xref: /petsc/src/mat/impls/aij/mpi/mpiov.c (revision a1e6e1df11c5d48eb2715319082945d8775b956c)
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->row2proc    = row2proc;
1703     smatis1->rmap        = rmap;
1704     smatis1->cmap        = cmap;
1705 #if defined(PETSC_USE_CTABLE)
1706     smatis1->rmap_loc    = rmap_loc;
1707     smatis1->cmap_loc    = cmap_loc;
1708 #endif
1709 
1710     smatis1->destroy     = submat->ops->destroy;
1711     submat->ops->destroy = MatDestroy_MPIAIJ_MatGetSubmatrices;
1712     submat->factortype   = C->factortype;
1713 
1714     /* compute rmax */
1715     rmax = 0;
1716     for (i=0; i<nrow; i++) rmax = PetscMax(rmax,lens[i]);
1717 
1718   } else { /* scall == MAT_REUSE_MATRIX */
1719     submat = submats[0];
1720     if (submat->rmap->n != nrow || submat->cmap->n != ncol) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Cannot reuse matrix. wrong size");
1721 
1722     subc    = (Mat_SeqAIJ*)submat->data;
1723     rmax    = subc->rmax;
1724     smatis1 = subc->submatis1;
1725     nrqs        = smatis1->nrqs;
1726     nrqr        = smatis1->nrqr;
1727     rbuf1       = smatis1->rbuf1;
1728     rbuf2       = smatis1->rbuf2;
1729     rbuf3       = smatis1->rbuf3;
1730     req_source2 = smatis1->req_source2;
1731 
1732     sbuf1     = smatis1->sbuf1;
1733     sbuf2     = smatis1->sbuf2;
1734     ptr       = smatis1->ptr;
1735     tmp       = smatis1->tmp;
1736     ctr       = smatis1->ctr;
1737 
1738     pa         = smatis1->pa;
1739     req_size   = smatis1->req_size;
1740     req_source1 = smatis1->req_source1;
1741 
1742     allcolumns = smatis1->allcolumns;
1743     row2proc   = smatis1->row2proc;
1744     rmap       = smatis1->rmap;
1745     cmap       = smatis1->cmap;
1746 #if defined(PETSC_USE_CTABLE)
1747     rmap_loc   = smatis1->rmap_loc;
1748     cmap_loc   = smatis1->cmap_loc;
1749 #endif
1750   }
1751 
1752   /* Post recv matrix values */
1753   ierr = PetscMalloc3(nrqs+1,&rbuf4, rmax,&subcols, rmax,&subvals);CHKERRQ(ierr);
1754   ierr = PetscMalloc4(nrqs+1,&r_waits4,nrqr+1,&s_waits4,nrqs+1,&r_status4,nrqr+1,&s_status4);CHKERRQ(ierr);
1755   ierr = PetscObjectGetNewTag((PetscObject)C,&tag4);CHKERRQ(ierr);
1756   for (i=0; i<nrqs; ++i) {
1757     ierr = PetscMalloc1(rbuf2[i][0]+1,&rbuf4[i]);CHKERRQ(ierr);
1758     ierr = MPI_Irecv(rbuf4[i],rbuf2[i][0],MPIU_SCALAR,req_source2[i],tag4,comm,r_waits4+i);CHKERRQ(ierr);
1759   }
1760 
1761   /* Allocate sending buffers for a->a, and send them off */
1762   ierr = PetscMalloc1(nrqr+1,&sbuf_aa);CHKERRQ(ierr);
1763   for (i=0,j=0; i<nrqr; i++) j += req_size[i];
1764   ierr = PetscMalloc1(j+1,&sbuf_aa[0]);CHKERRQ(ierr);
1765   for (i=1; i<nrqr; i++) sbuf_aa[i] = sbuf_aa[i-1] + req_size[i-1];
1766 
1767   for (i=0; i<nrqr; i++) {
1768     rbuf1_i   = rbuf1[i];
1769     sbuf_aa_i = sbuf_aa[i];
1770     ct1       = 2*rbuf1_i[0]+1;
1771     ct2       = 0;
1772     /* max1=rbuf1_i[0]; if (max1 != 1) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"max1 !=1"); */
1773 
1774     kmax = rbuf1_i[2];
1775     for (k=0; k<kmax; k++,ct1++) {
1776       row = rbuf1_i[ct1] - rstart;
1777       nzA = ai[row+1] - ai[row];
1778       nzB = bi[row+1] - bi[row];
1779       ncols  = nzA + nzB;
1780       cworkB = bj + bi[row];
1781       vworkA = a_a + ai[row];
1782       vworkB = b_a + bi[row];
1783 
1784       /* load the column values for this row into vals*/
1785       vals = sbuf_aa_i + ct2;
1786 
1787       lwrite = 0;
1788       for (l=0; l<nzB; l++) {
1789         if ((bmap[cworkB[l]]) < cstart) vals[lwrite++] = vworkB[l];
1790       }
1791       for (l=0; l<nzA; l++) vals[lwrite++] = vworkA[l];
1792       for (l=0; l<nzB; l++) {
1793         if ((bmap[cworkB[l]]) >= cend) vals[lwrite++] = vworkB[l];
1794       }
1795 
1796       ct2 += ncols;
1797     }
1798     ierr = MPI_Isend(sbuf_aa_i,req_size[i],MPIU_SCALAR,req_source1[i],tag4,comm,s_waits4+i);CHKERRQ(ierr);
1799   }
1800 
1801   /* Assemble submat */
1802   /* First assemble the local rows */
1803   for (j=0; j<nrow; j++) {
1804     row  = irow[j];
1805     proc = row2proc[j];
1806     if (proc == rank) {
1807       Crow = row - rstart;  /* local row index of C */
1808 #if defined(PETSC_USE_CTABLE)
1809       row = rmap_loc[Crow]; /* row index of submat */
1810 #else
1811       row = rmap[row];
1812 #endif
1813 
1814       if (allcolumns) {
1815         /* diagonal part A = c->A */
1816         ncols = ai[Crow+1] - ai[Crow];
1817         cols  = aj + ai[Crow];
