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root/OpenMD/trunk/src/parallel/ForceMatrixDecomposition.cpp
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branches/development/src/parallel/ForceDecomposition.cpp (file contents), Revision 1540 by gezelter, Mon Jan 17 21:34:36 2011 UTC vs.
trunk/src/parallel/ForceMatrixDecomposition.cpp (file contents), Revision 1896 by gezelter, Tue Jul 2 20:02:31 2013 UTC

# Line 35 | Line 35
35   *                                                                      
36   * [1]  Meineke, et al., J. Comp. Chem. 26, 252-271 (2005).            
37   * [2]  Fennell & Gezelter, J. Chem. Phys. 124, 234104 (2006).          
38 < * [3]  Sun, Lin & Gezelter, J. Chem. Phys. 128, 24107 (2008).          
39 < * [4]  Vardeman & Gezelter, in progress (2009).                        
38 > * [3]  Sun, Lin & Gezelter, J. Chem. Phys. 128, 234107 (2008).          
39 > * [4]  Kuang & Gezelter,  J. Chem. Phys. 133, 164101 (2010).
40 > * [5]  Vardeman, Stocker & Gezelter, J. Chem. Theory Comput. 7, 834 (2011).
41   */
42 < #include "parallel/ForceDecomposition.hpp"
42 < #include "parallel/Communicator.hpp"
42 > #include "parallel/ForceMatrixDecomposition.hpp"
43   #include "math/SquareMatrix3.hpp"
44 + #include "nonbonded/NonBondedInteraction.hpp"
45 + #include "brains/SnapshotManager.hpp"
46 + #include "brains/PairList.hpp"
47  
48 + using namespace std;
49   namespace OpenMD {
50  
51 <  void ForceDecomposition::distributeInitialData() {
51 >  ForceMatrixDecomposition::ForceMatrixDecomposition(SimInfo* info, InteractionManager* iMan) : ForceDecomposition(info, iMan) {
52 >
53 >    // In a parallel computation, row and colum scans must visit all
54 >    // surrounding cells (not just the 14 upper triangular blocks that
55 >    // are used when the processor can see all pairs)
56   #ifdef IS_MPI
57 +    cellOffsets_.clear();
58 +    cellOffsets_.push_back( Vector3i(-1,-1,-1) );
59 +    cellOffsets_.push_back( Vector3i( 0,-1,-1) );
60 +    cellOffsets_.push_back( Vector3i( 1,-1,-1) );                          
61 +    cellOffsets_.push_back( Vector3i(-1, 0,-1) );
62 +    cellOffsets_.push_back( Vector3i( 0, 0,-1) );
63 +    cellOffsets_.push_back( Vector3i( 1, 0,-1) );
64 +    cellOffsets_.push_back( Vector3i(-1, 1,-1) );
65 +    cellOffsets_.push_back( Vector3i( 0, 1,-1) );      
66 +    cellOffsets_.push_back( Vector3i( 1, 1,-1) );
67 +    cellOffsets_.push_back( Vector3i(-1,-1, 0) );
68 +    cellOffsets_.push_back( Vector3i( 0,-1, 0) );
69 +    cellOffsets_.push_back( Vector3i( 1,-1, 0) );
70 +    cellOffsets_.push_back( Vector3i(-1, 0, 0) );      
71 +    cellOffsets_.push_back( Vector3i( 0, 0, 0) );
72 +    cellOffsets_.push_back( Vector3i( 1, 0, 0) );
73 +    cellOffsets_.push_back( Vector3i(-1, 1, 0) );
74 +    cellOffsets_.push_back( Vector3i( 0, 1, 0) );
75 +    cellOffsets_.push_back( Vector3i( 1, 1, 0) );
76 +    cellOffsets_.push_back( Vector3i(-1,-1, 1) );
77 +    cellOffsets_.push_back( Vector3i( 0,-1, 1) );
78 +    cellOffsets_.push_back( Vector3i( 1,-1, 1) );
79 +    cellOffsets_.push_back( Vector3i(-1, 0, 1) );
80 +    cellOffsets_.push_back( Vector3i( 0, 0, 1) );
81 +    cellOffsets_.push_back( Vector3i( 1, 0, 1) );
82 +    cellOffsets_.push_back( Vector3i(-1, 1, 1) );
83 +    cellOffsets_.push_back( Vector3i( 0, 1, 1) );
84 +    cellOffsets_.push_back( Vector3i( 1, 1, 1) );
85 + #endif    
86 +  }
87  
50    int nAtoms;
51    int nGroups;
88  
89 <    AtomCommRealI = new Communicator<Row,RealType>(nAtoms);
90 <    AtomCommVectorI = new Communicator<Row,Vector3d>(nAtoms);
91 <    AtomCommMatrixI = new Communicator<Row,Mat3x3d>(nAtoms);
89 >  /**
90 >   * distributeInitialData is essentially a copy of the older fortran
91 >   * SimulationSetup
92 >   */
93 >  void ForceMatrixDecomposition::distributeInitialData() {
94 >    snap_ = sman_->getCurrentSnapshot();
95 >    storageLayout_ = sman_->getStorageLayout();
96 >    ff_ = info_->getForceField();
97 >    nLocal_ = snap_->getNumberOfAtoms();
98 >  
99 >    nGroups_ = info_->getNLocalCutoffGroups();
100 >    // gather the information for atomtype IDs (atids):
101 >    idents = info_->getIdentArray();
102 >    AtomLocalToGlobal = info_->getGlobalAtomIndices();
103 >    cgLocalToGlobal = info_->getGlobalGroupIndices();
104 >    vector<int> globalGroupMembership = info_->getGlobalGroupMembership();
105  
106 <    AtomCommRealJ = new Communicator<Column,RealType>(nAtoms);
58 <    AtomCommVectorJ = new Communicator<Column,Vector3d>(nAtoms);
59 <    AtomCommMatrixJ = new Communicator<Column,Mat3x3d>(nAtoms);
106 >    massFactors = info_->getMassFactors();
107  
108 <    cgCommVectorI = new Communicator<Row,Vector3d>(nGroups);
109 <    cgCommVectorJ = new Communicator<Column,Vector3d>(nGroups);
110 <    // more to come
108 >    PairList* excludes = info_->getExcludedInteractions();
109 >    PairList* oneTwo = info_->getOneTwoInteractions();
110 >    PairList* oneThree = info_->getOneThreeInteractions();
111 >    PairList* oneFour = info_->getOneFourInteractions();
112 >    
113 >    if (needVelocities_)
114 >      snap_->cgData.setStorageLayout(DataStorage::dslPosition |
115 >                                     DataStorage::dslVelocity);
116 >    else
117 >      snap_->cgData.setStorageLayout(DataStorage::dslPosition);
118 >    
119 > #ifdef IS_MPI
120 >
121 >    MPI::Intracomm row = rowComm.getComm();
122 >    MPI::Intracomm col = colComm.getComm();
123 >
124 >    AtomPlanIntRow = new Plan<int>(row, nLocal_);
125 >    AtomPlanRealRow = new Plan<RealType>(row, nLocal_);
126 >    AtomPlanVectorRow = new Plan<Vector3d>(row, nLocal_);
127 >    AtomPlanMatrixRow = new Plan<Mat3x3d>(row, nLocal_);
128 >    AtomPlanPotRow = new Plan<potVec>(row, nLocal_);
129 >
130 >    AtomPlanIntColumn = new Plan<int>(col, nLocal_);
131 >    AtomPlanRealColumn = new Plan<RealType>(col, nLocal_);
132 >    AtomPlanVectorColumn = new Plan<Vector3d>(col, nLocal_);
133 >    AtomPlanMatrixColumn = new Plan<Mat3x3d>(col, nLocal_);
134 >    AtomPlanPotColumn = new Plan<potVec>(col, nLocal_);
135 >
136 >    cgPlanIntRow = new Plan<int>(row, nGroups_);
137 >    cgPlanVectorRow = new Plan<Vector3d>(row, nGroups_);
138 >    cgPlanIntColumn = new Plan<int>(col, nGroups_);
139 >    cgPlanVectorColumn = new Plan<Vector3d>(col, nGroups_);
140 >
141 >    nAtomsInRow_ = AtomPlanIntRow->getSize();
142 >    nAtomsInCol_ = AtomPlanIntColumn->getSize();
143 >    nGroupsInRow_ = cgPlanIntRow->getSize();
144 >    nGroupsInCol_ = cgPlanIntColumn->getSize();
145 >
146 >    // Modify the data storage objects with the correct layouts and sizes:
147 >    atomRowData.resize(nAtomsInRow_);
148 >    atomRowData.setStorageLayout(storageLayout_);
149 >    atomColData.resize(nAtomsInCol_);
150 >    atomColData.setStorageLayout(storageLayout_);
151 >    cgRowData.resize(nGroupsInRow_);
152 >    cgRowData.setStorageLayout(DataStorage::dslPosition);
153 >    cgColData.resize(nGroupsInCol_);
154 >    if (needVelocities_)
155 >      // we only need column velocities if we need them.
