForRowAtom.clear();
156 >    toposForRowAtom.reserve(nAtomsInRow_);
157 >    for (int i = 0; i < nAtomsInRow_; i++) {
158 >      int iglob = AtomRowToGlobal[i];
159 >      int nTopos = 0;
160 >      for (int j = 0; j < nAtomsInCol_; j++) {
161 >        int jglob = AtomColToGlobal[j];        
162 >        if (oneTwo.hasPair(iglob, jglob)) {
163 >          toposForRowAtom[i].push_back(j);
164 >          topoDistRow[i][nTopos] = 1;
165 >          nTopos++;
166 >        }
167 >        if (oneThree.hasPair(iglob, jglob)) {
168 >          toposForRowAtom[i].push_back(j);
169 >          topoDistRow[i][nTopos] = 2;
170 >          nTopos++;
171 >        }
172 >        if (oneFour.hasPair(iglob, jglob)) {
173 >          toposForRowAtom[i].push_back(j);
174 >          topoDistRow[i][nTopos] = 3;
175 >          nTopos++;
176 >        }
177 >      }      
178 >    }
179  
100 #ifdef IS_MPI
101  int nProcs = MPI::COMM_WORLD.Get_size();
102  int worldRank = MPI::COMM_WORLD.Get_rank();
180   #endif
181  
182 <  // First time through, construct column stride.
183 <  if (communicators.size() == 0)
184 <  {
185 <    int nColumnsMax = (int) round(sqrt((float) nProcs));
186 <    for (int i = 0; i < nProcs; ++i)
187 <    {
188 <      if (nProcs%i==0) nColumns=i;
182 >    groupList_.clear();
183 >    groupList_.reserve(nGroups_);
184 >    for (int i = 0; i < nGroups_; i++) {
185 >      int gid = cgLocalToGlobal[i];
186 >      for (int j = 0; j < nLocal_; j++) {
187 >        int aid = AtomLocalToGlobal[j];
188 >        if (globalGroupMembership[aid] == gid)
189 >          groupList_[i].push_back(j);
190 >      }      
191      }
192  
193 <    int nRows = nProcs/nColumns;    
194 <    myRank_ = (int) worldRank%nColumns;
193 >    skipsForLocalAtom.clear();
194 >    skipsForLocalAtom.reserve(nLocal_);
195 >
196 >    for (int i = 0; i < nLocal_; i++) {
197 >      int iglob = AtomLocalToGlobal[i];
198 >      for (int j = 0; j < nLocal_; j++) {
199 >        int jglob = AtomLocalToGlobal[j];        
200 >        if (excludes.hasPair(iglob, jglob))
201 >          skipsForLocalAtom[i].push_back(j);      
202 >      }      
203 >    }
204 >
205 >    toposForLocalAtom.clear();
206 >    toposForLocalAtom.reserve(nLocal_);
207 >    for (int i = 0; i < nLocal_; i++) {
208 >      int iglob = AtomLocalToGlobal[i];
209 >      int nTopos = 0;
210 >      for (int j = 0; j < nLocal_; j++) {
211 >        int jglob = AtomLocalToGlobal[j];        
212 >        if (oneTwo.hasPair(iglob, jglob)) {
213 >          toposForLocalAtom[i].push_back(j);
214 >          topoDistLocal[i][nTopos] = 1;
215 >          nTopos++;
216 >        }
217 >        if (oneThree.hasPair(iglob, jglob)) {
218 >          toposForLocalAtom[i].push_back(j);
219 >          topoDistLocal[i][nTopos] = 2;
220 >          nTopos++;
221 >        }
222 >        if (oneFour.hasPair(iglob, jglob)) {
223 >          toposForLocalAtom[i].push_back(j);
224 >          topoDistLocal[i][nTopos] = 3;
225 >          nTopos++;
226 >        }
227 >      }      
228 >    }    
229 >
230    }
231 <  else
232 <  {
119 <    myRank_ = myRank/nColumns;
120 <  }
121 <  MPI::Comm newComm = MPI:COMM_WORLD.Split(myRank_,0);
122 <  
123 <  isColumn_ = false;
124 <  
125 < }
231 >  
232 >  void ForceMatrixDecomposition::createGtypeCutoffMap() {
233  
234 < ForceDecomposition::gather(sendbuf, receivebuf){
235 <  communicators(myIndex_).Allgatherv();
236 < }
234 >    RealType tol = 1e-6;
235 >    RealType rc;
236 >    int atid;
237 >    set<AtomType*> atypes = info_->getSimulatedAtomTypes();
238 >    vector<RealType> atypeCutoff;
239 >    atypeCutoff.reserve( atypes.size() );
240 >
241 >    for (set<AtomType*>::iterator at = atypes.begin(); at != atypes.end(); ++at){
242 >      rc = interactionMan_->getSuggestedCutoffRadius(*at);
243 >      atid = (*at)->getIdent();
244 >      atypeCutoff[atid] = rc;
245 >    }
246 >
247 >    vector<RealType> gTypeCutoffs;
248 >
249 >    // first we do a single loop over the cutoff groups to find the
250 >    // largest cutoff for any atypes present in this group.