1818         vals  = a->a + ai[Crow];
1819         i     = 0;
1820         for (k=0; k<ncols; k++) {
1821           subcols[i]   = cols[k] + cstart;
1822           subvals[i++] = vals[k];
1823         }
1824 
1825         /* off-diagonal part B = c->B */
1826         ncols = bi[Crow+1] - bi[Crow];
1827         cols  = bj + bi[Crow];
1828         vals  = b->a + bi[Crow];
1829         for (k=0; k<ncols; k++) {
1830           subcols[i]   = bmap[cols[k]];
1831           subvals[i++] = vals[k];
1832         }
1833 
1834         ierr = MatSetValues_SeqAIJ(submat,1,&row,i,subcols,subvals,INSERT_VALUES);CHKERRQ(ierr);
1835 
1836       } else { /* !allcolumns */
1837 #if defined(PETSC_USE_CTABLE)
1838         /* diagonal part A = c->A */
1839         ncols = ai[Crow+1] - ai[Crow];
1840         cols  = aj + ai[Crow];
1841         vals  = a->a + ai[Crow];
1842         i     = 0;
1843         for (k=0; k<ncols; k++) {
1844           tcol = cmap_loc[cols[k]];
1845           if (tcol) {
1846             subcols[i]   = --tcol;
1847             subvals[i++] = vals[k];
1848           }
1849         }
1850 
1851         /* off-diagonal part B = c->B */
1852         ncols = bi[Crow+1] - bi[Crow];
1853         cols  = bj + bi[Crow];
1854         vals  = b->a + bi[Crow];
1855         for (k=0; k<ncols; k++) {
1856           ierr = PetscTableFind(cmap,bmap[cols[k]]+1,&tcol);CHKERRQ(ierr);
1857           if (tcol) {
1858             subcols[i]   = --tcol;
1859             subvals[i++] = vals[k];
1860           }
1861         }
1862 #else
1863         /* diagonal part A = c->A */
1864         ncols = ai[Crow+1] - ai[Crow];
1865         cols  = aj + ai[Crow];
1866         vals  = a->a + ai[Crow];
1867         i     = 0;
1868         for (k=0; k<ncols; k++) {
1869           tcol = cmap[cols[k]+cstart];
1870           if (tcol) {
1871             subcols[i]   = --tcol;
1872             subvals[i++] = vals[k];
1873           }
1874         }
1875 
1876         /* off-diagonal part B = c->B */
1877         ncols = bi[Crow+1] - bi[Crow];
1878         cols  = bj + bi[Crow];
1879         vals  = b->a + bi[Crow];
1880         for (k=0; k<ncols; k++) {
1881           tcol = cmap[bmap[cols[k]]];
1882           if (tcol) {
1883             subcols[i]   = --tcol;
1884             subvals[i++] = vals[k];
1885           }
1886         }
1887 #endif
1888         ierr = MatSetValues_SeqAIJ(submat,1,&row,i,subcols,subvals,INSERT_VALUES);CHKERRQ(ierr);
1889       }
1890     }
1891   }
1892 
1893   /* Now assemble the off-proc rows */
1894   for (i=0; i<nrqs; i++) { /* for each requested message */
1895     /* recv values from other processes */
1896     ierr    = MPI_Waitany(nrqs,r_waits4,&idex,r_status4+i);CHKERRQ(ierr);
1897     proc    = pa[idex];
1898     sbuf1_i = sbuf1[proc];
1899     /* jmax    = sbuf1_i[0]; if (jmax != 1)SETERRQ1(PETSC_COMM_SELF,0,"jmax %d != 1",jmax); */
1900     ct1     = 2 + 1;
1901     ct2     = 0; /* count of received C->j */
1902     ct3     = 0; /* count of received C->j that will be inserted into submat */
1903     rbuf2_i = rbuf2[idex]; /* int** received length of C->j from other processes */
1904     rbuf3_i = rbuf3[idex]; /* int** received C->j from other processes */
1905     rbuf4_i = rbuf4[idex]; /* scalar** received C->a from other processes */
1906 
1907     /* is_no = sbuf1_i[2*j-1]; if (is_no != 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"is_no !=0"); */
1908     max1 = sbuf1_i[2];             /* num of rows */
1909     for (k=0; k<max1; k++,ct1++) { /* for each recved row */
1910       row = sbuf1_i[ct1]; /* row index of submat */
1911       if (!allcolumns) {
1912         idex = 0;
1913         if (scall == MAT_INITIAL_MATRIX) {
1914           nnz  = rbuf2_i[ct1]; /* num of C entries in this row */
1915           for (l=0; l<nnz; l++,ct2++) { /* for each recved column */
1916 #if defined(PETSC_USE_CTABLE)
1917             if (rbuf3_i[ct2] >= cstart && rbuf3_i[ct2] <cend) {
1918               tcol = cmap_loc[rbuf3_i[ct2] - cstart];
1919             } else {
1920               ierr = PetscTableFind(cmap,rbuf3_i[ct2]+1,&tcol);CHKERRQ(ierr);
1921             }
1922 #else
1923             tcol = cmap[rbuf3_i[ct2]];
1924 #endif
1925             if (tcol) {
1926               subcols[idex]   = --tcol;
1927               subvals[idex++] = rbuf4_i[ct2];
1928 
1929               /* We receive an entire column of C, but a subset of it needs to be inserted into submat.