156 >      cgColData.setStorageLayout(DataStorage::dslPosition |
157 >                                 DataStorage::dslVelocity);
158 >    else    
159 >      cgColData.setStorageLayout(DataStorage::dslPosition);
160 >      
161 >    identsRow.resize(nAtomsInRow_);
162 >    identsCol.resize(nAtomsInCol_);
163 >    
164 >    AtomPlanIntRow->gather(idents, identsRow);
165 >    AtomPlanIntColumn->gather(idents, identsCol);
166 >    
167 >    // allocate memory for the parallel objects
168 >    atypesRow.resize(nAtomsInRow_);
169 >    atypesCol.resize(nAtomsInCol_);
170 >
171 >    for (int i = 0; i < nAtomsInRow_; i++)
172 >      atypesRow[i] = ff_->getAtomType(identsRow[i]);
173 >    for (int i = 0; i < nAtomsInCol_; i++)
174 >      atypesCol[i] = ff_->getAtomType(identsCol[i]);        
175 >
176 >    pot_row.resize(nAtomsInRow_);
177 >    pot_col.resize(nAtomsInCol_);
178 >
179 >    expot_row.resize(nAtomsInRow_);
180 >    expot_col.resize(nAtomsInCol_);
181 >
182 >    AtomRowToGlobal.resize(nAtomsInRow_);
183 >    AtomColToGlobal.resize(nAtomsInCol_);
184 >    AtomPlanIntRow->gather(AtomLocalToGlobal, AtomRowToGlobal);
185 >    AtomPlanIntColumn->gather(AtomLocalToGlobal, AtomColToGlobal);
186 >
187 >    cgRowToGlobal.resize(nGroupsInRow_);
188 >    cgColToGlobal.resize(nGroupsInCol_);
189 >    cgPlanIntRow->gather(cgLocalToGlobal, cgRowToGlobal);
190 >    cgPlanIntColumn->gather(cgLocalToGlobal, cgColToGlobal);
191 >
192 >    massFactorsRow.resize(nAtomsInRow_);
193 >    massFactorsCol.resize(nAtomsInCol_);
194 >    AtomPlanRealRow->gather(massFactors, massFactorsRow);
195 >    AtomPlanRealColumn->gather(massFactors, massFactorsCol);
196 >
197 >    groupListRow_.clear();
198 >    groupListRow_.resize(nGroupsInRow_);
199 >    for (int i = 0; i < nGroupsInRow_; i++) {
200 >      int gid = cgRowToGlobal[i];
201 >      for (int j = 0; j < nAtomsInRow_; j++) {
202 >        int aid = AtomRowToGlobal[j];
203 >        if (globalGroupMembership[aid] == gid)
204 >          groupListRow_[i].push_back(j);
205 >      }      
206 >    }
207 >
208 >    groupListCol_.clear();
209 >    groupListCol_.resize(nGroupsInCol_);
210 >    for (int i = 0; i < nGroupsInCol_; i++) {
211 >      int gid = cgColToGlobal[i];
212 >      for (int j = 0; j < nAtomsInCol_; j++) {
213 >        int aid = AtomColToGlobal[j];
214 >        if (globalGroupMembership[aid] == gid)
215 >          groupListCol_[i].push_back(j);
216 >      }      
217 >    }
218 >
219 >    excludesForAtom.clear();
220 >    excludesForAtom.resize(nAtomsInRow_);
221 >    toposForAtom.clear();
222 >    toposForAtom.resize(nAtomsInRow_);
223 >    topoDist.clear();
224 >    topoDist.resize(nAtomsInRow_);
225 >    for (int i = 0; i < nAtomsInRow_; i++) {
226 >      int iglob = AtomRowToGlobal[i];
227 >
228 >      for (int j = 0; j < nAtomsInCol_; j++) {
229 >        int jglob = AtomColToGlobal[j];
230 >
231 >        if (excludes->hasPair(iglob, jglob))
232 >          excludesForAtom[i].push_back(j);      
233 >        
234 >        if (oneTwo->hasPair(iglob, jglob)) {
235 >          toposForAtom[i].push_back(j);
236 >          topoDist[i].push_back(1);
237 >        } else {
238 >          if (oneThree->hasPair(iglob, jglob)) {
239 >            toposForAtom[i].push_back(j);
240 >            topoDist[i].push_back(2);
241 >          } else {
242 >            if (oneFour->hasPair(iglob, jglob)) {
243 >              toposForAtom[i].push_back(j);
244 >              topoDist[i].push_back(3);
245 >            }
246 >          }
247 >        }
248 >      }      
249 >    }
250 >
251 > #else
252 >    excludesForAtom.clear();
253 >    excludesForAtom.resize(nLocal_);
254 >    toposForAtom.clear();
255 >    toposForAtom.resize(nLocal_);
256 >    topoDist.clear();
257 >    topoDist.resize(nLocal_);
258 >
259 >    for (int i = 0; i < nLocal_; i++) {
260 >      int iglob = AtomLocalToGlobal[i];
261 >
262 >      for (int j = 0; j < nLocal_; j++) {
263 >        int jglob = AtomLocalToGlobal[j];
264 >
265 >        if (excludes->hasPair(iglob, jglob))
266 >          excludesForAtom[i].push_back(j);              
267 >        
268 >        if (oneTwo->hasPair(iglob, jglob)) {
269 >          toposForAtom[i].push_back(j);
270 >          topoDist[i].push_back(1);
271 >        } else {
272 >          if (oneThree->hasPair(iglob, jglob)) {
273 >            toposForAtom[i].push_back(j);
274 >            topoDist[i].push_back(2);
275 >          } else {
276 >            if (oneFour->hasPair(iglob, jglob)) {
277 >              toposForAtom[i].push_back(j);
278 >              topoDist[i].push_back(3);
279 >            }
280 >          }
281 >        }
282 >      }      
283 >    }
284   #endif
285 +
286 +    // allocate memory for the parallel objects
287 +    atypesLocal.resize(nLocal_);
288 +
289 +    for (int i = 0; i < nLocal_; i++)
290 +      atypesLocal[i] = ff_->getAtomType(idents[i]);
291 +
292 +    groupList_.clear();
293 +    groupList_.resize(nGroups_);
294 +    for (int i = 0; i < nGroups_; i++) {
295 +      int gid = cgLocalToGlobal[i];
296 +      for (int j = 0; j < nLocal_; j++) {
297 +        int aid = AtomLocalToGlobal[j];
298 +        if (globalGroupMembership[aid] == gid) {
299 +          groupList_[i].push_back(j);
300 +        }
301 +      }      
302 +    }
303 +
304 +
305 +    createGtypeCutoffMap();
306 +
307    }
308 +  
309 +  void ForceMatrixDecomposition::createGtypeCutoffMap() {
310      
311 +    GrCut.clear();
312 +    GrCutSq.clear();
313 +    GrlistSq.clear();
314  
315 +    RealType tol = 1e-6;
316 +    largestRcut_ = 0.0;
317 +    int atid;
318 +    set<AtomType*> atypes = info_->getSimulatedAtomTypes();
319 +    
320 +    map<int, RealType> atypeCutoff;
321 +      
322 +    for (set<AtomType*>::iterator at = atypes.begin();
323 +         at != atypes.end(); ++at){
324 +      atid = (*at)->getIdent();
325 +      if (userChoseCutoff_)
326 +        atypeCutoff[atid] = userCutoff_;
327 +      else
328 +        atypeCutoff[atid] = interactionMan_->getSuggestedCutoffRadius(*at);
329 +    }
330 +    
331 +    vector<RealType> gTypeCutoffs;
332 +    // first we do a single loop over the cutoff groups to find the
333 +    // largest cutoff for any atypes present in this group.
334 + #ifdef IS_MPI
335 +    vector<RealType> groupCutoffRow(nGroupsInRow_, 0.0);
336 +    groupRowToGtype.resize(nGroupsInRow_);
337 +    for (int cg1 = 0; cg1 < nGroupsInRow_; cg1++) {
338 +      vector<int> atomListRow = getAtomsInGroupRow(cg1);
339 +      for (vector<int>::iterator ia = atomListRow.begin();
340 +           ia != atomListRow.end(); ++ia) {            
341 +        int atom1 = (*ia);
342 +        atid = identsRow[atom1];
343 +        if (atypeCutoff[atid] > groupCutoffRow[cg1]) {
344 +          groupCutoffRow[cg1] = atypeCutoff[atid];
345 +        }
346 +      }
347  
348 <  void ForceDecomposition::distributeData()  {
348 >      bool gTypeFound = false;
349 >      for (int gt = 0; gt < gTypeCutoffs.size(); gt++) {
350 >        if (abs(groupCutoffRow[cg1] - gTypeCutoffs[gt]) < tol) {
351 >          groupRowToGtype[cg1] = gt;
352 >          gTypeFound = true;
353 >        }
354 >      }
355 >      if (!gTypeFound) {
356 >        gTypeCutoffs.push_back( groupCutoffRow[cg1] );
357 >        groupRowToGtype[cg1] = gTypeCutoffs.size() - 1;
358 >      }
359 >      
360 >    }
361 >    vector<RealType> groupCutoffCol(nGroupsInCol_, 0.0);
362 >    groupColToGtype.resize(nGroupsInCol_);
363 >    for (int cg2 = 0; cg2 < nGroupsInCol_; cg2++) {
364 >      vector<int> atomListCol = getAtomsInGroupColumn(cg2);
365 >      for (vector<int>::iterator jb = atomListCol.begin();
366 >           jb != atomListCol.end(); ++jb) {            
367 >        int atom2 = (*jb);
368 >        atid = identsCol[atom2];
369 >        if (atypeCutoff[atid] > groupCutoffCol[cg2]) {
370 >          groupCutoffCol[cg2] = atypeCutoff[atid];
371 >        }
372 >      }
373 >      bool gTypeFound = false;
374 >      for (int gt = 0; gt < gTypeCutoffs.size(); gt++) {
375 >        if (abs(groupCutoffCol[cg2] - gTypeCutoffs[gt]) < tol) {
376 >          groupColToGtype[cg2] = gt;
377 >          gTypeFound = true;
378 >        }
379 >      }
380 >      if (!gTypeFound) {
381 >        gTypeCutoffs.push_back( groupCutoffCol[cg2] );
382 >        groupColToGtype[cg2] = gTypeCutoffs.size() - 1;
383 >      }
384 >    }
385 > #else
386 >
387 >    vector<RealType> groupCutoff(nGroups_, 0.0);
388 >    groupToGtype.resize(nGroups_);
389 >    for (int cg1 = 0; cg1 < nGroups_; cg1++) {
390 >      groupCutoff[cg1] = 0.0;
391 >      vector<int> atomList = getAtomsInGroupRow(cg1);
392 >      for (vector<int>::iterator ia = atomList.begin();
393 >           ia != atomList.end(); ++ia) {            
394 >        int atom1 = (*ia);
395 >        atid = idents[atom1];
396 >        if (atypeCutoff[atid] > groupCutoff[cg1])
397 >          groupCutoff[cg1] = atypeCutoff[atid];
398 >      }
399 >      
400 >      bool gTypeFound = false;
401 >      for (unsigned int gt = 0; gt < gTypeCutoffs.size(); gt++) {
402 >        if (abs(groupCutoff[cg1] - gTypeCutoffs[gt]) < tol) {
403 >          groupToGtype[cg1] = gt;
404 >          gTypeFound = true;
405 >        }
406 >      }
407 >      if (!gTypeFound) {      
408 >        gTypeCutoffs.push_back( groupCutoff[cg1] );
409 >        groupToGtype[cg1] = gTypeCutoffs.size() - 1;
410 >      }      
