xref: /petsc/src/mat/impls/aij/mpi/mpiov.c (revision 67918a83b8f04b4d738ff24f942e6e78dc07322f)
1 /*
2    Routines to compute overlapping regions of a parallel MPI matrix
3   and to find submatrices that were shared across processors.
4 */
5 #include <../src/mat/impls/aij/seq/aij.h>
6 #include <../src/mat/impls/aij/mpi/mpiaij.h>
7 #include <petscbt.h>
8 #include <petscsf.h>
9 
10 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Once(Mat,PetscInt,IS*);
11 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Local(Mat,PetscInt,char**,PetscInt*,PetscInt**,PetscTable*);
12 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Receive(Mat,PetscInt,PetscInt**,PetscInt**,PetscInt*);
13 extern PetscErrorCode MatGetRow_MPIAIJ(Mat,PetscInt,PetscInt*,PetscInt**,PetscScalar**);
14 extern PetscErrorCode MatRestoreRow_MPIAIJ(Mat,PetscInt,PetscInt*,PetscInt**,PetscScalar**);
15 
16 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Once_Scalable(Mat,PetscInt,IS*);
17 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Local_Scalable(Mat,PetscInt,IS*);
18 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Send_Scalable(Mat,PetscInt,PetscMPIInt,PetscMPIInt *,PetscInt *, PetscInt *,PetscInt **,PetscInt **);
19 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Receive_Scalable(Mat,PetscInt,IS*,PetscInt,PetscInt *);
20 
21 
22 PetscErrorCode MatIncreaseOverlap_MPIAIJ(Mat C,PetscInt imax,IS is[],PetscInt ov)
23 {
24   PetscErrorCode ierr;
25   PetscInt       i;
26 
27   PetscFunctionBegin;
28   if (ov < 0) SETERRQ(PetscObjectComm((PetscObject)C),PETSC_ERR_ARG_OUTOFRANGE,"Negative overlap specified");
29   for (i=0; i<ov; ++i) {
30     ierr = MatIncreaseOverlap_MPIAIJ_Once(C,imax,is);CHKERRQ(ierr);
31   }
32   PetscFunctionReturn(0);
33 }
34 
35 PetscErrorCode MatIncreaseOverlap_MPIAIJ_Scalable(Mat C,PetscInt imax,IS is[],PetscInt ov)
36 {
37   PetscErrorCode ierr;
38   PetscInt       i;
39 
40   PetscFunctionBegin;
41   if (ov < 0) SETERRQ(PetscObjectComm((PetscObject)C),PETSC_ERR_ARG_OUTOFRANGE,"Negative overlap specified");
42   for (i=0; i<ov; ++i) {
43     ierr = MatIncreaseOverlap_MPIAIJ_Once_Scalable(C,imax,is);CHKERRQ(ierr);
44   }
45   PetscFunctionReturn(0);
46 }
47 
48 
49 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Once_Scalable(Mat mat,PetscInt nidx,IS is[])
50 {
51   PetscErrorCode   ierr;
52   MPI_Comm         comm;
53   PetscInt        *length,length_i,tlength,*remoterows,nrrows,reducednrrows,*rrow_ranks,*rrow_isids,i,j,owner;
54   PetscInt         *tosizes,*tosizes_temp,*toffsets,*fromsizes,*todata,*fromdata;
55   PetscInt         nrecvrows,*sbsizes = 0,*sbdata = 0;
56   const PetscInt  *indices_i,**indices;
57   PetscLayout      rmap;
58   PetscMPIInt      rank,size,*toranks,*fromranks,nto,nfrom;
59   PetscSF          sf;
60   PetscSFNode     *remote;
61 
62   PetscFunctionBegin;
63   ierr = PetscObjectGetComm((PetscObject)mat,&comm);CHKERRQ(ierr);
64   ierr = MPI_Comm_rank(comm,&rank);CHKERRQ(ierr);
65   ierr = MPI_Comm_size(comm,&size);CHKERRQ(ierr);
66   /* get row map to determine where rows should be going */
67   ierr = MatGetLayouts(mat,&rmap,NULL);CHKERRQ(ierr);
68   /* retrieve IS data and put all together so that we
69    * can optimize communication
70    *  */
71   ierr = PetscCalloc2(nidx,(PetscInt ***)&indices,nidx,&length);CHKERRQ(ierr);
72   for (i=0,tlength=0; i<nidx; i++){
73     ierr = ISGetLocalSize(is[i],&length[i]);CHKERRQ(ierr);
74     tlength += length[i];
75     ierr = ISGetIndices(is[i],&indices[i]);CHKERRQ(ierr);
76   }
77   /* find these rows on remote processors */
78   ierr = PetscCalloc3(tlength,&remoterows,tlength,&rrow_ranks,tlength,&rrow_isids);CHKERRQ(ierr);
79   ierr = PetscCalloc3(size,&toranks,2*size,&tosizes,size,&tosizes_temp);CHKERRQ(ierr);
80   nrrows = 0;
81   for (i=0; i<nidx; i++){
82     length_i     = length[i];
83     indices_i    = indices[i];
84     for (j=0; j<length_i; j++){
85       owner = -1;
86       ierr = PetscLayoutFindOwner(rmap,indices_i[j],&owner);CHKERRQ(ierr);
87       /* remote processors */
88       if (owner != rank){
89         tosizes_temp[owner]++; /* number of rows to owner */
90         rrow_ranks[nrrows]  = owner; /* processor */
91         rrow_isids[nrrows]   = i; /* is id */
92         remoterows[nrrows++] = indices_i[j]; /* row */
93       }
94     }
95     ierr = ISRestoreIndices(is[i],&indices[i]);CHKERRQ(ierr);
96   }
97   ierr = PetscFree2(indices,length);CHKERRQ(ierr);
98   /* test if we need to exchange messages
99    * generally speaking, we do not need to exchange
100    * data when overlap is 1
101    * */
102   ierr = MPIU_Allreduce(&nrrows,&reducednrrows,1,MPIU_INT,MPIU_MAX,comm);CHKERRQ(ierr);
103   /* we do not have any messages
104    * It usually corresponds to overlap 1
105    * */
106   if (!reducednrrows){
107     ierr = PetscFree3(toranks,tosizes,tosizes_temp);CHKERRQ(ierr);
108     ierr = PetscFree3(remoterows,rrow_ranks,rrow_isids);CHKERRQ(ierr);
109     ierr = MatIncreaseOverlap_MPIAIJ_Local_Scalable(mat,nidx,is);CHKERRQ(ierr);
110     PetscFunctionReturn(0);
111   }
112   nto = 0;
113   /* send sizes and ranks for building a two-sided communcation */
114   for (i=0; i<size; i++){
115    if (tosizes_temp[i]){
116      tosizes[nto*2]  = tosizes_temp[i]*2; /* size */
117      tosizes_temp[i] = nto; /* a map from processor to index */
118      toranks[nto++]  = i; /* processor */
119    }
120   }
121   ierr = PetscCalloc1(nto+1,&toffsets);CHKERRQ(ierr);
122   for (i=0; i<nto; i++){
123     toffsets[i+1]  = toffsets[i]+tosizes[2*i]; /* offsets */
124     tosizes[2*i+1] = toffsets[i]; /* offsets to send */
125   }
126   /* send information to other processors */
127   ierr = PetscCommBuildTwoSided(comm,2,MPIU_INT,nto,toranks,tosizes,&nfrom,&fromranks,&fromsizes);CHKERRQ(ierr);
128   nrecvrows = 0;
129   for (i=0; i<nfrom; i++) nrecvrows += fromsizes[2*i];
130   ierr = PetscMalloc1(nrecvrows,&remote);CHKERRQ(ierr);
131   nrecvrows = 0;
132   for (i=0; i<nfrom; i++){
133     for (j=0; j<fromsizes[2*i]; j++){
134       remote[nrecvrows].rank    = fromranks[i];
135       remote[nrecvrows++].index = fromsizes[2*i+1]+j;
136     }
137   }
138   ierr = PetscSFCreate(comm,&sf);CHKERRQ(ierr);
139   ierr = PetscSFSetGraph(sf,nrecvrows,nrecvrows,NULL,PETSC_OWN_POINTER,remote,PETSC_OWN_POINTER);CHKERRQ(ierr);
140   /* use two-sided communication by default since OPENMPI has some bugs for one-sided one */
141   ierr = PetscSFSetType(sf,PETSCSFBASIC);CHKERRQ(ierr);
142   ierr = PetscSFSetFromOptions(sf);CHKERRQ(ierr);
143   /* message pair <no of is, row>  */
144   ierr = PetscCalloc2(2*nrrows,&todata,nrecvrows,&fromdata);CHKERRQ(ierr);
145   for (i=0; i<nrrows; i++){
146     owner = rrow_ranks[i]; /* processor */
147     j     = tosizes_temp[owner]; /* index */
148     todata[toffsets[j]++] = rrow_isids[i];
149     todata[toffsets[j]++] = remoterows[i];
150   }
151   ierr = PetscFree3(toranks,tosizes,tosizes_temp);CHKERRQ(ierr);
152   ierr = PetscFree3(remoterows,rrow_ranks,rrow_isids);CHKERRQ(ierr);
153   ierr = PetscFree(toffsets);CHKERRQ(ierr);
154   ierr = PetscSFBcastBegin(sf,MPIU_INT,todata,fromdata);CHKERRQ(ierr);
155   ierr = PetscSFBcastEnd(sf,MPIU_INT,todata,fromdata);CHKERRQ(ierr);
156   ierr = PetscSFDestroy(&sf);CHKERRQ(ierr);
157   /* send rows belonging to the remote so that then we could get the overlapping data back */
158   ierr = MatIncreaseOverlap_MPIAIJ_Send_Scalable(mat,nidx,nfrom,fromranks,fromsizes,fromdata,&sbsizes,&sbdata);CHKERRQ(ierr);
159   ierr = PetscFree2(todata,fromdata);CHKERRQ(ierr);
160   ierr = PetscFree(fromsizes);CHKERRQ(ierr);
161   ierr = PetscCommBuildTwoSided(comm,2,MPIU_INT,nfrom,fromranks,sbsizes,&nto,&toranks,&tosizes);CHKERRQ(ierr);
162   ierr = PetscFree(fromranks);CHKERRQ(ierr);
163   nrecvrows = 0;
164   for (i=0; i<nto; i++) nrecvrows += tosizes[2*i];
165   ierr = PetscCalloc1(nrecvrows,&todata);CHKERRQ(ierr);
166   ierr = PetscMalloc1(nrecvrows,&remote);CHKERRQ(ierr);
167   nrecvrows = 0;
168   for (i=0; i<nto; i++){
169     for (j=0; j<tosizes[2*i]; j++){
170       remote[nrecvrows].rank    = toranks[i];
171       remote[nrecvrows++].index = tosizes[2*i+1]+j;
172     }
173   }
174   ierr = PetscSFCreate(comm,&sf);CHKERRQ(ierr);
175   ierr = PetscSFSetGraph(sf,nrecvrows,nrecvrows,NULL,PETSC_OWN_POINTER,remote,PETSC_OWN_POINTER);CHKERRQ(ierr);
176   /* use two-sided communication by default since OPENMPI has some bugs for one-sided one */
177   ierr = PetscSFSetType(sf,PETSCSFBASIC);CHKERRQ(ierr);
178   ierr = PetscSFSetFromOptions(sf);CHKERRQ(ierr);
179   /* overlap communication and computation */
180   ierr = PetscSFBcastBegin(sf,MPIU_INT,sbdata,todata);CHKERRQ(ierr);
181   ierr = MatIncreaseOverlap_MPIAIJ_Local_Scalable(mat,nidx,is);CHKERRQ(ierr);
182   ierr = PetscSFBcastEnd(sf,MPIU_INT,sbdata,todata);CHKERRQ(ierr);
183   ierr = PetscSFDestroy(&sf);CHKERRQ(ierr);
184   ierr = PetscFree2(sbdata,sbsizes);CHKERRQ(ierr);
185   ierr = MatIncreaseOverlap_MPIAIJ_Receive_Scalable(mat,nidx,is,nrecvrows,todata);CHKERRQ(ierr);
186   ierr = PetscFree(toranks);CHKERRQ(ierr);
187   ierr = PetscFree(tosizes);CHKERRQ(ierr);
188   ierr = PetscFree(todata);CHKERRQ(ierr);
189   PetscFunctionReturn(0);
190 }
191 
192 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Receive_Scalable(Mat mat,PetscInt nidx, IS is[], PetscInt nrecvs, PetscInt *recvdata)
193 {
194   PetscInt         *isz,isz_i,i,j,is_id, data_size;
195   PetscInt          col,lsize,max_lsize,*indices_temp, *indices_i;
196   const PetscInt   *indices_i_temp;
197   PetscErrorCode    ierr;
198 
199   PetscFunctionBegin;
200   max_lsize = 0;
201   ierr = PetscMalloc1(nidx,&isz);CHKERRQ(ierr);
202   for (i=0; i<nidx; i++){
203     ierr = ISGetLocalSize(is[i],&lsize);CHKERRQ(ierr);
204     max_lsize = lsize>max_lsize ? lsize:max_lsize;
205     isz[i]    = lsize;
206   }
207   ierr = PetscMalloc1((max_lsize+nrecvs)*nidx,&indices_temp);CHKERRQ(ierr);
208   for (i=0; i<nidx; i++){
209     ierr = ISGetIndices(is[i],&indices_i_temp);CHKERRQ(ierr);
210     ierr = PetscMemcpy(indices_temp+i*(max_lsize+nrecvs),indices_i_temp, sizeof(PetscInt)*isz[i]);CHKERRQ(ierr);
211     ierr = ISRestoreIndices(is[i],&indices_i_temp);CHKERRQ(ierr);
212     ierr = ISDestroy(&is[i]);CHKERRQ(ierr);
213   }
214   /* retrieve information to get row id and its overlap */
215   for (i=0; i<nrecvs; ){
216     is_id      = recvdata[i++];
217     data_size  = recvdata[i++];
218     indices_i  = indices_temp+(max_lsize+nrecvs)*is_id;
219     isz_i      = isz[is_id];
220     for (j=0; j< data_size; j++){
221       col = recvdata[i++];
222       indices_i[isz_i++] = col;
223     }
224     isz[is_id] = isz_i;
225   }
226   /* remove duplicate entities */
227   for (i=0; i<nidx; i++){
228     indices_i  = indices_temp+(max_lsize+nrecvs)*i;
229     isz_i      = isz[i];
230     ierr = PetscSortRemoveDupsInt(&isz_i,indices_i);CHKERRQ(ierr);
231     ierr = ISCreateGeneral(PETSC_COMM_SELF,isz_i,indices_i,PETSC_COPY_VALUES,&is[i]);CHKERRQ(ierr);
232   }
233   ierr = PetscFree(isz);CHKERRQ(ierr);
234   ierr = PetscFree(indices_temp);CHKERRQ(ierr);
235   PetscFunctionReturn(0);
236 }
237 
238 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Send_Scalable(Mat mat,PetscInt nidx, PetscMPIInt nfrom,PetscMPIInt *fromranks,PetscInt *fromsizes, PetscInt *fromrows, PetscInt **sbrowsizes, PetscInt **sbrows)
239 {
240   PetscLayout       rmap,cmap;
241   PetscInt          i,j,k,l,*rows_i,*rows_data_ptr,**rows_data,max_fszs,rows_pos,*rows_pos_i;
242   PetscInt          is_id,tnz,an,bn,rstart,cstart,row,start,end,col,totalrows,*sbdata;
243   PetscInt         *indv_counts,indvc_ij,*sbsizes,*indices_tmp,*offsets;
244   const PetscInt   *gcols,*ai,*aj,*bi,*bj;
245   Mat               amat,bmat;
246   PetscMPIInt       rank;
247   PetscBool         done;
248   MPI_Comm          comm;
249   PetscErrorCode    ierr;
250 
251   PetscFunctionBegin;
252   ierr = PetscObjectGetComm((PetscObject)mat,&comm);CHKERRQ(ierr);
253   ierr = MPI_Comm_rank(comm,&rank);CHKERRQ(ierr);
254   ierr = MatMPIAIJGetSeqAIJ(mat,&amat,&bmat,&gcols);CHKERRQ(ierr);
255   /* Even if the mat is symmetric, we still assume it is not symmetric */
256   ierr = MatGetRowIJ(amat,0,PETSC_FALSE,PETSC_FALSE,&an,&ai,&aj,&done);CHKERRQ(ierr);
257   if (!done) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"can not get row IJ \n");
258   ierr = MatGetRowIJ(bmat,0,PETSC_FALSE,PETSC_FALSE,&bn,&bi,&bj,&done);CHKERRQ(ierr);
259   if (!done) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"can not get row IJ \n");
260   /* total number of nonzero values is used to estimate the memory usage in the next step */
261   tnz  = ai[an]+bi[bn];
262   ierr = MatGetLayouts(mat,&rmap,&cmap);CHKERRQ(ierr);
263   ierr = PetscLayoutGetRange(rmap,&rstart,NULL);CHKERRQ(ierr);
264   ierr = PetscLayoutGetRange(cmap,&cstart,NULL);CHKERRQ(ierr);
265   /* to find the longest message */
266   max_fszs = 0;
267   for (i=0; i<nfrom; i++) max_fszs = fromsizes[2*i]>max_fszs ? fromsizes[2*i]:max_fszs;
268   /* better way to estimate number of nonzero in the mat??? */
269   ierr = PetscCalloc5(max_fszs*nidx,&rows_data_ptr,nidx,&rows_data,nidx,&rows_pos_i,nfrom*nidx,&indv_counts,tnz,&indices_tmp);CHKERRQ(ierr);
270   for (i=0; i<nidx; i++) rows_data[i] = rows_data_ptr+max_fszs*i;
271   rows_pos  = 0;
272   totalrows = 0;
273   for (i=0; i<nfrom; i++){
274     ierr = PetscMemzero(rows_pos_i,sizeof(PetscInt)*nidx);CHKERRQ(ierr);
275     /* group data together */
276     for (j=0; j<fromsizes[2*i]; j+=2){
277       is_id                       = fromrows[rows_pos++];/* no of is */
278       rows_i                      = rows_data[is_id];
279       rows_i[rows_pos_i[is_id]++] = fromrows[rows_pos++];/* row */
280     }
281     /* estimate a space to avoid multiple allocations  */
282     for (j=0; j<nidx; j++){
283       indvc_ij = 0;
284       rows_i   = rows_data[j];
285       for (l=0; l<rows_pos_i[j]; l++){
286         row    = rows_i[l]-rstart;
287         start  = ai[row];
288         end    = ai[row+1];
289         for (k=start; k<end; k++){ /* Amat */
290           col = aj[k] + cstart;
291           indices_tmp[indvc_ij++] = col;/* do not count the rows from the original rank */
292         }
293         start = bi[row];
294         end   = bi[row+1];
295         for (k=start; k<end; k++) { /* Bmat */
296           col = gcols[bj[k]];
297           indices_tmp[indvc_ij++] = col;
298         }
299       }
300       ierr = PetscSortRemoveDupsInt(&indvc_ij,indices_tmp);CHKERRQ(ierr);
301       indv_counts[i*nidx+j] = indvc_ij;
302       totalrows            += indvc_ij;
303     }
304   }
305   /* message triple <no of is, number of rows, rows> */
306   ierr = PetscCalloc2(totalrows+nidx*nfrom*2,&sbdata,2*nfrom,&sbsizes);CHKERRQ(ierr);
307   totalrows = 0;
308   rows_pos  = 0;
309   /* use this code again */
310   for (i=0;i<nfrom;i++){
311     ierr = PetscMemzero(rows_pos_i,sizeof(PetscInt)*nidx);CHKERRQ(ierr);
312     for (j=0; j<fromsizes[2*i]; j+=2){
313       is_id                       = fromrows[rows_pos++];
314       rows_i                      = rows_data[is_id];
315       rows_i[rows_pos_i[is_id]++] = fromrows[rows_pos++];
316     }
317     /* add data  */
318     for (j=0; j<nidx; j++){
319       if (!indv_counts[i*nidx+j]) continue;
320       indvc_ij = 0;
321       sbdata[totalrows++] = j;
322       sbdata[totalrows++] = indv_counts[i*nidx+j];
323       sbsizes[2*i]       += 2;
324       rows_i              = rows_data[j];
325       for (l=0; l<rows_pos_i[j]; l++){
326         row   = rows_i[l]-rstart;
327         start = ai[row];
328         end   = ai[row+1];
329         for (k=start; k<end; k++){ /* Amat */
330           col = aj[k] + cstart;
331           indices_tmp[indvc_ij++] = col;
332         }
333         start = bi[row];
334         end   = bi[row+1];
335         for (k=start; k<end; k++) { /* Bmat */
336           col = gcols[bj[k]];
337           indices_tmp[indvc_ij++] = col;
338         }
339       }
340       ierr = PetscSortRemoveDupsInt(&indvc_ij,indices_tmp);CHKERRQ(ierr);
341       sbsizes[2*i]  += indvc_ij;
342       ierr = PetscMemcpy(sbdata+totalrows,indices_tmp,sizeof(PetscInt)*indvc_ij);CHKERRQ(ierr);
343       totalrows += indvc_ij;
344     }
345   }
346   ierr = PetscCalloc1(nfrom+1,&offsets);CHKERRQ(ierr);
347   for (i=0; i<nfrom; i++){
348     offsets[i+1]   = offsets[i] + sbsizes[2*i];
349     sbsizes[2*i+1] = offsets[i];
350   }
351   ierr = PetscFree(offsets);CHKERRQ(ierr);
352   if (sbrowsizes) *sbrowsizes = sbsizes;
353   if (sbrows) *sbrows = sbdata;
354   ierr = PetscFree5(rows_data_ptr,rows_data,rows_pos_i,indv_counts,indices_tmp);CHKERRQ(ierr);
355   ierr = MatRestoreRowIJ(amat,0,PETSC_FALSE,PETSC_FALSE,&an,&ai,&aj,&done);CHKERRQ(ierr);
356   ierr = MatRestoreRowIJ(bmat,0,PETSC_FALSE,PETSC_FALSE,&bn,&bi,&bj,&done);CHKERRQ(ierr);
357   PetscFunctionReturn(0);
358 }
359 
360 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Local_Scalable(Mat mat,PetscInt nidx, IS is[])