1930                For reuse, we replace received C->j with index that should be inserted to submat */
1931               rbuf3_i[ct3++] = ct2;
1932             }
1933           }
1934           ierr = MatSetValues_SeqAIJ(submat,1,&row,idex,subcols,subvals,INSERT_VALUES);CHKERRQ(ierr);
1935 
1936         } else { /* scall == MAT_REUSE_MATRIX */
1937           submat = submats[0];
1938           subc   = (Mat_SeqAIJ*)submat->data;
1939 
1940           nnz = subc->i[row+1] - subc->i[row]; /* num of submat entries in this row */
1941           for (l=0; l<nnz; l++) {
1942             ct2 = rbuf3_i[ct3++]; /* index of rbuf4_i[] which needs to be inserted into submat */
1943             subvals[idex++] = rbuf4_i[ct2];
1944           }
1945 
1946           bj = subc->j + subc->i[row];
1947           ierr = MatSetValues_SeqAIJ(submat,1,&row,nnz,bj,subvals,INSERT_VALUES);CHKERRQ(ierr);
1948         }
1949       } else { /* allcolumns */
1950         nnz  = rbuf2_i[ct1]; /* num of C entries in this row */
1951         ierr = MatSetValues_SeqAIJ(submat,1,&row,nnz,rbuf3_i+ct2,rbuf4_i+ct2,INSERT_VALUES);CHKERRQ(ierr);
1952         ct2 += nnz;
1953       }
1954     }
1955   }
1956 
1957   /* sending a->a are done */
1958   ierr = MPI_Waitall(nrqr,s_waits4,s_status4);CHKERRQ(ierr);
1959   ierr = PetscFree4(r_waits4,s_waits4,r_status4,s_status4);CHKERRQ(ierr);
1960 
1961   ierr = MatAssemblyBegin(submat,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
1962   ierr = MatAssemblyEnd(submat,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
1963   submats[0] = submat;
1964 
1965   /* Restore the indices */
1966   ierr = ISRestoreIndices(isrow[0],&irow);CHKERRQ(ierr);
1967   if (!allcolumns) {
1968     ierr = ISRestoreIndices(iscol[0],&icol);CHKERRQ(ierr);
1969   }
1970 
1971   /* Destroy allocated memory */
1972   for (i=0; i<nrqs; ++i) {
1973     ierr = PetscFree3(rbuf4[i],subcols,subvals);CHKERRQ(ierr);
1974   }
1975   ierr = PetscFree3(rbuf4,subcols,subvals);CHKERRQ(ierr);
1976   ierr = PetscFree(sbuf_aa[0]);CHKERRQ(ierr);
1977   ierr = PetscFree(sbuf_aa);CHKERRQ(ierr);
1978 
1979   if (scall == MAT_INITIAL_MATRIX) {
1980     ierr = PetscFree(lens);CHKERRQ(ierr);
1981     ierr = PetscFree(sbuf_aj[0]);CHKERRQ(ierr);
1982     ierr = PetscFree(sbuf_aj);CHKERRQ(ierr);
1983   }
1984   PetscFunctionReturn(0);
1985 }
1986 
1987 PetscErrorCode MatGetSubMatrices_MPIAIJ_SingleIS(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[])
1988 {
1989   PetscErrorCode ierr;
1990   PetscInt       ncol;
1991   PetscBool      colflag,allcolumns=PETSC_FALSE;
1992 
1993   PetscFunctionBegin;
1994   /* Allocate memory to hold all the submatrices */
1995   if (scall == MAT_INITIAL_MATRIX) {
1996     ierr = PetscMalloc1(1,submat);CHKERRQ(ierr);
1997   }
1998 
1999   /* Check for special case: each processor gets entire matrix columns */
2000   ierr = ISIdentity(iscol[0],&colflag);CHKERRQ(ierr);
2001   ierr = ISGetLocalSize(iscol[0],&ncol);CHKERRQ(ierr);
2002   if (colflag && ncol == C->cmap->N) allcolumns = PETSC_TRUE;
2003 
2004   ierr = MatGetSubMatrices_MPIAIJ_SingleIS_Local(C,ismax,isrow,iscol,scall,allcolumns,*submat);CHKERRQ(ierr);
2005   PetscFunctionReturn(0);
2006 }
2007 
2008 PetscErrorCode MatGetSubMatrices_MPIAIJ(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[])
2009 {
2010   PetscErrorCode ierr;
2011   PetscInt       nmax,nstages,i,pos,max_no,nrow,ncol,in[2],out[2];
2012   PetscBool      rowflag,colflag,wantallmatrix=PETSC_FALSE;
2013 
2014   PetscFunctionBegin;
2015 #if 0
2016   /* Check for special case: each processor gets entire matrix */
2017   if (C->submat_singleis) { /* flag is set in PCSetUp_ASM() to skip several MPIU_Allreduce() */
2018     ierr = MatGetSubMatrices_MPIAIJ_SingleIS(C,ismax,isrow,iscol,scall,submat);CHKERRQ(ierr);
2019     PetscFunctionReturn(0);
2020   }
2021 #endif
2022 
2023   if (ismax == 1 && C->rmap->N == C->cmap->N) {
2024     ierr = ISIdentity(*isrow,&rowflag);CHKERRQ(ierr);
2025     ierr = ISIdentity(*iscol,&colflag);CHKERRQ(ierr);
2026     ierr = ISGetLocalSize(*isrow,&nrow);CHKERRQ(ierr);
2027     ierr = ISGetLocalSize(*iscol,&ncol);CHKERRQ(ierr);
2028     if (rowflag && colflag && nrow == C->rmap->N && ncol == C->cmap->N) {
2029       wantallmatrix = PETSC_TRUE;
2030 
2031       ierr = PetscOptionsGetBool(((PetscObject)C)->options,((PetscObject)C)->prefix,"-use_fast_submatrix",&wantallmatrix,NULL);CHKERRQ(ierr);