251 > #ifdef IS_MPI
252 >    vector<RealType> groupCutoffRow(nGroupsInRow_, 0.0);
253 >    for (int cg1 = 0; cg1 < nGroupsInRow_; cg1++) {
254 >      vector<int> atomListRow = getAtomsInGroupRow(cg1);
255 >      for (vector<int>::iterator ia = atomListRow.begin();
256 >           ia != atomListRow.end(); ++ia) {            
257 >        int atom1 = (*ia);
258 >        atid = identsRow[atom1];
259 >        if (atypeCutoff[atid] > groupCutoffRow[cg1]) {
260 >          groupCutoffRow[cg1] = atypeCutoff[atid];
261 >        }
262 >      }
263 >
264 >      bool gTypeFound = false;
265 >      for (int gt = 0; gt < gTypeCutoffs.size(); gt++) {
266 >        if (abs(groupCutoffRow[cg1] - gTypeCutoffs[gt]) < tol) {
267 >          groupRowToGtype[cg1] = gt;
268 >          gTypeFound = true;
269 >        }
270 >      }
271 >      if (!gTypeFound) {
272 >        gTypeCutoffs.push_back( groupCutoffRow[cg1] );
273 >        groupRowToGtype[cg1] = gTypeCutoffs.size() - 1;
274 >      }
275 >      
276 >    }
277 >    vector<RealType> groupCutoffCol(nGroupsInCol_, 0.0);
278 >    for (int cg2 = 0; cg2 < nGroupsInCol_; cg2++) {
279 >      vector<int> atomListCol = getAtomsInGroupColumn(cg2);
280 >      for (vector<int>::iterator jb = atomListCol.begin();
281 >           jb != atomListCol.end(); ++jb) {            
282 >        int atom2 = (*jb);
283 >        atid = identsCol[atom2];
284 >        if (atypeCutoff[atid] > groupCutoffCol[cg2]) {
285 >          groupCutoffCol[cg2] = atypeCutoff[atid];
286 >        }
287 >      }
288 >      bool gTypeFound = false;
289 >      for (int gt = 0; gt < gTypeCutoffs.size(); gt++) {
290 >        if (abs(groupCutoffCol[cg2] - gTypeCutoffs[gt]) < tol) {
291 >          groupColToGtype[cg2] = gt;
292 >          gTypeFound = true;
293 >        }
294 >      }
295 >      if (!gTypeFound) {
296 >        gTypeCutoffs.push_back( groupCutoffCol[cg2] );
297 >        groupColToGtype[cg2] = gTypeCutoffs.size() - 1;
298 >      }
299 >    }
300 > #else
301 >    vector<RealType> groupCutoff(nGroups_, 0.0);
302 >    for (int cg1 = 0; cg1 < nGroups_; cg1++) {
303 >      groupCutoff[cg1] = 0.0;
304 >      vector<int> atomList = getAtomsInGroupRow(cg1);
305 >      for (vector<int>::iterator ia = atomList.begin();
306 >           ia != atomList.end(); ++ia) {            
307 >        int atom1 = (*ia);
308 >        atid = identsLocal[atom1];
309 >        if (atypeCutoff[atid] > groupCutoff[cg1]) {
310 >          groupCutoff[cg1] = atypeCutoff[atid];
311 >        }
312 >      }
313 >
314 >      bool gTypeFound = false;
315 >      for (int gt = 0; gt < gTypeCutoffs.size(); gt++) {
316 >        if (abs(groupCutoff[cg1] - gTypeCutoffs[gt]) < tol) {
317 >          groupToGtype[cg1] = gt;
318 >          gTypeFound = true;
319 >        }
320 >      }
321 >      if (!gTypeFound) {
322 >        gTypeCutoffs.push_back( groupCutoff[cg1] );
323 >        groupToGtype[cg1] = gTypeCutoffs.size() - 1;
324 >      }      
325 >    }
326 > #endif
327 >
328 >    // Now we find the maximum group cutoff value present in the simulation
329 >
330 >    vector<RealType>::iterator groupMaxLoc = max_element(gTypeCutoffs.begin(), gTypeCutoffs.end());
331 >    RealType groupMax = *groupMaxLoc;
332 >
333 > #ifdef IS_MPI
334 >    MPI::COMM_WORLD.Allreduce(&groupMax, &groupMax, 1, MPI::REALTYPE, MPI::MAX);
335 > #endif
336 >    
337 >    RealType tradRcut = groupMax;
338 >
339 >    for (int i = 0; i < gTypeCutoffs.size();  i++) {
340 >      for (int j = 0; j < gTypeCutoffs.size();  j++) {
341 >        
342 >        RealType thisRcut;
343 >        switch(cutoffPolicy_) {
344 >        case TRADITIONAL:
345 >          thisRcut = tradRcut;
346 >        case MIX:
347 >          thisRcut = 0.5 * (gTypeCutoffs[i] + gTypeCutoffs[j]);
348 >        case MAX:
349 >          thisRcut = max(gTypeCutoffs[i], gTypeCutoffs[j]);
350 >        default:
351 >          sprintf(painCave.errMsg,
352 >                  "ForceMatrixDecomposition::createGtypeCutoffMap "
353 >                  "hit an unknown cutoff policy!\n");
354 >          painCave.severity = OPENMD_ERROR;
355 >          painCave.isFatal = 1;
356 >          simError();              
357 >        }
358 >
359 >        pair<int,int> key = make_pair(i,j);
360 >        gTypeCutoffMap[key].first = thisRcut;
361 >
362 >        if (thisRcut > largestRcut_) largestRcut_ = thisRcut;
363 >
364 >        gTypeCutoffMap[key].second = thisRcut*thisRcut;
365 >        
366 >        gTypeCutoffMap[key].third = pow(thisRcut + skinThickness_, 2);
367 >
368 >        // sanity check
369 >        
370 >        if (userChoseCutoff_) {
371 >          if (abs(gTypeCutoffMap[key].first - userCutoff_) > 0.0001) {
372 >            sprintf(painCave.errMsg,
373 >                    "ForceMatrixDecomposition::createGtypeCutoffMap "
374 >                    "user-specified rCut does not match computed group Cutoff\n");
375 >            painCave.severity = OPENMD_ERROR;
376 >            painCave.isFatal = 1;
377 >            simError();            