361 {
362   const PetscInt   *gcols,*ai,*aj,*bi,*bj, *indices;
363   PetscInt          tnz,an,bn,i,j,row,start,end,rstart,cstart,col,k,*indices_temp;
364   PetscInt          lsize,lsize_tmp,owner;
365   PetscMPIInt       rank;
366   Mat               amat,bmat;
367   PetscBool         done;
368   PetscLayout       cmap,rmap;
369   MPI_Comm          comm;
370   PetscErrorCode    ierr;
371 
372   PetscFunctionBegin;
373   ierr = PetscObjectGetComm((PetscObject)mat,&comm);CHKERRQ(ierr);
374   ierr = MPI_Comm_rank(comm,&rank);CHKERRQ(ierr);
375   ierr = MatMPIAIJGetSeqAIJ(mat,&amat,&bmat,&gcols);CHKERRQ(ierr);
376   ierr = MatGetRowIJ(amat,0,PETSC_FALSE,PETSC_FALSE,&an,&ai,&aj,&done);CHKERRQ(ierr);
377   if (!done) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"can not get row IJ \n");
378   ierr = MatGetRowIJ(bmat,0,PETSC_FALSE,PETSC_FALSE,&bn,&bi,&bj,&done);CHKERRQ(ierr);
379   if (!done) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"can not get row IJ \n");
380   /* is it a safe way to compute number of nonzero values ? */
381   tnz  = ai[an]+bi[bn];
382   ierr = MatGetLayouts(mat,&rmap,&cmap);CHKERRQ(ierr);
383   ierr = PetscLayoutGetRange(rmap,&rstart,NULL);CHKERRQ(ierr);
384   ierr = PetscLayoutGetRange(cmap,&cstart,NULL);CHKERRQ(ierr);
385   /* it is a better way to estimate memory than the old implementation
386    * where global size of matrix is used
387    * */
388   ierr = PetscMalloc1(tnz,&indices_temp);CHKERRQ(ierr);
389   for (i=0; i<nidx; i++) {
390     ierr = ISGetLocalSize(is[i],&lsize);CHKERRQ(ierr);
391     ierr = ISGetIndices(is[i],&indices);CHKERRQ(ierr);
392     lsize_tmp = 0;
393     for (j=0; j<lsize; j++) {
394       owner = -1;
395       row   = indices[j];
396       ierr = PetscLayoutFindOwner(rmap,row,&owner);CHKERRQ(ierr);
397       if (owner != rank) continue;
398       /* local number */
399       row  -= rstart;
400       start = ai[row];
401       end   = ai[row+1];
402       for (k=start; k<end; k++) { /* Amat */
403         col = aj[k] + cstart;
404         indices_temp[lsize_tmp++] = col;
405       }
406       start = bi[row];
407       end   = bi[row+1];
408       for (k=start; k<end; k++) { /* Bmat */
409         col = gcols[bj[k]];
410         indices_temp[lsize_tmp++] = col;
411       }
412     }
413    ierr = ISRestoreIndices(is[i],&indices);CHKERRQ(ierr);
414    ierr = ISDestroy(&is[i]);CHKERRQ(ierr);
415    ierr = PetscSortRemoveDupsInt(&lsize_tmp,indices_temp);CHKERRQ(ierr);
416    ierr = ISCreateGeneral(PETSC_COMM_SELF,lsize_tmp,indices_temp,PETSC_COPY_VALUES,&is[i]);CHKERRQ(ierr);
417   }
418   ierr = PetscFree(indices_temp);CHKERRQ(ierr);
419   ierr = MatRestoreRowIJ(amat,0,PETSC_FALSE,PETSC_FALSE,&an,&ai,&aj,&done);CHKERRQ(ierr);
420   ierr = MatRestoreRowIJ(bmat,0,PETSC_FALSE,PETSC_FALSE,&bn,&bi,&bj,&done);CHKERRQ(ierr);
421   PetscFunctionReturn(0);
422 }
423 
424 
425 /*
426   Sample message format:
427   If a processor A wants processor B to process some elements corresponding
428   to index sets is[1],is[5]
429   mesg [0] = 2   (no of index sets in the mesg)
430   -----------
431   mesg [1] = 1 => is[1]
432   mesg [2] = sizeof(is[1]);
433   -----------
434   mesg [3] = 5  => is[5]
435   mesg [4] = sizeof(is[5]);
436   -----------
437   mesg [5]
438   mesg [n]  datas[1]
439   -----------
440   mesg[n+1]
441   mesg[m]  data(is[5])
442   -----------
443 
444   Notes:
445   nrqs - no of requests sent (or to be sent out)
446   nrqr - no of requests recieved (which have to be or which have been processed
447 */
448 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Once(Mat C,PetscInt imax,IS is[])
449 {
450   Mat_MPIAIJ     *c = (Mat_MPIAIJ*)C->data;
451   PetscMPIInt    *w1,*w2,nrqr,*w3,*w4,*onodes1,*olengths1,*onodes2,*olengths2;
452   const PetscInt **idx,*idx_i;
453   PetscInt       *n,**data,len;
454 #if defined(PETSC_USE_CTABLE)
455   PetscTable     *table_data,table_data_i;
456   PetscInt       *tdata,tcount,tcount_max;
457 #else
458   PetscInt       *data_i,*d_p;
459 #endif
460   PetscErrorCode ierr;
461   PetscMPIInt    size,rank,tag1,tag2;
462   PetscInt       M,i,j,k,**rbuf,row,proc = 0,nrqs,msz,**outdat,**ptr;
463   PetscInt       *ctr,*pa,*tmp,*isz,*isz1,**xdata,**rbuf2;
464   PetscBT        *table;
465   MPI_Comm       comm;
466   MPI_Request    *s_waits1,*r_waits1,*s_waits2,*r_waits2;
467   MPI_Status     *s_status,*recv_status;
468   char           *t_p;
469 
470   PetscFunctionBegin;
471   ierr = PetscObjectGetComm((PetscObject)C,&comm);CHKERRQ(ierr);
472   size = c->size;
473   rank = c->rank;
474   M    = C->rmap->N;
475 
476   ierr = PetscObjectGetNewTag((PetscObject)C,&tag1);CHKERRQ(ierr);
477   ierr = PetscObjectGetNewTag((PetscObject)C,&tag2);CHKERRQ(ierr);
478 
479   ierr = PetscMalloc2(imax,&idx,imax,&n);CHKERRQ(ierr);
480 
481   for (i=0; i<imax; i++) {
482     ierr = ISGetIndices(is[i],&idx[i]);CHKERRQ(ierr);
483     ierr = ISGetLocalSize(is[i],&n[i]);CHKERRQ(ierr);
484   }
485 
486   /* evaluate communication - mesg to who,length of mesg, and buffer space
487      required. Based on this, buffers are allocated, and data copied into them  */
488   ierr = PetscMalloc4(size,&w1,size,&w2,size,&w3,size,&w4);CHKERRQ(ierr);
489   ierr = PetscMemzero(w1,size*sizeof(PetscMPIInt));CHKERRQ(ierr); /* initialise work vector*/
490   ierr = PetscMemzero(w2,size*sizeof(PetscMPIInt));CHKERRQ(ierr); /* initialise work vector*/
491   ierr = PetscMemzero(w3,size*sizeof(PetscMPIInt));CHKERRQ(ierr); /* initialise work vector*/
492   for (i=0; i<imax; i++) {
493     ierr  = PetscMemzero(w4,size*sizeof(PetscMPIInt));CHKERRQ(ierr); /* initialise work vector*/
494     idx_i = idx[i];
495     len   = n[i];
496     for (j=0; j<len; j++) {
497       row = idx_i[j];
498       if (row < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"Index set cannot have negative entries");
499       ierr = PetscLayoutFindOwner(C->rmap,row,&proc);CHKERRQ(ierr);
500       w4[proc]++;
501     }
502     for (j=0; j<size; j++) {
503       if (w4[j]) { w1[j] += w4[j]; w3[j]++;}
504     }
505   }
506 
507   nrqs     = 0;              /* no of outgoing messages */
508   msz      = 0;              /* total mesg length (for all proc */
509   w1[rank] = 0;              /* no mesg sent to intself */
510   w3[rank] = 0;
511   for (i=0; i<size; i++) {
512     if (w1[i])  {w2[i] = 1; nrqs++;} /* there exists a message to proc i */
513   }
514   /* pa - is list of processors to communicate with */
515   ierr = PetscMalloc1(nrqs+1,&pa);CHKERRQ(ierr);
516   for (i=0,j=0; i<size; i++) {
517     if (w1[i]) {pa[j] = i; j++;}
518   }
519 
520   /* Each message would have a header = 1 + 2*(no of IS) + data */
521   for (i=0; i<nrqs; i++) {
522     j      = pa[i];
523     w1[j] += w2[j] + 2*w3[j];
524     msz   += w1[j];
525   }
526 
527   /* Determine the number of messages to expect, their lengths, from from-ids */
528   ierr = PetscGatherNumberOfMessages(comm,w2,w1,&nrqr);CHKERRQ(ierr);
529   ierr = PetscGatherMessageLengths(comm,nrqs,nrqr,w1,&onodes1,&olengths1);CHKERRQ(ierr);
530 
531   /* Now post the Irecvs corresponding to these messages */
532   ierr = PetscPostIrecvInt(comm,tag1,nrqr,onodes1,olengths1,&rbuf,&r_waits1);CHKERRQ(ierr);
533 
534   /* Allocate Memory for outgoing messages */
535   ierr = PetscMalloc4(size,&outdat,size,&ptr,msz,&tmp,size,&ctr);CHKERRQ(ierr);
536   ierr = PetscMemzero(outdat,size*sizeof(PetscInt*));CHKERRQ(ierr);
537   ierr = PetscMemzero(ptr,size*sizeof(PetscInt*));CHKERRQ(ierr);
538 
539   {
540     PetscInt *iptr = tmp,ict  = 0;
541     for (i=0; i<nrqs; i++) {
542       j         = pa[i];
543       iptr     +=  ict;
544       outdat[j] = iptr;
545       ict       = w1[j];
546     }
547   }
548 
549   /* Form the outgoing messages */
550   /* plug in the headers */
551   for (i=0; i<nrqs; i++) {
552     j            = pa[i];
553     outdat[j][0] = 0;
554     ierr         = PetscMemzero(outdat[j]+1,2*w3[j]*sizeof(PetscInt));CHKERRQ(ierr);
555     ptr[j]       = outdat[j] + 2*w3[j] + 1;
556   }
557 
558   /* Memory for doing local proc's work */
559   {
560     PetscInt M_BPB_imax = 0;
561 #if defined(PETSC_USE_CTABLE)
562     ierr = PetscIntMultError((M/PETSC_BITS_PER_BYTE+1),imax, &M_BPB_imax);CHKERRQ(ierr);
563     ierr = PetscMalloc1(imax,&table_data);CHKERRQ(ierr);
564     for (i=0; i<imax; i++) {
565       ierr = PetscTableCreate(n[i]+1,M+1,&table_data[i]);CHKERRQ(ierr);
566     }
567     ierr = PetscCalloc4(imax,&table, imax,&data, imax,&isz, M_BPB_imax,&t_p);CHKERRQ(ierr);
568     for (i=0; i<imax; i++) {
569       table[i] = t_p + (M/PETSC_BITS_PER_BYTE+1)*i;
570     }
571 #else
572     PetscInt Mimax = 0;
573     ierr = PetscIntMultError(M,imax, &Mimax);CHKERRQ(ierr);
574     ierr = PetscIntMultError((M/PETSC_BITS_PER_BYTE+1),imax, &M_BPB_imax);CHKERRQ(ierr);
575     ierr = PetscCalloc5(imax,&table, imax,&data, imax,&isz, Mimax,&d_p, M_BPB_imax,&t_p);CHKERRQ(ierr);
576     for (i=0; i<imax; i++) {
577       table[i] = t_p + (M/PETSC_BITS_PER_BYTE+1)*i;
578       data[i]  = d_p + M*i;
579     }
580 #endif
581   }
582 
583   /* Parse the IS and update local tables and the outgoing buf with the data */
584   {
585     PetscInt n_i,isz_i,*outdat_j,ctr_j;
586     PetscBT  table_i;
587 
588     for (i=0; i<imax; i++) {
589       ierr    = PetscMemzero(ctr,size*sizeof(PetscInt));CHKERRQ(ierr);
590       n_i     = n[i];
591       table_i = table[i];
592       idx_i   = idx[i];
593 #if defined(PETSC_USE_CTABLE)
594       table_data_i = table_data[i];
595 #else
596       data_i  = data[i];
597 #endif
598       isz_i   = isz[i];
599       for (j=0; j<n_i; j++) {   /* parse the indices of each IS */
600         row  = idx_i[j];
601         ierr = PetscLayoutFindOwner(C->rmap,row,&proc);CHKERRQ(ierr);
602         if (proc != rank) { /* copy to the outgoing buffer */
603           ctr[proc]++;
604           *ptr[proc] = row;
605           ptr[proc]++;
606         } else if (!PetscBTLookupSet(table_i,row)) {
607 #if defined(PETSC_USE_CTABLE)
608           ierr = PetscTableAdd(table_data_i,row+1,isz_i+1,INSERT_VALUES);CHKERRQ(ierr);
609 #else
610           data_i[isz_i] = row; /* Update the local table */
611 #endif
612           isz_i++;
613         }
614       }
615       /* Update the headers for the current IS */
616       for (j=0; j<size; j++) { /* Can Optimise this loop by using pa[] */
617         if ((ctr_j = ctr[j])) {
618           outdat_j        = outdat[j];
619           k               = ++outdat_j[0];
620           outdat_j[2*k]   = ctr_j;
621           outdat_j[2*k-1] = i;
622         }
623       }
624       isz[i] = isz_i;
625     }
626   }
627 
628   /*  Now  post the sends */
629   ierr = PetscMalloc1(nrqs+1,&s_waits1);CHKERRQ(ierr);
630   for (i=0; i<nrqs; ++i) {
631     j    = pa[i];
632     ierr = MPI_Isend(outdat[j],w1[j],MPIU_INT,j,tag1,comm,s_waits1+i);CHKERRQ(ierr);
633   }
634 
635   /* No longer need the original indices */
636   for (i=0; i<imax; ++i) {
637     ierr = ISRestoreIndices(is[i],idx+i);CHKERRQ(ierr);
638   }
639   ierr = PetscFree2(idx,n);CHKERRQ(ierr);
640 
641   for (i=0; i<imax; ++i) {
642     ierr = ISDestroy(&is[i]);CHKERRQ(ierr);
643   }
644 
645   /* Do Local work */
646 #if defined(PETSC_USE_CTABLE)
647   ierr = MatIncreaseOverlap_MPIAIJ_Local(C,imax,table,isz,NULL,table_data);CHKERRQ(ierr);
648 #else
649   ierr = MatIncreaseOverlap_MPIAIJ_Local(C,imax,table,isz,data,NULL);CHKERRQ(ierr);
650 #endif
651 
652   /* Receive messages */
653   ierr = PetscMalloc1(nrqr+1,&recv_status);CHKERRQ(ierr);
654   if (nrqr) {ierr = MPI_Waitall(nrqr,r_waits1,recv_status);CHKERRQ(ierr);}
655 
656   ierr = PetscMalloc1(nrqs+1,&s_status);CHKERRQ(ierr);
657   if (nrqs) {ierr = MPI_Waitall(nrqs,s_waits1,s_status);CHKERRQ(ierr);}
658 
659   /* Phase 1 sends are complete - deallocate buffers */
660   ierr = PetscFree4(outdat,ptr,tmp,ctr);CHKERRQ(ierr);
661   ierr = PetscFree4(w1,w2,w3,w4);CHKERRQ(ierr);
662 
663   ierr = PetscMalloc1(nrqr+1,&xdata);CHKERRQ(ierr);
664   ierr = PetscMalloc1(nrqr+1,&isz1);CHKERRQ(ierr);
665   ierr = MatIncreaseOverlap_MPIAIJ_Receive(C,nrqr,rbuf,xdata,isz1);CHKERRQ(ierr);
666   ierr = PetscFree(rbuf[0]);CHKERRQ(ierr);
667   ierr = PetscFree(rbuf);CHKERRQ(ierr);
668 
669 
670   /* Send the data back */
671   /* Do a global reduction to know the buffer space req for incoming messages */
672   {
673     PetscMPIInt *rw1;
674 
675     ierr = PetscCalloc1(size,&rw1);CHKERRQ(ierr);
676 
677     for (i=0; i<nrqr; ++i) {
678       proc = recv_status[i].MPI_SOURCE;
679 
680       if (proc != onodes1[i]) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"MPI_SOURCE mismatch");
681       rw1[proc] = isz1[i];
682     }
683     ierr = PetscFree(onodes1);CHKERRQ(ierr);
684     ierr = PetscFree(olengths1);CHKERRQ(ierr);
685 
686     /* Determine the number of messages to expect, their lengths, from from-ids */
687     ierr = PetscGatherMessageLengths(comm,nrqr,nrqs,rw1,&onodes2,&olengths2);CHKERRQ(ierr);
688     ierr = PetscFree(rw1);CHKERRQ(ierr);
689   }
690   /* Now post the Irecvs corresponding to these messages */
691   ierr = PetscPostIrecvInt(comm,tag2,nrqs,onodes2,olengths2,&rbuf2,&r_waits2);CHKERRQ(ierr);
692 
693   /* Now  post the sends */
694   ierr = PetscMalloc1(nrqr+1,&s_waits2);CHKERRQ(ierr);
695   for (i=0; i<nrqr; ++i) {
696     j    = recv_status[i].MPI_SOURCE;
697     ierr = MPI_Isend(xdata[i],isz1[i],MPIU_INT,j,tag2,comm,s_waits2+i);CHKERRQ(ierr);
698   }
699 
700   /* receive work done on other processors */
701   {
702     PetscInt    is_no,ct1,max,*rbuf2_i,isz_i,jmax;
703     PetscMPIInt idex;
704     PetscBT     table_i;
705     MPI_Status  *status2;
706 
707     ierr = PetscMalloc1((PetscMax(nrqr,nrqs)+1),&status2);CHKERRQ(ierr);
708     for (i=0; i<nrqs; ++i) {
709       ierr = MPI_Waitany(nrqs,r_waits2,&idex,status2+i);CHKERRQ(ierr);
710       /* Process the message */
711       rbuf2_i = rbuf2[idex];
712       ct1     = 2*rbuf2_i[0]+1;
713       jmax    = rbuf2[idex][0];
714       for (j=1; j<=jmax; j++) {
715         max     = rbuf2_i[2*j];
716         is_no   = rbuf2_i[2*j-1];
717         isz_i   = isz[is_no];
718         table_i = table[is_no];
719 #if defined(PETSC_USE_CTABLE)
720         table_data_i = table_data[is_no];
721 #else
722         data_i  = data[is_no];
723 #endif
724         for (k=0; k<max; k++,ct1++) {
725           row = rbuf2_i[ct1];
726           if (!PetscBTLookupSet(table_i,row)) {
727 #if defined(PETSC_USE_CTABLE)
728             ierr = PetscTableAdd(table_data_i,row+1,isz_i+1,INSERT_VALUES);CHKERRQ(ierr);
729 #else
730             data_i[isz_i] = row;
731 #endif
732             isz_i++;
733           }
734         }
735         isz[is_no] = isz_i;
736       }
737     }
738 
739     if (nrqr) {ierr = MPI_Waitall(nrqr,s_waits2,status2);CHKERRQ(ierr);}
740     ierr = PetscFree(status2);CHKERRQ(ierr);
741   }
742 
743 #if defined(PETSC_USE_CTABLE)
744   tcount_max = 0;
745   for (i=0; i<imax; ++i) {
746     table_data_i = table_data[i];
747     ierr = PetscTableGetCount(table_data_i,&tcount);CHKERRQ(ierr);
748     if (tcount_max < tcount) tcount_max = tcount;
749   }
750   ierr = PetscMalloc1(tcount_max+1,&tdata);CHKERRQ(ierr);
751 #endif
752 
753   for (i=0; i<imax; ++i) {
754 #if defined(PETSC_USE_CTABLE)
755     PetscTablePosition tpos;
756     table_data_i = table_data[i];
757 
758     ierr = PetscTableGetHeadPosition(table_data_i,&tpos);CHKERRQ(ierr);
759     while (tpos) {
760       ierr = PetscTableGetNext(table_data_i,&tpos,&k,&j);CHKERRQ(ierr);
761       tdata[--j] = --k;
762     }
763     ierr = ISCreateGeneral(PETSC_COMM_SELF,isz[i],tdata,PETSC_COPY_VALUES,is+i);CHKERRQ(ierr);
764 #else
765     ierr = ISCreateGeneral(PETSC_COMM_SELF,isz[i],data[i],PETSC_COPY_VALUES,is+i);CHKERRQ(ierr);
766 #endif
767   }
768 
769   ierr = PetscFree(onodes2);CHKERRQ(ierr);
770   ierr = PetscFree(olengths2);CHKERRQ(ierr);
771 
772   ierr = PetscFree(pa);CHKERRQ(ierr);
773   ierr = PetscFree(rbuf2[0]);CHKERRQ(ierr);
774   ierr = PetscFree(rbuf2);CHKERRQ(ierr);
775   ierr = PetscFree(s_waits1);CHKERRQ(ierr);
776   ierr = PetscFree(r_waits1);CHKERRQ(ierr);
777   ierr = PetscFree(s_waits2);CHKERRQ(ierr);
778   ierr = PetscFree(r_waits2);CHKERRQ(ierr);
779   ierr = PetscFree(s_status);CHKERRQ(ierr);
780   ierr = PetscFree(recv_status);CHKERRQ(ierr);
781   ierr = PetscFree(xdata[0]);CHKERRQ(ierr);
782   ierr = PetscFree(xdata);CHKERRQ(ierr);
783   ierr = PetscFree(isz1);CHKERRQ(ierr);
784 #if defined(PETSC_USE_CTABLE)
785   for (i=0; i<imax; i++) {
786     ierr = PetscTableDestroy((PetscTable*)&table_data[i]);CHKERRQ(ierr);
787   }
788   ierr = PetscFree(table_data);CHKERRQ(ierr);
789   ierr = PetscFree(tdata);CHKERRQ(ierr);
790   ierr = PetscFree4(table,data,isz,t_p);CHKERRQ(ierr);
791 #else
792   ierr = PetscFree5(table,data,isz,d_p,t_p);CHKERRQ(ierr);
793 #endif
794   PetscFunctionReturn(0);
795 }
796 
797 /*
798    MatIncreaseOverlap_MPIAIJ_Local - Called by MatincreaseOverlap, to do
799        the work on the local processor.