2032     }
2033   }
2034 
2035   /* Determine the number of stages through which submatrices are done
2036      Each stage will extract nmax submatrices.
2037      nmax is determined by the matrix column dimension.
2038      If the original matrix has 20M columns, only one submatrix per stage is allowed, etc.
2039   */
2040   nmax = 20*1000000 / (C->cmap->N * sizeof(PetscInt));
2041   if (!nmax) nmax = 1;
2042   nstages = ismax/nmax + ((ismax % nmax) ? 1 : 0); /* local nstages */
2043 
2044   /* Collect global wantallmatrix and nstages */
2045   in[0] = -1*wantallmatrix;
2046   in[1] = nstages;
2047   ierr = MPIU_Allreduce(in,out,2,MPIU_INT,MPI_MAX,PetscObjectComm((PetscObject)C));CHKERRQ(ierr);
2048   wantallmatrix = (PetscBool)(-out[0]);
2049   nstages       = out[1]; /* Make sure every processor loops through the global nstages */
2050 
2051   if (wantallmatrix) {
2052     ierr = MatGetSubMatrix_MPIAIJ_All(C,MAT_GET_VALUES,scall,submat);CHKERRQ(ierr);
2053     PetscFunctionReturn(0);
2054   }
2055 
2056   /* Allocate memory to hold all the submatrices */
2057   if (scall == MAT_INITIAL_MATRIX) {
2058     ierr = PetscMalloc1(ismax+1,submat);CHKERRQ(ierr);
2059   }
2060 
2061   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");
2062 
2063   for (i=0,pos=0; i<nstages; i++) {
2064     if (pos+nmax <= ismax) max_no = nmax;
2065     else if (pos == ismax) max_no = 0;
2066     else                   max_no = ismax-pos;
2067     ierr = MatGetSubMatrices_MPIAIJ_Local(C,max_no,isrow+pos,iscol+pos,scall,*submat+pos);CHKERRQ(ierr);
2068     pos += max_no;
2069   }
2070   PetscFunctionReturn(0);
2071 }
2072 
2073 /* -------------------------------------------------------------------------*/
2074 PetscErrorCode MatGetSubMatrices_MPIAIJ_Local(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submats)
2075 {
2076   Mat_MPIAIJ     *c = (Mat_MPIAIJ*)C->data;
2077   Mat            A  = c->A;
2078   Mat_SeqAIJ     *a = (Mat_SeqAIJ*)A->data,*b = (Mat_SeqAIJ*)c->B->data,*subc;
2079   const PetscInt **icol,**irow;
2080   PetscInt       *nrow,*ncol,start;
2081   PetscErrorCode ierr;
2082   PetscMPIInt    rank,size,tag0,tag2,tag3,tag4,*w1,*w2,*w3,*w4,nrqr;
2083   PetscInt       **sbuf1,**sbuf2,i,j,k,l,ct1,ct2,**rbuf1,row,proc=-1;
2084   PetscInt       nrqs=0,msz,**ptr=NULL,*req_size=NULL,*ctr=NULL,*pa,*tmp=NULL,tcol;
2085   PetscInt       **rbuf3=NULL,*req_source1=NULL,*req_source2,**sbuf_aj,**rbuf2=NULL,max1,max2;
2086   PetscInt       **lens,is_no,ncols,*cols,mat_i,*mat_j,tmp2,jmax;
2087 #if defined(PETSC_USE_CTABLE)
2088   PetscTable     *cmap,cmap_i=NULL,*rmap,rmap_i;
2089 #else
2090   PetscInt       **cmap,*cmap_i=NULL,**rmap,*rmap_i;
2091 #endif
2092   const PetscInt *irow_i;
2093   PetscInt       ctr_j,*sbuf1_j,*sbuf_aj_i,*rbuf1_i,kmax,*lens_i;
2094   MPI_Request    *s_waits1,*r_waits1,*s_waits2,*r_waits2,*r_waits3;
2095   MPI_Request    *r_waits4,*s_waits3,*s_waits4;
2096   MPI_Status     *r_status1,*r_status2,*s_status1,*s_status3,*s_status2;
2097   MPI_Status     *r_status3,*r_status4,*s_status4;
2098   MPI_Comm       comm;
2099   PetscScalar    **rbuf4,**sbuf_aa,*vals,*mat_a,*sbuf_aa_i;
2100   PetscMPIInt    *onodes1,*olengths1,end;
2101   PetscInt       **row2proc,*row2proc_i;
2102   Mat_SubMat     **smats,*smat_i;
2103   PetscBool      *issorted,*allcolumns;
2104 
2105   PetscFunctionBegin;
2106   ierr = PetscObjectGetComm((PetscObject)C,&comm);CHKERRQ(ierr);
2107   size = c->size;
2108   rank = c->rank;
2109 
2110   ierr = PetscMalloc1(ismax+1,&allcolumns);CHKERRQ(ierr);
2111   //if (scall == MAT_INITIAL_MATRIX) {
2112     PetscBool      colflag;
2113     PetscInt       ncol_i;
2114 
2115     for (i=0; i<ismax; i++) {
2116       ierr = ISIdentity(iscol[i],&colflag);CHKERRQ(ierr);
2117       ierr = ISGetLocalSize(iscol[i],&ncol_i);CHKERRQ(ierr);
2118       if (colflag && ncol_i == C->cmap->N) {
2119         allcolumns[i] = PETSC_TRUE;