378 >          }
379 >        }
380 >      }
381 >    }
382 >  }
383 >
384 >
385 >  groupCutoffs ForceMatrixDecomposition::getGroupCutoffs(int cg1, int cg2) {
386 >    int i, j;
387 >
388 > #ifdef IS_MPI
389 >    i = groupRowToGtype[cg1];
390 >    j = groupColToGtype[cg2];
391 > #else
392 >    i = groupToGtype[cg1];
393 >    j = groupToGtype[cg2];
394 > #endif
395 >    
396 >    return gTypeCutoffMap[make_pair(i,j)];
397 >  }
398 >
399 >
400 >  void ForceMatrixDecomposition::zeroWorkArrays() {
401 >
402 >    for (int j = 0; j < N_INTERACTION_FAMILIES; j++) {
403 >      longRangePot_[j] = 0.0;
404 >    }
405 >
406 > #ifdef IS_MPI
407 >    if (storageLayout_ & DataStorage::dslForce) {
408 >      fill(atomRowData.force.begin(), atomRowData.force.end(), V3Zero);
409 >      fill(atomColData.force.begin(), atomColData.force.end(), V3Zero);
410 >    }
411 >
412 >    if (storageLayout_ & DataStorage::dslTorque) {
413 >      fill(atomRowData.torque.begin(), atomRowData.torque.end(), V3Zero);
414 >      fill(atomColData.torque.begin(), atomColData.torque.end(), V3Zero);
415 >    }
416 >    
417 >    fill(pot_row.begin(), pot_row.end(),
418 >         Vector<RealType, N_INTERACTION_FAMILIES> (0.0));
419 >
420 >    fill(pot_col.begin(), pot_col.end(),
421 >         Vector<RealType, N_INTERACTION_FAMILIES> (0.0));
422 >    
423 >    pot_local = Vector<RealType, N_INTERACTION_FAMILIES>(0.0);
424 >
425 >    if (storageLayout_ & DataStorage::dslParticlePot) {    
426 >      fill(atomRowData.particlePot.begin(), atomRowData.particlePot.end(), 0.0);
427 >      fill(atomColData.particlePot.begin(), atomColData.particlePot.end(), 0.0);
428 >    }
429 >
430 >    if (storageLayout_ & DataStorage::dslDensity) {      
431 >      fill(atomRowData.density.begin(), atomRowData.density.end(), 0.0);
432 >      fill(atomColData.density.begin(), atomColData.density.end(), 0.0);
433 >    }
434 >
435 >    if (storageLayout_ & DataStorage::dslFunctional) {  
436 >      fill(atomRowData.functional.begin(), atomRowData.functional.end(), 0.0);
437 >      fill(atomColData.functional.begin(), atomColData.functional.end(), 0.0);
438 >    }
439 >
440 >    if (storageLayout_ & DataStorage::dslFunctionalDerivative) {      
441 >      fill(atomRowData.functionalDerivative.begin(),
442 >           atomRowData.functionalDerivative.end(), 0.0);
443 >      fill(atomColData.functionalDerivative.begin(),
444 >           atomColData.functionalDerivative.end(), 0.0);
445 >    }
446 >
447 > #else
448 >    
449 >    if (storageLayout_ & DataStorage::dslParticlePot) {      
450 >      fill(snap_->atomData.particlePot.begin(),
451 >           snap_->atomData.particlePot.end(), 0.0);
452 >    }
453 >    
454 >    if (storageLayout_ & DataStorage::dslDensity) {      
455 >      fill(snap_->atomData.density.begin(),
456 >           snap_->atomData.density.end(), 0.0);
457 >    }
458 >    if (storageLayout_ & DataStorage::dslFunctional) {
459 >      fill(snap_->atomData.functional.begin(),
460 >           snap_->atomData.functional.end(), 0.0);
461 >    }
462 >    if (storageLayout_ & DataStorage::dslFunctionalDerivative) {      
463 >      fill(snap_->atomData.functionalDerivative.begin(),
464 >           snap_->atomData.functionalDerivative.end(), 0.0);
465 >    }
466 > #endif
467 >    
468 >  }
469 >
470 >
471 >  void ForceMatrixDecomposition::distributeData()  {
472 >    snap_ = sman_->getCurrentSnapshot();
473 >    storageLayout_ = sman_->getStorageLayout();
474 > #ifdef IS_MPI
475 >    
476 >    // gather up the atomic positions
477 >    AtomCommVectorRow->gather(snap_->atomData.position,
478 >                              atomRowData.position);
479 >    AtomCommVectorColumn->gather(snap_->atomData.position,
480 >                                 atomColData.position);
481 >    
482 >    // gather up the cutoff group positions
483 >    cgCommVectorRow->gather(snap_->cgData.position,
484 >                            cgRowData.position);
485 >    cgCommVectorColumn->gather(snap_->cgData.position,
486 >                               cgColData.position);
487 >    
488 >    // if needed, gather the atomic rotation matrices
489 >    if (storageLayout_ & DataStorage::dslAmat) {
490 >      AtomCommMatrixRow->gather(snap_->atomData.aMat,
491 >                                atomRowData.aMat);
492 >      AtomCommMatrixColumn->gather(snap_->atomData.aMat,
493 >                                   atomColData.aMat);
494 >    }
495 >    
496 >    // if needed, gather the atomic eletrostatic frames
497 >    if (storageLayout_ & DataStorage::dslElectroFrame) {
498 >      AtomCommMatrixRow->gather(snap_->atomData.electroFrame,
499 >                                atomRowData.electroFrame);
500 >      AtomCommMatrixColumn->gather(snap_->atomData.electroFrame,
501 >                                   atomColData.electroFrame);
502 >    }
503 > #endif      
504 >  }
505 >  
506 >  /* collects information obtained during the pre-pair loop onto local
507 >   * data structures.