800 
801      Inputs:
802       C      - MAT_MPIAIJ;
803       imax - total no of index sets processed at a time;
804       table  - an array of char - size = m bits.
805 
806      Output:
807       isz    - array containing the count of the solution elements corresponding
808                to each index set;
809       data or table_data  - pointer to the solutions
810 */
811 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Local(Mat C,PetscInt imax,PetscBT *table,PetscInt *isz,PetscInt **data,PetscTable *table_data)
812 {
813   Mat_MPIAIJ *c = (Mat_MPIAIJ*)C->data;
814   Mat        A  = c->A,B = c->B;
815   Mat_SeqAIJ *a = (Mat_SeqAIJ*)A->data,*b = (Mat_SeqAIJ*)B->data;
816   PetscInt   start,end,val,max,rstart,cstart,*ai,*aj;
817   PetscInt   *bi,*bj,*garray,i,j,k,row,isz_i;
818   PetscBT    table_i;
819 #if defined(PETSC_USE_CTABLE)
820   PetscTable         table_data_i;
821   PetscErrorCode     ierr;
822   PetscTablePosition tpos;
823   PetscInt           tcount,*tdata;
824 #else
825   PetscInt           *data_i;
826 #endif
827 
828   PetscFunctionBegin;
829   rstart = C->rmap->rstart;
830   cstart = C->cmap->rstart;
831   ai     = a->i;
832   aj     = a->j;
833   bi     = b->i;
834   bj     = b->j;
835   garray = c->garray;
836 
837   for (i=0; i<imax; i++) {
838 #if defined(PETSC_USE_CTABLE)
839     /* copy existing entries of table_data_i into tdata[] */
840     table_data_i = table_data[i];
841     ierr = PetscTableGetCount(table_data_i,&tcount);CHKERRQ(ierr);
842     if (tcount != isz[i]) SETERRQ3(PETSC_COMM_SELF,0," tcount %d != isz[%d] %d",tcount,i,isz[i]);
843 
844     ierr = PetscMalloc1(tcount,&tdata);CHKERRQ(ierr);
845     ierr = PetscTableGetHeadPosition(table_data_i,&tpos);CHKERRQ(ierr);
846     while (tpos) {
847       ierr = PetscTableGetNext(table_data_i,&tpos,&row,&j);CHKERRQ(ierr);
848       tdata[--j] = --row;
849       if (j > tcount - 1) SETERRQ2(PETSC_COMM_SELF,0," j %d >= tcount %d",j,tcount);
850     }
851 #else
852     data_i  = data[i];
853 #endif
854     table_i = table[i];
855     isz_i   = isz[i];
856     max     = isz[i];
857 
858     for (j=0; j<max; j++) {
859 #if defined(PETSC_USE_CTABLE)
860       row   = tdata[j] - rstart;
861 #else
862       row   = data_i[j] - rstart;
863 #endif
864       start = ai[row];
865       end   = ai[row+1];
866       for (k=start; k<end; k++) { /* Amat */
867         val = aj[k] + cstart;
868         if (!PetscBTLookupSet(table_i,val)) {
869 #if defined(PETSC_USE_CTABLE)
870           ierr = PetscTableAdd(table_data_i,val+1,isz_i+1,INSERT_VALUES);CHKERRQ(ierr);
871 #else
872           data_i[isz_i] = val;
873 #endif
874           isz_i++;
875         }
876       }
877       start = bi[row];
878       end   = bi[row+1];
879       for (k=start; k<end; k++) { /* Bmat */
880         val = garray[bj[k]];
881         if (!PetscBTLookupSet(table_i,val)) {
882 #if defined(PETSC_USE_CTABLE)
883           ierr = PetscTableAdd(table_data_i,val+1,isz_i+1,INSERT_VALUES);CHKERRQ(ierr);
884 #else
885           data_i[isz_i] = val;
886 #endif
887           isz_i++;
888         }
889       }
890     }
891     isz[i] = isz_i;
892 
893 #if defined(PETSC_USE_CTABLE)
894     ierr = PetscFree(tdata);CHKERRQ(ierr);
895 #endif
896   }
897   PetscFunctionReturn(0);
898 }
899 
900 /*
901       MatIncreaseOverlap_MPIAIJ_Receive - Process the recieved messages,
902          and return the output
903 
904          Input:
905            C    - the matrix
906            nrqr - no of messages being processed.
907            rbuf - an array of pointers to the recieved requests
908 
909          Output:
910            xdata - array of messages to be sent back
911            isz1  - size of each message
912 
913   For better efficiency perhaps we should malloc separately each xdata[i],
914 then if a remalloc is required we need only copy the data for that one row
915 rather then all previous rows as it is now where a single large chunck of
916 memory is used.
917 
918 */
919 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Receive(Mat C,PetscInt nrqr,PetscInt **rbuf,PetscInt **xdata,PetscInt * isz1)
920 {
921   Mat_MPIAIJ     *c = (Mat_MPIAIJ*)C->data;
922   Mat            A  = c->A,B = c->B;
923   Mat_SeqAIJ     *a = (Mat_SeqAIJ*)A->data,*b = (Mat_SeqAIJ*)B->data;
924   PetscErrorCode ierr;
925   PetscInt       rstart,cstart,*ai,*aj,*bi,*bj,*garray,i,j,k;
926   PetscInt       row,total_sz,ct,ct1,ct2,ct3,mem_estimate,oct2,l,start,end;
927   PetscInt       val,max1,max2,m,no_malloc =0,*tmp,new_estimate,ctr;
928   PetscInt       *rbuf_i,kmax,rbuf_0;
929   PetscBT        xtable;
930 
931   PetscFunctionBegin;
932   m      = C->rmap->N;
933   rstart = C->rmap->rstart;
934   cstart = C->cmap->rstart;
935   ai     = a->i;
936   aj     = a->j;
937   bi     = b->i;
938   bj     = b->j;
939   garray = c->garray;
940 
941 
942   for (i=0,ct=0,total_sz=0; i<nrqr; ++i) {
943     rbuf_i =  rbuf[i];
944     rbuf_0 =  rbuf_i[0];
945     ct    += rbuf_0;
946     for (j=1; j<=rbuf_0; j++) total_sz += rbuf_i[2*j];
947   }
948 
949   if (C->rmap->n) max1 = ct*(a->nz + b->nz)/C->rmap->n;
950   else max1 = 1;
951   mem_estimate = 3*((total_sz > max1 ? total_sz : max1)+1);
952   ierr         = PetscMalloc1(mem_estimate,&xdata[0]);CHKERRQ(ierr);
953   ++no_malloc;
954   ierr = PetscBTCreate(m,&xtable);CHKERRQ(ierr);
955   ierr = PetscMemzero(isz1,nrqr*sizeof(PetscInt));CHKERRQ(ierr);
956 
957   ct3 = 0;
958   for (i=0; i<nrqr; i++) { /* for easch mesg from proc i */
959     rbuf_i =  rbuf[i];
960     rbuf_0 =  rbuf_i[0];
961     ct1    =  2*rbuf_0+1;
962     ct2    =  ct1;
963     ct3   += ct1;
964     for (j=1; j<=rbuf_0; j++) { /* for each IS from proc i*/
965       ierr = PetscBTMemzero(m,xtable);CHKERRQ(ierr);
966       oct2 = ct2;
967       kmax = rbuf_i[2*j];
968       for (k=0; k<kmax; k++,ct1++) {
969         row = rbuf_i[ct1];
970         if (!PetscBTLookupSet(xtable,row)) {
971           if (!(ct3 < mem_estimate)) {
972             new_estimate = (PetscInt)(1.5*mem_estimate)+1;
973             ierr         = PetscMalloc1(new_estimate,&tmp);CHKERRQ(ierr);
974             ierr         = PetscMemcpy(tmp,xdata[0],mem_estimate*sizeof(PetscInt));CHKERRQ(ierr);
975             ierr         = PetscFree(xdata[0]);CHKERRQ(ierr);
976             xdata[0]     = tmp;
977             mem_estimate = new_estimate; ++no_malloc;
978             for (ctr=1; ctr<=i; ctr++) xdata[ctr] = xdata[ctr-1] + isz1[ctr-1];
979           }
980           xdata[i][ct2++] = row;
981           ct3++;
982         }
983       }
984       for (k=oct2,max2=ct2; k<max2; k++) {
985         row   = xdata[i][k] - rstart;
986         start = ai[row];
987         end   = ai[row+1];
988         for (l=start; l<end; l++) {
989           val = aj[l] + cstart;
990           if (!PetscBTLookupSet(xtable,val)) {
991             if (!(ct3 < mem_estimate)) {
992               new_estimate = (PetscInt)(1.5*mem_estimate)+1;
993               ierr         = PetscMalloc1(new_estimate,&tmp);CHKERRQ(ierr);
994               ierr         = PetscMemcpy(tmp,xdata[0],mem_estimate*sizeof(PetscInt));CHKERRQ(ierr);
995               ierr         = PetscFree(xdata[0]);CHKERRQ(ierr);
996               xdata[0]     = tmp;
997               mem_estimate = new_estimate; ++no_malloc;
998               for (ctr=1; ctr<=i; ctr++) xdata[ctr] = xdata[ctr-1] + isz1[ctr-1];
999             }
1000             xdata[i][ct2++] = val;
1001             ct3++;
1002           }
1003         }
1004         start = bi[row];
1005         end   = bi[row+1];
1006         for (l=start; l<end; l++) {
1007           val = garray[bj[l]];
1008           if (!PetscBTLookupSet(xtable,val)) {
1009             if (!(ct3 < mem_estimate)) {
1010               new_estimate = (PetscInt)(1.5*mem_estimate)+1;
1011               ierr         = PetscMalloc1(new_estimate,&tmp);CHKERRQ(ierr);
1012               ierr         = PetscMemcpy(tmp,xdata[0],mem_estimate*sizeof(PetscInt));CHKERRQ(ierr);
1013               ierr         = PetscFree(xdata[0]);CHKERRQ(ierr);
1014               xdata[0]     = tmp;
1015               mem_estimate = new_estimate; ++no_malloc;
1016               for (ctr =1; ctr <=i; ctr++) xdata[ctr] = xdata[ctr-1] + isz1[ctr-1];
1017             }
1018             xdata[i][ct2++] = val;
1019             ct3++;
1020           }
1021         }
1022       }
1023       /* Update the header*/
1024       xdata[i][2*j]   = ct2 - oct2; /* Undo the vector isz1 and use only a var*/
1025       xdata[i][2*j-1] = rbuf_i[2*j-1];
1026     }
1027     xdata[i][0] = rbuf_0;
1028     xdata[i+1]  = xdata[i] + ct2;
1029     isz1[i]     = ct2; /* size of each message */
1030   }
1031   ierr = PetscBTDestroy(&xtable);CHKERRQ(ierr);
1032   ierr = PetscInfo3(C,"Allocated %D bytes, required %D bytes, no of mallocs = %D\n",mem_estimate,ct3,no_malloc);CHKERRQ(ierr);
1033   PetscFunctionReturn(0);
1034 }
1035 /* -------------------------------------------------------------------------*/
1036 extern PetscErrorCode MatGetSubMatrices_MPIAIJ_Local(Mat,PetscInt,const IS[],const IS[],MatReuse,Mat*);
1037 extern PetscErrorCode MatAssemblyEnd_SeqAIJ(Mat,MatAssemblyType);
1038 /*
1039     Every processor gets the entire matrix
1040 */
1041 PetscErrorCode MatGetSubMatrix_MPIAIJ_All(Mat A,MatGetSubMatrixOption flag,MatReuse scall,Mat *Bin[])
1042 {
1043   Mat            B;
1044   Mat_MPIAIJ     *a = (Mat_MPIAIJ*)A->data;
1045   Mat_SeqAIJ     *b,*ad = (Mat_SeqAIJ*)a->A->data,*bd = (Mat_SeqAIJ*)a->B->data;
1046   PetscErrorCode ierr;
1047   PetscMPIInt    size,rank,*recvcounts = 0,*displs = 0;
1048   PetscInt       sendcount,i,*rstarts = A->rmap->range,n,cnt,j;
1049   PetscInt       m,*b_sendj,*garray = a->garray,*lens,*jsendbuf,*a_jsendbuf,*b_jsendbuf;
1050   MatScalar      *sendbuf,*recvbuf,*a_sendbuf,*b_sendbuf;
1051 
1052   PetscFunctionBegin;
1053   ierr = MPI_Comm_size(PetscObjectComm((PetscObject)A),&size);CHKERRQ(ierr);
1054   ierr = MPI_Comm_rank(PetscObjectComm((PetscObject)A),&rank);CHKERRQ(ierr);
1055 
1056   if (scall == MAT_INITIAL_MATRIX) {
1057     /* ----------------------------------------------------------------
1058          Tell every processor the number of nonzeros per row
1059     */
1060     ierr = PetscMalloc1(A->rmap->N,&lens);CHKERRQ(ierr);
1061     for (i=A->rmap->rstart; i<A->rmap->rend; i++) {
1062       lens[i] = ad->i[i-A->rmap->rstart+1] - ad->i[i-A->rmap->rstart] + bd->i[i-A->rmap->rstart+1] - bd->i[i-A->rmap->rstart];
1063     }
1064     ierr      = PetscMalloc2(size,&recvcounts,size,&displs);CHKERRQ(ierr);
1065     for (i=0; i<size; i++) {
1066       recvcounts[i] = A->rmap->range[i+1] - A->rmap->range[i];
1067       displs[i]     = A->rmap->range[i];
1068     }
1069 #if defined(PETSC_HAVE_MPI_IN_PLACE)
1070     ierr = MPI_Allgatherv(MPI_IN_PLACE,0,MPI_DATATYPE_NULL,lens,recvcounts,displs,MPIU_INT,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1071 #else
1072     sendcount = A->rmap->rend - A->rmap->rstart;
1073     ierr = MPI_Allgatherv(lens+A->rmap->rstart,sendcount,MPIU_INT,lens,recvcounts,displs,MPIU_INT,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1074 #endif
1075     /* ---------------------------------------------------------------
1076          Create the sequential matrix of the same type as the local block diagonal
1077     */
1078     ierr  = MatCreate(PETSC_COMM_SELF,&B);CHKERRQ(ierr);
1079     ierr  = MatSetSizes(B,A->rmap->N,A->cmap->N,PETSC_DETERMINE,PETSC_DETERMINE);CHKERRQ(ierr);
1080     ierr  = MatSetBlockSizesFromMats(B,A,A);CHKERRQ(ierr);
1081     ierr  = MatSetType(B,((PetscObject)a->A)->type_name);CHKERRQ(ierr);
1082     ierr  = MatSeqAIJSetPreallocation(B,0,lens);CHKERRQ(ierr);
1083     ierr  = PetscMalloc1(1,Bin);CHKERRQ(ierr);
1084     **Bin = B;
1085     b     = (Mat_SeqAIJ*)B->data;
1086 
1087     /*--------------------------------------------------------------------
1088        Copy my part of matrix column indices over
1089     */
1090     sendcount  = ad->nz + bd->nz;
1091     jsendbuf   = b->j + b->i[rstarts[rank]];
1092     a_jsendbuf = ad->j;
1093     b_jsendbuf = bd->j;
1094     n          = A->rmap->rend - A->rmap->rstart;
1095     cnt        = 0;
1096     for (i=0; i<n; i++) {
1097 
1098       /* put in lower diagonal portion */
1099       m = bd->i[i+1] - bd->i[i];
1100       while (m > 0) {
1101         /* is it above diagonal (in bd (compressed) numbering) */
1102         if (garray[*b_jsendbuf] > A->rmap->rstart + i) break;
1103         jsendbuf[cnt++] = garray[*b_jsendbuf++];
1104         m--;
1105       }
1106 
1107       /* put in diagonal portion */
1108       for (j=ad->i[i]; j<ad->i[i+1]; j++) {
1109         jsendbuf[cnt++] = A->rmap->rstart + *a_jsendbuf++;
1110       }
1111 
1112       /* put in upper diagonal portion */
1113       while (m-- > 0) {
1114         jsendbuf[cnt++] = garray[*b_jsendbuf++];
1115       }
1116     }
1117     if (cnt != sendcount) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Corrupted PETSc matrix: nz given %D actual nz %D",sendcount,cnt);
1118 
1119     /*--------------------------------------------------------------------
1120        Gather all column indices to all processors
1121     */
1122     for (i=0; i<size; i++) {
1123       recvcounts[i] = 0;
1124       for (j=A->rmap->range[i]; j<A->rmap->range[i+1]; j++) {
1125         recvcounts[i] += lens[j];
1126       }
1127     }
1128     displs[0] = 0;
1129     for (i=1; i<size; i++) {
1130       displs[i] = displs[i-1] + recvcounts[i-1];
1131     }
1132 #if defined(PETSC_HAVE_MPI_IN_PLACE)
1133     ierr = MPI_Allgatherv(MPI_IN_PLACE,0,MPI_DATATYPE_NULL,b->j,recvcounts,displs,MPIU_INT,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1134 #else
1135     ierr = MPI_Allgatherv(jsendbuf,sendcount,MPIU_INT,b->j,recvcounts,displs,MPIU_INT,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1136 #endif
1137     /*--------------------------------------------------------------------
1138         Assemble the matrix into useable form (note numerical values not yet set)
1139     */
1140     /* set the b->ilen (length of each row) values */
1141     ierr = PetscMemcpy(b->ilen,lens,A->rmap->N*sizeof(PetscInt));CHKERRQ(ierr);
1142     /* set the b->i indices */
1143     b->i[0] = 0;
1144     for (i=1; i<=A->rmap->N; i++) {
1145       b->i[i] = b->i[i-1] + lens[i-1];
1146     }
1147     ierr = PetscFree(lens);CHKERRQ(ierr);
1148     ierr = MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
1149     ierr = MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
1150 
1151   } else {
1152     B = **Bin;
1153     b = (Mat_SeqAIJ*)B->data;
1154   }
1155 
1156   /*--------------------------------------------------------------------
1157        Copy my part of matrix numerical values into the values location
1158   */
1159   if (flag == MAT_GET_VALUES) {
1160     sendcount = ad->nz + bd->nz;
1161     sendbuf   = b->a + b->i[rstarts[rank]];
1162     a_sendbuf = ad->a;
1163     b_sendbuf = bd->a;
1164     b_sendj   = bd->j;
1165     n         = A->rmap->rend - A->rmap->rstart;
1166     cnt       = 0;
1167     for (i=0; i<n; i++) {
1168 
1169       /* put in lower diagonal portion */
1170       m = bd->i[i+1] - bd->i[i];
1171       while (m > 0) {
1172         /* is it above diagonal (in bd (compressed) numbering) */
1173         if (garray[*b_sendj] > A->rmap->rstart + i) break;
1174         sendbuf[cnt++] = *b_sendbuf++;
1175         m--;
1176         b_sendj++;
1177       }
1178 
1179       /* put in diagonal portion */
1180       for (j=ad->i[i]; j<ad->i[i+1]; j++) {
1181         sendbuf[cnt++] = *a_sendbuf++;
1182       }
1183 
1184       /* put in upper diagonal portion */
1185       while (m-- > 0) {
1186         sendbuf[cnt++] = *b_sendbuf++;
1187         b_sendj++;
1188       }
1189     }
1190     if (cnt != sendcount) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Corrupted PETSc matrix: nz given %D actual nz %D",sendcount,cnt);
1191 
1192     /* -----------------------------------------------------------------
1193        Gather all numerical values to all processors
1194     */
1195     if (!recvcounts) {
1196       ierr = PetscMalloc2(size,&recvcounts,size,&displs);CHKERRQ(ierr);
1197     }
1198     for (i=0; i<size; i++) {
1199       recvcounts[i] = b->i[rstarts[i+1]] - b->i[rstarts[i]];
1200     }
1201     displs[0] = 0;
1202     for (i=1; i<size; i++) {
1203       displs[i] = displs[i-1] + recvcounts[i-1];
1204     }
1205     recvbuf = b->a;
1206 #if defined(PETSC_HAVE_MPI_IN_PLACE)
1207     ierr = MPI_Allgatherv(MPI_IN_PLACE,0,MPI_DATATYPE_NULL,recvbuf,recvcounts,displs,MPIU_SCALAR,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1208 #else
1209     ierr = MPI_Allgatherv(sendbuf,sendcount,MPIU_SCALAR,recvbuf,recvcounts,displs,MPIU_SCALAR,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1210 #endif
1211   }  /* endof (flag == MAT_GET_VALUES) */
1212   ierr = PetscFree2(recvcounts,displs);CHKERRQ(ierr);
1213 
1214   if (A->symmetric) {
1215     ierr = MatSetOption(B,MAT_SYMMETRIC,PETSC_TRUE);CHKERRQ(ierr);
1216   } else if (A->hermitian) {
1217     ierr = MatSetOption(B,MAT_HERMITIAN,PETSC_TRUE);CHKERRQ(ierr);