2120       } else {
2121         allcolumns[i] = PETSC_FALSE;
2122       }
2123     }
2124 
2125   ierr = PetscMalloc5(ismax,&irow,ismax,&icol,ismax,&nrow,ismax,&ncol,ismax,&issorted);CHKERRQ(ierr);
2126   for (i=0; i<ismax; i++) {
2127     ierr = ISSorted(isrow[i],&issorted[i]);CHKERRQ(ierr);
2128 
2129     ierr = ISGetIndices(isrow[i],&irow[i]);CHKERRQ(ierr);
2130     ierr = ISGetLocalSize(isrow[i],&nrow[i]);CHKERRQ(ierr);
2131     if (allcolumns[i]) {
2132       icol[i] = NULL;
2133       ncol[i] = C->cmap->N;
2134     } else {
2135       ierr = ISGetIndices(iscol[i],&icol[i]);CHKERRQ(ierr);
2136       ierr = ISGetLocalSize(iscol[i],&ncol[i]);CHKERRQ(ierr);
2137     }
2138   }
2139 
2140   ierr = PetscMalloc1(ismax,&smats);CHKERRQ(ierr);
2141   ierr = PetscMalloc1(ismax,&row2proc);CHKERRQ(ierr);
2142   ierr = PetscMalloc2(ismax,&cmap,ismax,&rmap);CHKERRQ(ierr);
2143 
2144   if (scall == MAT_REUSE_MATRIX) {
2145     /* Assumes new rows are same length as the old rows */
2146     for (i=0; i<ismax; i++) {
2147       subc = (Mat_SeqAIJ*)(submats[i]->data);
2148       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");
2149 
2150       /* Initial matrix as if empty */
2151       ierr = PetscMemzero(subc->ilen,submats[i]->rmap->n*sizeof(PetscInt));CHKERRQ(ierr);
2152 
2153       /* Initial matrix as if empty */
2154       submats[i]->factortype = C->factortype;
2155 
2156       smat_i   = subc->submatis1;
2157       smats[i] = smat_i;
2158 
2159       nrqs        = smat_i->nrqs;
2160       nrqr        = smat_i->nrqr;
2161       rbuf1       = smat_i->rbuf1;
2162       rbuf2       = smat_i->rbuf2;
2163       rbuf3       = smat_i->rbuf3;
2164       req_source2 = smat_i->req_source2;
2165 
2166       sbuf1     = smat_i->sbuf1;
2167       sbuf2     = smat_i->sbuf2;
2168       ptr       = smat_i->ptr;
2169       tmp       = smat_i->tmp;
2170       ctr       = smat_i->ctr;
2171 
2172       pa          = smat_i->pa;
2173       req_size    = smat_i->req_size;
2174       req_source1 = smat_i->req_source1;
2175 
2176       allcolumns[i] = smat_i->allcolumns;
2177       row2proc[i]   = smat_i->row2proc;
2178       rmap[i]       = smat_i->rmap;
2179       cmap[i]       = smat_i->cmap;
2180     }
2181   } else { /* scall == MAT_INITIAL_MATRIX */
2182     /* Get some new tags to keep the communication clean */
2183     ierr = PetscObjectGetNewTag((PetscObject)C,&tag2);CHKERRQ(ierr);
2184     ierr = PetscObjectGetNewTag((PetscObject)C,&tag3);CHKERRQ(ierr);
2185 
2186     /* evaluate communication - mesg to who, length of mesg, and buffer space
2187      required. Based on this, buffers are allocated, and data copied into them*/
2188     ierr = PetscCalloc4(size,&w1,size,&w2,size,&w3,size,&w4);CHKERRQ(ierr);   /* mesg size, initialize work vectors */
2189 
2190     for (i=0; i<ismax; i++) {
2191       jmax   = nrow[i];
2192       irow_i = irow[i];
2193 
2194       ierr   = PetscMalloc1(jmax,&row2proc_i);CHKERRQ(ierr);
2195       row2proc[i] = row2proc_i;
2196 
2197       if (issorted[i]) proc = 0;
2198       for (j=0; j<jmax; j++) {
2199         if (!issorted[i]) proc = 0;
2200         row = irow_i[j];
2201         while (row >= C->rmap->range[proc+1]) proc++;
2202         w4[proc]++;
2203         row2proc_i[j] = proc; /* map row index to proc */
2204       }
2205       for (j=0; j<size; j++) {
2206         if (w4[j]) { w1[j] += w4[j];  w3[j]++; w4[j] = 0;}
2207       }
2208     }
2209 
2210     nrqs     = 0;              /* no of outgoing messages */
2211     msz      = 0;              /* total mesg length (for all procs) */
2212     w1[rank] = 0;              /* no mesg sent to self */
2213     w3[rank] = 0;
2214     for (i=0; i<size; i++) {
2215       if (w1[i])  { w2[i] = 1; nrqs++;} /* there exists a message to proc i */
2216     }
2217     ierr = PetscMalloc1(nrqs+1,&pa);CHKERRQ(ierr); /*(proc -array)*/
2218     for (i=0,j=0; i<size; i++) {