411 >    }
412 > #endif
413 >
414 >    // Now we find the maximum group cutoff value present in the simulation
415 >
416 >    RealType groupMax = *max_element(gTypeCutoffs.begin(),
417 >                                     gTypeCutoffs.end());
418 >
419   #ifdef IS_MPI
420 <    Snapshot* snap = sman_->getCurrentSnapshot();
420 >    MPI::COMM_WORLD.Allreduce(&groupMax, &groupMax, 1, MPI::REALTYPE,
421 >                              MPI::MAX);
422 > #endif
423      
424 +    RealType tradRcut = groupMax;
425 +
426 +    GrCut.resize( gTypeCutoffs.size() );
427 +    GrCutSq.resize( gTypeCutoffs.size() );
428 +    GrlistSq.resize( gTypeCutoffs.size() );
429 +
430 +
431 +    for (unsigned int i = 0; i < gTypeCutoffs.size();  i++) {
432 +      GrCut[i].resize( gTypeCutoffs.size() , 0.0);
433 +      GrCutSq[i].resize( gTypeCutoffs.size(), 0.0 );
434 +      GrlistSq[i].resize( gTypeCutoffs.size(), 0.0 );
435 +
436 +      for (unsigned int j = 0; j < gTypeCutoffs.size();  j++) {      
437 +        RealType thisRcut;
438 +        switch(cutoffPolicy_) {
439 +        case TRADITIONAL:
440 +          thisRcut = tradRcut;
441 +          break;
442 +        case MIX:
443 +          thisRcut = 0.5 * (gTypeCutoffs[i] + gTypeCutoffs[j]);
444 +          break;
445 +        case MAX:
446 +          thisRcut = max(gTypeCutoffs[i], gTypeCutoffs[j]);
447 +          break;
448 +        default:
449 +          sprintf(painCave.errMsg,
450 +                  "ForceMatrixDecomposition::createGtypeCutoffMap "
451 +                  "hit an unknown cutoff policy!\n");
452 +          painCave.severity = OPENMD_ERROR;
453 +          painCave.isFatal = 1;
454 +          simError();
455 +          break;
456 +        }
457 +
458 +        GrCut[i][j] = thisRcut;
459 +        if (thisRcut > largestRcut_) largestRcut_ = thisRcut;
460 +        GrCutSq[i][j] = thisRcut * thisRcut;
461 +        GrlistSq[i][j] = pow(thisRcut + skinThickness_, 2);
462 +
463 +        // pair<int,int> key = make_pair(i,j);
464 +        // gTypeCutoffMap[key].first = thisRcut;
465 +        // gTypeCutoffMap[key].third = pow(thisRcut + skinThickness_, 2);
466 +        // sanity check
467 +        
468 +        if (userChoseCutoff_) {
469 +          if (abs(GrCut[i][j] - userCutoff_) > 0.0001) {
470 +            sprintf(painCave.errMsg,
471 +                    "ForceMatrixDecomposition::createGtypeCutoffMap "
472 +                    "user-specified rCut (%lf) does not match computed group Cutoff\n", userCutoff_);
473 +            painCave.severity = OPENMD_ERROR;
474 +            painCave.isFatal = 1;
475 +            simError();            
476 +          }
477 +        }
478 +      }
479 +    }
480 +  }
481 +
482 +  void ForceMatrixDecomposition::getGroupCutoffs(int &cg1, int &cg2, RealType &rcut, RealType &rcutsq, RealType &rlistsq) {
483 +    int i, j;  
484 + #ifdef IS_MPI
485 +    i = groupRowToGtype[cg1];
486 +    j = groupColToGtype[cg2];
487 + #else
488 +    i = groupToGtype[cg1];
489 +    j = groupToGtype[cg2];
490 + #endif    
491 +    rcut = GrCut[i][j];
492 +    rcutsq = GrCutSq[i][j];
493 +    rlistsq = GrlistSq[i][j];
494 +    return;
495 +    //return gTypeCutoffMap[make_pair(i,j)];
496 +  }
497 +
498 +  int ForceMatrixDecomposition::getTopologicalDistance(int atom1, int atom2) {
499 +    for (unsigned int j = 0; j < toposForAtom[atom1].size(); j++) {
500 +      if (toposForAtom[atom1][j] == atom2)
501 +        return topoDist[atom1][j];
502 +    }                                          
503 +    return 0;
504 +  }
505 +
506 +  void ForceMatrixDecomposition::zeroWorkArrays() {
507 +    pairwisePot = 0.0;
508 +    embeddingPot = 0.0;
509 +    excludedPot = 0.0;
510 +    excludedSelfPot = 0.0;
511 +
512 + #ifdef IS_MPI
513 +    if (storageLayout_ & DataStorage::dslForce) {
514 +      fill(atomRowData.force.begin(), atomRowData.force.end(), V3Zero);
515 +      fill(atomColData.force.begin(), atomColData.force.end(), V3Zero);
516 +    }
517 +
518 +    if (storageLayout_ & DataStorage::dslTorque) {
519 +      fill(atomRowData.torque.begin(), atomRowData.torque.end(), V3Zero);
520 +      fill(atomColData.torque.begin(), atomColData.torque.end(), V3Zero);
521 +    }
522 +    
523 +    fill(pot_row.begin(), pot_row.end(),
524 +         Vector<RealType, N_INTERACTION_FAMILIES> (0.0));
525 +
526 +    fill(pot_col.begin(), pot_col.end(),
527 +         Vector<RealType, N_INTERACTION_FAMILIES> (0.0));  
528 +
529 +    fill(expot_row.begin(), expot_row.end(),
530 +         Vector<RealType, N_INTERACTION_FAMILIES> (0.0));
531 +
532 +    fill(expot_col.begin(), expot_col.end(),
533 +         Vector<RealType, N_INTERACTION_FAMILIES> (0.0));  
534 +
535 +    if (storageLayout_ & DataStorage::dslParticlePot) {    
536 +      fill(atomRowData.particlePot.begin(), atomRowData.particlePot.end(),
537 +           0.0);
538 +      fill(atomColData.particlePot.begin(), atomColData.particlePot.end(),
539 +           0.0);
540 +    }
541 +
542 +    if (storageLayout_ & DataStorage::dslDensity) {      
543 +      fill(atomRowData.density.begin(), atomRowData.density.end(), 0.0);
544 +      fill(atomColData.density.begin(), atomColData.density.end(), 0.0);
545 +    }
546 +
547 +    if (storageLayout_ & DataStorage::dslFunctional) {  
548 +      fill(atomRowData.functional.begin(), atomRowData.functional.end(),
549 +           0.0);
550 +      fill(atomColData.functional.begin(), atomColData.functional.end(),
551 +           0.0);
552 +    }
553 +
554 +    if (storageLayout_ & DataStorage::dslFunctionalDerivative) {      
555 +      fill(atomRowData.functionalDerivative.begin(),
556 +           atomRowData.functionalDerivative.end(), 0.0);
557 +      fill(atomColData.functionalDerivative.begin(),
558 +           atomColData.functionalDerivative.end(), 0.0);
559 +    }
560 +
561 +    if (storageLayout_ & DataStorage::dslSkippedCharge) {      
562 +      fill(atomRowData.skippedCharge.begin(),
563 +           atomRowData.skippedCharge.end(), 0.0);
564 +      fill(atomColData.skippedCharge.begin(),
565 +           atomColData.skippedCharge.end(), 0.0);
566 +    }
567 +
568 +    if (storageLayout_ & DataStorage::dslFlucQForce) {      
569 +      fill(atomRowData.flucQFrc.begin(),
570 +           atomRowData.flucQFrc.end(), 0.0);
571 +      fill(atomColData.flucQFrc.begin(),
572 +           atomColData.flucQFrc.end(), 0.0);
573 +    }
574 +
575 +    if (storageLayout_ & DataStorage::dslElectricField) {    
576 +      fill(atomRowData.electricField.begin(),
577 +           atomRowData.electricField.end(), V3Zero);
578 +      fill(atomColData.electricField.begin(),
579 +           atomColData.electricField.end(), V3Zero);
580 +    }
581 +
582 + #endif
583 +    // even in parallel, we need to zero out the local arrays:
584 +
585 +    if (storageLayout_ & DataStorage::dslParticlePot) {      
586 +      fill(snap_->atomData.particlePot.begin(),
587 +           snap_->atomData.particlePot.end(), 0.0);
588 +    }
589 +    
590 +    if (storageLayout_ & DataStorage::dslDensity) {      
591 +      fill(snap_->atomData.density.begin(),
592 +           snap_->atomData.density.end(), 0.0);
593 +    }
594 +
595 +    if (storageLayout_ & DataStorage::dslFunctional) {
596 +      fill(snap_->atomData.functional.begin(),
597 +           snap_->atomData.functional.end(), 0.0);
598 +    }
599 +
600 +    if (storageLayout_ & DataStorage::dslFunctionalDerivative) {      
601 +      fill(snap_->atomData.functionalDerivative.begin(),
602 +           snap_->atomData.functionalDerivative.end(), 0.0);
603 +    }
604 +
605 +    if (storageLayout_ & DataStorage::dslSkippedCharge) {      
606 +      fill(snap_->atomData.skippedCharge.begin(),
607 +           snap_->atomData.skippedCharge.end(), 0.0);
608 +    }
609 +
610 +    if (storageLayout_ & DataStorage::dslElectricField) {      
611 +      fill(snap_->atomData.electricField.begin(),
612 +           snap_->atomData.electricField.end(), V3Zero);
613 +    }
614 +  }
615 +
616 +
617 +  void ForceMatrixDecomposition::distributeData()  {
618 +    snap_ = sman_->getCurrentSnapshot();
619 +    storageLayout_ = sman_->getStorageLayout();
620 + #ifdef IS_MPI
621 +    
622      // gather up the atomic positions
623 <    AtomCommVectorI->gather(snap->atomData.position,
624 <                            snap->atomIData.position);
625 <    AtomCommVectorJ->gather(snap->atomData.position,
626 <                            snap->atomJData.position);
623 >    AtomPlanVectorRow->gather(snap_->atomData.position,
624 >                              atomRowData.position);
625 >    AtomPlanVectorColumn->gather(snap_->atomData.position,
626 >                                 atomColData.position);
627      
628      // gather up the cutoff group positions
629 <    cgCommVectorI->gather(snap->cgData.position,
630 <                          snap->cgIData.position);
631 <    cgCommVectorJ->gather(snap->cgData.position,
632 <                          snap->cgJData.position);
629 >
630 >    cgPlanVectorRow->gather(snap_->cgData.position,
631 >                            cgRowData.position);
632 >
633 >    cgPlanVectorColumn->gather(snap_->cgData.position,
634 >                               cgColData.position);
635 >
636 >
637 >
638 >    if (needVelocities_) {
639 >      // gather up the atomic velocities
640 >      AtomPlanVectorColumn->gather(snap_->atomData.velocity,