508 >   */
509 >  void ForceMatrixDecomposition::collectIntermediateData() {
510 >    snap_ = sman_->getCurrentSnapshot();
511 >    storageLayout_ = sman_->getStorageLayout();
512 > #ifdef IS_MPI
513 >    
514 >    if (storageLayout_ & DataStorage::dslDensity) {
515 >      
516 >      AtomCommRealRow->scatter(atomRowData.density,
517 >                               snap_->atomData.density);
518 >      
519 >      int n = snap_->atomData.density.size();
520 >      vector<RealType> rho_tmp(n, 0.0);
521 >      AtomCommRealColumn->scatter(atomColData.density, rho_tmp);
522 >      for (int i = 0; i < n; i++)
523 >        snap_->atomData.density[i] += rho_tmp[i];
524 >    }
525 > #endif
526 >  }
527 >
528 >  /*
529 >   * redistributes information obtained during the pre-pair loop out to
530 >   * row and column-indexed data structures
531 >   */
532 >  void ForceMatrixDecomposition::distributeIntermediateData() {
533 >    snap_ = sman_->getCurrentSnapshot();
534 >    storageLayout_ = sman_->getStorageLayout();
535 > #ifdef IS_MPI
536 >    if (storageLayout_ & DataStorage::dslFunctional) {
537 >      AtomCommRealRow->gather(snap_->atomData.functional,
538 >                              atomRowData.functional);
539 >      AtomCommRealColumn->gather(snap_->atomData.functional,
540 >                                 atomColData.functional);
541 >    }
542 >    
543 >    if (storageLayout_ & DataStorage::dslFunctionalDerivative) {
544 >      AtomCommRealRow->gather(snap_->atomData.functionalDerivative,
545 >                              atomRowData.functionalDerivative);
546 >      AtomCommRealColumn->gather(snap_->atomData.functionalDerivative,
547 >                                 atomColData.functionalDerivative);
548 >    }
549 > #endif
550 >  }
551 >  
552 >  
553 >  void ForceMatrixDecomposition::collectData() {
554 >    snap_ = sman_->getCurrentSnapshot();
555 >    storageLayout_ = sman_->getStorageLayout();
556 > #ifdef IS_MPI    
557 >    int n = snap_->atomData.force.size();
558 >    vector<Vector3d> frc_tmp(n, V3Zero);
559 >    
560 >    AtomCommVectorRow->scatter(atomRowData.force, frc_tmp);
561 >    for (int i = 0; i < n; i++) {
562 >      snap_->atomData.force[i] += frc_tmp[i];
563 >      frc_tmp[i] = 0.0;
564 >    }
565 >    
566 >    AtomCommVectorColumn->scatter(atomColData.force, frc_tmp);
567 >    for (int i = 0; i < n; i++)
568 >      snap_->atomData.force[i] += frc_tmp[i];
569 >    
570 >    
571 >    if (storageLayout_ & DataStorage::dslTorque) {
572  
573 +      int nt = snap_->atomData.force.size();
574 +      vector<Vector3d> trq_tmp(nt, V3Zero);
575  
576 +      AtomCommVectorRow->scatter(atomRowData.torque, trq_tmp);
577 +      for (int i = 0; i < n; i++) {
578 +        snap_->atomData.torque[i] += trq_tmp[i];
579 +        trq_tmp[i] = 0.0;
580 +      }
581 +      
582 +      AtomCommVectorColumn->scatter(atomColData.torque, trq_tmp);
583 +      for (int i = 0; i < n; i++)
584 +        snap_->atomData.torque[i] += trq_tmp[i];
585 +    }
586 +    
587 +    nLocal_ = snap_->getNumberOfAtoms();
588  
589 < ForceDecomposition::scatter(sbuffer, rbuffer){
590 <  communicators(myIndex_).Reduce_scatter(sbuffer, recevbuf. recvcounts, MPI::DOUBLE, MPI::SUM);
591 < }
589 >    vector<potVec> pot_temp(nLocal_,
590 >                            Vector<RealType, N_INTERACTION_FAMILIES> (0.0));
591 >
592 >    // scatter/gather pot_row into the members of my column
593 >          
594 >    AtomCommPotRow->scatter(pot_row, pot_temp);
595 >
596 >    for (int ii = 0;  ii < pot_temp.size(); ii++ )
597 >      pot_local += pot_temp[ii];
598 >    
599 >    fill(pot_temp.begin(), pot_temp.end(),
600 >         Vector<RealType, N_INTERACTION_FAMILIES> (0.0));
601 >      
602 >    AtomCommPotColumn->scatter(pot_col, pot_temp);    
603 >    
604 >    for (int ii = 0;  ii < pot_temp.size(); ii++ )
605 >      pot_local += pot_temp[ii];
606 >    
607 > #endif
608 >  }
609 >
610 >  int ForceMatrixDecomposition::getNAtomsInRow() {  
611 > #ifdef IS_MPI
612 >    return nAtomsInRow_;
613 > #else
614 >    return nLocal_;
615 > #endif
616 >  }
617 >
618 >  /**
619 >   * returns the list of atoms belonging to this group.  