1218   } else if (A->structurally_symmetric) {
1219     ierr = MatSetOption(B,MAT_STRUCTURALLY_SYMMETRIC,PETSC_TRUE);CHKERRQ(ierr);
1220   }
1221   PetscFunctionReturn(0);
1222 }
1223 
1224 PetscErrorCode MatDestroy_MPIAIJ_MatGetSubmatrices(Mat C)
1225 {
1226   PetscErrorCode ierr;
1227   Mat_SeqAIJ     *c = (Mat_SeqAIJ*)C->data;
1228   Mat_SubMat     *submatj = c->submatis1;
1229   PetscInt       i;
1230 
1231   PetscFunctionBegin;
1232   if (!submatj->id) { /* delete data that are linked only to submats[id=0] */
1233     ierr = PetscFree4(submatj->sbuf1,submatj->ptr,submatj->tmp,submatj->ctr);CHKERRQ(ierr);
1234 
1235     for (i=0; i<submatj->nrqr; ++i) {
1236       ierr = PetscFree(submatj->sbuf2[i]);CHKERRQ(ierr);
1237     }
1238     ierr = PetscFree3(submatj->sbuf2,submatj->req_size,submatj->req_source1);CHKERRQ(ierr);
1239 
1240     if (submatj->rbuf1) {
1241       ierr = PetscFree(submatj->rbuf1[0]);CHKERRQ(ierr);
1242       ierr = PetscFree(submatj->rbuf1);CHKERRQ(ierr);
1243     }
1244 
1245     for (i=0; i<submatj->nrqs; ++i) {
1246       ierr = PetscFree(submatj->rbuf3[i]);CHKERRQ(ierr);
1247     }
1248     ierr = PetscFree3(submatj->req_source2,submatj->rbuf2,submatj->rbuf3);CHKERRQ(ierr);
1249     ierr = PetscFree(submatj->pa);CHKERRQ(ierr);
1250   }
1251 
1252 #if defined(PETSC_USE_CTABLE)
1253   ierr = PetscTableDestroy((PetscTable*)&submatj->rmap);CHKERRQ(ierr);
1254   if (submatj->cmap_loc) {ierr = PetscFree(submatj->cmap_loc);CHKERRQ(ierr);}
1255   ierr = PetscFree(submatj->rmap_loc);CHKERRQ(ierr);
1256 #else
1257   ierr = PetscFree(submatj->rmap);CHKERRQ(ierr);
1258 #endif
1259 
1260   if (!submatj->allcolumns) {
1261 #if defined(PETSC_USE_CTABLE)
1262     ierr = PetscTableDestroy((PetscTable*)&submatj->cmap);CHKERRQ(ierr);
1263 #else
1264     ierr = PetscFree(submatj->cmap);CHKERRQ(ierr);
1265 #endif
1266   }
1267   ierr = submatj->destroy(C);CHKERRQ(ierr);
1268   ierr = PetscFree(submatj->row2proc);CHKERRQ(ierr);
1269 
1270   ierr = PetscFree(submatj);CHKERRQ(ierr);
1271   PetscFunctionReturn(0);
1272 }
1273 
1274 PetscErrorCode MatGetSubMatrices_MPIAIJ_SingleIS_Local(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,PetscBool allcolumns,Mat *submats)
1275 {
1276   Mat_MPIAIJ     *c = (Mat_MPIAIJ*)C->data;
1277   Mat            submat,A = c->A,B = c->B;
1278   Mat_SeqAIJ     *a = (Mat_SeqAIJ*)A->data,*b = (Mat_SeqAIJ*)B->data,*subc;
1279   PetscInt       *ai=a->i,*aj=a->j,*bi=b->i,*bj=b->j,nzA,nzB;
1280   PetscInt       cstart = C->cmap->rstart,cend = C->cmap->rend,rstart = C->rmap->rstart,*bmap = c->garray;
1281   const PetscInt *icol,*irow;
1282   PetscInt       nrow,ncol,start;
1283   PetscErrorCode ierr;
1284   PetscMPIInt    rank,size,tag1,tag2,tag3,tag4,*w1,*w2,nrqr;
1285   PetscInt       **sbuf1,**sbuf2,i,j,k,l,ct1,ct2,ct3,**rbuf1,row,proc;
1286   PetscInt       nrqs=0,msz,**ptr,*req_size,*ctr,*pa,*tmp,tcol,*iptr;
1287   PetscInt       **rbuf3,*req_source1,*req_source2,**sbuf_aj,**rbuf2,max1,nnz;
1288   PetscInt       *lens,rmax,ncols,*cols,Crow;
1289 #if defined(PETSC_USE_CTABLE)
1290   PetscTable     cmap,rmap;
1291   PetscInt       *cmap_loc,*rmap_loc;
1292 #else
1293   PetscInt       *cmap,*rmap;
1294 #endif
1295   PetscInt       ctr_j,*sbuf1_j,*sbuf_aj_i,*rbuf1_i,kmax,*sbuf1_i,*rbuf2_i,*rbuf3_i;
1296   PetscInt       *cworkB,lwrite,*subcols,*row2proc;
1297   PetscScalar    *vworkA,*vworkB,*a_a = a->a,*b_a = b->a,*subvals=NULL;
1298   MPI_Request    *s_waits1,*r_waits1,*s_waits2,*r_waits2,*r_waits3;
1299   MPI_Request    *r_waits4,*s_waits3 = NULL,*s_waits4;
1300   MPI_Status     *r_status1,*r_status2,*s_status1,*s_status3 = NULL,*s_status2;
1301   MPI_Status     *r_status3 = NULL,*r_status4,*s_status4;
1302   MPI_Comm       comm;
1303   PetscScalar    **rbuf4,**sbuf_aa,*vals,*sbuf_aa_i,*rbuf4_i;
1304   PetscMPIInt    *onodes1,*olengths1,idex,end;
1305   Mat_SubMat     *smatis1;
1306   PetscBool      isrowsorted;
1307 
1308   PetscFunctionBegin;
1309   if (ismax != 1) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"This routine only works when all processes have ismax=1");
1310 
1311   ierr = PetscObjectGetComm((PetscObject)C,&comm);CHKERRQ(ierr);
1312   size = c->size;
1313   rank = c->rank;
1314 
1315   ierr = ISSorted(isrow[0],&isrowsorted);CHKERRQ(ierr);
1316   if (!isrowsorted) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"isrow[0] must be sorted");
1317 
1318   ierr = ISGetIndices(isrow[0],&irow);CHKERRQ(ierr);
1319   ierr = ISGetLocalSize(isrow[0],&nrow);CHKERRQ(ierr);
1320   if (allcolumns) {
1321     icol = NULL;
1322     ncol = C->cmap->N;
1323   } else {
1324     ierr = ISGetIndices(iscol[0],&icol);CHKERRQ(ierr);
1325     ierr = ISGetLocalSize(iscol[0],&ncol);CHKERRQ(ierr);
1326   }
1327 
1328   if (scall == MAT_INITIAL_MATRIX) {
1329     PetscInt *sbuf2_i,*cworkA,lwrite,ctmp;
1330 
1331     /* Get some new tags to keep the communication clean */
1332     tag1 = ((PetscObject)C)->tag;
1333     ierr = PetscObjectGetNewTag((PetscObject)C,&tag2);CHKERRQ(ierr);
1334     ierr = PetscObjectGetNewTag((PetscObject)C,&tag3);CHKERRQ(ierr);
1335 
1336     /* evaluate communication - mesg to who, length of mesg, and buffer space
1337      required. Based on this, buffers are allocated, and data copied into them */
1338     ierr = PetscCalloc2(size,&w1,size,&w2);CHKERRQ(ierr);
1339     ierr = PetscMalloc1(nrow,&row2proc);CHKERRQ(ierr);
1340 
1341     /* w1[proc] = num of rows owned by proc -- to be requested */
1342     proc = 0;
1343     nrqs = 0; /* num of outgoing messages */
1344     for (j=0; j<nrow; j++) {
1345       row  = irow[j]; /* sorted! */
1346       while (row >= C->rmap->range[proc+1]) proc++;
1347       w1[proc]++;
1348       row2proc[j] = proc; /* map row index to proc */
1349 
1350       if (proc != rank && !w2[proc]) {
1351         w2[proc] = 1; nrqs++;
1352       }
1353     }
1354     w1[rank] = 0;  /* rows owned by self will not be requested */
1355 
1356     ierr = PetscMalloc1(nrqs+1,&pa);CHKERRQ(ierr); /*(proc -array)*/
1357     for (proc=0,j=0; proc<size; proc++) {
1358       if (w1[proc]) { pa[j++] = proc;}
1359     }
1360 
1361     /* Each message would have a header = 1 + 2*(num of IS) + data (here,num of IS = 1) */
1362     msz = 0;              /* total mesg length (for all procs) */
1363     for (i=0; i<nrqs; i++) {
1364       proc      = pa[i];
1365       w1[proc] += 3;
1366       msz      += w1[proc];
1367     }
1368     ierr = PetscInfo2(0,"Number of outgoing messages %D Total message length %D\n",nrqs,msz);CHKERRQ(ierr);
1369 
1370     /* Determine nrqr, the number of messages to expect, their lengths, from from-ids */
1371     /* if w2[proc]=1, a message of length w1[proc] will be sent to proc; */
1372     ierr = PetscGatherNumberOfMessages(comm,w2,w1,&nrqr);CHKERRQ(ierr);
1373 
1374     /* Input: nrqs: nsend; nrqr: nrecv; w1: msg length to be sent;
1375        Output: onodes1: recv node-ids; olengths1: corresponding recv message length */
1376     ierr = PetscGatherMessageLengths(comm,nrqs,nrqr,w1,&onodes1,&olengths1);CHKERRQ(ierr);
1377 
1378     /* Now post the Irecvs corresponding to these messages */
1379     ierr = PetscPostIrecvInt(comm,tag1,nrqr,onodes1,olengths1,&rbuf1,&r_waits1);CHKERRQ(ierr);
1380 
1381     ierr = PetscFree(onodes1);CHKERRQ(ierr);
1382     ierr = PetscFree(olengths1);CHKERRQ(ierr);
1383 
1384     /* Allocate Memory for outgoing messages */
1385     ierr = PetscMalloc4(size,&sbuf1,size,&ptr,2*msz,&tmp,size,&ctr);CHKERRQ(ierr);
1386     ierr = PetscMemzero(sbuf1,size*sizeof(PetscInt*));CHKERRQ(ierr);
1387     ierr = PetscMemzero(ptr,size*sizeof(PetscInt*));CHKERRQ(ierr);
1388 
1389     /* subf1[pa[0]] = tmp, subf1[pa[i]] = subf1[pa[i-1]] + w1[pa[i-1]] */
1390     iptr = tmp;
1391     for (i=0; i<nrqs; i++) {
1392       proc        = pa[i];
1393       sbuf1[proc] = iptr;
1394       iptr       += w1[proc];
1395     }
1396 
1397     /* Form the outgoing messages */
1398     /* Initialize the header space */
1399     for (i=0; i<nrqs; i++) {
1400       proc      = pa[i];
1401       ierr      = PetscMemzero(sbuf1[proc],3*sizeof(PetscInt));CHKERRQ(ierr);
1402       ptr[proc] = sbuf1[proc] + 3;
1403     }
1404 
1405     /* Parse the isrow and copy data into outbuf */
1406     ierr = PetscMemzero(ctr,size*sizeof(PetscInt));CHKERRQ(ierr);
1407     for (j=0; j<nrow; j++) {  /* parse the indices of each IS */
1408       proc = row2proc[j];
1409       if (proc != rank) { /* copy to the outgoing buf*/
1410         *ptr[proc] = irow[j];
1411         ctr[proc]++; ptr[proc]++;
1412       }
1413     }
1414 
1415     /* Update the headers for the current IS */
1416     for (j=0; j<size; j++) { /* Can Optimise this loop too */
1417       if ((ctr_j = ctr[j])) {
1418         sbuf1_j        = sbuf1[j];
1419         k              = ++sbuf1_j[0];
1420         sbuf1_j[2*k]   = ctr_j;
1421         sbuf1_j[2*k-1] = 0;
1422       }
1423     }
1424 
1425     /* Now post the sends */
1426     ierr = PetscMalloc1(nrqs+1,&s_waits1);CHKERRQ(ierr);
1427     for (i=0; i<nrqs; ++i) {
1428       proc = pa[i];
1429       ierr = MPI_Isend(sbuf1[proc],w1[proc],MPIU_INT,proc,tag1,comm,s_waits1+i);CHKERRQ(ierr);
1430     }
1431 
1432     /* Post Receives to capture the buffer size */
1433     ierr = PetscMalloc4(nrqs+1,&r_status2,nrqr+1,&s_waits2,nrqs+1,&r_waits2,nrqr+1,&s_status2);CHKERRQ(ierr);
1434     ierr = PetscMalloc3(nrqs+1,&req_source2,nrqs+1,&rbuf2,nrqs+1,&rbuf3);CHKERRQ(ierr);
1435 
1436     rbuf2[0] = tmp + msz;
1437     for (i=1; i<nrqs; ++i) rbuf2[i] = rbuf2[i-1] + w1[pa[i-1]];
1438 
1439     for (i=0; i<nrqs; ++i) {
1440       proc = pa[i];
1441       ierr = MPI_Irecv(rbuf2[i],w1[proc],MPIU_INT,proc,tag2,comm,r_waits2+i);CHKERRQ(ierr);
1442     }
1443 
1444     ierr = PetscFree2(w1,w2);CHKERRQ(ierr);
1445 
1446     /* Send to other procs the buf size they should allocate */
1447     /* Receive messages*/
1448     ierr = PetscMalloc1(nrqr+1,&r_status1);CHKERRQ(ierr);
1449     ierr = PetscMalloc3(nrqr,&sbuf2,nrqr,&req_size,nrqr,&req_source1);CHKERRQ(ierr);
1450 
1451     ierr = MPI_Waitall(nrqr,r_waits1,r_status1);CHKERRQ(ierr);
1452     for (i=0; i<nrqr; ++i) {
1453       req_size[i] = 0;
1454       rbuf1_i        = rbuf1[i];
1455       start          = 2*rbuf1_i[0] + 1;
1456       ierr           = MPI_Get_count(r_status1+i,MPIU_INT,&end);CHKERRQ(ierr);
1457       ierr           = PetscMalloc1(end+1,&sbuf2[i]);CHKERRQ(ierr);
1458       sbuf2_i        = sbuf2[i];
1459       for (j=start; j<end; j++) {
1460         k            = rbuf1_i[j] - rstart;
1461         ncols        = ai[k+1] - ai[k] + bi[k+1] - bi[k];
1462         sbuf2_i[j]   = ncols;
1463         req_size[i] += ncols;
1464       }
1465       req_source1[i] = r_status1[i].MPI_SOURCE;
1466 
1467       /* form the header */
1468       sbuf2_i[0] = req_size[i];
1469       for (j=1; j<start; j++) sbuf2_i[j] = rbuf1_i[j];
1470 
1471       ierr = MPI_Isend(sbuf2_i,end,MPIU_INT,req_source1[i],tag2,comm,s_waits2+i);CHKERRQ(ierr);
1472     }
1473 
1474     ierr = PetscFree(r_status1);CHKERRQ(ierr);
1475     ierr = PetscFree(r_waits1);CHKERRQ(ierr);
1476 
1477     /* rbuf2 is received, Post recv column indices a->j */
1478     ierr = MPI_Waitall(nrqs,r_waits2,r_status2);CHKERRQ(ierr);
1479 
1480     ierr = PetscMalloc4(nrqs+1,&r_waits3,nrqr+1,&s_waits3,nrqs+1,&r_status3,nrqr+1,&s_status3);CHKERRQ(ierr);
1481     for (i=0; i<nrqs; ++i) {
1482       ierr = PetscMalloc1(rbuf2[i][0]+1,&rbuf3[i]);CHKERRQ(ierr);
1483       req_source2[i] = r_status2[i].MPI_SOURCE;
1484       ierr = MPI_Irecv(rbuf3[i],rbuf2[i][0],MPIU_INT,req_source2[i],tag3,comm,r_waits3+i);CHKERRQ(ierr);
1485     }
1486 
1487     /* Wait on sends1 and sends2 */
1488     ierr = PetscMalloc1(nrqs+1,&s_status1);CHKERRQ(ierr);
1489     ierr = MPI_Waitall(nrqs,s_waits1,s_status1);CHKERRQ(ierr);
1490     ierr = PetscFree(s_waits1);CHKERRQ(ierr);
1491     ierr = PetscFree(s_status1);CHKERRQ(ierr);
1492 
1493     ierr = MPI_Waitall(nrqr,s_waits2,s_status2);CHKERRQ(ierr);
1494     ierr = PetscFree4(r_status2,s_waits2,r_waits2,s_status2);CHKERRQ(ierr);
1495 
1496     /* Now allocate sending buffers for a->j, and send them off */
1497     ierr = PetscMalloc1(nrqr+1,&sbuf_aj);CHKERRQ(ierr);
1498     for (i=0,j=0; i<nrqr; i++) j += req_size[i];
1499     ierr = PetscMalloc1(j+1,&sbuf_aj[0]);CHKERRQ(ierr);
1500     for (i=1; i<nrqr; i++) sbuf_aj[i] = sbuf_aj[i-1] + req_size[i-1];
1501 
1502     for (i=0; i<nrqr; i++) { /* for each requested message */
1503       rbuf1_i   = rbuf1[i];
1504       sbuf_aj_i = sbuf_aj[i];
1505       ct1       = 2*rbuf1_i[0] + 1;
1506       ct2       = 0;
1507       /* max1=rbuf1_i[0]; if (max1 != 1) SETERRQ1(PETSC_COMM_SELF,0,"max1 %d != 1",max1); */
1508 
1509       kmax = rbuf1[i][2];
1510       for (k=0; k<kmax; k++,ct1++) { /* for each row */
1511         row    = rbuf1_i[ct1] - rstart;
1512         nzA    = ai[row+1] - ai[row];
1513         nzB    = bi[row+1] - bi[row];
1514         ncols  = nzA + nzB;
1515         cworkA = aj + ai[row]; cworkB = bj + bi[row];
1516 
1517         /* load the column indices for this row into cols*/
1518         cols = sbuf_aj_i + ct2;
1519 
1520         lwrite = 0;
1521         for (l=0; l<nzB; l++) {
1522           if ((ctmp = bmap[cworkB[l]]) < cstart) cols[lwrite++] = ctmp;
1523         }
1524         for (l=0; l<nzA; l++) cols[lwrite++] = cstart + cworkA[l];
1525         for (l=0; l<nzB; l++) {
1526           if ((ctmp = bmap[cworkB[l]]) >= cend) cols[lwrite++] = ctmp;
1527         }
1528 
1529         ct2 += ncols;
1530       }
1531       ierr = MPI_Isend(sbuf_aj_i,req_size[i],MPIU_INT,req_source1[i],tag3,comm,s_waits3+i);CHKERRQ(ierr);
1532     }
1533 
1534     /* create column map (cmap): global col of C -> local col of submat */
1535 #if defined(PETSC_USE_CTABLE)
1536     if (!allcolumns) {
1537       ierr = PetscTableCreate(ncol+1,C->cmap->N+1,&cmap);CHKERRQ(ierr);
1538       ierr = PetscCalloc1(C->cmap->n,&cmap_loc);CHKERRQ(ierr);
1539       for (j=0; j<ncol; j++) { /* use array cmap_loc[] for local col indices */
1540         if (icol[j] >= cstart && icol[j] <cend) {
1541           cmap_loc[icol[j] - cstart] = j+1;
1542         } else { /* use PetscTable for non-local col indices */
1543           ierr = PetscTableAdd(cmap,icol[j]+1,j+1,INSERT_VALUES);CHKERRQ(ierr);
1544         }
1545       }
1546     } else {
1547       cmap     = NULL;
1548       cmap_loc = NULL;
1549     }
1550     ierr = PetscCalloc1(C->rmap->n,&rmap_loc);CHKERRQ(ierr);
1551 #else
1552     if (!allcolumns) {
1553       ierr   = PetscCalloc1(C->cmap->N,&cmap);CHKERRQ(ierr);
1554       for (j=0; j<ncol; j++) cmap[icol[j]] = j+1;
1555     } else {
1556       cmap = NULL;
1557     }
1558 #endif
1559 
1560     /* Create lens for MatSeqAIJSetPreallocation() */
1561     ierr = PetscCalloc1(nrow,&lens);CHKERRQ(ierr);
1562 
1563     /* Compute lens from local part of C */
1564     for (j=0; j<nrow; j++) {
1565       row  = irow[j];
1566       proc = row2proc[j];
1567       if (proc == rank) {
1568         /* diagonal part A = c->A */
1569         ncols = ai[row-rstart+1] - ai[row-rstart];
1570         cols  = aj + ai[row-rstart];
1571         if (!allcolumns) {
1572           for (k=0; k<ncols; k++) {
1573 #if defined(PETSC_USE_CTABLE)
1574             tcol = cmap_loc[cols[k]];
1575 #else
1576             tcol = cmap[cols[k]+cstart];
1577 #endif
1578             if (tcol) lens[j]++;
1579           }
1580         } else { /* allcolumns */
1581           lens[j] = ncols;
1582         }
1583 
1584         /* off-diagonal part B = c->B */
1585         ncols = bi[row-rstart+1] - bi[row-rstart];
1586         cols  = bj + bi[row-rstart];
1587         if (!allcolumns) {
1588           for (k=0; k<ncols; k++) {
1589 #if defined(PETSC_USE_CTABLE)
1590             ierr = PetscTableFind(cmap,bmap[cols[k]]+1,&tcol);CHKERRQ(ierr);
1591 #else
1592             tcol = cmap[bmap[cols[k]]];
1593 #endif
1594             if (tcol) lens[j]++;
1595           }
1596         } else { /* allcolumns */
1597           lens[j] += ncols;
1598         }
1599       }
1600     }
1601 
1602     /* Create row map (rmap): global row of C -> local row of submat */
1603 #if defined(PETSC_USE_CTABLE)
1604     ierr = PetscTableCreate(nrow+1,C->rmap->N+1,&rmap);CHKERRQ(ierr);
1605     for (j=0; j<nrow; j++) {
1606       row  = irow[j];
1607       proc = row2proc[j];
1608       if (proc == rank) { /* a local row */
1609         rmap_loc[row - rstart] = j;
1610       } else {
1611         ierr = PetscTableAdd(rmap,irow[j]+1,j+1,INSERT_VALUES);CHKERRQ(ierr);
1612       }
1613     }
1614 #else
1615     ierr = PetscCalloc1(C->rmap->N,&rmap);CHKERRQ(ierr);
1616     for (j=0; j<nrow; j++) {
1617       rmap[irow[j]] = j;
1618     }
1619 #endif
1620 
1621     /* Update lens from offproc data */
1622     /* recv a->j is done */
1623     ierr    = MPI_Waitall(nrqs,r_waits3,r_status3);CHKERRQ(ierr);
1624     for (i=0; i<nrqs; i++) {
1625       proc    = pa[i];
1626       sbuf1_i = sbuf1[proc];
1627       /* jmax    = sbuf1_i[0]; if (jmax != 1) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"jmax !=1"); */
1628       ct1     = 2 + 1;
1629       ct2     = 0;