641 >                                   atomColData.velocity);
642 >      
643 >      cgPlanVectorColumn->gather(snap_->cgData.velocity,
644 >                                 cgColData.velocity);
645 >    }
646 >
647      
648      // if needed, gather the atomic rotation matrices
649 <    if (snap->atomData.getStorageLayout() & DataStorage::dslAmat) {
650 <      AtomCommMatrixI->gather(snap->atomData.aMat,
651 <                              snap->atomIData.aMat);
652 <      AtomCommMatrixJ->gather(snap->atomData.aMat,
653 <                              snap->atomJData.aMat);
649 >    if (storageLayout_ & DataStorage::dslAmat) {
650 >      AtomPlanMatrixRow->gather(snap_->atomData.aMat,
651 >                                atomRowData.aMat);
652 >      AtomPlanMatrixColumn->gather(snap_->atomData.aMat,
653 >                                   atomColData.aMat);
654      }
655 <    
656 <    // if needed, gather the atomic eletrostatic frames
657 <    if (snap->atomData.getStorageLayout() & DataStorage::dslElectroFrame) {
658 <      AtomCommMatrixI->gather(snap->atomData.electroFrame,
659 <                              snap->atomIData.electroFrame);
660 <      AtomCommMatrixJ->gather(snap->atomData.electroFrame,
661 <                              snap->atomJData.electroFrame);
655 >
656 >    // if needed, gather the atomic eletrostatic information
657 >    if (storageLayout_ & DataStorage::dslDipole) {
658 >      AtomPlanVectorRow->gather(snap_->atomData.dipole,
659 >                                atomRowData.dipole);
660 >      AtomPlanVectorColumn->gather(snap_->atomData.dipole,
661 >                                   atomColData.dipole);
662      }
663 +
664 +    if (storageLayout_ & DataStorage::dslQuadrupole) {
665 +      AtomPlanMatrixRow->gather(snap_->atomData.quadrupole,
666 +                                atomRowData.quadrupole);
667 +      AtomPlanMatrixColumn->gather(snap_->atomData.quadrupole,
668 +                                   atomColData.quadrupole);
669 +    }
670 +        
671 +    // if needed, gather the atomic fluctuating charge values
672 +    if (storageLayout_ & DataStorage::dslFlucQPosition) {
673 +      AtomPlanRealRow->gather(snap_->atomData.flucQPos,
674 +                              atomRowData.flucQPos);
675 +      AtomPlanRealColumn->gather(snap_->atomData.flucQPos,
676 +                                 atomColData.flucQPos);
677 +    }
678 +
679   #endif      
680    }
681    
682 <  void ForceDecomposition::collectIntermediateData() {
682 >  /* collects information obtained during the pre-pair loop onto local
683 >   * data structures.
684 >   */
685 >  void ForceMatrixDecomposition::collectIntermediateData() {
686 >    snap_ = sman_->getCurrentSnapshot();
687 >    storageLayout_ = sman_->getStorageLayout();
688   #ifdef IS_MPI
105    Snapshot* snap = sman_->getCurrentSnapshot();
689      
690 <    if (snap->atomData.getStorageLayout() & DataStorage::dslDensity) {
691 <      AtomCommRealI->scatter(snap->atomIData.density,
692 <                             snap->atomData.density);
693 <      std::vector<RealType> rho_tmp;
694 <      int n = snap->getNumberOfAtoms();
695 <      rho_tmp.reserve( n );
696 <      AtomCommRealJ->scatter(snap->atomJData.density, rho_tmp);
690 >    if (storageLayout_ & DataStorage::dslDensity) {
691 >      
692 >      AtomPlanRealRow->scatter(atomRowData.density,
693 >                               snap_->atomData.density);
694 >      
695 >      int n = snap_->atomData.density.size();
696 >      vector<RealType> rho_tmp(n, 0.0);
697 >      AtomPlanRealColumn->scatter(atomColData.density, rho_tmp);
698        for (int i = 0; i < n; i++)
699 <        snap->atomData.density[i] += rho_tmp[i];
699 >        snap_->atomData.density[i] += rho_tmp[i];
700      }
701 +
702 +    // this isn't necessary if we don't have polarizable atoms, but
703 +    // we'll leave it here for now.
704 +    if (storageLayout_ & DataStorage::dslElectricField) {
705 +      
706 +      AtomPlanVectorRow->scatter(atomRowData.electricField,
707 +                                 snap_->atomData.electricField);
708 +      
709 +      int n = snap_->atomData.electricField.size();
710 +      vector<Vector3d> field_tmp(n, V3Zero);
711 +      AtomPlanVectorColumn->scatter(atomColData.electricField,
712 +                                    field_tmp);
713 +      for (int i = 0; i < n; i++)
714 +        snap_->atomData.electricField[i] += field_tmp[i];
715 +    }
716   #endif
717    }
718 <  
719 <  void ForceDecomposition::distributeIntermediateData() {
718 >
719 >  /*
720 >   * redistributes information obtained during the pre-pair loop out to
721 >   * row and column-indexed data structures
722 >   */
723 >  void ForceMatrixDecomposition::distributeIntermediateData() {
724 >    snap_ = sman_->getCurrentSnapshot();
725 >    storageLayout_ = sman_->getStorageLayout();
726   #ifdef IS_MPI
727 <    Snapshot* snap = sman_->getCurrentSnapshot();
728 <    if (snap->atomData.getStorageLayout() & DataStorage::dslFunctional) {
729 <      AtomCommRealI->gather(snap->atomData.functional,
730 <                            snap->atomIData.functional);
731 <      AtomCommRealJ->gather(snap->atomData.functional,
127 <                            snap->atomJData.functional);
727 >    if (storageLayout_ & DataStorage::dslFunctional) {
728 >      AtomPlanRealRow->gather(snap_->atomData.functional,
729 >                              atomRowData.functional);
730 >      AtomPlanRealColumn->gather(snap_->atomData.functional,
731 >                                 atomColData.functional);
732      }
733      
734 <    if (snap->atomData.getStorageLayout() & DataStorage::dslFunctionalDerivative) {
735 <      AtomCommRealI->gather(snap->atomData.functionalDerivative,
736 <                            snap->atomIData.functionalDerivative);
737 <      AtomCommRealJ->gather(snap->atomData.functionalDerivative,
738 <                            snap->atomJData.functionalDerivative);
734 >    if (storageLayout_ & DataStorage::dslFunctionalDerivative) {
735 >      AtomPlanRealRow->gather(snap_->atomData.functionalDerivative,
736 >                              atomRowData.functionalDerivative);
737 >      AtomPlanRealColumn->gather(snap_->atomData.functionalDerivative,
738 >                                 atomColData.functionalDerivative);
739      }
740   #endif
741    }
742    
743    
744 <  void ForceDecomposition::collectData() {
745 < #ifdef IS_MPI
746 <    Snapshot* snap = sman_->getCurrentSnapshot();
747 <    int n = snap->getNumberOfAtoms();
748 <
749 <    std::vector<Vector3d> frc_tmp;
146 <    frc_tmp.reserve( n );
744 >  void ForceMatrixDecomposition::collectData() {
745 >    snap_ = sman_->getCurrentSnapshot();
746 >    storageLayout_ = sman_->getStorageLayout();
747 > #ifdef IS_MPI    
748 >    int n = snap_->atomData.force.size();
749 >    vector<Vector3d> frc_tmp(n, V3Zero);
750      
751 <    AtomCommVectorI->scatter(snap->atomIData.force, frc_tmp);
752 <    for (int i = 0; i < n; i++)
753 <      snap->atomData.force[i] += frc_tmp[i];
751 >    AtomPlanVectorRow->scatter(atomRowData.force, frc_tmp);
752 >    for (int i = 0; i < n; i++) {
753 >      snap_->atomData.force[i] += frc_tmp[i];
754 >      frc_tmp[i] = 0.0;
755 >    }
756      
757 <    AtomCommVectorJ->scatter(snap->atomJData.force, frc_tmp);
758 <    for (int i = 0; i < n; i++)
759 <      snap->atomData.force[i] += frc_tmp[i];
760 <    
761 <    
762 <    if (snap->atomData.getStorageLayout() & DataStorage::dslTorque) {
763 <      std::vector<Vector3d> trq_tmp;
764 <      trq_tmp.reserve( n );
757 >    AtomPlanVectorColumn->scatter(atomColData.force, frc_tmp);
758 >    for (int i = 0; i < n; i++) {
759 >      snap_->atomData.force[i] += frc_tmp[i];
760 >    }
761 >        
762 >    if (storageLayout_ & DataStorage::dslTorque) {
763 >
764 >      int nt = snap_->atomData.torque.size();
765 >      vector<Vector3d> trq_tmp(nt, V3Zero);
766 >
767 >      AtomPlanVectorRow->scatter(atomRowData.torque, trq_tmp);
768 >      for (int i = 0; i < nt; i++) {
769 >        snap_->atomData.torque[i] += trq_tmp[i];
770 >        trq_tmp[i] = 0.0;
771 >      }
772        
773 <      AtomCommVectorI->scatter(snap->atomIData.torque, trq_tmp);
774 <      for (int i = 0; i < n; i++)
775 <        snap->atomData.torque[i] += trq_tmp[i];
773 >      AtomPlanVectorColumn->scatter(atomColData.torque, trq_tmp);
774 >      for (int i = 0; i < nt; i++)
775 >        snap_->atomData.torque[i] += trq_tmp[i];
776 >    }
777 >
778 >    if (storageLayout_ & DataStorage::dslSkippedCharge) {
779 >
780 >      int ns = snap_->atomData.skippedCharge.size();
781 >      vector<RealType> skch_tmp(ns, 0.0);
782 >
783 >      AtomPlanRealRow->scatter(atomRowData.skippedCharge, skch_tmp);
784 >      for (int i = 0; i < ns; i++) {
785 >        snap_->atomData.skippedCharge[i] += skch_tmp[i];
786 >        skch_tmp[i] = 0.0;
787 >      }
788        
789 <      AtomCommVectorJ->scatter(snap->atomJData.torque, trq_tmp);
790 <      for (int i = 0; i < n; i++)
791 <        snap->atomData.torque[i] += trq_tmp[i];
789 >      AtomPlanRealColumn->scatter(atomColData.skippedCharge, skch_tmp);
790 >      for (int i = 0; i < ns; i++)
791 >        snap_->atomData.skippedCharge[i] += skch_tmp[i];
792 >            
793      }
794      
795 <    // Still need pot!