620 >   */
621 >  vector<int> ForceMatrixDecomposition::getAtomsInGroupRow(int cg1){
622 > #ifdef IS_MPI
623 >    return groupListRow_[cg1];
624 > #else
625 >    return groupList_[cg1];
626 > #endif
627 >  }
628 >
629 >  vector<int> ForceMatrixDecomposition::getAtomsInGroupColumn(int cg2){
630 > #ifdef IS_MPI
631 >    return groupListCol_[cg2];
632 > #else
633 >    return groupList_[cg2];
634 > #endif
635 >  }
636 >  
637 >  Vector3d ForceMatrixDecomposition::getIntergroupVector(int cg1, int cg2){
638 >    Vector3d d;
639 >    
640 > #ifdef IS_MPI
641 >    d = cgColData.position[cg2] - cgRowData.position[cg1];
642 > #else
643 >    d = snap_->cgData.position[cg2] - snap_->cgData.position[cg1];
644 > #endif
645 >    
646 >    snap_->wrapVector(d);
647 >    return d;    
648 >  }
649 >
650 >
651 >  Vector3d ForceMatrixDecomposition::getAtomToGroupVectorRow(int atom1, int cg1){
652 >
653 >    Vector3d d;
654 >    
655 > #ifdef IS_MPI
656 >    d = cgRowData.position[cg1] - atomRowData.position[atom1];
657 > #else
658 >    d = snap_->cgData.position[cg1] - snap_->atomData.position[atom1];
659 > #endif
660 >
661 >    snap_->wrapVector(d);
662 >    return d;    
663 >  }
664 >  
665 >  Vector3d ForceMatrixDecomposition::getAtomToGroupVectorColumn(int atom2, int cg2){
666 >    Vector3d d;
667 >    
668 > #ifdef IS_MPI
669 >    d = cgColData.position[cg2] - atomColData.position[atom2];
670 > #else
671 >    d = snap_->cgData.position[cg2] - snap_->atomData.position[atom2];
672 > #endif
673 >    
674 >    snap_->wrapVector(d);
675 >    return d;    
676 >  }
677 >
678 >  RealType ForceMatrixDecomposition::getMassFactorRow(int atom1) {
679 > #ifdef IS_MPI
680 >    return massFactorsRow[atom1];
681 > #else
682 >    return massFactorsLocal[atom1];
683 > #endif
684 >  }
685 >
686 >  RealType ForceMatrixDecomposition::getMassFactorColumn(int atom2) {
687 > #ifdef IS_MPI
688 >    return massFactorsCol[atom2];
689 > #else
690 >    return massFactorsLocal[atom2];
691 > #endif
692 >
693 >  }
694 >    
695 >  Vector3d ForceMatrixDecomposition::getInteratomicVector(int atom1, int atom2){
696 >    Vector3d d;
697 >    
698 > #ifdef IS_MPI
699 >    d = atomColData.position[atom2] - atomRowData.position[atom1];
700 > #else
701 >    d = snap_->atomData.position[atom2] - snap_->atomData.position[atom1];
702 > #endif
703 >
704 >    snap_->wrapVector(d);
705 >    return d;    
706 >  }
707 >
708 >  vector<int> ForceMatrixDecomposition::getSkipsForRowAtom(int atom1) {
709 > #ifdef IS_MPI
710 >    return skipsForRowAtom[atom1];
711 > #else
712 >    return skipsForLocalAtom[atom1];
713 > #endif
714 >  }
715 >
716 >  /**
717 >   * There are a number of reasons to skip a pair or a
718 >   * particle. Mostly we do this to exclude atoms who are involved in
719 >   * short range interactions (bonds, bends, torsions), but we also
720 >   * need to exclude some overcounted interactions that result from
721 >   * the parallel decomposition.