1630       rbuf2_i = rbuf2[i]; /* received length of C->j */
1631       rbuf3_i = rbuf3[i]; /* received C->j */
1632 
1633       /* is_no  = sbuf1_i[2*j-1]; if (is_no != 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"is_no !=0"); */
1634       max1   = sbuf1_i[2];
1635       for (k=0; k<max1; k++,ct1++) {
1636 #if defined(PETSC_USE_CTABLE)
1637         ierr = PetscTableFind(rmap,sbuf1_i[ct1]+1,&row);CHKERRQ(ierr);
1638         row--;
1639         if (row < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"row not found in table");
1640 #else
1641         row = rmap[sbuf1_i[ct1]]; /* the row index in submat */
1642 #endif
1643         /* Now, store row index of submat in sbuf1_i[ct1] */
1644         sbuf1_i[ct1] = row;
1645 
1646         nnz = rbuf2_i[ct1];
1647         if (!allcolumns) {
1648           for (l=0; l<nnz; l++,ct2++) {
1649 #if defined(PETSC_USE_CTABLE)
1650             if (rbuf3_i[ct2] >= cstart && rbuf3_i[ct2] <cend) {
1651               tcol = cmap_loc[rbuf3_i[ct2] - cstart];
1652             } else {
1653               ierr = PetscTableFind(cmap,rbuf3_i[ct2]+1,&tcol);CHKERRQ(ierr);
1654             }
1655 #else
1656             tcol = cmap[rbuf3_i[ct2]]; /* column index in submat */
1657 #endif
1658             if (tcol) lens[row]++;
1659           }
1660         } else { /* allcolumns */
1661           lens[row] += nnz;
1662         }
1663       }
1664     }
1665     ierr = MPI_Waitall(nrqr,s_waits3,s_status3);CHKERRQ(ierr);
1666     ierr = PetscFree4(r_waits3,s_waits3,r_status3,s_status3);CHKERRQ(ierr);
1667 
1668     /* Create the submatrices */
1669     ierr = MatCreate(PETSC_COMM_SELF,&submat);CHKERRQ(ierr);
1670     ierr = MatSetSizes(submat,nrow,ncol,PETSC_DETERMINE,PETSC_DETERMINE);CHKERRQ(ierr);
1671 
1672     ierr = ISGetBlockSize(isrow[0],&i);CHKERRQ(ierr);
1673     ierr = ISGetBlockSize(iscol[0],&j);CHKERRQ(ierr);
1674     ierr = MatSetBlockSizes(submat,i,j);CHKERRQ(ierr);
1675     ierr = MatSetType(submat,((PetscObject)A)->type_name);CHKERRQ(ierr);
1676     ierr = MatSeqAIJSetPreallocation(submat,0,lens);CHKERRQ(ierr);
1677 
1678     /* create struct Mat_SubMat and attached it to submat */
1679     ierr = PetscNew(&smatis1);CHKERRQ(ierr);
1680     subc = (Mat_SeqAIJ*)submat->data;
1681     subc->submatis1 = smatis1;
1682 
1683     smatis1->id          = 0;
1684     smatis1->nrqs        = nrqs;
1685     smatis1->nrqr        = nrqr;
1686     smatis1->rbuf1       = rbuf1;
1687     smatis1->rbuf2       = rbuf2;
1688     smatis1->rbuf3       = rbuf3;
1689     smatis1->sbuf2       = sbuf2;
1690     smatis1->req_source2 = req_source2;
1691 
1692     smatis1->sbuf1       = sbuf1;
1693     smatis1->ptr         = ptr;
1694     smatis1->tmp         = tmp;
1695     smatis1->ctr         = ctr;
1696 
1697     smatis1->pa           = pa;
1698     smatis1->req_size     = req_size;
1699     smatis1->req_source1  = req_source1;
1700 
1701     smatis1->allcolumns  = allcolumns;
1702     smatis1->singleis    = PETSC_TRUE;
1703     smatis1->row2proc    = row2proc;
1704     smatis1->rmap        = rmap;
1705     smatis1->cmap        = cmap;
1706 #if defined(PETSC_USE_CTABLE)
1707     smatis1->rmap_loc    = rmap_loc;
1708     smatis1->cmap_loc    = cmap_loc;
1709 #endif
1710 
1711     smatis1->destroy     = submat->ops->destroy;
1712     submat->ops->destroy = MatDestroy_MPIAIJ_MatGetSubmatrices;
1713     submat->factortype   = C->factortype;
1714 
1715     /* compute rmax */
1716     rmax = 0;
1717     for (i=0; i<nrow; i++) rmax = PetscMax(rmax,lens[i]);
1718 
1719   } else { /* scall == MAT_REUSE_MATRIX */
1720     submat = submats[0];
1721     if (submat->rmap->n != nrow || submat->cmap->n != ncol) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Cannot reuse matrix. wrong size");
1722 
1723     subc    = (Mat_SeqAIJ*)submat->data;
1724     rmax    = subc->rmax;
1725     smatis1 = subc->submatis1;
1726     nrqs        = smatis1->nrqs;
1727     nrqr        = smatis1->nrqr;
1728     rbuf1       = smatis1->rbuf1;
1729     rbuf2       = smatis1->rbuf2;
1730     rbuf3       = smatis1->rbuf3;
1731     req_source2 = smatis1->req_source2;
1732 
1733     sbuf1     = smatis1->sbuf1;
1734     sbuf2     = smatis1->sbuf2;
1735     ptr       = smatis1->ptr;
1736     tmp       = smatis1->tmp;
1737     ctr       = smatis1->ctr;
1738 
1739     pa         = smatis1->pa;
1740     req_size   = smatis1->req_size;
1741     req_source1 = smatis1->req_source1;
1742 
1743     allcolumns = smatis1->allcolumns;
1744     row2proc   = smatis1->row2proc;
1745     rmap       = smatis1->rmap;
1746     cmap       = smatis1->cmap;
1747 #if defined(PETSC_USE_CTABLE)
1748     rmap_loc   = smatis1->rmap_loc;
1749     cmap_loc   = smatis1->cmap_loc;
1750 #endif
1751   }
1752 
1753   /* Post recv matrix values */
1754   ierr = PetscMalloc3(nrqs+1,&rbuf4, rmax,&subcols, rmax,&subvals);CHKERRQ(ierr);
1755   ierr = PetscMalloc4(nrqs+1,&r_waits4,nrqr+1,&s_waits4,nrqs+1,&r_status4,nrqr+1,&s_status4);CHKERRQ(ierr);
1756   ierr = PetscObjectGetNewTag((PetscObject)C,&tag4);CHKERRQ(ierr);
1757   for (i=0; i<nrqs; ++i) {
1758     ierr = PetscMalloc1(rbuf2[i][0]+1,&rbuf4[i]);CHKERRQ(ierr);
1759     ierr = MPI_Irecv(rbuf4[i],rbuf2[i][0],MPIU_SCALAR,req_source2[i],tag4,comm,r_waits4+i);CHKERRQ(ierr);
1760   }
1761 
1762   /* Allocate sending buffers for a->a, and send them off */
1763   ierr = PetscMalloc1(nrqr+1,&sbuf_aa);CHKERRQ(ierr);
1764   for (i=0,j=0; i<nrqr; i++) j += req_size[i];
1765   ierr = PetscMalloc1(j+1,&sbuf_aa[0]);CHKERRQ(ierr);
1766   for (i=1; i<nrqr; i++) sbuf_aa[i] = sbuf_aa[i-1] + req_size[i-1];
1767 
1768   for (i=0; i<nrqr; i++) {
1769     rbuf1_i   = rbuf1[i];
1770     sbuf_aa_i = sbuf_aa[i];
1771     ct1       = 2*rbuf1_i[0]+1;
1772     ct2       = 0;
1773     /* max1=rbuf1_i[0]; if (max1 != 1) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"max1 !=1"); */
1774 
1775     kmax = rbuf1_i[2];
1776     for (k=0; k<kmax; k++,ct1++) {
1777       row = rbuf1_i[ct1] - rstart;
1778       nzA = ai[row+1] - ai[row];
1779       nzB = bi[row+1] - bi[row];
1780       ncols  = nzA + nzB;
1781       cworkB = bj + bi[row];
1782       vworkA = a_a + ai[row];
1783       vworkB = b_a + bi[row];
1784 
1785       /* load the column values for this row into vals*/
1786       vals = sbuf_aa_i + ct2;
1787 
1788       lwrite = 0;
1789       for (l=0; l<nzB; l++) {
1790         if ((bmap[cworkB[l]]) < cstart) vals[lwrite++] = vworkB[l];
1791       }
1792       for (l=0; l<nzA; l++) vals[lwrite++] = vworkA[l];
1793       for (l=0; l<nzB; l++) {
1794         if ((bmap[cworkB[l]]) >= cend) vals[lwrite++] = vworkB[l];
1795       }
1796 
1797       ct2 += ncols;
1798     }
1799     ierr = MPI_Isend(sbuf_aa_i,req_size[i],MPIU_SCALAR,req_source1[i],tag4,comm,s_waits4+i);CHKERRQ(ierr);
1800   }
1801 
1802   /* Assemble submat */
1803   /* First assemble the local rows */
1804   for (j=0; j<nrow; j++) {
1805     row  = irow[j];
1806     proc = row2proc[j];
1807     if (proc == rank) {
1808       Crow = row - rstart;  /* local row index of C */
1809 #if defined(PETSC_USE_CTABLE)
1810       row = rmap_loc[Crow]; /* row index of submat */
1811 #else
1812       row = rmap[row];
1813 #endif
1814 
1815       if (allcolumns) {
1816         /* diagonal part A = c->A */
1817         ncols = ai[Crow+1] - ai[Crow];
1818         cols  = aj + ai[Crow];
1819         vals  = a->a + ai[Crow];
1820         i     = 0;
1821         for (k=0; k<ncols; k++) {
1822           subcols[i]   = cols[k] + cstart;
1823           subvals[i++] = vals[k];
1824         }
1825 
1826         /* off-diagonal part B = c->B */
1827         ncols = bi[Crow+1] - bi[Crow];
1828         cols  = bj + bi[Crow];
1829         vals  = b->a + bi[Crow];
1830         for (k=0; k<ncols; k++) {
1831           subcols[i]   = bmap[cols[k]];
1832           subvals[i++] = vals[k];
1833         }
1834 
1835         ierr = MatSetValues_SeqAIJ(submat,1,&row,i,subcols,subvals,INSERT_VALUES);CHKERRQ(ierr);
1836 
1837       } else { /* !allcolumns */
1838 #if defined(PETSC_USE_CTABLE)
1839         /* diagonal part A = c->A */
1840         ncols = ai[Crow+1] - ai[Crow];
1841         cols  = aj + ai[Crow];
1842         vals  = a->a + ai[Crow];
1843         i     = 0;
1844         for (k=0; k<ncols; k++) {
1845           tcol = cmap_loc[cols[k]];
1846           if (tcol) {
1847             subcols[i]   = --tcol;
1848             subvals[i++] = vals[k];
1849           }
1850         }
1851 
1852         /* off-diagonal part B = c->B */
1853         ncols = bi[Crow+1] - bi[Crow];
1854         cols  = bj + bi[Crow];
1855         vals  = b->a + bi[Crow];
1856         for (k=0; k<ncols; k++) {
1857           ierr = PetscTableFind(cmap,bmap[cols[k]]+1,&tcol);CHKERRQ(ierr);
1858           if (tcol) {
1859             subcols[i]   = --tcol;
1860             subvals[i++] = vals[k];
1861           }
1862         }
1863 #else
1864         /* diagonal part A = c->A */
1865         ncols = ai[Crow+1] - ai[Crow];
1866         cols  = aj + ai[Crow];
1867         vals  = a->a + ai[Crow];
1868         i     = 0;
1869         for (k=0; k<ncols; k++) {
1870           tcol = cmap[cols[k]+cstart];
1871           if (tcol) {
1872             subcols[i]   = --tcol;
1873             subvals[i++] = vals[k];
1874           }
1875         }
1876 
1877         /* off-diagonal part B = c->B */
1878         ncols = bi[Crow+1] - bi[Crow];
1879         cols  = bj + bi[Crow];
1880         vals  = b->a + bi[Crow];
1881         for (k=0; k<ncols; k++) {
1882           tcol = cmap[bmap[cols[k]]];
1883           if (tcol) {
1884             subcols[i]   = --tcol;
1885             subvals[i++] = vals[k];
1886           }
1887         }
1888 #endif
1889         ierr = MatSetValues_SeqAIJ(submat,1,&row,i,subcols,subvals,INSERT_VALUES);CHKERRQ(ierr);
1890       }
1891     }
1892   }
1893 
1894   /* Now assemble the off-proc rows */
1895   for (i=0; i<nrqs; i++) { /* for each requested message */
1896     /* recv values from other processes */
1897     ierr    = MPI_Waitany(nrqs,r_waits4,&idex,r_status4+i);CHKERRQ(ierr);
1898     proc    = pa[idex];
1899     sbuf1_i = sbuf1[proc];
1900     /* jmax    = sbuf1_i[0]; if (jmax != 1)SETERRQ1(PETSC_COMM_SELF,0,"jmax %d != 1",jmax); */
1901     ct1     = 2 + 1;
1902     ct2     = 0; /* count of received C->j */
1903     ct3     = 0; /* count of received C->j that will be inserted into submat */
1904     rbuf2_i = rbuf2[idex]; /* int** received length of C->j from other processes */
1905     rbuf3_i = rbuf3[idex]; /* int** received C->j from other processes */
1906     rbuf4_i = rbuf4[idex]; /* scalar** received C->a from other processes */
1907 
1908     /* is_no = sbuf1_i[2*j-1]; if (is_no != 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"is_no !=0"); */
1909     max1 = sbuf1_i[2];             /* num of rows */
1910     for (k=0; k<max1; k++,ct1++) { /* for each recved row */
1911       row = sbuf1_i[ct1]; /* row index of submat */
1912       if (!allcolumns) {
1913         idex = 0;
1914         if (scall == MAT_INITIAL_MATRIX) {
1915           nnz  = rbuf2_i[ct1]; /* num of C entries in this row */
1916           for (l=0; l<nnz; l++,ct2++) { /* for each recved column */
1917 #if defined(PETSC_USE_CTABLE)
1918             if (rbuf3_i[ct2] >= cstart && rbuf3_i[ct2] <cend) {
1919               tcol = cmap_loc[rbuf3_i[ct2] - cstart];
1920             } else {
1921               ierr = PetscTableFind(cmap,rbuf3_i[ct2]+1,&tcol);CHKERRQ(ierr);
1922             }
1923 #else
1924             tcol = cmap[rbuf3_i[ct2]];
1925 #endif
1926             if (tcol) {
1927               subcols[idex]   = --tcol;
1928               subvals[idex++] = rbuf4_i[ct2];
1929 
1930               /* We receive an entire column of C, but a subset of it needs to be inserted into submat.
1931                For reuse, we replace received C->j with index that should be inserted to submat */
1932               rbuf3_i[ct3++] = ct2;
1933             }
1934           }
1935           ierr = MatSetValues_SeqAIJ(submat,1,&row,idex,subcols,subvals,INSERT_VALUES);CHKERRQ(ierr);
1936 
1937         } else { /* scall == MAT_REUSE_MATRIX */
1938           submat = submats[0];
1939           subc   = (Mat_SeqAIJ*)submat->data;
1940 
1941           nnz = subc->i[row+1] - subc->i[row]; /* num of submat entries in this row */
1942           for (l=0; l<nnz; l++) {
1943             ct2 = rbuf3_i[ct3++]; /* index of rbuf4_i[] which needs to be inserted into submat */
1944             subvals[idex++] = rbuf4_i[ct2];
1945           }
1946 
1947           bj = subc->j + subc->i[row];
1948           ierr = MatSetValues_SeqAIJ(submat,1,&row,nnz,bj,subvals,INSERT_VALUES);CHKERRQ(ierr);
1949         }
1950       } else { /* allcolumns */
1951         nnz  = rbuf2_i[ct1]; /* num of C entries in this row */
1952         ierr = MatSetValues_SeqAIJ(submat,1,&row,nnz,rbuf3_i+ct2,rbuf4_i+ct2,INSERT_VALUES);CHKERRQ(ierr);
1953         ct2 += nnz;
1954       }
1955     }
1956   }
1957 
1958   /* sending a->a are done */
1959   ierr = MPI_Waitall(nrqr,s_waits4,s_status4);CHKERRQ(ierr);
1960   ierr = PetscFree4(r_waits4,s_waits4,r_status4,s_status4);CHKERRQ(ierr);
1961 
1962   ierr = MatAssemblyBegin(submat,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
1963   ierr = MatAssemblyEnd(submat,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
1964   submats[0] = submat;
1965 
1966   /* Restore the indices */
1967   ierr = ISRestoreIndices(isrow[0],&irow);CHKERRQ(ierr);
1968   if (!allcolumns) {
1969     ierr = ISRestoreIndices(iscol[0],&icol);CHKERRQ(ierr);
1970   }
1971 
1972   /* Destroy allocated memory */
1973   for (i=0; i<nrqs; ++i) {
1974     ierr = PetscFree3(rbuf4[i],subcols,subvals);CHKERRQ(ierr);
1975   }
1976   ierr = PetscFree3(rbuf4,subcols,subvals);CHKERRQ(ierr);
1977   ierr = PetscFree(sbuf_aa[0]);CHKERRQ(ierr);
1978   ierr = PetscFree(sbuf_aa);CHKERRQ(ierr);
1979 
1980   if (scall == MAT_INITIAL_MATRIX) {
1981     ierr = PetscFree(lens);CHKERRQ(ierr);
1982     ierr = PetscFree(sbuf_aj[0]);CHKERRQ(ierr);
1983     ierr = PetscFree(sbuf_aj);CHKERRQ(ierr);
1984   }
1985   PetscFunctionReturn(0);
1986 }
1987 
1988 PetscErrorCode MatGetSubMatrices_MPIAIJ_SingleIS(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[])
1989 {
1990   PetscErrorCode ierr;
1991   PetscInt       ncol;
1992   PetscBool      colflag,allcolumns=PETSC_FALSE;
1993 
1994   PetscFunctionBegin;
1995   /* Allocate memory to hold all the submatrices */
1996   if (scall == MAT_INITIAL_MATRIX) {
1997     ierr = PetscMalloc1(1,submat);CHKERRQ(ierr);
1998   }
1999 
2000   /* Check for special case: each processor gets entire matrix columns */
2001   ierr = ISIdentity(iscol[0],&colflag);CHKERRQ(ierr);
2002   ierr = ISGetLocalSize(iscol[0],&ncol);CHKERRQ(ierr);
2003   if (colflag && ncol == C->cmap->N) allcolumns = PETSC_TRUE;
2004 
2005   ierr = MatGetSubMatrices_MPIAIJ_SingleIS_Local(C,ismax,isrow,iscol,scall,allcolumns,*submat);CHKERRQ(ierr);
2006   PetscFunctionReturn(0);
2007 }
2008 
2009 PetscErrorCode MatGetSubMatrices_MPIAIJ(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[])
2010 {
2011   PetscErrorCode ierr;
2012   PetscInt       nmax,nstages,i,pos,max_no,nrow,ncol,in[2],out[2];
2013   PetscBool      rowflag,colflag,wantallmatrix=PETSC_FALSE;
2014   Mat_SeqAIJ     *subc;
2015   Mat_SubMat     *smat;
2016 
2017   PetscFunctionBegin;
2018   /* Check for special case: each processor has a single IS */
2019   if (C->submat_singleis) { /* flag is set in PCSetUp_ASM() to skip MPIU_Allreduce() */
2020     ierr = MatGetSubMatrices_MPIAIJ_SingleIS(C,ismax,isrow,iscol,scall,submat);CHKERRQ(ierr);
2021     C->submat_singleis = PETSC_FALSE; /* resume its default value in case C will be used for non-singlis */
2022     PetscFunctionReturn(0);
2023   }
2024 
2025   if (scall == MAT_REUSE_MATRIX && !ismax) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"n=0 is not supported for MatGetSubMatrices(mat,n,isrow,iscol,MAT_REUSE_MATRIX,...). Set n=1 with zero-length isrow and iscolumn instead");
2026 
2027   /* Collect global wantallmatrix and nstages */
2028   if (!C->cmap->N) nmax=20*1000000/sizeof(PetscInt);
2029   else nmax = 20*1000000 / (C->cmap->N * sizeof(PetscInt));
2030   if (!nmax) nmax = 1;
2031 
2032   if (scall == MAT_INITIAL_MATRIX) {
2033     /* Collect global wantallmatrix and nstages */
2034     if (ismax == 1 && C->rmap->N == C->cmap->N) {
2035       ierr = ISIdentity(*isrow,&rowflag);CHKERRQ(ierr);
2036       ierr = ISIdentity(*iscol,&colflag);CHKERRQ(ierr);
2037       ierr = ISGetLocalSize(*isrow,&nrow);CHKERRQ(ierr);
2038       ierr = ISGetLocalSize(*iscol,&ncol);CHKERRQ(ierr);
2039       if (rowflag && colflag && nrow == C->rmap->N && ncol == C->cmap->N) {
2040         wantallmatrix = PETSC_TRUE;
2041 
2042         ierr = PetscOptionsGetBool(((PetscObject)C)->options,((PetscObject)C)->prefix,"-use_fast_submatrix",&wantallmatrix,NULL);CHKERRQ(ierr);
2043       }
2044     }
2045 
2046     /* Determine the number of stages through which submatrices are done
2047        Each stage will extract nmax submatrices.
2048        nmax is determined by the matrix column dimension.