795 >    if (storageLayout_ & DataStorage::dslFlucQForce) {
796 >
797 >      int nq = snap_->atomData.flucQFrc.size();
798 >      vector<RealType> fqfrc_tmp(nq, 0.0);
799 >
800 >      AtomPlanRealRow->scatter(atomRowData.flucQFrc, fqfrc_tmp);
801 >      for (int i = 0; i < nq; i++) {
802 >        snap_->atomData.flucQFrc[i] += fqfrc_tmp[i];
803 >        fqfrc_tmp[i] = 0.0;
804 >      }
805 >      
806 >      AtomPlanRealColumn->scatter(atomColData.flucQFrc, fqfrc_tmp);
807 >      for (int i = 0; i < nq; i++)
808 >        snap_->atomData.flucQFrc[i] += fqfrc_tmp[i];
809 >            
810 >    }
811 >
812 >    if (storageLayout_ & DataStorage::dslElectricField) {
813 >
814 >      int nef = snap_->atomData.electricField.size();
815 >      vector<Vector3d> efield_tmp(nef, V3Zero);
816 >
817 >      AtomPlanVectorRow->scatter(atomRowData.electricField, efield_tmp);
818 >      for (int i = 0; i < nef; i++) {
819 >        snap_->atomData.electricField[i] += efield_tmp[i];
820 >        efield_tmp[i] = 0.0;
821 >      }
822 >      
823 >      AtomPlanVectorColumn->scatter(atomColData.electricField, efield_tmp);
824 >      for (int i = 0; i < nef; i++)
825 >        snap_->atomData.electricField[i] += efield_tmp[i];
826 >    }
827 >
828 >
829 >    nLocal_ = snap_->getNumberOfAtoms();
830 >
831 >    vector<potVec> pot_temp(nLocal_,
832 >                            Vector<RealType, N_INTERACTION_FAMILIES> (0.0));
833 >    vector<potVec> expot_temp(nLocal_,
834 >                              Vector<RealType, N_INTERACTION_FAMILIES> (0.0));
835 >
836 >    // scatter/gather pot_row into the members of my column
837 >          
838 >    AtomPlanPotRow->scatter(pot_row, pot_temp);
839 >    AtomPlanPotRow->scatter(expot_row, expot_temp);
840 >
841 >    for (int ii = 0;  ii < pot_temp.size(); ii++ )
842 >      pairwisePot += pot_temp[ii];
843 >
844 >    for (int ii = 0;  ii < expot_temp.size(); ii++ )
845 >      excludedPot += expot_temp[ii];
846 >        
847 >    if (storageLayout_ & DataStorage::dslParticlePot) {
848 >      // This is the pairwise contribution to the particle pot.  The
849 >      // embedding contribution is added in each of the low level
850 >      // non-bonded routines.  In single processor, this is done in
851 >      // unpackInteractionData, not in collectData.
852 >      for (int ii = 0; ii < N_INTERACTION_FAMILIES; ii++) {
853 >        for (int i = 0; i < nLocal_; i++) {
854 >          // factor of two is because the total potential terms are divided
855 >          // by 2 in parallel due to row/ column scatter      
856 >          snap_->atomData.particlePot[i] += 2.0 * pot_temp[i](ii);
857 >        }
858 >      }
859 >    }
860 >
861 >    fill(pot_temp.begin(), pot_temp.end(),
862 >         Vector<RealType, N_INTERACTION_FAMILIES> (0.0));
863 >    fill(expot_temp.begin(), expot_temp.end(),
864 >         Vector<RealType, N_INTERACTION_FAMILIES> (0.0));
865 >      
866 >    AtomPlanPotColumn->scatter(pot_col, pot_temp);    
867 >    AtomPlanPotColumn->scatter(expot_col, expot_temp);    
868      
869 +    for (int ii = 0;  ii < pot_temp.size(); ii++ )
870 +      pairwisePot += pot_temp[ii];    
871  
872 +    for (int ii = 0;  ii < expot_temp.size(); ii++ )
873 +      excludedPot += expot_temp[ii];    
874  
875 +    if (storageLayout_ & DataStorage::dslParticlePot) {
876 +      // This is the pairwise contribution to the particle pot.  The
877 +      // embedding contribution is added in each of the low level
878 +      // non-bonded routines.  In single processor, this is done in
879 +      // unpackInteractionData, not in collectData.
880 +      for (int ii = 0; ii < N_INTERACTION_FAMILIES; ii++) {
881 +        for (int i = 0; i < nLocal_; i++) {
882 +          // factor of two is because the total potential terms are divided
883 +          // by 2 in parallel due to row/ column scatter      
884 +          snap_->atomData.particlePot[i] += 2.0 * pot_temp[i](ii);
885 +        }
886 +      }
887 +    }
888 +    
889 +    if (storageLayout_ & DataStorage::dslParticlePot) {
890 +      int npp = snap_->atomData.particlePot.size();
891 +      vector<RealType> ppot_temp(npp, 0.0);
892 +
893 +      // This is the direct or embedding contribution to the particle
894 +      // pot.
895 +      
896 +      AtomPlanRealRow->scatter(atomRowData.particlePot, ppot_temp);
897 +      for (int i = 0; i < npp; i++) {
898 +        snap_->atomData.particlePot[i] += ppot_temp[i];
899 +      }
900 +
901 +      fill(ppot_temp.begin(), ppot_temp.end(), 0.0);
902 +      
903 +      AtomPlanRealColumn->scatter(atomColData.particlePot, ppot_temp);
904 +      for (int i = 0; i < npp; i++) {
905 +        snap_->atomData.particlePot[i] += ppot_temp[i];
906 +      }
907 +    }
908 +
909 +    for (int ii = 0; ii < N_INTERACTION_FAMILIES; ii++) {
910 +      RealType ploc1 = pairwisePot[ii];
911 +      RealType ploc2 = 0.0;
912 +      MPI::COMM_WORLD.Allreduce(&ploc1, &ploc2, 1, MPI::REALTYPE, MPI::SUM);
913 +      pairwisePot[ii] = ploc2;
914 +    }
915 +
916 +    for (int ii = 0; ii < N_INTERACTION_FAMILIES; ii++) {
917 +      RealType ploc1 = excludedPot[ii];
918 +      RealType ploc2 = 0.0;
919 +      MPI::COMM_WORLD.Allreduce(&ploc1, &ploc2, 1, MPI::REALTYPE, MPI::SUM);
920 +      excludedPot[ii] = ploc2;
921 +    }
922 +
923 +    // Here be dragons.
924 +    MPI::Intracomm col = colComm.getComm();
925 +
926 +    col.Allreduce(MPI::IN_PLACE,
927 +                  &snap_->frameData.conductiveHeatFlux[0], 3,
928 +                  MPI::REALTYPE, MPI::SUM);
929 +
930 +
931   #endif
932 +
933    }
934 +
935 +  /**
936 +   * Collects information obtained during the post-pair (and embedding
937 +   * functional) loops onto local data structures.
938 +   */
939 +  void ForceMatrixDecomposition::collectSelfData() {
940 +    snap_ = sman_->getCurrentSnapshot();
941 +    storageLayout_ = sman_->getStorageLayout();
942 +
943 + #ifdef IS_MPI
944 +    for (int ii = 0; ii < N_INTERACTION_FAMILIES; ii++) {
945 +      RealType ploc1 = embeddingPot[ii];
946 +      RealType ploc2 = 0.0;
947 +      MPI::COMM_WORLD.Allreduce(&ploc1, &ploc2, 1, MPI::REALTYPE, MPI::SUM);
948 +      embeddingPot[ii] = ploc2;
949 +    }    
950 +    for (int ii = 0; ii < N_INTERACTION_FAMILIES; ii++) {
951 +      RealType ploc1 = excludedSelfPot[ii];
952 +      RealType ploc2 = 0.0;
953 +      MPI::COMM_WORLD.Allreduce(&ploc1, &ploc2, 1, MPI::REALTYPE, MPI::SUM);
954 +      excludedSelfPot[ii] = ploc2;
955 +    }    
956 + #endif
957 +    
958 +  }
959 +
960 +
961 +
962 +  int& ForceMatrixDecomposition::getNAtomsInRow() {  
963 + #ifdef IS_MPI
964 +    return nAtomsInRow_;
965 + #else
966 +    return nLocal_;
967 + #endif
968 +  }
969 +
970 +  /**
971 +   * returns the list of atoms belonging to this group.  