722 >   */
723 >  bool ForceMatrixDecomposition::skipAtomPair(int atom1, int atom2) {
724 >    int unique_id_1, unique_id_2;
725 >
726 > #ifdef IS_MPI
727 >    // in MPI, we have to look up the unique IDs for each atom
728 >    unique_id_1 = AtomRowToGlobal[atom1];
729 >    unique_id_2 = AtomColToGlobal[atom2];
730 >
731 >    // this situation should only arise in MPI simulations
732 >    if (unique_id_1 == unique_id_2) return true;
733 >    
734 >    // this prevents us from doing the pair on multiple processors
735 >    if (unique_id_1 < unique_id_2) {
736 >      if ((unique_id_1 + unique_id_2) % 2 == 0) return true;
737 >    } else {
738 >      if ((unique_id_1 + unique_id_2) % 2 == 1) return true;
739 >    }
740 > #else
741 >    // in the normal loop, the atom numbers are unique
742 >    unique_id_1 = atom1;
743 >    unique_id_2 = atom2;
744 > #endif
745 >    
746 > #ifdef IS_MPI
747 >    for (vector<int>::iterator i = skipsForRowAtom[atom1].begin();
748 >         i != skipsForRowAtom[atom1].end(); ++i) {
749 >      if ( (*i) == unique_id_2 ) return true;
750 >    }    
751 > #else
752 >    for (vector<int>::iterator i = skipsForLocalAtom[atom1].begin();
753 >         i != skipsForLocalAtom[atom1].end(); ++i) {
754 >      if ( (*i) == unique_id_2 ) return true;
755 >    }    
756 > #endif
757 >  }
758 >
759 >  int ForceMatrixDecomposition::getTopoDistance(int atom1, int atom2) {
760 >    
761 > #ifdef IS_MPI
762 >    for (int i = 0; i < toposForRowAtom[atom1].size(); i++) {
763 >      if ( toposForRowAtom[atom1][i] == atom2 ) return topoDistRow[atom1][i];
764 >    }
765 > #else
766 >    for (int i = 0; i < toposForLocalAtom[atom1].size(); i++) {
767 >      if ( toposForLocalAtom[atom1][i] == atom2 ) return topoDistLocal[atom1][i];
768 >    }
769 > #endif
770 >
771 >    // zero is default for unconnected (i.e. normal) pair interactions
772 >    return 0;
773 >  }
774 >
775 >  void ForceMatrixDecomposition::addForceToAtomRow(int atom1, Vector3d fg){
776 > #ifdef IS_MPI
777 >    atomRowData.force[atom1] += fg;
778 > #else
779 >    snap_->atomData.force[atom1] += fg;
780 > #endif
781 >  }
782 >
783 >  void ForceMatrixDecomposition::addForceToAtomColumn(int atom2, Vector3d fg){
784 > #ifdef IS_MPI
785 >    atomColData.force[atom2] += fg;
786 > #else
787 >    snap_->atomData.force[atom2] += fg;
788 > #endif
789 >  }
790 >
791 >    // filling interaction blocks with pointers
792 >  InteractionData ForceMatrixDecomposition::fillInteractionData(int atom1, int atom2) {    
793 >    InteractionData idat;
794 >
795 > #ifdef IS_MPI
796 >    
797 >    idat.atypes = make_pair( ff_->getAtomType(identsRow[atom1]),
798 >                             ff_->getAtomType(identsCol[atom2]) );
799 >
800 >    
801 >    if (storageLayout_ & DataStorage::dslAmat) {
802 >      idat.A1 = &(atomRowData.aMat[atom1]);
803 >      idat.A2 = &(atomColData.aMat[atom2]);
804 >    }
805 >    
806 >    if (storageLayout_ & DataStorage::dslElectroFrame) {
807 >      idat.eFrame1 = &(atomRowData.electroFrame[atom1]);
808 >      idat.eFrame2 = &(atomColData.electroFrame[atom2]);
809 >    }
810 >
811 >    if (storageLayout_ & DataStorage::dslTorque) {
812 >      idat.t1 = &(atomRowData.torque[atom1]);
813 >      idat.t2 = &(atomColData.torque[atom2]);
814 >    }
815 >
816 >    if (storageLayout_ & DataStorage::dslDensity) {
817 >      idat.rho1 = &(atomRowData.density[atom1]);
818 >      idat.rho2 = &(atomColData.density[atom2]);
819 >    }
820 >
821 >    if (storageLayout_ & DataStorage::dslFunctional) {
822 >      idat.frho1 = &(atomRowData.functional[atom1]);
823 >      idat.frho2 = &(atomColData.functional[atom2]);
824 >    }
825 >
826 >    if (storageLayout_ & DataStorage::dslFunctionalDerivative) {
827 >      idat.dfrho1 = &(atomRowData.functionalDerivative[atom1]);
828 >      idat.dfrho2 = &(atomColData.functionalDerivative[atom2]);
829 >    }
830 >
831 >    if (storageLayout_ & DataStorage::dslParticlePot) {
832 >      idat.particlePot1 = &(atomRowData.particlePot[atom1]);
833 >      idat.particlePot2 = &(atomColData.particlePot[atom2]);
834 >    }
835  
836 + #else
837  
838 +    idat.atypes = make_pair( ff_->getAtomType(identsLocal[atom1]),
839 +                             ff_->getAtomType(identsLocal[atom2]) );
840 +
841 +    if (storageLayout_ & DataStorage::dslAmat) {
842 +      idat.A1 = &(snap_->atomData.aMat[atom1]);
843 +      idat.A2 = &(snap_->atomData.aMat[atom2]);
844 +    }
845 +
846 +    if (storageLayout_ & DataStorage::dslElectroFrame) {
847 +      idat.eFrame1 = &(snap_->atomData.electroFrame[atom1]);
848 +      idat.eFrame2 = &(snap_->atomData.electroFrame[atom2]);
849 +    }
850 +
851 +    if (storageLayout_ & DataStorage::dslTorque) {
852 +      idat.t1 = &(snap_->atomData.torque[atom1]);
853 +      idat.t2 = &(snap_->atomData.torque[atom2]);
854 +    }
855 +
856 +    if (storageLayout_ & DataStorage::dslDensity) {
857 +      idat.rho1 = &(snap_->atomData.density[atom1]);