2049        If the original matrix has 20M columns, only one submatrix per stage is allowed, etc.
2050     */
2051     nstages = ismax/nmax + ((ismax % nmax) ? 1 : 0); /* local nstages */
2052 
2053     in[0] = -1*(PetscInt)wantallmatrix;
2054     in[1] = nstages;
2055     ierr = MPIU_Allreduce(in,out,2,MPIU_INT,MPI_MAX,PetscObjectComm((PetscObject)C));CHKERRQ(ierr);
2056     wantallmatrix = (PetscBool)(-out[0]);
2057     nstages       = out[1]; /* Make sure every processor loops through the global nstages */
2058 
2059   } else { /* MAT_REUSE_MATRIX */
2060     subc = (Mat_SeqAIJ*)((*submat)[0]->data);
2061     smat   = subc->submatis1;
2062     if (!smat) {
2063       /* smat is not generated by MatGetSubMatrix_MPIAIJ_All(...,MAT_INITIAL_MATRIX,...) */
2064       wantallmatrix = PETSC_TRUE;
2065     } else if (smat->singleis) {
2066       ierr = MatGetSubMatrices_MPIAIJ_SingleIS(C,ismax,isrow,iscol,scall,submat);CHKERRQ(ierr);
2067       PetscFunctionReturn(0);
2068     } else {
2069       nstages = smat->nstages;
2070     }
2071   }
2072 
2073   if (wantallmatrix) {
2074     ierr = MatGetSubMatrix_MPIAIJ_All(C,MAT_GET_VALUES,scall,submat);CHKERRQ(ierr);
2075     PetscFunctionReturn(0);
2076   }
2077 
2078   /* Allocate memory to hold all the submatrices */
2079   if (scall == MAT_INITIAL_MATRIX) {
2080     ierr = PetscMalloc1(ismax+1,submat);CHKERRQ(ierr);
2081   }
2082 
2083   for (i=0,pos=0; i<nstages; i++) {
2084     if (pos+nmax <= ismax) max_no = nmax;
2085     else if (pos == ismax) max_no = 0;
2086     else                   max_no = ismax-pos;
2087     ierr = MatGetSubMatrices_MPIAIJ_Local(C,max_no,isrow+pos,iscol+pos,scall,*submat+pos);CHKERRQ(ierr);
2088     pos += max_no;
2089   }
2090 
2091   if (scall == MAT_INITIAL_MATRIX && ismax) {
2092     /* save nstages for reuse */
2093     subc = (Mat_SeqAIJ*)((*submat)[0]->data);
2094     smat = subc->submatis1;
2095     if (!smat) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_NULL,"smat does not exit");
2096     smat->nstages = nstages;
2097   }
2098   PetscFunctionReturn(0);
2099 }
2100 
2101 /* -------------------------------------------------------------------------*/
2102 PetscErrorCode MatGetSubMatrices_MPIAIJ_Local(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submats)
2103 {
2104   Mat_MPIAIJ     *c = (Mat_MPIAIJ*)C->data;
2105   Mat            A  = c->A;
2106   Mat_SeqAIJ     *a = (Mat_SeqAIJ*)A->data,*b = (Mat_SeqAIJ*)c->B->data,*subc;
2107   const PetscInt **icol,**irow;
2108   PetscInt       *nrow,*ncol,start;
2109   PetscErrorCode ierr;
2110   PetscMPIInt    rank,size,tag0,tag2,tag3,tag4,*w1,*w2,*w3,*w4,nrqr;
2111   PetscInt       **sbuf1,**sbuf2,i,j,k,l,ct1,ct2,**rbuf1,row,proc=-1;
2112   PetscInt       nrqs=0,msz,**ptr=NULL,*req_size=NULL,*ctr=NULL,*pa,*tmp=NULL,tcol;
2113   PetscInt       **rbuf3=NULL,*req_source1=NULL,*req_source2,**sbuf_aj,**rbuf2=NULL,max1,max2;
2114   PetscInt       **lens,is_no,ncols,*cols,mat_i,*mat_j,tmp2,jmax;
2115 #if defined(PETSC_USE_CTABLE)
2116   PetscTable     *cmap,cmap_i=NULL,*rmap,rmap_i;
2117 #else
2118   PetscInt       **cmap,*cmap_i=NULL,**rmap,*rmap_i;
2119 #endif
2120   const PetscInt *irow_i;
2121   PetscInt       ctr_j,*sbuf1_j,*sbuf_aj_i,*rbuf1_i,kmax,*lens_i;
2122   MPI_Request    *s_waits1,*r_waits1,*s_waits2,*r_waits2,*r_waits3;
2123   MPI_Request    *r_waits4,*s_waits3,*s_waits4;
2124   MPI_Status     *r_status1,*r_status2,*s_status1,*s_status3,*s_status2;
2125   MPI_Status     *r_status3,*r_status4,*s_status4;
2126   MPI_Comm       comm;
2127   PetscScalar    **rbuf4,*rbuf4_i,**sbuf_aa,*vals,*mat_a,*imat_a,*sbuf_aa_i;
2128   PetscMPIInt    *onodes1,*olengths1,end;
2129   PetscInt       **row2proc,*row2proc_i,ilen_row,*imat_ilen,*imat_j,*imat_i,old_row;
2130   Mat_SubMat     **smats,*smat_i;
2131   PetscBool      *issorted,*allcolumns,colflag,iscsorted=PETSC_TRUE;
2132   PetscInt       *sbuf1_i,*rbuf2_i,*rbuf3_i,ilen;
2133 
2134   PetscFunctionBegin;
2135   ierr = PetscObjectGetComm((PetscObject)C,&comm);CHKERRQ(ierr);
2136   size = c->size;
2137   rank = c->rank;
2138 
2139   ierr = PetscMalloc5(ismax,&smats,ismax,&row2proc,ismax,&cmap,ismax,&rmap,ismax,&allcolumns);CHKERRQ(ierr);
2140   ierr = PetscMalloc5(ismax,&irow,ismax,&icol,ismax,&nrow,ismax,&ncol,ismax,&issorted);CHKERRQ(ierr);
2141 
2142   for (i=0; i<ismax; i++) {
2143     ierr = ISSorted(iscol[i],&issorted[i]);CHKERRQ(ierr);
2144     if (!issorted[i]) iscsorted = issorted[i];
2145 
2146     ierr = ISSorted(isrow[i],&issorted[i]);CHKERRQ(ierr);
2147 
2148     ierr = ISGetIndices(isrow[i],&irow[i]);CHKERRQ(ierr);
2149     ierr = ISGetLocalSize(isrow[i],&nrow[i]);CHKERRQ(ierr);
2150 
2151     /* Check for special case: allcolumn */
2152     ierr = ISIdentity(iscol[i],&colflag);CHKERRQ(ierr);
2153     ierr = ISGetLocalSize(iscol[i],&ncol[i]);CHKERRQ(ierr);
2154     if (colflag && ncol[i] == C->cmap->N) {
2155       allcolumns[i] = PETSC_TRUE;
2156       icol[i] = NULL;
2157     } else {
2158       allcolumns[i] = PETSC_FALSE;
2159       ierr = ISGetIndices(iscol[i],&icol[i]);CHKERRQ(ierr);
2160     }
2161   }
2162 
2163   if (scall == MAT_REUSE_MATRIX) {
2164     /* Assumes new rows are same length as the old rows */
2165     for (i=0; i<ismax; i++) {
2166       subc = (Mat_SeqAIJ*)(submats[i]->data);
2167       if ((submats[i]->rmap->n != nrow[i]) || (submats[i]->cmap->n != ncol[i])) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Cannot reuse matrix. wrong size");
2168 
2169       /* Initial matrix as if empty */
2170       ierr = PetscMemzero(subc->ilen,submats[i]->rmap->n*sizeof(PetscInt));CHKERRQ(ierr);
2171 
2172       /* Initial matrix as if empty */
2173       submats[i]->factortype = C->factortype;
2174 
2175       smat_i   = subc->submatis1;
2176       smats[i] = smat_i;
2177 
2178       nrqs        = smat_i->nrqs;
2179       nrqr        = smat_i->nrqr;
2180       rbuf1       = smat_i->rbuf1;
2181       rbuf2       = smat_i->rbuf2;
2182       rbuf3       = smat_i->rbuf3;
2183       req_source2 = smat_i->req_source2;
2184 
2185       sbuf1     = smat_i->sbuf1;
2186       sbuf2     = smat_i->sbuf2;
2187       ptr       = smat_i->ptr;
2188       tmp       = smat_i->tmp;
2189       ctr       = smat_i->ctr;
2190 
2191       pa          = smat_i->pa;
2192       req_size    = smat_i->req_size;
2193       req_source1 = smat_i->req_source1;
2194 
2195       allcolumns[i] = smat_i->allcolumns;
2196       row2proc[i]   = smat_i->row2proc;
2197       rmap[i]       = smat_i->rmap;
2198       cmap[i]       = smat_i->cmap;
2199     }
2200   } else { /* scall == MAT_INITIAL_MATRIX */
2201     /* Get some new tags to keep the communication clean */
2202     ierr = PetscObjectGetNewTag((PetscObject)C,&tag2);CHKERRQ(ierr);
2203     ierr = PetscObjectGetNewTag((PetscObject)C,&tag3);CHKERRQ(ierr);
2204 
2205     /* evaluate communication - mesg to who, length of mesg, and buffer space
2206      required. Based on this, buffers are allocated, and data copied into them*/
2207     ierr = PetscCalloc4(size,&w1,size,&w2,size,&w3,size,&w4);CHKERRQ(ierr);   /* mesg size, initialize work vectors */
2208 
2209     for (i=0; i<ismax; i++) {
2210       jmax   = nrow[i];
2211       irow_i = irow[i];
2212 
2213       ierr   = PetscMalloc1(jmax,&row2proc_i);CHKERRQ(ierr);
2214       row2proc[i] = row2proc_i;
2215 
2216       if (issorted[i]) proc = 0;
2217       for (j=0; j<jmax; j++) {
2218         if (!issorted[i]) proc = 0;
2219         row = irow_i[j];
2220         while (row >= C->rmap->range[proc+1]) proc++;
2221         w4[proc]++;
2222         row2proc_i[j] = proc; /* map row index to proc */
2223       }
2224       for (j=0; j<size; j++) {
2225         if (w4[j]) { w1[j] += w4[j];  w3[j]++; w4[j] = 0;}
2226       }
2227     }
2228 
2229     nrqs     = 0;              /* no of outgoing messages */
2230     msz      = 0;              /* total mesg length (for all procs) */
2231     w1[rank] = 0;              /* no mesg sent to self */
2232     w3[rank] = 0;
2233     for (i=0; i<size; i++) {
2234       if (w1[i])  { w2[i] = 1; nrqs++;} /* there exists a message to proc i */
2235     }
2236     ierr = PetscMalloc1(nrqs+1,&pa);CHKERRQ(ierr); /*(proc -array)*/
2237     for (i=0,j=0; i<size; i++) {
2238       if (w1[i]) { pa[j] = i; j++; }
2239     }
2240 
2241     /* Each message would have a header = 1 + 2*(no of IS) + data */
2242     for (i=0; i<nrqs; i++) {
2243       j      = pa[i];
2244       w1[j] += w2[j] + 2* w3[j];
2245       msz   += w1[j];
2246     }
2247     ierr = PetscInfo2(0,"Number of outgoing messages %D Total message length %D\n",nrqs,msz);CHKERRQ(ierr);
2248 
2249     /* Determine the number of messages to expect, their lengths, from from-ids */
2250     ierr = PetscGatherNumberOfMessages(comm,w2,w1,&nrqr);CHKERRQ(ierr);
2251     ierr = PetscGatherMessageLengths(comm,nrqs,nrqr,w1,&onodes1,&olengths1);CHKERRQ(ierr);
2252 
2253     /* Now post the Irecvs corresponding to these messages */
2254     tag0 = ((PetscObject)C)->tag;
2255     ierr = PetscPostIrecvInt(comm,tag0,nrqr,onodes1,olengths1,&rbuf1,&r_waits1);CHKERRQ(ierr);
2256 
2257     ierr = PetscFree(onodes1);CHKERRQ(ierr);
2258     ierr = PetscFree(olengths1);CHKERRQ(ierr);
2259 
2260     /* Allocate Memory for outgoing messages */
2261     ierr = PetscMalloc4(size,&sbuf1,size,&ptr,2*msz,&tmp,size,&ctr);CHKERRQ(ierr);
2262     ierr = PetscMemzero(sbuf1,size*sizeof(PetscInt*));CHKERRQ(ierr);
2263     ierr = PetscMemzero(ptr,size*sizeof(PetscInt*));CHKERRQ(ierr);
2264 
2265     {
2266       PetscInt *iptr = tmp;
2267       k    = 0;
2268       for (i=0; i<nrqs; i++) {
2269         j        = pa[i];
2270         iptr    += k;
2271         sbuf1[j] = iptr;
2272         k        = w1[j];
2273       }
2274     }
2275 
2276     /* Form the outgoing messages. Initialize the header space */
2277     for (i=0; i<nrqs; i++) {
2278       j           = pa[i];
2279       sbuf1[j][0] = 0;
2280       ierr        = PetscMemzero(sbuf1[j]+1,2*w3[j]*sizeof(PetscInt));CHKERRQ(ierr);
2281       ptr[j]      = sbuf1[j] + 2*w3[j] + 1;
2282     }
2283 
2284     /* Parse the isrow and copy data into outbuf */
2285     for (i=0; i<ismax; i++) {
2286       row2proc_i = row2proc[i];
2287       ierr   = PetscMemzero(ctr,size*sizeof(PetscInt));CHKERRQ(ierr);
2288       irow_i = irow[i];
2289       jmax   = nrow[i];
2290       for (j=0; j<jmax; j++) {  /* parse the indices of each IS */
2291         proc = row2proc_i[j];
2292         if (proc != rank) { /* copy to the outgoing buf*/
2293           ctr[proc]++;
2294           *ptr[proc] = irow_i[j];
2295           ptr[proc]++;
2296         }
2297       }
2298       /* Update the headers for the current IS */
2299       for (j=0; j<size; j++) { /* Can Optimise this loop too */
2300         if ((ctr_j = ctr[j])) {
2301           sbuf1_j        = sbuf1[j];
2302           k              = ++sbuf1_j[0];
2303           sbuf1_j[2*k]   = ctr_j;
2304           sbuf1_j[2*k-1] = i;
2305         }
2306       }
2307     }
2308 
2309     /*  Now  post the sends */
2310     ierr = PetscMalloc1(nrqs+1,&s_waits1);CHKERRQ(ierr);
2311     for (i=0; i<nrqs; ++i) {
2312       j    = pa[i];
2313       ierr = MPI_Isend(sbuf1[j],w1[j],MPIU_INT,j,tag0,comm,s_waits1+i);CHKERRQ(ierr);
2314     }
2315 
2316     /* Post Receives to capture the buffer size */
2317     ierr = PetscMalloc1(nrqs+1,&r_waits2);CHKERRQ(ierr);
2318     ierr = PetscMalloc3(nrqs+1,&req_source2,nrqs+1,&rbuf2,nrqs+1,&rbuf3);CHKERRQ(ierr);
2319     rbuf2[0] = tmp + msz;
2320     for (i=1; i<nrqs; ++i) {
2321       rbuf2[i] = rbuf2[i-1]+w1[pa[i-1]];
2322     }
2323     for (i=0; i<nrqs; ++i) {
2324       j    = pa[i];
2325       ierr = MPI_Irecv(rbuf2[i],w1[j],MPIU_INT,j,tag2,comm,r_waits2+i);CHKERRQ(ierr);
2326     }
2327 
2328     /* Send to other procs the buf size they should allocate */
2329     /* Receive messages*/
2330     ierr = PetscMalloc1(nrqr+1,&s_waits2);CHKERRQ(ierr);
2331     ierr = PetscMalloc1(nrqr+1,&r_status1);CHKERRQ(ierr);
2332     ierr = PetscMalloc3(nrqr,&sbuf2,nrqr,&req_size,nrqr,&req_source1);CHKERRQ(ierr);
2333     {
2334       PetscInt   *sAi = a->i,*sBi = b->i,id,rstart = C->rmap->rstart;
2335       PetscInt   *sbuf2_i;
2336 
2337       ierr = MPI_Waitall(nrqr,r_waits1,r_status1);CHKERRQ(ierr);
2338       for (i=0; i<nrqr; ++i) {
2339         req_size[i] = 0;
2340         rbuf1_i        = rbuf1[i];
2341         start          = 2*rbuf1_i[0] + 1;
2342         ierr           = MPI_Get_count(r_status1+i,MPIU_INT,&end);CHKERRQ(ierr);
2343         ierr           = PetscMalloc1(end+1,&sbuf2[i]);CHKERRQ(ierr);
2344         sbuf2_i        = sbuf2[i];
2345         for (j=start; j<end; j++) {
2346           id              = rbuf1_i[j] - rstart;
2347           ncols           = sAi[id+1] - sAi[id] + sBi[id+1] - sBi[id];
2348           sbuf2_i[j]      = ncols;
2349           req_size[i] += ncols;
2350         }
2351         req_source1[i] = r_status1[i].MPI_SOURCE;
2352         /* form the header */
2353         sbuf2_i[0] = req_size[i];
2354         for (j=1; j<start; j++) sbuf2_i[j] = rbuf1_i[j];
2355 
2356         ierr = MPI_Isend(sbuf2_i,end,MPIU_INT,req_source1[i],tag2,comm,s_waits2+i);CHKERRQ(ierr);
2357       }
2358     }
2359     ierr = PetscFree(r_status1);CHKERRQ(ierr);
2360     ierr = PetscFree(r_waits1);CHKERRQ(ierr);
2361     ierr = PetscFree4(w1,w2,w3,w4);CHKERRQ(ierr);
2362 
2363     /* Receive messages*/
2364     ierr = PetscMalloc1(nrqs+1,&r_waits3);CHKERRQ(ierr);
2365     ierr = PetscMalloc1(nrqs+1,&r_status2);CHKERRQ(ierr);
2366 
2367     ierr = MPI_Waitall(nrqs,r_waits2,r_status2);CHKERRQ(ierr);
2368     for (i=0; i<nrqs; ++i) {
2369       ierr = PetscMalloc1(rbuf2[i][0]+1,&rbuf3[i]);CHKERRQ(ierr);
2370       req_source2[i] = r_status2[i].MPI_SOURCE;
2371       ierr = MPI_Irecv(rbuf3[i],rbuf2[i][0],MPIU_INT,req_source2[i],tag3,comm,r_waits3+i);CHKERRQ(ierr);
2372     }
2373     ierr = PetscFree(r_status2);CHKERRQ(ierr);
2374     ierr = PetscFree(r_waits2);CHKERRQ(ierr);
2375 
2376     /* Wait on sends1 and sends2 */
2377     ierr = PetscMalloc1(nrqs+1,&s_status1);CHKERRQ(ierr);
2378     ierr = PetscMalloc1(nrqr+1,&s_status2);CHKERRQ(ierr);
2379 
2380     if (nrqs) {ierr = MPI_Waitall(nrqs,s_waits1,s_status1);CHKERRQ(ierr);}
2381     if (nrqr) {ierr = MPI_Waitall(nrqr,s_waits2,s_status2);CHKERRQ(ierr);}
2382     ierr = PetscFree(s_status1);CHKERRQ(ierr);
2383     ierr = PetscFree(s_status2);CHKERRQ(ierr);
2384     ierr = PetscFree(s_waits1);CHKERRQ(ierr);
2385     ierr = PetscFree(s_waits2);CHKERRQ(ierr);
2386 
2387     /* Now allocate sending buffers for a->j, and send them off */
2388     ierr = PetscMalloc1(nrqr+1,&sbuf_aj);CHKERRQ(ierr);
2389     for (i=0,j=0; i<nrqr; i++) j += req_size[i];
2390     ierr = PetscMalloc1(j+1,&sbuf_aj[0]);CHKERRQ(ierr);
2391     for (i=1; i<nrqr; i++) sbuf_aj[i] = sbuf_aj[i-1] + req_size[i-1];
2392 
2393     ierr = PetscMalloc1(nrqr+1,&s_waits3);CHKERRQ(ierr);
2394     {
2395       PetscInt nzA,nzB,*a_i = a->i,*b_i = b->i,lwrite;
2396       PetscInt *cworkA,*cworkB,cstart = C->cmap->rstart,rstart = C->rmap->rstart,*bmap = c->garray;
2397       PetscInt cend = C->cmap->rend;
2398       PetscInt *a_j = a->j,*b_j = b->j,ctmp;
2399 
2400       for (i=0; i<nrqr; i++) {
2401         rbuf1_i   = rbuf1[i];
2402         sbuf_aj_i = sbuf_aj[i];
2403         ct1       = 2*rbuf1_i[0] + 1;
2404         ct2       = 0;
2405         for (j=1,max1=rbuf1_i[0]; j<=max1; j++) {
2406           kmax = rbuf1[i][2*j];
2407           for (k=0; k<kmax; k++,ct1++) {
2408             row    = rbuf1_i[ct1] - rstart;
2409             nzA    = a_i[row+1] - a_i[row]; nzB = b_i[row+1] - b_i[row];
2410             ncols  = nzA + nzB;
2411             cworkA = a_j + a_i[row]; cworkB = b_j + b_i[row];
2412 
2413             /* load the column indices for this row into cols */
2414             cols = sbuf_aj_i + ct2;
2415 
2416             lwrite = 0;
2417             for (l=0; l<nzB; l++) {
2418               if ((ctmp = bmap[cworkB[l]]) < cstart) cols[lwrite++] = ctmp;
2419             }
2420             for (l=0; l<nzA; l++) cols[lwrite++] = cstart + cworkA[l];
2421             for (l=0; l<nzB; l++) {
2422               if ((ctmp = bmap[cworkB[l]]) >= cend) cols[lwrite++] = ctmp;
2423             }
2424 
2425             ct2 += ncols;
2426           }
2427         }
2428         ierr = MPI_Isend(sbuf_aj_i,req_size[i],MPIU_INT,req_source1[i],tag3,comm,s_waits3+i);CHKERRQ(ierr);
2429       }
2430     }
2431     ierr = PetscMalloc2(nrqs+1,&r_status3,nrqr+1,&s_status3);CHKERRQ(ierr);
2432 
2433     /* create col map: global col of C -> local col of submatrices */
2434     {
2435       const PetscInt *icol_i;