972 +   */
973 +  vector<int>& ForceMatrixDecomposition::getAtomsInGroupRow(int cg1){
974 + #ifdef IS_MPI
975 +    return groupListRow_[cg1];
976 + #else
977 +    return groupList_[cg1];
978 + #endif
979 +  }
980 +
981 +  vector<int>& ForceMatrixDecomposition::getAtomsInGroupColumn(int cg2){
982 + #ifdef IS_MPI
983 +    return groupListCol_[cg2];
984 + #else
985 +    return groupList_[cg2];
986 + #endif
987 +  }
988    
989 +  Vector3d ForceMatrixDecomposition::getIntergroupVector(int cg1, int cg2){
990 +    Vector3d d;
991 +    
992 + #ifdef IS_MPI
993 +    d = cgColData.position[cg2] - cgRowData.position[cg1];
994 + #else
995 +    d = snap_->cgData.position[cg2] - snap_->cgData.position[cg1];
996 + #endif
997 +    
998 +    if (usePeriodicBoundaryConditions_) {
999 +      snap_->wrapVector(d);
1000 +    }
1001 +    return d;    
1002 +  }
1003 +
1004 +  Vector3d& ForceMatrixDecomposition::getGroupVelocityColumn(int cg2){
1005 + #ifdef IS_MPI
1006 +    return cgColData.velocity[cg2];
1007 + #else
1008 +    return snap_->cgData.velocity[cg2];
1009 + #endif
1010 +  }
1011 +
1012 +  Vector3d& ForceMatrixDecomposition::getAtomVelocityColumn(int atom2){
1013 + #ifdef IS_MPI
1014 +    return atomColData.velocity[atom2];
1015 + #else
1016 +    return snap_->atomData.velocity[atom2];
1017 + #endif
1018 +  }
1019 +
1020 +
1021 +  Vector3d ForceMatrixDecomposition::getAtomToGroupVectorRow(int atom1, int cg1){
1022 +
1023 +    Vector3d d;
1024 +    
1025 + #ifdef IS_MPI
1026 +    d = cgRowData.position[cg1] - atomRowData.position[atom1];
1027 + #else
1028 +    d = snap_->cgData.position[cg1] - snap_->atomData.position[atom1];
1029 + #endif
1030 +    if (usePeriodicBoundaryConditions_) {
1031 +      snap_->wrapVector(d);
1032 +    }
1033 +    return d;    
1034 +  }
1035 +  
1036 +  Vector3d ForceMatrixDecomposition::getAtomToGroupVectorColumn(int atom2, int cg2){
1037 +    Vector3d d;
1038 +    
1039 + #ifdef IS_MPI
1040 +    d = cgColData.position[cg2] - atomColData.position[atom2];
1041 + #else
1042 +    d = snap_->cgData.position[cg2] - snap_->atomData.position[atom2];
1043 + #endif
1044 +    if (usePeriodicBoundaryConditions_) {
1045 +      snap_->wrapVector(d);
1046 +    }
1047 +    return d;    
1048 +  }
1049 +
1050 +  RealType& ForceMatrixDecomposition::getMassFactorRow(int atom1) {
1051 + #ifdef IS_MPI
1052 +    return massFactorsRow[atom1];
1053 + #else
1054 +    return massFactors[atom1];
1055 + #endif
1056 +  }
1057 +
1058 +  RealType& ForceMatrixDecomposition::getMassFactorColumn(int atom2) {
1059 + #ifdef IS_MPI
1060 +    return massFactorsCol[atom2];
1061 + #else
1062 +    return massFactors[atom2];
1063 + #endif
1064 +
1065 +  }
1066 +    
1067 +  Vector3d ForceMatrixDecomposition::getInteratomicVector(int atom1, int atom2){
1068 +    Vector3d d;
1069 +    
1070 + #ifdef IS_MPI
1071 +    d = atomColData.position[atom2] - atomRowData.position[atom1];
1072 + #else
1073 +    d = snap_->atomData.position[atom2] - snap_->atomData.position[atom1];
1074 + #endif
1075 +    if (usePeriodicBoundaryConditions_) {
1076 +      snap_->wrapVector(d);
1077 +    }
1078 +    return d;    
1079 +  }
1080 +
1081 +  vector<int>& ForceMatrixDecomposition::getExcludesForAtom(int atom1) {
1082 +    return excludesForAtom[atom1];
1083 +  }
1084 +
1085 +  /**
1086 +   * We need to exclude some overcounted interactions that result from
1087 +   * the parallel decomposition.
1088 +   */
1089 +  bool ForceMatrixDecomposition::skipAtomPair(int atom1, int atom2, int cg1, int cg2) {
1090 +    int unique_id_1, unique_id_2;
1091 +        
1092 + #ifdef IS_MPI
1093 +    // in MPI, we have to look up the unique IDs for each atom
1094 +    unique_id_1 = AtomRowToGlobal[atom1];
1095 +    unique_id_2 = AtomColToGlobal[atom2];
1096 +    // group1 = cgRowToGlobal[cg1];
1097 +    // group2 = cgColToGlobal[cg2];
1098 + #else
1099 +    unique_id_1 = AtomLocalToGlobal[atom1];
1100 +    unique_id_2 = AtomLocalToGlobal[atom2];
1101 +    int group1 = cgLocalToGlobal[cg1];
1102 +    int group2 = cgLocalToGlobal[cg2];
1103 + #endif  
1104 +
1105 +    if (unique_id_1 == unique_id_2) return true;
1106 +
1107 + #ifdef IS_MPI
1108 +    // this prevents us from doing the pair on multiple processors
1109 +    if (unique_id_1 < unique_id_2) {
1110 +      if ((unique_id_1 + unique_id_2) % 2 == 0) return true;
1111 +    } else {
1112 +      if ((unique_id_1 + unique_id_2) % 2 == 1) return true;
1113 +    }
1114 + #endif    
1115 +
1116 + #ifndef IS_MPI
1117 +    if (group1 == group2) {
1118 +      if (unique_id_1 < unique_id_2) return true;
1119 +    }
1120 + #endif
1121 +    
1122 +    return false;
1123 +  }
1124 +
1125 +  /**
1126 +   * We need to handle the interactions for atoms who are involved in
1127 +   * the same rigid body as well as some short range interactions
1128 +   * (bonds, bends, torsions) differently from other interactions.
1129 +   * We'll still visit the pairwise routines, but with a flag that
1130 +   * tells those routines to exclude the pair from direct long range
1131 +   * interactions.  Some indirect interactions (notably reaction
1132 +   * field) must still be handled for these pairs.
1133 +   */
1134 +  bool ForceMatrixDecomposition::excludeAtomPair(int atom1, int atom2) {
1135 +
1136 +    // excludesForAtom was constructed to use row/column indices in the MPI
1137 +    // version, and to use local IDs in the non-MPI version:
1138 +    
1139 +    for (vector<int>::iterator i = excludesForAtom[atom1].begin();
1140 +         i != excludesForAtom[atom1].end(); ++i) {
1141 +      if ( (*i) == atom2 ) return true;
1142 +    }
1143 +
1144 +    return false;
1145 +  }
1146 +
1147 +
1148 +  void ForceMatrixDecomposition::addForceToAtomRow(int atom1, Vector3d fg){
1149 + #ifdef IS_MPI
1150 +    atomRowData.force[atom1] += fg;
1151 + #else
1152 +    snap_->atomData.force[atom1] += fg;
1153 + #endif
1154 +  }
1155 +
1156 +  void ForceMatrixDecomposition::addForceToAtomColumn(int atom2, Vector3d fg){
1157 + #ifdef IS_MPI
1158 +    atomColData.force[atom2] += fg;
1159 + #else
1160 +    snap_->atomData.force[atom2] += fg;
1161 + #endif
1162 +  }
1163 +
1164 +    // filling interaction blocks with pointers
1165 +  void ForceMatrixDecomposition::fillInteractionData(InteractionData &idat,
1166 +                                                     int atom1, int atom2) {
1167 +
1168 +    idat.excluded = excludeAtomPair(atom1, atom2);
1169 +  
1170 + #ifdef IS_MPI
1171 +    idat.atypes = make_pair( atypesRow[atom1], atypesCol[atom2]);
1172 +    idat.atid1 = identsRow[atom1];
1173 +    idat.atid2 = identsCol[atom2];
1174 +    //idat.atypes = make_pair( ff_->getAtomType(identsRow[atom1]),
1175 +    //                         ff_->getAtomType(identsCol[atom2]) );
1176 +    
1177 +    if (storageLayout_ & DataStorage::dslAmat) {
1178 +      idat.A1 = &(atomRowData.aMat[atom1]);
1179 +      idat.A2 = &(atomColData.aMat[atom2]);
1180 +    }
1181 +    
1182 +    if (storageLayout_ & DataStorage::dslTorque) {
1183 +      idat.t1 = &(atomRowData.torque[atom1]);
1184 +      idat.t2 = &(atomColData.torque[atom2]);
1185 +    }
1186 +
1187 +    if (storageLayout_ & DataStorage::dslDipole) {
1188 +      idat.dipole1 = &(atomRowData.dipole[atom1]);
1189 +      idat.dipole2 = &(atomColData.dipole[atom2]);
1190 +    }
1191 +
1192 +    if (storageLayout_ & DataStorage::dslQuadrupole) {
1193 +      idat.quadrupole1 = &(atomRowData.quadrupole[atom1]);
1194 +      idat.quadrupole2 = &(atomColData.quadrupole[atom2]);
1195 +    }
1196 +
1197 +    if (storageLayout_ & DataStorage::dslDensity) {
1198 +      idat.rho1 = &(atomRowData.density[atom1]);
1199 +      idat.rho2 = &(atomColData.density[atom2]);
1200 +    }
1201 +
1202 +    if (storageLayout_ & DataStorage::dslFunctional) {
1203 +      idat.frho1 = &(atomRowData.functional[atom1]);
1204 +      idat.frho2 = &(atomColData.functional[atom2]);
1205 +    }
1206 +
1207 +    if (storageLayout_ & DataStorage::dslFunctionalDerivative) {
1208 +      idat.dfrho1 = &(atomRowData.functionalDerivative[atom1]);