858 +      idat.rho2 = &(snap_->atomData.density[atom2]);
859 +    }
860 +
861 +    if (storageLayout_ & DataStorage::dslFunctional) {
862 +      idat.frho1 = &(snap_->atomData.functional[atom1]);
863 +      idat.frho2 = &(snap_->atomData.functional[atom2]);
864 +    }
865 +
866 +    if (storageLayout_ & DataStorage::dslFunctionalDerivative) {
867 +      idat.dfrho1 = &(snap_->atomData.functionalDerivative[atom1]);
868 +      idat.dfrho2 = &(snap_->atomData.functionalDerivative[atom2]);
869 +    }
870 +
871 +    if (storageLayout_ & DataStorage::dslParticlePot) {
872 +      idat.particlePot1 = &(snap_->atomData.particlePot[atom1]);
873 +      idat.particlePot2 = &(snap_->atomData.particlePot[atom2]);
874 +    }
875 +
876 + #endif
877 +    return idat;
878 +  }
879 +
880 +  
881 +  void ForceMatrixDecomposition::unpackInteractionData(InteractionData idat, int atom1, int atom2) {    
882 + #ifdef IS_MPI
883 +    pot_row[atom1] += 0.5 *  *(idat.pot);
884 +    pot_col[atom2] += 0.5 *  *(idat.pot);
885 +
886 +    atomRowData.force[atom1] += *(idat.f1);
887 +    atomColData.force[atom2] -= *(idat.f1);
888 + #else
889 +    longRangePot_ += *(idat.pot);
890 +    
891 +    snap_->atomData.force[atom1] += *(idat.f1);
892 +    snap_->atomData.force[atom2] -= *(idat.f1);
893 + #endif
894 +
895 +  }
896 +
897 +
898 +  InteractionData ForceMatrixDecomposition::fillSkipData(int atom1, int atom2){
899 +
900 +    InteractionData idat;
901 + #ifdef IS_MPI
902 +    idat.atypes = make_pair( ff_->getAtomType(identsRow[atom1]),
903 +                             ff_->getAtomType(identsCol[atom2]) );
904 +
905 +    if (storageLayout_ & DataStorage::dslElectroFrame) {
906 +      idat.eFrame1 = &(atomRowData.electroFrame[atom1]);
907 +      idat.eFrame2 = &(atomColData.electroFrame[atom2]);
908 +    }
909 +    if (storageLayout_ & DataStorage::dslTorque) {
910 +      idat.t1 = &(atomRowData.torque[atom1]);
911 +      idat.t2 = &(atomColData.torque[atom2]);
912 +    }
913 + #else
914 +    idat.atypes = make_pair( ff_->getAtomType(identsLocal[atom1]),
915 +                             ff_->getAtomType(identsLocal[atom2]) );
916 +
917 +    if (storageLayout_ & DataStorage::dslElectroFrame) {
918 +      idat.eFrame1 = &(snap_->atomData.electroFrame[atom1]);
919 +      idat.eFrame2 = &(snap_->atomData.electroFrame[atom2]);
920 +    }
921 +    if (storageLayout_ & DataStorage::dslTorque) {
922 +      idat.t1 = &(snap_->atomData.torque[atom1]);
923 +      idat.t2 = &(snap_->atomData.torque[atom2]);
924 +    }
925 + #endif    
926 +  }
927 +
928 +  /*
929 +   * buildNeighborList
930 +   *
931 +   * first element of pair is row-indexed CutoffGroup
932 +   * second element of pair is column-indexed CutoffGroup
933 +   */
934 +  vector<pair<int, int> > ForceMatrixDecomposition::buildNeighborList() {
935 +      
936 +    vector<pair<int, int> > neighborList;
937 +    groupCutoffs cuts;
938 + #ifdef IS_MPI
939 +    cellListRow_.clear();
940 +    cellListCol_.clear();
941 + #else
942 +    cellList_.clear();
943 + #endif
944 +
945 +    RealType rList_ = (largestRcut_ + skinThickness_);
946 +    RealType rl2 = rList_ * rList_;
947 +    Snapshot* snap_ = sman_->getCurrentSnapshot();
948 +    Mat3x3d Hmat = snap_->getHmat();
949 +    Vector3d Hx = Hmat.getColumn(0);
950 +    Vector3d Hy = Hmat.getColumn(1);
951 +    Vector3d Hz = Hmat.getColumn(2);
952 +
953 +    nCells_.x() = (int) ( Hx.length() )/ rList_;
954 +    nCells_.y() = (int) ( Hy.length() )/ rList_;
955 +    nCells_.z() = (int) ( Hz.length() )/ rList_;
956 +
957 +    Mat3x3d invHmat = snap_->getInvHmat();
958 +    Vector3d rs, scaled, dr;
959 +    Vector3i whichCell;
960 +    int cellIndex;
961 +
962 + #ifdef IS_MPI
963 +    for (int i = 0; i < nGroupsInRow_; i++) {
964 +      rs = cgRowData.position[i];
965 +      // scaled positions relative to the box vectors
966 +      scaled = invHmat * rs;
967 +      // wrap the vector back into the unit box by subtracting integer box
968 +      // numbers
969 +      for (int j = 0; j < 3; j++)
970 +        scaled[j] -= roundMe(scaled[j]);
971 +    
972 +      // find xyz-indices of cell that cutoffGroup is in.
973 +      whichCell.x() = nCells_.x() * scaled.x();
974 +      whichCell.y() = nCells_.y() * scaled.y();
975 +      whichCell.z() = nCells_.z() * scaled.z();
976 +
977 +      // find single index of this cell:
978 +      cellIndex = Vlinear(whichCell, nCells_);
979 +      // add this cutoff group to the list of groups in this cell;
980 +      cellListRow_[cellIndex].push_back(i);
981 +    }
982 +
983 +    for (int i = 0; i < nGroupsInCol_; i++) {
984 +      rs = cgColData.position[i];
985 +      // scaled positions relative to the box vectors
986 +      scaled = invHmat * rs;
987 +      // wrap the vector back into the unit box by subtracting integer box
988 +      // numbers
989 +      for (int j = 0; j < 3; j++)
990 +        scaled[j] -= roundMe(scaled[j]);
991 +
992 +      // find xyz-indices of cell that cutoffGroup is in.