2436 #if defined(PETSC_USE_CTABLE)
2437       for (i=0; i<ismax; i++) {
2438         if (!allcolumns[i]) {
2439           ierr = PetscTableCreate(ncol[i]+1,C->cmap->N+1,&cmap[i]);CHKERRQ(ierr);
2440 
2441           jmax   = ncol[i];
2442           icol_i = icol[i];
2443           cmap_i = cmap[i];
2444           for (j=0; j<jmax; j++) {
2445             ierr = PetscTableAdd(cmap[i],icol_i[j]+1,j+1,INSERT_VALUES);CHKERRQ(ierr);
2446           }
2447         } else cmap[i] = NULL;
2448       }
2449 #else
2450       for (i=0; i<ismax; i++) {
2451         if (!allcolumns[i]) {
2452           ierr   = PetscCalloc1(C->cmap->N,&cmap[i]);CHKERRQ(ierr);
2453           jmax   = ncol[i];
2454           icol_i = icol[i];
2455           cmap_i = cmap[i];
2456           for (j=0; j<jmax; j++) {
2457             cmap_i[icol_i[j]] = j+1;
2458           }
2459         } else cmap[i] = NULL;
2460       }
2461 #endif
2462     }
2463 
2464     /* Create lens which is required for MatCreate... */
2465     for (i=0,j=0; i<ismax; i++) j += nrow[i];
2466     ierr = PetscMalloc1(ismax,&lens);CHKERRQ(ierr);
2467 
2468     if (ismax) {
2469       ierr = PetscCalloc1(j,&lens[0]);CHKERRQ(ierr);
2470     }
2471     for (i=1; i<ismax; i++) lens[i] = lens[i-1] + nrow[i-1];
2472 
2473     /* Update lens from local data */
2474     for (i=0; i<ismax; i++) {
2475       row2proc_i = row2proc[i];
2476       jmax = nrow[i];
2477       if (!allcolumns[i]) cmap_i = cmap[i];
2478       irow_i = irow[i];
2479       lens_i = lens[i];
2480       for (j=0; j<jmax; j++) {
2481         row = irow_i[j];
2482         proc = row2proc_i[j];
2483         if (proc == rank) {
2484           ierr = MatGetRow_MPIAIJ(C,row,&ncols,&cols,0);CHKERRQ(ierr);
2485           if (!allcolumns[i]) {
2486             for (k=0; k<ncols; k++) {
2487 #if defined(PETSC_USE_CTABLE)
2488               ierr = PetscTableFind(cmap_i,cols[k]+1,&tcol);CHKERRQ(ierr);
2489 #else
2490               tcol = cmap_i[cols[k]];
2491 #endif
2492               if (tcol) lens_i[j]++;
2493             }
2494           } else { /* allcolumns */
2495             lens_i[j] = ncols;
2496           }
2497           ierr = MatRestoreRow_MPIAIJ(C,row,&ncols,&cols,0);CHKERRQ(ierr);
2498         }
2499       }
2500     }
2501 
2502     /* Create row map: global row of C -> local row of submatrices */
2503 #if defined(PETSC_USE_CTABLE)
2504     for (i=0; i<ismax; i++) {
2505       ierr   = PetscTableCreate(nrow[i]+1,C->rmap->N+1,&rmap[i]);CHKERRQ(ierr);
2506       irow_i = irow[i];
2507       jmax   = nrow[i];
2508       for (j=0; j<jmax; j++) {
2509       ierr = PetscTableAdd(rmap[i],irow_i[j]+1,j+1,INSERT_VALUES);CHKERRQ(ierr);
2510       }
2511     }
2512 #else
2513     for (i=0; i<ismax; i++) {
2514       ierr   = PetscCalloc1(C->rmap->N,&rmap[i]);CHKERRQ(ierr);
2515       rmap_i = rmap[i];
2516       irow_i = irow[i];
2517       jmax   = nrow[i];
2518       for (j=0; j<jmax; j++) {
2519         rmap_i[irow_i[j]] = j;
2520       }
2521     }
2522 #endif
2523 
2524     /* Update lens from offproc data */
2525     {
2526       PetscInt *rbuf2_i,*rbuf3_i,*sbuf1_i;
2527 
2528       ierr    = MPI_Waitall(nrqs,r_waits3,r_status3);CHKERRQ(ierr);
2529       for (tmp2=0; tmp2<nrqs; tmp2++) {
2530         sbuf1_i = sbuf1[pa[tmp2]];
2531         jmax    = sbuf1_i[0];
2532         ct1     = 2*jmax+1;
2533         ct2     = 0;
2534         rbuf2_i = rbuf2[tmp2];
2535         rbuf3_i = rbuf3[tmp2];
2536         for (j=1; j<=jmax; j++) {
2537           is_no  = sbuf1_i[2*j-1];
2538           max1   = sbuf1_i[2*j];
2539           lens_i = lens[is_no];
2540           if (!allcolumns[is_no]) cmap_i = cmap[is_no];
2541           rmap_i = rmap[is_no];
2542           for (k=0; k<max1; k++,ct1++) {
2543 #if defined(PETSC_USE_CTABLE)
2544             ierr = PetscTableFind(rmap_i,sbuf1_i[ct1]+1,&row);CHKERRQ(ierr);
2545             row--;
2546             if (row < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"row not found in table");
2547 #else
2548             row = rmap_i[sbuf1_i[ct1]]; /* the val in the new matrix to be */
2549 #endif
2550             max2 = rbuf2_i[ct1];
2551             for (l=0; l<max2; l++,ct2++) {
2552               if (!allcolumns[is_no]) {
2553 #if defined(PETSC_USE_CTABLE)
2554                 ierr = PetscTableFind(cmap_i,rbuf3_i[ct2]+1,&tcol);CHKERRQ(ierr);
2555 #else
2556                 tcol = cmap_i[rbuf3_i[ct2]];
2557 #endif
2558                 if (tcol) lens_i[row]++;
2559               } else { /* allcolumns */
2560                 lens_i[row]++; /* lens_i[row] += max2 ? */
2561               }
2562             }
2563           }
2564         }
2565       }
2566     }
2567     ierr = PetscFree(r_waits3);CHKERRQ(ierr);
2568     if (nrqr) {ierr = MPI_Waitall(nrqr,s_waits3,s_status3);CHKERRQ(ierr);}
2569     ierr = PetscFree2(r_status3,s_status3);CHKERRQ(ierr);
2570     ierr = PetscFree(s_waits3);CHKERRQ(ierr);
2571 
2572     /* Create the submatrices */
2573     for (i=0; i<ismax; i++) {
2574       PetscInt    rbs,cbs;
2575 
2576       ierr = ISGetBlockSize(isrow[i],&rbs);CHKERRQ(ierr);
2577       ierr = ISGetBlockSize(iscol[i],&cbs);CHKERRQ(ierr);
2578 
2579       ierr = MatCreate(PETSC_COMM_SELF,submats+i);CHKERRQ(ierr);
2580       ierr = MatSetSizes(submats[i],nrow[i],ncol[i],PETSC_DETERMINE,PETSC_DETERMINE);CHKERRQ(ierr);
2581 
2582       ierr = MatSetBlockSizes(submats[i],rbs,cbs);CHKERRQ(ierr);
2583       ierr = MatSetType(submats[i],((PetscObject)A)->type_name);CHKERRQ(ierr);
2584       ierr = MatSeqAIJSetPreallocation(submats[i],0,lens[i]);CHKERRQ(ierr);
2585 
2586       /* create struct Mat_SubMat and attached it to submat */
2587       ierr = PetscNew(&smat_i);CHKERRQ(ierr);
2588       subc = (Mat_SeqAIJ*)submats[i]->data;
2589       subc->submatis1 = smat_i;
2590       smats[i]        = smat_i;
2591 
2592       smat_i->destroy          = submats[i]->ops->destroy;
2593       submats[i]->ops->destroy = MatDestroy_MPIAIJ_MatGetSubmatrices;
2594       submats[i]->factortype   = C->factortype;
2595 
2596       smat_i->id          = i;
2597       smat_i->nrqs        = nrqs;
2598       smat_i->nrqr        = nrqr;
2599       smat_i->rbuf1       = rbuf1;
2600       smat_i->rbuf2       = rbuf2;
2601       smat_i->rbuf3       = rbuf3;
2602       smat_i->sbuf2       = sbuf2;
2603       smat_i->req_source2 = req_source2;
2604 
2605       smat_i->sbuf1       = sbuf1;
2606       smat_i->ptr         = ptr;
2607       smat_i->tmp         = tmp;
2608       smat_i->ctr         = ctr;
2609 
2610       smat_i->pa           = pa;
2611       smat_i->req_size     = req_size;
2612       smat_i->req_source1  = req_source1;
2613 
2614       smat_i->allcolumns  = allcolumns[i];
2615       smat_i->singleis    = PETSC_FALSE;
2616       smat_i->row2proc    = row2proc[i];
2617       smat_i->rmap        = rmap[i];
2618       smat_i->cmap        = cmap[i];
2619     }
2620 
2621     if (ismax) {ierr = PetscFree(lens[0]);CHKERRQ(ierr);}
2622     ierr = PetscFree(lens);CHKERRQ(ierr);
2623     ierr = PetscFree(sbuf_aj[0]);CHKERRQ(ierr);
2624     ierr = PetscFree(sbuf_aj);CHKERRQ(ierr);
2625 
2626   } /* endof scall == MAT_INITIAL_MATRIX */
2627 
2628   /* Post recv matrix values */
2629   ierr = PetscObjectGetNewTag((PetscObject)C,&tag4);CHKERRQ(ierr);
2630   ierr = PetscMalloc1(nrqs+1,&rbuf4);CHKERRQ(ierr);
2631   ierr = PetscMalloc1(nrqs+1,&r_waits4);CHKERRQ(ierr);
2632   ierr = PetscMalloc1(nrqs+1,&r_status4);CHKERRQ(ierr);
2633   ierr = PetscMalloc1(nrqr+1,&s_status4);CHKERRQ(ierr);
2634   for (i=0; i<nrqs; ++i) {
2635     ierr = PetscMalloc1(rbuf2[i][0]+1,&rbuf4[i]);CHKERRQ(ierr);
2636     ierr = MPI_Irecv(rbuf4[i],rbuf2[i][0],MPIU_SCALAR,req_source2[i],tag4,comm,r_waits4+i);CHKERRQ(ierr);
2637   }
2638 
2639   /* Allocate sending buffers for a->a, and send them off */
2640   ierr = PetscMalloc1(nrqr+1,&sbuf_aa);CHKERRQ(ierr);
2641   for (i=0,j=0; i<nrqr; i++) j += req_size[i];
2642   ierr = PetscMalloc1(j+1,&sbuf_aa[0]);CHKERRQ(ierr);
2643   for (i=1; i<nrqr; i++) sbuf_aa[i] = sbuf_aa[i-1] + req_size[i-1];
2644 
2645   ierr = PetscMalloc1(nrqr+1,&s_waits4);CHKERRQ(ierr);
2646   {
2647     PetscInt    nzA,nzB,*a_i = a->i,*b_i = b->i, *cworkB,lwrite;
2648     PetscInt    cstart = C->cmap->rstart,rstart = C->rmap->rstart,*bmap = c->garray;
2649     PetscInt    cend   = C->cmap->rend;
2650     PetscInt    *b_j   = b->j;
2651     PetscScalar *vworkA,*vworkB,*a_a = a->a,*b_a = b->a;
2652 
2653     for (i=0; i<nrqr; i++) {
2654       rbuf1_i   = rbuf1[i];
2655       sbuf_aa_i = sbuf_aa[i];
2656       ct1       = 2*rbuf1_i[0]+1;
2657       ct2       = 0;
2658       for (j=1,max1=rbuf1_i[0]; j<=max1; j++) {
2659         kmax = rbuf1_i[2*j];
2660         for (k=0; k<kmax; k++,ct1++) {
2661           row    = rbuf1_i[ct1] - rstart;
2662           nzA    = a_i[row+1] - a_i[row];     nzB = b_i[row+1] - b_i[row];
2663           ncols  = nzA + nzB;
2664           cworkB = b_j + b_i[row];
2665           vworkA = a_a + a_i[row];
2666           vworkB = b_a + b_i[row];
2667 
2668           /* load the column values for this row into vals*/
2669           vals = sbuf_aa_i+ct2;
2670 
2671           lwrite = 0;
2672           for (l=0; l<nzB; l++) {
2673             if ((bmap[cworkB[l]]) < cstart) vals[lwrite++] = vworkB[l];
2674           }
2675           for (l=0; l<nzA; l++) vals[lwrite++] = vworkA[l];
2676           for (l=0; l<nzB; l++) {
2677             if ((bmap[cworkB[l]]) >= cend) vals[lwrite++] = vworkB[l];
2678           }
2679 
2680           ct2 += ncols;
2681         }
2682       }
2683       ierr = MPI_Isend(sbuf_aa_i,req_size[i],MPIU_SCALAR,req_source1[i],tag4,comm,s_waits4+i);CHKERRQ(ierr);
2684     }
2685   }
2686 
2687   if (!ismax) {
2688     ierr = PetscFree(rbuf1[0]);CHKERRQ(ierr);
2689     ierr = PetscFree(rbuf1);CHKERRQ(ierr);
2690   }
2691 
2692   /* Assemble the matrices */
2693   /* First assemble the local rows */
2694   for (i=0; i<ismax; i++) {
2695     row2proc_i = row2proc[i];
2696     subc      = (Mat_SeqAIJ*)submats[i]->data;
2697     imat_ilen = subc->ilen;
2698     imat_j    = subc->j;
2699     imat_i    = subc->i;
2700     imat_a    = subc->a;
2701 
2702     if (!allcolumns[i]) cmap_i = cmap[i];
2703     rmap_i = rmap[i];
2704     irow_i = irow[i];
2705     jmax   = nrow[i];
2706     for (j=0; j<jmax; j++) {
2707       row  = irow_i[j];
2708       proc = row2proc_i[j];
2709       if (proc == rank) {
2710         old_row = row;
2711 #if defined(PETSC_USE_CTABLE)
2712         ierr = PetscTableFind(rmap_i,row+1,&row);CHKERRQ(ierr);
2713         row--;
2714 #else
2715         row = rmap_i[row];
2716 #endif
2717         ilen_row = imat_ilen[row];
2718         ierr     = MatGetRow_MPIAIJ(C,old_row,&ncols,&cols,&vals);CHKERRQ(ierr);
2719         mat_i    = imat_i[row];
2720         mat_a    = imat_a + mat_i;
2721         mat_j    = imat_j + mat_i;
2722         if (!allcolumns[i]) {
2723           for (k=0; k<ncols; k++) {
2724 #if defined(PETSC_USE_CTABLE)
2725             ierr = PetscTableFind(cmap_i,cols[k]+1,&tcol);CHKERRQ(ierr);
2726 #else
2727             tcol = cmap_i[cols[k]];
2728 #endif
2729             if (tcol) {
2730               *mat_j++ = tcol - 1;
2731               *mat_a++ = vals[k];
2732               ilen_row++;
2733             }
2734           }
2735         } else { /* allcolumns */
2736           for (k=0; k<ncols; k++) {
2737             *mat_j++ = cols[k];  /* global col index! */
2738             *mat_a++ = vals[k];
2739             ilen_row++;
2740           }
2741         }
2742         ierr = MatRestoreRow_MPIAIJ(C,old_row,&ncols,&cols,&vals);CHKERRQ(ierr);
2743 
2744         imat_ilen[row] = ilen_row;
2745       }
2746     }
2747   }
2748 
2749   /* Now assemble the off proc rows */
2750   ierr    = MPI_Waitall(nrqs,r_waits4,r_status4);CHKERRQ(ierr);
2751   for (tmp2=0; tmp2<nrqs; tmp2++) {
2752     sbuf1_i = sbuf1[pa[tmp2]];
2753     jmax    = sbuf1_i[0];
2754     ct1     = 2*jmax + 1;
2755     ct2     = 0;
2756     rbuf2_i = rbuf2[tmp2];
2757     rbuf3_i = rbuf3[tmp2];
2758     rbuf4_i = rbuf4[tmp2];
2759     for (j=1; j<=jmax; j++) {
2760       is_no     = sbuf1_i[2*j-1];
2761       rmap_i    = rmap[is_no];
2762       if (!allcolumns[is_no]) cmap_i = cmap[is_no];
2763       subc      = (Mat_SeqAIJ*)submats[is_no]->data;
2764       imat_ilen = subc->ilen;
2765       imat_j    = subc->j;
2766       imat_i    = subc->i;
2767       imat_a    = subc->a;
2768       max1      = sbuf1_i[2*j];
2769       for (k=0; k<max1; k++,ct1++) {
2770         row = sbuf1_i[ct1];
2771 #if defined(PETSC_USE_CTABLE)
2772         ierr = PetscTableFind(rmap_i,row+1,&row);CHKERRQ(ierr);
2773         row--;
2774 #else
2775         row = rmap_i[row];
2776 #endif
2777         ilen  = imat_ilen[row];
2778         mat_i = imat_i[row];
2779         mat_a = imat_a + mat_i;
2780         mat_j = imat_j + mat_i;
2781         max2  = rbuf2_i[ct1];
2782         if (!allcolumns[is_no]) {
2783           for (l=0; l<max2; l++,ct2++) {
2784 #if defined(PETSC_USE_CTABLE)
2785             ierr = PetscTableFind(cmap_i,rbuf3_i[ct2]+1,&tcol);CHKERRQ(ierr);
2786 #else
2787             tcol = cmap_i[rbuf3_i[ct2]];
2788 #endif
2789             if (tcol) {
2790               *mat_j++ = tcol - 1;
2791               *mat_a++ = rbuf4_i[ct2];
2792               ilen++;
2793             }
2794           }
2795         } else { /* allcolumns */
2796           for (l=0; l<max2; l++,ct2++) {
2797             *mat_j++ = rbuf3_i[ct2]; /* same global column index of C */
2798             *mat_a++ = rbuf4_i[ct2];
2799             ilen++;
2800           }
2801         }
2802         imat_ilen[row] = ilen;
2803       }
2804     }
2805   }
2806 
2807   if (!iscsorted) { /* sort column indices of the rows */
2808     for (i=0; i<ismax; i++) {
2809       subc       = (Mat_SeqAIJ*)submats[i]->data;
2810       imat_j    = subc->j;
2811       imat_i    = subc->i;
2812       imat_a    = subc->a;
2813       imat_ilen = subc->ilen;
2814 
2815       if (allcolumns[i]) continue;
2816       jmax = nrow[i];
2817       for (j=0; j<jmax; j++) {
2818         PetscInt ilen;
2819 
2820         mat_i = imat_i[j];
2821         mat_a = imat_a + mat_i;
2822         mat_j = imat_j + mat_i;
2823         ilen  = imat_ilen[j];
2824         ierr  = PetscSortIntWithScalarArray(ilen,mat_j,mat_a);CHKERRQ(ierr);
2825       }
2826     }
2827   }
2828 
2829   ierr = PetscFree(r_status4);CHKERRQ(ierr);
2830   ierr = PetscFree(r_waits4);CHKERRQ(ierr);
2831   if (nrqr) {ierr = MPI_Waitall(nrqr,s_waits4,s_status4);CHKERRQ(ierr);}
2832   ierr = PetscFree(s_waits4);CHKERRQ(ierr);
2833   ierr = PetscFree(s_status4);CHKERRQ(ierr);
2834 
2835   /* Restore the indices */
2836   for (i=0; i<ismax; i++) {
2837     ierr = ISRestoreIndices(isrow[i],irow+i);CHKERRQ(ierr);
2838     if (!allcolumns[i]) {
2839       ierr = ISRestoreIndices(iscol[i],icol+i);CHKERRQ(ierr);
2840     }
2841   }
2842 
2843   for (i=0; i<ismax; i++) {
2844     ierr = MatAssemblyBegin(submats[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
2845     ierr = MatAssemblyEnd(submats[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
2846   }
2847 
2848   /* Destroy allocated memory */
2849   if (!ismax) {
2850     ierr = PetscFree(pa);CHKERRQ(ierr);
2851 
2852     ierr = PetscFree4(sbuf1,ptr,tmp,ctr);CHKERRQ(ierr);
2853     for (i=0; i<nrqr; ++i) {
2854       ierr = PetscFree(sbuf2[i]);CHKERRQ(ierr);
2855     }
2856     for (i=0; i<nrqs; ++i) {
2857       ierr = PetscFree(rbuf3[i]);CHKERRQ(ierr);
2858     }
2859 
2860     ierr = PetscFree3(sbuf2,req_size,req_source1);CHKERRQ(ierr);
2861     ierr = PetscFree3(req_source2,rbuf2,rbuf3);CHKERRQ(ierr);
2862   }
2863 
2864   ierr = PetscFree(sbuf_aa[0]);CHKERRQ(ierr);
2865   ierr = PetscFree(sbuf_aa);CHKERRQ(ierr);
2866   ierr = PetscFree5(irow,icol,nrow,ncol,issorted);CHKERRQ(ierr);
2867 
2868   for (i=0; i<nrqs; ++i) {
2869     ierr = PetscFree(rbuf4[i]);CHKERRQ(ierr);
2870   }
2871   ierr = PetscFree(rbuf4);CHKERRQ(ierr);
2872 
2873   ierr = PetscFree5(smats,row2proc,cmap,rmap,allcolumns);CHKERRQ(ierr);
2874   PetscFunctionReturn(0);
2875 }
2876 
2877 /*
2878  Permute A & B into C's *local* index space using rowemb,dcolemb for A and rowemb,ocolemb for B.
2879  Embeddings are supposed to be injections and the above implies that the range of rowemb is a subset
2880  of [0,m), dcolemb is in [0,n) and ocolemb is in [N-n).
2881  If pattern == DIFFERENT_NONZERO_PATTERN, C is preallocated according to A&B.
2882  After that B's columns are mapped into C's global column space, so that C is in the "disassembled"
2883  state, and needs to be "assembled" later by compressing B's column space.