1209 +      idat.dfrho2 = &(atomColData.functionalDerivative[atom2]);
1210 +    }
1211 +
1212 +    if (storageLayout_ & DataStorage::dslParticlePot) {
1213 +      idat.particlePot1 = &(atomRowData.particlePot[atom1]);
1214 +      idat.particlePot2 = &(atomColData.particlePot[atom2]);
1215 +    }
1216 +
1217 +    if (storageLayout_ & DataStorage::dslSkippedCharge) {              
1218 +      idat.skippedCharge1 = &(atomRowData.skippedCharge[atom1]);
1219 +      idat.skippedCharge2 = &(atomColData.skippedCharge[atom2]);
1220 +    }
1221 +
1222 +    if (storageLayout_ & DataStorage::dslFlucQPosition) {              
1223 +      idat.flucQ1 = &(atomRowData.flucQPos[atom1]);
1224 +      idat.flucQ2 = &(atomColData.flucQPos[atom2]);
1225 +    }
1226 +
1227 + #else
1228 +    
1229 +    idat.atypes = make_pair( atypesLocal[atom1], atypesLocal[atom2]);
1230 +    idat.atid1 = idents[atom1];
1231 +    idat.atid2 = idents[atom2];
1232 +
1233 +    if (storageLayout_ & DataStorage::dslAmat) {
1234 +      idat.A1 = &(snap_->atomData.aMat[atom1]);
1235 +      idat.A2 = &(snap_->atomData.aMat[atom2]);
1236 +    }
1237 +
1238 +    if (storageLayout_ & DataStorage::dslTorque) {
1239 +      idat.t1 = &(snap_->atomData.torque[atom1]);
1240 +      idat.t2 = &(snap_->atomData.torque[atom2]);
1241 +    }
1242 +
1243 +    if (storageLayout_ & DataStorage::dslDipole) {
1244 +      idat.dipole1 = &(snap_->atomData.dipole[atom1]);
1245 +      idat.dipole2 = &(snap_->atomData.dipole[atom2]);
1246 +    }
1247 +
1248 +    if (storageLayout_ & DataStorage::dslQuadrupole) {
1249 +      idat.quadrupole1 = &(snap_->atomData.quadrupole[atom1]);
1250 +      idat.quadrupole2 = &(snap_->atomData.quadrupole[atom2]);
1251 +    }
1252 +
1253 +    if (storageLayout_ & DataStorage::dslDensity) {    
1254 +      idat.rho1 = &(snap_->atomData.density[atom1]);
1255 +      idat.rho2 = &(snap_->atomData.density[atom2]);
1256 +    }
1257 +
1258 +    if (storageLayout_ & DataStorage::dslFunctional) {
1259 +      idat.frho1 = &(snap_->atomData.functional[atom1]);
1260 +      idat.frho2 = &(snap_->atomData.functional[atom2]);
1261 +    }
1262 +
1263 +    if (storageLayout_ & DataStorage::dslFunctionalDerivative) {
1264 +      idat.dfrho1 = &(snap_->atomData.functionalDerivative[atom1]);
1265 +      idat.dfrho2 = &(snap_->atomData.functionalDerivative[atom2]);
1266 +    }
1267 +
1268 +    if (storageLayout_ & DataStorage::dslParticlePot) {
1269 +      idat.particlePot1 = &(snap_->atomData.particlePot[atom1]);
1270 +      idat.particlePot2 = &(snap_->atomData.particlePot[atom2]);
1271 +    }
1272 +
1273 +    if (storageLayout_ & DataStorage::dslSkippedCharge) {
1274 +      idat.skippedCharge1 = &(snap_->atomData.skippedCharge[atom1]);
1275 +      idat.skippedCharge2 = &(snap_->atomData.skippedCharge[atom2]);
1276 +    }
1277 +
1278 +    if (storageLayout_ & DataStorage::dslFlucQPosition) {              
1279 +      idat.flucQ1 = &(snap_->atomData.flucQPos[atom1]);
1280 +      idat.flucQ2 = &(snap_->atomData.flucQPos[atom2]);
1281 +    }
1282 +
1283 + #endif
1284 +  }
1285 +
1286 +  
1287 +  void ForceMatrixDecomposition::unpackInteractionData(InteractionData &idat, int atom1, int atom2) {    
1288 + #ifdef IS_MPI
1289 +    pot_row[atom1] += RealType(0.5) *  *(idat.pot);
1290 +    pot_col[atom2] += RealType(0.5) *  *(idat.pot);
1291 +    expot_row[atom1] += RealType(0.5) *  *(idat.excludedPot);
1292 +    expot_col[atom2] += RealType(0.5) *  *(idat.excludedPot);
1293 +
1294 +    atomRowData.force[atom1] += *(idat.f1);
1295 +    atomColData.force[atom2] -= *(idat.f1);
1296 +
1297 +    if (storageLayout_ & DataStorage::dslFlucQForce) {              
1298 +      atomRowData.flucQFrc[atom1] -= *(idat.dVdFQ1);
1299 +      atomColData.flucQFrc[atom2] -= *(idat.dVdFQ2);
1300 +    }
1301 +
1302 +    if (storageLayout_ & DataStorage::dslElectricField) {              
1303 +      atomRowData.electricField[atom1] += *(idat.eField1);
1304 +      atomColData.electricField[atom2] += *(idat.eField2);
1305 +    }
1306 +
1307 + #else
1308 +    pairwisePot += *(idat.pot);
1309 +    excludedPot += *(idat.excludedPot);
1310 +
1311 +    snap_->atomData.force[atom1] += *(idat.f1);
1312 +    snap_->atomData.force[atom2] -= *(idat.f1);
1313 +
1314 +    if (idat.doParticlePot) {
1315 +      // This is the pairwise contribution to the particle pot.  The
1316 +      // embedding contribution is added in each of the low level
1317 +      // non-bonded routines.  In parallel, this calculation is done
1318 +      // in collectData, not in unpackInteractionData.
1319 +      snap_->atomData.particlePot[atom1] += *(idat.vpair) * *(idat.sw);
1320 +      snap_->atomData.particlePot[atom2] += *(idat.vpair) * *(idat.sw);
1321 +    }
1322 +    
1323 +    if (storageLayout_ & DataStorage::dslFlucQForce) {              
1324 +      snap_->atomData.flucQFrc[atom1] -= *(idat.dVdFQ1);
1325 +      snap_->atomData.flucQFrc[atom2] -= *(idat.dVdFQ2);
1326 +    }
1327 +
1328 +    if (storageLayout_ & DataStorage::dslElectricField) {              
1329 +      snap_->atomData.electricField[atom1] += *(idat.eField1);
1330 +      snap_->atomData.electricField[atom2] += *(idat.eField2);
1331 +    }
1332 +
1333 + #endif
1334 +    
1335 +  }
1336 +
1337 +  /*
1338 +   * buildNeighborList
1339 +   *
1340 +   * first element of pair is row-indexed CutoffGroup
1341 +   * second element of pair is column-indexed CutoffGroup
1342 +   */
1343 +  void ForceMatrixDecomposition::buildNeighborList(vector<pair<int,int> >& neighborList) {
1344 +    
1345 +    neighborList.clear();
1346 +    groupCutoffs cuts;
1347 +    bool doAllPairs = false;
1348 +
1349 +    RealType rList_ = (largestRcut_ + skinThickness_);
1350 +    RealType rcut, rcutsq, rlistsq;
1351 +    Snapshot* snap_ = sman_->getCurrentSnapshot();
1352 +    Mat3x3d box;
1353 +    Mat3x3d invBox;
1354 +
1355 +    Vector3d rs, scaled, dr;
1356 +    Vector3i whichCell;
1357 +    int cellIndex;
1358 +
1359 + #ifdef IS_MPI
1360 +    cellListRow_.clear();
1361 +    cellListCol_.clear();
1362 + #else
1363 +    cellList_.clear();
1364 + #endif
1365 +    
1366 +    if (!usePeriodicBoundaryConditions_) {
1367 +      box = snap_->getBoundingBox();
1368 +      invBox = snap_->getInvBoundingBox();
1369 +    } else {
1370 +      box = snap_->getHmat();
1371 +      invBox = snap_->getInvHmat();
1372 +    }
1373 +    
1374 +    Vector3d boxX = box.getColumn(0);
1375 +    Vector3d boxY = box.getColumn(1);
1376 +    Vector3d boxZ = box.getColumn(2);
1377 +    
1378 +    nCells_.x() = (int) ( boxX.length() )/ rList_;
1379 +    nCells_.y() = (int) ( boxY.length() )/ rList_;
1380 +    nCells_.z() = (int) ( boxZ.length() )/ rList_;
1381 +    
1382 +    // handle small boxes where the cell offsets can end up repeating cells
1383 +    
1384 +    if (nCells_.x() < 3) doAllPairs = true;
1385 +    if (nCells_.y() < 3) doAllPairs = true;
1386 +    if (nCells_.z() < 3) doAllPairs = true;
1387 +    
1388 +    int nCtot = nCells_.x() * nCells_.y() * nCells_.z();
1389 +    
1390 + #ifdef IS_MPI
1391 +    cellListRow_.resize(nCtot);
1392 +    cellListCol_.resize(nCtot);
1393 + #else
1394 +    cellList_.resize(nCtot);
1395 + #endif
1396 +    
1397 +    if (!doAllPairs) {
1398 + #ifdef IS_MPI
1399 +      
1400 +      for (int i = 0; i < nGroupsInRow_; i++) {
1401 +        rs = cgRowData.position[i];
1402 +        
1403 +        // scaled positions relative to the box vectors
1404 +        scaled = invBox * rs;
1405 +        
1406 +        // wrap the vector back into the unit box by subtracting integer box
1407 +        // numbers
1408 +        for (int j = 0; j < 3; j++) {
1409 +          scaled[j] -= roundMe(scaled[j]);
1410 +          scaled[j] += 0.5;
1411 +          // Handle the special case when an object is exactly on the
1412 +          // boundary (a scaled coordinate of 1.0 is the same as
1413 +          // scaled coordinate of 0.0)
1414 +          if (scaled[j] >= 1.0) scaled[j] -= 1.0;
1415 +        }
1416 +        
1417 +        // find xyz-indices of cell that cutoffGroup is in.