2219       if (w1[i]) { pa[j] = i; j++; }
2220     }
2221 
2222     /* Each message would have a header = 1 + 2*(no of IS) + data */
2223     for (i=0; i<nrqs; i++) {
2224       j      = pa[i];
2225       w1[j] += w2[j] + 2* w3[j];
2226       msz   += w1[j];
2227     }
2228     ierr = PetscInfo2(0,"Number of outgoing messages %D Total message length %D\n",nrqs,msz);CHKERRQ(ierr);
2229 
2230     /* Determine the number of messages to expect, their lengths, from from-ids */
2231     ierr = PetscGatherNumberOfMessages(comm,w2,w1,&nrqr);CHKERRQ(ierr);
2232     ierr = PetscGatherMessageLengths(comm,nrqs,nrqr,w1,&onodes1,&olengths1);CHKERRQ(ierr);
2233 
2234     /* Now post the Irecvs corresponding to these messages */
2235     tag0 = ((PetscObject)C)->tag;
2236     ierr = PetscPostIrecvInt(comm,tag0,nrqr,onodes1,olengths1,&rbuf1,&r_waits1);CHKERRQ(ierr);
2237 
2238     ierr = PetscFree(onodes1);CHKERRQ(ierr);
2239     ierr = PetscFree(olengths1);CHKERRQ(ierr);
2240 
2241     /* Allocate Memory for outgoing messages */
2242     ierr = PetscMalloc4(size,&sbuf1,size,&ptr,2*msz,&tmp,size,&ctr);CHKERRQ(ierr);
2243     ierr = PetscMemzero(sbuf1,size*sizeof(PetscInt*));CHKERRQ(ierr);
2244     ierr = PetscMemzero(ptr,size*sizeof(PetscInt*));CHKERRQ(ierr);
2245 
2246     {
2247       PetscInt *iptr = tmp;
2248       k    = 0;
2249       for (i=0; i<nrqs; i++) {
2250         j        = pa[i];
2251         iptr    += k;
2252         sbuf1[j] = iptr;
2253         k        = w1[j];
2254       }
2255     }
2256 
2257     /* Form the outgoing messages. Initialize the header space */
2258     for (i=0; i<nrqs; i++) {
2259       j           = pa[i];
2260       sbuf1[j][0] = 0;
2261       ierr        = PetscMemzero(sbuf1[j]+1,2*w3[j]*sizeof(PetscInt));CHKERRQ(ierr);
2262       ptr[j]      = sbuf1[j] + 2*w3[j] + 1;
2263     }
2264 
2265     /* Parse the isrow and copy data into outbuf */
2266     for (i=0; i<ismax; i++) {
2267       row2proc_i = row2proc[i];
2268       ierr   = PetscMemzero(ctr,size*sizeof(PetscInt));CHKERRQ(ierr);
2269       irow_i = irow[i];
2270       jmax   = nrow[i];
2271       for (j=0; j<jmax; j++) {  /* parse the indices of each IS */
2272         proc = row2proc_i[j];
2273         if (proc != rank) { /* copy to the outgoing buf*/
2274           ctr[proc]++;
2275           *ptr[proc] = irow_i[j];
2276           ptr[proc]++;
2277         }
2278       }
2279       /* Update the headers for the current IS */
2280       for (j=0; j<size; j++) { /* Can Optimise this loop too */
2281         if ((ctr_j = ctr[j])) {
2282           sbuf1_j        = sbuf1[j];
2283           k              = ++sbuf1_j[0];
2284           sbuf1_j[2*k]   = ctr_j;
2285           sbuf1_j[2*k-1] = i;
2286         }
2287       }
2288     }
2289 
2290     /*  Now  post the sends */
2291     ierr = PetscMalloc1(nrqs+1,&s_waits1);CHKERRQ(ierr);
2292     for (i=0; i<nrqs; ++i) {
2293       j    = pa[i];
2294       ierr = MPI_Isend(sbuf1[j],w1[j],MPIU_INT,j,tag0,comm,s_waits1+i);CHKERRQ(ierr);
2295     }
2296 
2297     /* Post Receives to capture the buffer size */
2298     ierr = PetscMalloc1(nrqs+1,&r_waits2);CHKERRQ(ierr);
2299     ierr = PetscMalloc3(nrqs+1,&req_source2,nrqs+1,&rbuf2,nrqs+1,&rbuf3);CHKERRQ(ierr);
2300     rbuf2[0] = tmp + msz;
2301     for (i=1; i<nrqs; ++i) {
2302       rbuf2[i] = rbuf2[i-1]+w1[pa[i-1]];
2303     }
2304     for (i=0; i<nrqs; ++i) {
2305       j    = pa[i];
2306       ierr = MPI_Irecv(rbuf2[i],w1[j],MPIU_INT,j,tag2,comm,r_waits2+i);CHKERRQ(ierr);
2307     }
2308 
2309     /* Send to other procs the buf size they should allocate */
2310     /* Receive messages*/
2311     ierr = PetscMalloc1(nrqr+1,&s_waits2);CHKERRQ(ierr);
2312     ierr = PetscMalloc1(nrqr+1,&r_status1);CHKERRQ(ierr);
2313     ierr = PetscMalloc3(nrqr,&sbuf2,nrqr,&req_size,nrqr,&req_source1);CHKERRQ(ierr);
2314     {
2315       PetscInt   *sAi = a->i,*sBi = b->i,id,rstart = C->rmap->rstart;