2884 
2885  This function may be called in lieu of preallocation, so C should not be expected to be preallocated.
2886  Following this call, C->A & C->B have been created, even if empty.
2887  */
2888 PetscErrorCode MatSetSeqMats_MPIAIJ(Mat C,IS rowemb,IS dcolemb,IS ocolemb,MatStructure pattern,Mat A,Mat B)
2889 {
2890   /* If making this function public, change the error returned in this function away from _PLIB. */
2891   PetscErrorCode ierr;
2892   Mat_MPIAIJ     *aij;
2893   Mat_SeqAIJ     *Baij;
2894   PetscBool      seqaij,Bdisassembled;
2895   PetscInt       m,n,*nz,i,j,ngcol,col,rstart,rend,shift,count;
2896   PetscScalar    v;
2897   const PetscInt *rowindices,*colindices;
2898 
2899   PetscFunctionBegin;
2900   /* Check to make sure the component matrices (and embeddings) are compatible with C. */
2901   if (A) {
2902     ierr = PetscObjectTypeCompare((PetscObject)A,MATSEQAIJ,&seqaij);CHKERRQ(ierr);
2903     if (!seqaij) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Diagonal matrix is of wrong type");
2904     if (rowemb) {
2905       ierr = ISGetLocalSize(rowemb,&m);CHKERRQ(ierr);
2906       if (m != A->rmap->n) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Row IS of size %D is incompatible with diag matrix row size %D",m,A->rmap->n);
2907     } else {
2908       if (C->rmap->n != A->rmap->n) {
2909 	SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Diag seq matrix is row-incompatible with the MPIAIJ matrix");
2910       }
2911     }
2912     if (dcolemb) {
2913       ierr = ISGetLocalSize(dcolemb,&n);CHKERRQ(ierr);
2914       if (n != A->cmap->n) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Diag col IS of size %D is incompatible with diag matrix col size %D",n,A->cmap->n);
2915     } else {
2916       if (C->cmap->n != A->cmap->n) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Diag seq matrix is col-incompatible with the MPIAIJ matrix");
2917     }
2918   }
2919   if (B) {
2920     ierr = PetscObjectTypeCompare((PetscObject)B,MATSEQAIJ,&seqaij);CHKERRQ(ierr);
2921     if (!seqaij) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Off-diagonal matrix is of wrong type");
2922     if (rowemb) {
2923       ierr = ISGetLocalSize(rowemb,&m);CHKERRQ(ierr);
2924       if (m != B->rmap->n) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Row IS of size %D is incompatible with off-diag matrix row size %D",m,A->rmap->n);
2925     } else {
2926       if (C->rmap->n != B->rmap->n) {
2927 	SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Off-diag seq matrix is row-incompatible with the MPIAIJ matrix");
2928       }
2929     }
2930     if (ocolemb) {
2931       ierr = ISGetLocalSize(ocolemb,&n);CHKERRQ(ierr);
2932       if (n != B->cmap->n) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Off-diag col IS of size %D is incompatible with off-diag matrix col size %D",n,B->cmap->n);
2933     } else {
2934       if (C->cmap->N - C->cmap->n != B->cmap->n) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Off-diag seq matrix is col-incompatible with the MPIAIJ matrix");
2935     }
2936   }
2937 
2938   aij    = (Mat_MPIAIJ*)(C->data);
2939   if (!aij->A) {
2940     /* Mimic parts of MatMPIAIJSetPreallocation() */
2941     ierr   = MatCreate(PETSC_COMM_SELF,&aij->A);CHKERRQ(ierr);
2942     ierr   = MatSetSizes(aij->A,C->rmap->n,C->cmap->n,C->rmap->n,C->cmap->n);CHKERRQ(ierr);
2943     ierr   = MatSetBlockSizesFromMats(aij->A,C,C);CHKERRQ(ierr);
2944     ierr   = MatSetType(aij->A,MATSEQAIJ);CHKERRQ(ierr);
2945     ierr   = PetscLogObjectParent((PetscObject)C,(PetscObject)aij->A);CHKERRQ(ierr);
2946   }
2947   if (A) {
2948     ierr   = MatSetSeqMat_SeqAIJ(aij->A,rowemb,dcolemb,pattern,A);CHKERRQ(ierr);
2949   } else {
2950     ierr = MatSetUp(aij->A);CHKERRQ(ierr);
2951   }
2952   if (B) { /* Destroy the old matrix or the column map, depending on the sparsity pattern. */
2953     /*
2954       If pattern == DIFFERENT_NONZERO_PATTERN, we reallocate B and
2955       need to "disassemble" B -- convert it to using C's global indices.
2956       To insert the values we take the safer, albeit more expensive, route of MatSetValues().
2957 
2958       If pattern == SUBSET_NONZERO_PATTERN, we do not "disassemble" B and do not reallocate;
2959       we MatZeroValues(B) first, so there may be a bunch of zeros that, perhaps, could be compacted out.
2960 
2961       TODO: Put B's values into aij->B's aij structure in place using the embedding ISs?
2962       At least avoid calling MatSetValues() and the implied searches?
2963     */
2964 
2965     if (B && pattern == DIFFERENT_NONZERO_PATTERN) {
2966 #if defined(PETSC_USE_CTABLE)
2967       ierr = PetscTableDestroy(&aij->colmap);CHKERRQ(ierr);
2968 #else
2969       ierr = PetscFree(aij->colmap);CHKERRQ(ierr);
2970       /* A bit of a HACK: ideally we should deal with case aij->B all in one code block below. */
2971       if (aij->B) {
2972         ierr = PetscLogObjectMemory((PetscObject)C,-aij->B->cmap->n*sizeof(PetscInt));CHKERRQ(ierr);
2973       }
2974 #endif
2975       ngcol = 0;
2976       if (aij->lvec) {
2977 	ierr = VecGetSize(aij->lvec,&ngcol);CHKERRQ(ierr);
2978       }
2979       if (aij->garray) {
2980 	ierr = PetscFree(aij->garray);CHKERRQ(ierr);
2981 	ierr = PetscLogObjectMemory((PetscObject)C,-ngcol*sizeof(PetscInt));CHKERRQ(ierr);
2982       }
2983       ierr = VecDestroy(&aij->lvec);CHKERRQ(ierr);
2984       ierr = VecScatterDestroy(&aij->Mvctx);CHKERRQ(ierr);
2985     }
2986     if (aij->B && B && pattern == DIFFERENT_NONZERO_PATTERN) {
2987       ierr = MatDestroy(&aij->B);CHKERRQ(ierr);
2988     }
2989     if (aij->B && B && pattern == SUBSET_NONZERO_PATTERN) {
2990       ierr = MatZeroEntries(aij->B);CHKERRQ(ierr);
2991     }
2992   }
2993   Bdisassembled = PETSC_FALSE;
2994   if (!aij->B) {
2995     ierr = MatCreate(PETSC_COMM_SELF,&aij->B);CHKERRQ(ierr);
2996     ierr = PetscLogObjectParent((PetscObject)C,(PetscObject)aij->B);CHKERRQ(ierr);
2997     ierr = MatSetSizes(aij->B,C->rmap->n,C->cmap->N,C->rmap->n,C->cmap->N);CHKERRQ(ierr);
2998     ierr = MatSetBlockSizesFromMats(aij->B,B,B);CHKERRQ(ierr);
2999     ierr = MatSetType(aij->B,MATSEQAIJ);CHKERRQ(ierr);
3000     Bdisassembled = PETSC_TRUE;
3001   }
3002   if (B) {
3003     Baij = (Mat_SeqAIJ*)(B->data);
3004     if (pattern == DIFFERENT_NONZERO_PATTERN) {
3005       ierr = PetscMalloc1(B->rmap->n,&nz);CHKERRQ(ierr);
3006       for (i=0; i<B->rmap->n; i++) {
3007 	nz[i] = Baij->i[i+1] - Baij->i[i];
3008       }
3009       ierr = MatSeqAIJSetPreallocation(aij->B,0,nz);CHKERRQ(ierr);
3010       ierr = PetscFree(nz);CHKERRQ(ierr);
3011     }
3012 
3013     ierr  = PetscLayoutGetRange(C->rmap,&rstart,&rend);CHKERRQ(ierr);
3014     shift = rend-rstart;
3015     count = 0;
3016     rowindices = NULL;
3017     colindices = NULL;
3018     if (rowemb) {
3019       ierr = ISGetIndices(rowemb,&rowindices);CHKERRQ(ierr);
3020     }
3021     if (ocolemb) {
3022       ierr = ISGetIndices(ocolemb,&colindices);CHKERRQ(ierr);
3023     }
3024     for (i=0; i<B->rmap->n; i++) {
3025       PetscInt row;
3026       row = i;
3027       if (rowindices) row = rowindices[i];
3028       for (j=Baij->i[i]; j<Baij->i[i+1]; j++) {
3029 	col  = Baij->j[count];
3030 	if (colindices) col = colindices[col];
3031 	if (Bdisassembled && col>=rstart) col += shift;
3032 	v    = Baij->a[count];
3033 	ierr = MatSetValues(aij->B,1,&row,1,&col,&v,INSERT_VALUES);CHKERRQ(ierr);
3034 	++count;
3035       }
3036     }
3037     /* No assembly for aij->B is necessary. */
3038     /* FIXME: set aij->B's nonzerostate correctly. */
3039   } else {
3040     ierr = MatSetUp(aij->B);CHKERRQ(ierr);
3041   }
3042   C->preallocated  = PETSC_TRUE;
3043   C->was_assembled = PETSC_FALSE;
3044   C->assembled     = PETSC_FALSE;
3045    /*
3046       C will need to be assembled so that aij->B can be compressed into local form in MatSetUpMultiply_MPIAIJ().
3047       Furthermore, its nonzerostate will need to be based on that of aij->A's and aij->B's.
3048    */
3049   PetscFunctionReturn(0);
3050 }
3051 
3052 /*
3053   B uses local indices with column indices ranging between 0 and N-n; they  must be interpreted using garray.
3054  */
3055 PetscErrorCode MatGetSeqMats_MPIAIJ(Mat C,Mat *A,Mat *B)
3056 {
3057   Mat_MPIAIJ *aij = (Mat_MPIAIJ*) (C->data);
3058 
3059   PetscFunctionBegin;
3060   PetscValidPointer(A,2);
3061   PetscValidPointer(B,3);
3062   /* FIXME: make sure C is assembled */
3063   *A = aij->A;
3064   *B = aij->B;
3065   /* Note that we don't incref *A and *B, so be careful! */
3066   PetscFunctionReturn(0);
3067 }
3068 
3069 /*
3070   Extract MPI submatrices encoded by pairs of IS that may live on subcomms of C.
3071   NOT SCALABLE due to the use of ISGetNonlocalIS() (see below).
3072 */
3073 PetscErrorCode MatGetSubMatricesMPI_MPIXAIJ(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[],
3074                                                  PetscErrorCode(*getsubmats_seq)(Mat,PetscInt,const IS[],const IS[],MatReuse,Mat**),
3075 					         PetscErrorCode(*getlocalmats)(Mat,Mat*,Mat*),
3076 					         PetscErrorCode(*setseqmat)(Mat,IS,IS,MatStructure,Mat),
3077 					         PetscErrorCode(*setseqmats)(Mat,IS,IS,IS,MatStructure,Mat,Mat))
3078 {
3079   PetscErrorCode ierr;
3080   PetscMPIInt    isize,flag;
3081   PetscInt       i,ii,cismax,ispar;
3082   Mat            *A,*B;
3083   IS             *isrow_p,*iscol_p,*cisrow,*ciscol,*ciscol_p;
3084 
3085   PetscFunctionBegin;
3086   if (!ismax) PetscFunctionReturn(0);
3087 
3088   for (i = 0, cismax = 0; i < ismax; ++i) {
3089     PetscMPIInt isize;
3090     ierr = MPI_Comm_compare(((PetscObject)isrow[i])->comm,((PetscObject)iscol[i])->comm,&flag);CHKERRQ(ierr);
3091     if (flag != MPI_IDENT) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Row and column index sets must have the same communicator");
3092     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm, &isize);CHKERRQ(ierr);
3093     if (isize > 1) ++cismax;
3094   }
3095 
3096   /*
3097      If cismax is zero on all C's ranks, then and only then can we use purely sequential matrix extraction.
3098      ispar counts the number of parallel ISs across C's comm.
3099   */
3100   ierr = MPIU_Allreduce(&cismax,&ispar,1,MPIU_INT,MPI_MAX,PetscObjectComm((PetscObject)C));CHKERRQ(ierr);
3101   if (!ispar) { /* Sequential ISs only across C's comm, so can call the sequential matrix extraction subroutine. */
3102     ierr = (*getsubmats_seq)(C,ismax,isrow,iscol,scall,submat);CHKERRQ(ierr);
3103     PetscFunctionReturn(0);
3104   }
3105 
3106   /* if (ispar) */
3107   /*
3108     Construct the "complements" -- the off-processor indices -- of the iscol ISs for parallel ISs only.
3109     These are used to extract the off-diag portion of the resulting parallel matrix.
3110     The row IS for the off-diag portion is the same as for the diag portion,
3111     so we merely alias (without increfing) the row IS, while skipping those that are sequential.
3112   */
3113   ierr = PetscMalloc2(cismax,&cisrow,cismax,&ciscol);CHKERRQ(ierr);
3114   ierr = PetscMalloc1(cismax,&ciscol_p);CHKERRQ(ierr);
3115   for (i = 0, ii = 0; i < ismax; ++i) {
3116     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm,&isize);CHKERRQ(ierr);
3117     if (isize > 1) {
3118       /*
3119 	 TODO: This is the part that's ***NOT SCALABLE***.
3120 	 To fix this we need to extract just the indices of C's nonzero columns
3121 	 that lie on the intersection of isrow[i] and ciscol[ii] -- the nonlocal
3122 	 part of iscol[i] -- without actually computing ciscol[ii]. This also has
3123 	 to be done without serializing on the IS list, so, most likely, it is best
3124 	 done by rewriting MatGetSubMatrices_MPIAIJ() directly.
3125       */
3126       ierr = ISGetNonlocalIS(iscol[i],&(ciscol[ii]));CHKERRQ(ierr);
3127       /* Now we have to
3128 	 (a) make sure ciscol[ii] is sorted, since, even if the off-proc indices
3129 	     were sorted on each rank, concatenated they might no longer be sorted;
3130 	 (b) Use ISSortPermutation() to construct ciscol_p, the mapping from the
3131 	     indices in the nondecreasing order to the original index positions.
3132 	 If ciscol[ii] is strictly increasing, the permutation IS is NULL.
3133       */
3134       ierr = ISSortPermutation(ciscol[ii],PETSC_FALSE,ciscol_p+ii);CHKERRQ(ierr);
3135       ierr = ISSort(ciscol[ii]);CHKERRQ(ierr);
3136       ++ii;
3137     }
3138   }
3139   ierr = PetscMalloc2(ismax,&isrow_p,ismax,&iscol_p);CHKERRQ(ierr);
3140   for (i = 0, ii = 0; i < ismax; ++i) {
3141     PetscInt       j,issize;
3142     const PetscInt *indices;
3143 
3144     /*
3145        Permute the indices into a nondecreasing order. Reject row and col indices with duplicates.
3146      */
3147     ierr = ISSortPermutation(isrow[i],PETSC_FALSE,isrow_p+i);CHKERRQ(ierr);
3148     ierr = ISSort(isrow[i]);CHKERRQ(ierr);
3149     ierr = ISGetLocalSize(isrow[i],&issize);CHKERRQ(ierr);
3150     ierr = ISGetIndices(isrow[i],&indices);CHKERRQ(ierr);
3151     for (j = 1; j < issize; ++j) {
3152       if (indices[j] == indices[j-1]) {
3153 	SETERRQ4(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONG,"Repeated indices in row IS %D: indices at %D and %D are both %D",i,j-1,j,indices[j]);
3154       }
3155     }
3156     ierr = ISRestoreIndices(isrow[i],&indices);CHKERRQ(ierr);
3157 
3158 
3159     ierr = ISSortPermutation(iscol[i],PETSC_FALSE,iscol_p+i);CHKERRQ(ierr);
3160     ierr = ISSort(iscol[i]);CHKERRQ(ierr);
3161     ierr = ISGetLocalSize(iscol[i],&issize);CHKERRQ(ierr);
3162     ierr = ISGetIndices(iscol[i],&indices);CHKERRQ(ierr);
3163     for (j = 1; j < issize; ++j) {
3164       if (indices[j-1] == indices[j]) {
3165 	SETERRQ4(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONG,"Repeated indices in col IS %D: indices at %D and %D are both %D",i,j-1,j,indices[j]);
3166       }
3167     }
3168     ierr = ISRestoreIndices(iscol[i],&indices);CHKERRQ(ierr);
3169     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm,&isize);CHKERRQ(ierr);
3170     if (isize > 1) {
3171       cisrow[ii] = isrow[i];
3172       ++ii;
3173     }
3174   }
3175   /*
3176     Allocate the necessary arrays to hold the resulting parallel matrices as well as the intermediate
3177     array of sequential matrices underlying the resulting parallel matrices.
3178     Which arrays to allocate is based on the value of MatReuse scall and whether ISs are sorted and/or
3179     contain duplicates.
3180 
3181     There are as many diag matrices as there are original index sets. There are only as many parallel
3182     and off-diag matrices, as there are parallel (comm size > 1) index sets.
3183 
3184     ARRAYS that can hold Seq matrices get allocated in any event -- either here or by getsubmats_seq():
3185     - If the array of MPI matrices already exists and is being reused, we need to allocate the array
3186       and extract the underlying seq matrices into it to serve as placeholders, into which getsubmats_seq
3187       will deposite the extracted diag and off-diag parts. Thus, we allocate the A&B arrays and fill them
3188       with A[i] and B[ii] extracted from the corresponding MPI submat.
3189     - However, if the rows, A's column indices or B's column indices are not sorted, the extracted A[i] & B[ii]
3190       will have a different order from what getsubmats_seq expects.  To handle this case -- indicated
3191       by a nonzero isrow_p[i], iscol_p[i], or ciscol_p[ii] -- we duplicate A[i] --> AA[i], B[ii] --> BB[ii]
3192       (retrieve composed AA[i] or BB[ii]) and reuse them here. AA[i] and BB[ii] are then used to permute its
3193       values into A[i] and B[ii] sitting inside the corresponding submat.
3194     - If no reuse is taking place then getsubmats_seq will allocate the A&B arrays and create the corresponding
3195       A[i], B[ii], AA[i] or BB[ii] matrices.
3196   */
3197   /* Parallel matrix array is allocated here only if no reuse is taking place. If reused, it is passed in by the caller. */
3198   if (scall == MAT_INITIAL_MATRIX) {
3199     ierr = PetscMalloc1(ismax,submat);CHKERRQ(ierr);
3200   }
3201 
3202   /* Now obtain the sequential A and B submatrices separately. */
3203   /* scall=MAT_REUSE_MATRIX is not handled yet, because getsubmats_seq() requires reuse of A and B */
3204   ierr = (*getsubmats_seq)(C,ismax,isrow,iscol,MAT_INITIAL_MATRIX,&A);CHKERRQ(ierr);
3205   ierr = (*getsubmats_seq)(C,cismax,cisrow,ciscol,MAT_INITIAL_MATRIX,&B);CHKERRQ(ierr);
3206 
3207   /*
3208     If scall == MAT_REUSE_MATRIX AND the permutations are NULL, we are done, since the sequential
3209     matrices A & B have been extracted directly into the parallel matrices containing them, or
3210     simply into the sequential matrix identical with the corresponding A (if isize == 1).
3211     Note that in that case colmap doesn't need to be rebuilt, since the matrices are expected
3212     to have the same sparsity pattern.
3213     Otherwise, A and/or B have to be properly embedded into C's index spaces and the correct colmap
3214     must be constructed for C. This is done by setseqmat(s).
3215   */
3216   for (i = 0, ii = 0; i < ismax; ++i) {
3217     /*
3218        TODO: cache ciscol, permutation ISs and maybe cisrow? What about isrow & iscol?
3219        That way we can avoid sorting and computing permutations when reusing.
3220        To this end:
3221         - remove the old cache, if it exists, when extracting submatrices with MAT_INITIAL_MATRIX
3222 	- if caching arrays to hold the ISs, make and compose a container for them so that it can
3223 	  be destroyed upon destruction of C (use PetscContainerUserDestroy() to clear out the contents).
3224     */
3225     MatStructure pattern;
3226     pattern = DIFFERENT_NONZERO_PATTERN;
3227 
3228     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm,&isize);CHKERRQ(ierr);
3229     /* Construct submat[i] from the Seq pieces A (and B, if necessary). */
3230     if (isize > 1) {
3231       if (scall == MAT_INITIAL_MATRIX) {
3232 	ierr = MatCreate(((PetscObject)isrow[i])->comm,(*submat)+i);CHKERRQ(ierr);
3233 	ierr = MatSetSizes((*submat)[i],A[i]->rmap->n,A[i]->cmap->n,PETSC_DETERMINE,PETSC_DETERMINE);CHKERRQ(ierr);
3234 	ierr = MatSetType((*submat)[i],MATMPIAIJ);CHKERRQ(ierr);
3235 	ierr = PetscLayoutSetUp((*submat)[i]->rmap);CHKERRQ(ierr);
3236 	ierr = PetscLayoutSetUp((*submat)[i]->cmap);CHKERRQ(ierr);
3237       }
3238       /*
3239 	For each parallel isrow[i], insert the extracted sequential matrices into the parallel matrix.
3240       */
3241       {
3242 	Mat AA,BB;
3243         AA = A[i];
3244         BB = B[ii];
3245 	if (AA || BB) {
3246 	  ierr = setseqmats((*submat)[i],isrow_p[i],iscol_p[i],ciscol_p[ii],pattern,AA,BB);CHKERRQ(ierr);
3247 	  ierr = MatAssemblyBegin((*submat)[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
3248 	  ierr = MatAssemblyEnd((*submat)[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
3249 	}
3250 
3251         ierr = MatDestroy(&AA);CHKERRQ(ierr);
3252         ierr = MatDestroy(&BB);CHKERRQ(ierr);
3253       }
3254       ierr = ISDestroy(ciscol+ii);CHKERRQ(ierr);
3255       ierr = ISDestroy(ciscol_p+ii);CHKERRQ(ierr);
3256       ++ii;
3257     } else { /* if (isize == 1) */
3258       if (scall == MAT_REUSE_MATRIX) {
3259         ierr = MatDestroy(&(*submat)[i]);CHKERRQ(ierr);
3260       }
3261       if (isrow_p[i] || iscol_p[i]) {
3262         ierr = MatDuplicate(A[i],MAT_DO_NOT_COPY_VALUES,(*submat)+i);CHKERRQ(ierr);
3263         ierr = setseqmat((*submat)[i],isrow_p[i],iscol_p[i],pattern,A[i]);CHKERRQ(ierr);
3264 	/* Otherwise A is extracted straight into (*submats)[i]. */
3265 	/* TODO: Compose A[i] on (*submat([i] for future use, if ((isrow_p[i] || iscol_p[i]) && MAT_INITIAL_MATRIX). */
3266 	ierr = MatDestroy(A+i);CHKERRQ(ierr);
3267       } else (*submat)[i] = A[i];
3268     }
3269     ierr = ISDestroy(&isrow_p[i]);CHKERRQ(ierr);
3270     ierr = ISDestroy(&iscol_p[i]);CHKERRQ(ierr);
3271   }
3272   ierr = PetscFree2(cisrow,ciscol);CHKERRQ(ierr);
3273   ierr = PetscFree2(isrow_p,iscol_p);CHKERRQ(ierr);
3274   ierr = PetscFree(ciscol_p);CHKERRQ(ierr);
3275   ierr = PetscFree(A);CHKERRQ(ierr);
3276   ierr = PetscFree(B);CHKERRQ(ierr);
3277   PetscFunctionReturn(0);
3278 }
3279 
3280 PetscErrorCode MatGetSubMatricesMPI_MPIAIJ(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[])
3281 {
3282   PetscErrorCode ierr;
3283 
3284   PetscFunctionBegin;
3285   ierr = MatGetSubMatricesMPI_MPIXAIJ(C,ismax,isrow,iscol,scall,submat,MatGetSubMatrices_MPIAIJ,MatGetSeqMats_MPIAIJ,MatSetSeqMat_SeqAIJ,MatSetSeqMats_MPIAIJ);CHKERRQ(ierr);
3286   PetscFunctionReturn(0);
3287 }
3288