993 +      whichCell.x() = nCells_.x() * scaled.x();
994 +      whichCell.y() = nCells_.y() * scaled.y();
995 +      whichCell.z() = nCells_.z() * scaled.z();
996 +
997 +      // find single index of this cell:
998 +      cellIndex = Vlinear(whichCell, nCells_);
999 +      // add this cutoff group to the list of groups in this cell;
1000 +      cellListCol_[cellIndex].push_back(i);
1001 +    }
1002 + #else
1003 +    for (int i = 0; i < nGroups_; i++) {
1004 +      rs = snap_->cgData.position[i];
1005 +      // scaled positions relative to the box vectors
1006 +      scaled = invHmat * rs;
1007 +      // wrap the vector back into the unit box by subtracting integer box
1008 +      // numbers
1009 +      for (int j = 0; j < 3; j++)
1010 +        scaled[j] -= roundMe(scaled[j]);
1011 +
1012 +      // find xyz-indices of cell that cutoffGroup is in.
1013 +      whichCell.x() = nCells_.x() * scaled.x();
1014 +      whichCell.y() = nCells_.y() * scaled.y();
1015 +      whichCell.z() = nCells_.z() * scaled.z();
1016 +
1017 +      // find single index of this cell:
1018 +      cellIndex = Vlinear(whichCell, nCells_);
1019 +      // add this cutoff group to the list of groups in this cell;
1020 +      cellList_[cellIndex].push_back(i);
1021 +    }
1022 + #endif
1023 +
1024 +    for (int m1z = 0; m1z < nCells_.z(); m1z++) {
1025 +      for (int m1y = 0; m1y < nCells_.y(); m1y++) {
1026 +        for (int m1x = 0; m1x < nCells_.x(); m1x++) {
1027 +          Vector3i m1v(m1x, m1y, m1z);
1028 +          int m1 = Vlinear(m1v, nCells_);
1029 +
1030 +          for (vector<Vector3i>::iterator os = cellOffsets_.begin();
1031 +               os != cellOffsets_.end(); ++os) {
1032 +            
1033 +            Vector3i m2v = m1v + (*os);
1034 +            
1035 +            if (m2v.x() >= nCells_.x()) {
1036 +              m2v.x() = 0;          
1037 +            } else if (m2v.x() < 0) {
1038 +              m2v.x() = nCells_.x() - 1;
1039 +            }
1040 +            
1041 +            if (m2v.y() >= nCells_.y()) {
1042 +              m2v.y() = 0;          
1043 +            } else if (m2v.y() < 0) {
1044 +              m2v.y() = nCells_.y() - 1;
1045 +            }
1046 +            
1047 +            if (m2v.z() >= nCells_.z()) {
1048 +              m2v.z() = 0;          
1049 +            } else if (m2v.z() < 0) {
1050 +              m2v.z() = nCells_.z() - 1;
1051 +            }
1052 +            
1053 +            int m2 = Vlinear (m2v, nCells_);
1054 +
1055 + #ifdef IS_MPI
1056 +            for (vector<int>::iterator j1 = cellListRow_[m1].begin();
1057 +                 j1 != cellListRow_[m1].end(); ++j1) {
1058 +              for (vector<int>::iterator j2 = cellListCol_[m2].begin();
1059 +                   j2 != cellListCol_[m2].end(); ++j2) {
1060 +                              
1061 +                // Always do this if we're in different cells or if
1062 +                // we're in the same cell and the global index of the
1063 +                // j2 cutoff group is less than the j1 cutoff group
1064 +
1065 +                if (m2 != m1 || cgColToGlobal[(*j2)] < cgRowToGlobal[(*j1)]) {
1066 +                  dr = cgColData.position[(*j2)] - cgRowData.position[(*j1)];
1067 +                  snap_->wrapVector(dr);
1068 +                  cuts = getGroupCutoffs( (*j1), (*j2) );
1069 +                  if (dr.lengthSquare() < cuts.third) {
1070 +                    neighborList.push_back(make_pair((*j1), (*j2)));
1071 +                  }
1072 +                }
1073 +              }
1074 +            }
1075 + #else
1076 +            for (vector<int>::iterator j1 = cellList_[m1].begin();
1077 +                 j1 != cellList_[m1].end(); ++j1) {
1078 +              for (vector<int>::iterator j2 = cellList_[m2].begin();
1079 +                   j2 != cellList_[m2].end(); ++j2) {
1080 +                              
1081 +                // Always do this if we're in different cells or if
1082 +                // we're in the same cell and the global index of the
1083 +                // j2 cutoff group is less than the j1 cutoff group
1084 +
1085 +                if (m2 != m1 || (*j2) < (*j1)) {
1086 +                  dr = snap_->cgData.position[(*j2)] - snap_->cgData.position[(*j1)];
1087 +                  snap_->wrapVector(dr);
1088 +                  cuts = getGroupCutoffs( (*j1), (*j2) );
1089 +                  if (dr.lengthSquare() < cuts.third) {
1090 +                    neighborList.push_back(make_pair((*j1), (*j2)));
1091 +                  }
1092 +                }
1093 +              }
1094 +            }
1095 + #endif
1096 +          }
1097 +        }
1098 +      }
1099 +    }
1100 +
1101 +    // save the local cutoff group positions for the check that is
1102 +    // done on each loop:
1103 +    saved_CG_positions_.clear();
1104 +    for (int i = 0; i < nGroups_; i++)
1105 +      saved_CG_positions_.push_back(snap_->cgData.position[i]);
1106 +
1107 +    return neighborList;
1108 +  }
1109 + } //end namespace OpenMD

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