2316       PetscInt   *sbuf2_i;
2317 
2318       ierr = MPI_Waitall(nrqr,r_waits1,r_status1);CHKERRQ(ierr);
2319       for (i=0; i<nrqr; ++i) {
2320         req_size[i] = 0;
2321         rbuf1_i        = rbuf1[i];
2322         start          = 2*rbuf1_i[0] + 1;
2323         ierr           = MPI_Get_count(r_status1+i,MPIU_INT,&end);CHKERRQ(ierr);
2324         ierr           = PetscMalloc1(end+1,&sbuf2[i]);CHKERRQ(ierr);
2325         sbuf2_i        = sbuf2[i];
2326         for (j=start; j<end; j++) {
2327           id              = rbuf1_i[j] - rstart;
2328           ncols           = sAi[id+1] - sAi[id] + sBi[id+1] - sBi[id];
2329           sbuf2_i[j]      = ncols;
2330           req_size[i] += ncols;
2331         }
2332         req_source1[i] = r_status1[i].MPI_SOURCE;
2333         /* form the header */
2334         sbuf2_i[0] = req_size[i];
2335         for (j=1; j<start; j++) sbuf2_i[j] = rbuf1_i[j];
2336 
2337         ierr = MPI_Isend(sbuf2_i,end,MPIU_INT,req_source1[i],tag2,comm,s_waits2+i);CHKERRQ(ierr);
2338       }
2339     }
2340     ierr = PetscFree(r_status1);CHKERRQ(ierr);
2341     ierr = PetscFree(r_waits1);CHKERRQ(ierr);
2342     ierr = PetscFree4(w1,w2,w3,w4);CHKERRQ(ierr);
2343 
2344     /* Receive messages*/
2345     ierr = PetscMalloc1(nrqs+1,&r_waits3);CHKERRQ(ierr);
2346     ierr = PetscMalloc1(nrqs+1,&r_status2);CHKERRQ(ierr);
2347 
2348     ierr = MPI_Waitall(nrqs,r_waits2,r_status2);CHKERRQ(ierr);
2349     for (i=0; i<nrqs; ++i) {
2350       ierr = PetscMalloc1(rbuf2[i][0]+1,&rbuf3[i]);CHKERRQ(ierr);
2351       req_source2[i] = r_status2[i].MPI_SOURCE;
2352       ierr = MPI_Irecv(rbuf3[i],rbuf2[i][0],MPIU_INT,req_source2[i],tag3,comm,r_waits3+i);CHKERRQ(ierr);
2353     }
2354     ierr = PetscFree(r_status2);CHKERRQ(ierr);
2355     ierr = PetscFree(r_waits2);CHKERRQ(ierr);
2356 
2357     /* Wait on sends1 and sends2 */
2358     ierr = PetscMalloc1(nrqs+1,&s_status1);CHKERRQ(ierr);
2359     ierr = PetscMalloc1(nrqr+1,&s_status2);CHKERRQ(ierr);
2360 
2361     if (nrqs) {ierr = MPI_Waitall(nrqs,s_waits1,s_status1);CHKERRQ(ierr);}
2362     if (nrqr) {ierr = MPI_Waitall(nrqr,s_waits2,s_status2);CHKERRQ(ierr);}
2363     ierr = PetscFree(s_status1);CHKERRQ(ierr);
2364     ierr = PetscFree(s_status2);CHKERRQ(ierr);
2365     ierr = PetscFree(s_waits1);CHKERRQ(ierr);
2366     ierr = PetscFree(s_waits2);CHKERRQ(ierr);
2367 
2368     /* Now allocate sending buffers for a->j, and send them off */
2369     ierr = PetscMalloc1(nrqr+1,&sbuf_aj);CHKERRQ(ierr);
2370     for (i=0,j=0; i<nrqr; i++) j += req_size[i];
2371     ierr = PetscMalloc1(j+1,&sbuf_aj[0]);CHKERRQ(ierr);
2372     for (i=1; i<nrqr; i++) sbuf_aj[i] = sbuf_aj[i-1] + req_size[i-1];
2373 
2374     ierr = PetscMalloc1(nrqr+1,&s_waits3);CHKERRQ(ierr);
2375     {
2376       PetscInt nzA,nzB,*a_i = a->i,*b_i = b->i,lwrite;
2377       PetscInt *cworkA,*cworkB,cstart = C->cmap->rstart,rstart = C->rmap->rstart,*bmap = c->garray;
2378       PetscInt cend = C->cmap->rend;
2379       PetscInt *a_j = a->j,*b_j = b->j,ctmp;
2380 
2381       for (i=0; i<nrqr; i++) {
2382         rbuf1_i   = rbuf1[i];
2383         sbuf_aj_i = sbuf_aj[i];
2384         ct1       = 2*rbuf1_i[0] + 1;
2385         ct2       = 0;
2386         for (j=1,max1=rbuf1_i[0]; j<=max1; j++) {
2387           kmax = rbuf1[i][2*j];
2388           for (k=0; k<kmax; k++,ct1++) {
2389             row    = rbuf1_i[ct1] - rstart;
2390             nzA    = a_i[row+1] - a_i[row]; nzB = b_i[row+1] - b_i[row];
2391             ncols  = nzA + nzB;
2392             cworkA = a_j + a_i[row]; cworkB = b_j + b_i[row];
2393 
2394             /* load the column indices for this row into sorted cols */
2395             cols = sbuf_aj_i + ct2;
2396 
2397             lwrite = 0;
2398             for (l=0; l<nzB; l++) {
2399               if ((ctmp = bmap[cworkB[l]]) < cstart) cols[lwrite++] = ctmp;
2400             }