1418 +        whichCell.x() = nCells_.x() * scaled.x();
1419 +        whichCell.y() = nCells_.y() * scaled.y();
1420 +        whichCell.z() = nCells_.z() * scaled.z();
1421 +        
1422 +        // find single index of this cell:
1423 +        cellIndex = Vlinear(whichCell, nCells_);
1424 +        
1425 +        // add this cutoff group to the list of groups in this cell;
1426 +        cellListRow_[cellIndex].push_back(i);
1427 +      }
1428 +      for (int i = 0; i < nGroupsInCol_; i++) {
1429 +        rs = cgColData.position[i];
1430 +        
1431 +        // scaled positions relative to the box vectors
1432 +        scaled = invBox * rs;
1433 +        
1434 +        // wrap the vector back into the unit box by subtracting integer box
1435 +        // numbers
1436 +        for (int j = 0; j < 3; j++) {
1437 +          scaled[j] -= roundMe(scaled[j]);
1438 +          scaled[j] += 0.5;
1439 +          // Handle the special case when an object is exactly on the
1440 +          // boundary (a scaled coordinate of 1.0 is the same as
1441 +          // scaled coordinate of 0.0)
1442 +          if (scaled[j] >= 1.0) scaled[j] -= 1.0;
1443 +        }
1444 +        
1445 +        // find xyz-indices of cell that cutoffGroup is in.
1446 +        whichCell.x() = nCells_.x() * scaled.x();
1447 +        whichCell.y() = nCells_.y() * scaled.y();
1448 +        whichCell.z() = nCells_.z() * scaled.z();
1449 +        
1450 +        // find single index of this cell:
1451 +        cellIndex = Vlinear(whichCell, nCells_);
1452 +        
1453 +        // add this cutoff group to the list of groups in this cell;
1454 +        cellListCol_[cellIndex].push_back(i);
1455 +      }
1456 +      
1457 + #else
1458 +      for (int i = 0; i < nGroups_; i++) {
1459 +        rs = snap_->cgData.position[i];
1460 +        
1461 +        // scaled positions relative to the box vectors
1462 +        scaled = invBox * rs;
1463 +        
1464 +        // wrap the vector back into the unit box by subtracting integer box
1465 +        // numbers
1466 +        for (int j = 0; j < 3; j++) {
1467 +          scaled[j] -= roundMe(scaled[j]);
1468 +          scaled[j] += 0.5;
1469 +          // Handle the special case when an object is exactly on the
1470 +          // boundary (a scaled coordinate of 1.0 is the same as
1471 +          // scaled coordinate of 0.0)
1472 +          if (scaled[j] >= 1.0) scaled[j] -= 1.0;
1473 +        }
1474 +        
1475 +        // find xyz-indices of cell that cutoffGroup is in.
1476 +        whichCell.x() = nCells_.x() * scaled.x();
1477 +        whichCell.y() = nCells_.y() * scaled.y();
1478 +        whichCell.z() = nCells_.z() * scaled.z();
1479 +        
1480 +        // find single index of this cell:
1481 +        cellIndex = Vlinear(whichCell, nCells_);
1482 +        
1483 +        // add this cutoff group to the list of groups in this cell;
1484 +        cellList_[cellIndex].push_back(i);
1485 +      }
1486 +
1487 + #endif
1488 +
1489 +      for (int m1z = 0; m1z < nCells_.z(); m1z++) {
1490 +        for (int m1y = 0; m1y < nCells_.y(); m1y++) {
1491 +          for (int m1x = 0; m1x < nCells_.x(); m1x++) {
1492 +            Vector3i m1v(m1x, m1y, m1z);
1493 +            int m1 = Vlinear(m1v, nCells_);
1494 +            
1495 +            for (vector<Vector3i>::iterator os = cellOffsets_.begin();
1496 +                 os != cellOffsets_.end(); ++os) {
1497 +              
1498 +              Vector3i m2v = m1v + (*os);
1499 +            
1500 +
1501 +              if (m2v.x() >= nCells_.x()) {
1502 +                m2v.x() = 0;          
1503 +              } else if (m2v.x() < 0) {
1504 +                m2v.x() = nCells_.x() - 1;
1505 +              }
1506 +              
1507 +              if (m2v.y() >= nCells_.y()) {
1508 +                m2v.y() = 0;          
1509 +              } else if (m2v.y() < 0) {
1510 +                m2v.y() = nCells_.y() - 1;
1511 +              }
1512 +              
1513 +              if (m2v.z() >= nCells_.z()) {
1514 +                m2v.z() = 0;          
1515 +              } else if (m2v.z() < 0) {
1516 +                m2v.z() = nCells_.z() - 1;
1517 +              }
1518 +
1519 +              int m2 = Vlinear (m2v, nCells_);
1520 +              
1521 + #ifdef IS_MPI
1522 +              for (vector<int>::iterator j1 = cellListRow_[m1].begin();
1523 +                   j1 != cellListRow_[m1].end(); ++j1) {
1524 +                for (vector<int>::iterator j2 = cellListCol_[m2].begin();
1525 +                     j2 != cellListCol_[m2].end(); ++j2) {
1526 +                  
1527 +                  // In parallel, we need to visit *all* pairs of row
1528 +                  // & column indicies and will divide labor in the
1529 +                  // force evaluation later.
1530 +                  dr = cgColData.position[(*j2)] - cgRowData.position[(*j1)];
1531 +                  if (usePeriodicBoundaryConditions_) {
1532 +                    snap_->wrapVector(dr);
1533 +                  }
1534 +                  getGroupCutoffs( (*j1), (*j2), rcut, rcutsq, rlistsq );
1535 +                  if (dr.lengthSquare() < rlistsq) {
1536 +                    neighborList.push_back(make_pair((*j1), (*j2)));
1537 +                  }                  
1538 +                }
1539 +              }
1540 + #else
1541 +              for (vector<int>::iterator j1 = cellList_[m1].begin();
1542 +                   j1 != cellList_[m1].end(); ++j1) {
1543 +                for (vector<int>::iterator j2 = cellList_[m2].begin();
1544 +                     j2 != cellList_[m2].end(); ++j2) {
1545 +    
1546 +                  // Always do this if we're in different cells or if
1547 +                  // we're in the same cell and the global index of
1548 +                  // the j2 cutoff group is greater than or equal to
1549 +                  // the j1 cutoff group.  Note that Rappaport's code
1550 +                  // has a "less than" conditional here, but that
1551 +                  // deals with atom-by-atom computation.  OpenMD
1552 +                  // allows atoms within a single cutoff group to
1553 +                  // interact with each other.
1554 +
1555 +                  if (m2 != m1 || (*j2) >= (*j1) ) {
1556 +
1557 +                    dr = snap_->cgData.position[(*j2)] - snap_->cgData.position[(*j1)];
1558 +                    if (usePeriodicBoundaryConditions_) {
1559 +                      snap_->wrapVector(dr);
1560 +                    }
1561 +                    getGroupCutoffs( (*j1), (*j2), rcut, rcutsq, rlistsq );
1562 +                    if (dr.lengthSquare() < rlistsq) {
1563 +                      neighborList.push_back(make_pair((*j1), (*j2)));
1564 +                    }
1565 +                  }
1566 +                }
1567 +              }
1568 + #endif
1569 +            }
1570 +          }
1571 +        }
1572 +      }
1573 +    } else {
1574 +      // branch to do all cutoff group pairs
1575 + #ifdef IS_MPI
1576 +      for (int j1 = 0; j1 < nGroupsInRow_; j1++) {
1577 +        for (int j2 = 0; j2 < nGroupsInCol_; j2++) {    
1578 +          dr = cgColData.position[j2] - cgRowData.position[j1];
1579 +          if (usePeriodicBoundaryConditions_) {
1580 +            snap_->wrapVector(dr);
1581 +          }
1582 +          getGroupCutoffs( j1, j2, rcut, rcutsq, rlistsq);
1583 +          if (dr.lengthSquare() < rlistsq) {
1584 +            neighborList.push_back(make_pair(j1, j2));
1585 +          }
1586 +        }
1587 +      }      
1588 + #else
1589 +      // include all groups here.
1590 +      for (int j1 = 0; j1 < nGroups_; j1++) {
1591 +        // include self group interactions j2 == j1
1592 +        for (int j2 = j1; j2 < nGroups_; j2++) {
1593 +          dr = snap_->cgData.position[j2] - snap_->cgData.position[j1];
1594 +          if (usePeriodicBoundaryConditions_) {
1595 +            snap_->wrapVector(dr);
1596 +          }
1597 +          getGroupCutoffs( j1, j2, rcut, rcutsq, rlistsq );
1598 +          if (dr.lengthSquare() < rlistsq) {
1599 +            neighborList.push_back(make_pair(j1, j2));
1600 +          }
1601 +        }    
1602 +      }
1603 + #endif
1604 +    }
1605 +      
1606 +    // save the local cutoff group positions for the check that is
1607 +    // done on each loop:
1608 +    saved_CG_positions_.clear();
1609 +    for (int i = 0; i < nGroups_; i++)
1610 +      saved_CG_positions_.push_back(snap_->cgData.position[i]);
1611 +  }
1612   } //end namespace OpenMD

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