2401             for (l=0; l<nzA; l++) cols[lwrite++] = cstart + cworkA[l];
2402             for (l=0; l<nzB; l++) {
2403               if ((ctmp = bmap[cworkB[l]]) >= cend) cols[lwrite++] = ctmp;
2404             }
2405 
2406             ct2 += ncols;
2407           }
2408         }
2409         ierr = MPI_Isend(sbuf_aj_i,req_size[i],MPIU_INT,req_source1[i],tag3,comm,s_waits3+i);CHKERRQ(ierr);
2410       }
2411     }
2412     ierr = PetscMalloc1(nrqs+1,&r_status3);CHKERRQ(ierr);
2413     ierr = PetscMalloc1(nrqr+1,&s_status3);CHKERRQ(ierr);
2414 
2415     /* create col map: global col of C -> local col of submatrices */
2416     {
2417       const PetscInt *icol_i;
2418 #if defined(PETSC_USE_CTABLE)
2419       for (i=0; i<ismax; i++) {
2420         if (!allcolumns[i]) {
2421           ierr = PetscTableCreate(ncol[i]+1,C->cmap->N+1,&cmap[i]);CHKERRQ(ierr);
2422 
2423           jmax   = ncol[i];
2424           icol_i = icol[i];
2425           cmap_i = cmap[i];
2426           for (j=0; j<jmax; j++) {
2427             ierr = PetscTableAdd(cmap[i],icol_i[j]+1,j+1,INSERT_VALUES);CHKERRQ(ierr);
2428           }
2429         } else cmap[i] = NULL;
2430       }
2431 #else
2432       for (i=0; i<ismax; i++) {
2433         if (!allcolumns[i]) {
2434           ierr   = PetscCalloc1(C->cmap->N,&cmap[i]);CHKERRQ(ierr);
2435           jmax   = ncol[i];
2436           icol_i = icol[i];
2437           cmap_i = cmap[i];
2438           for (j=0; j<jmax; j++) {
2439             cmap_i[icol_i[j]] = j+1;
2440           }
2441         } else cmap[i] = NULL;
2442       }
2443 #endif
2444     }
2445 
2446     /* Create lens which is required for MatCreate... */
2447     for (i=0,j=0; i<ismax; i++) j += nrow[i];
2448     ierr = PetscMalloc1(ismax,&lens);CHKERRQ(ierr);
2449 
2450     if (ismax) {
2451       ierr = PetscCalloc1(j,&lens[0]);CHKERRQ(ierr);
2452     }
2453     for (i=1; i<ismax; i++) lens[i] = lens[i-1] + nrow[i-1];
2454 
2455     /* Update lens from local data */
2456     for (i=0; i<ismax; i++) {
2457       row2proc_i = row2proc[i];
2458       jmax = nrow[i];
2459       if (!allcolumns[i]) cmap_i = cmap[i];
2460       irow_i = irow[i];
2461       lens_i = lens[i];
2462       for (j=0; j<jmax; j++) {
2463         row = irow_i[j];
2464         proc = row2proc_i[j];
2465         if (proc == rank) {
2466           ierr = MatGetRow_MPIAIJ(C,row,&ncols,&cols,0);CHKERRQ(ierr);
2467           if (!allcolumns[i]) {
2468             for (k=0; k<ncols; k++) {
2469 #if defined(PETSC_USE_CTABLE)
2470               ierr = PetscTableFind(cmap_i,cols[k]+1,&tcol);CHKERRQ(ierr);
2471 #else
2472               tcol = cmap_i[cols[k]];
2473 #endif
2474               if (tcol) lens_i[j]++;
2475             }
2476           } else { /* allcolumns */
2477             lens_i[j] = ncols;
2478           }
2479           ierr = MatRestoreRow_MPIAIJ(C,row,&ncols,&cols,0);CHKERRQ(ierr);
2480         }
2481       }
2482     }
2483 
2484     /* Create row map: global row of C -> local row of submatrices */
2485 #if defined(PETSC_USE_CTABLE)
2486     for (i=0; i<ismax; i++) {
2487       ierr   = PetscTableCreate(nrow[i]+1,C->rmap->N+1,&rmap[i]);CHKERRQ(ierr);
2488       irow_i = irow[i];
2489       jmax   = nrow[i];
2490       for (j=0; j<jmax; j++) {
2491       ierr = PetscTableAdd(rmap[i],irow_i[j]+1,j+1,INSERT_VALUES);CHKERRQ(ierr);
2492       }
2493     }
2494 #else
2495     for (i=0; i<ismax; i++) {
2496       ierr   = PetscCalloc1(C->rmap->N,&rmap[i]);CHKERRQ(ierr);
2497       rmap_i = rmap[i];
2498       irow_i = irow[i];
2499       jmax   = nrow[i];
2500       for (j=0; j<jmax; j++) {
2501         rmap_i[irow_i[j]] = j;
2502       }
2503     }
2504 #endif
2505 
2506     /* Update lens from offproc data */
2507     {
2508     PetscInt *rbuf2_i,*rbuf3_i,*sbuf1_i;
2509 
2510     ierr    = MPI_Waitall(nrqs,r_waits3,r_status3);CHKERRQ(ierr);
2511     for (tmp2=0; tmp2<nrqs; tmp2++) {
2512       sbuf1_i = sbuf1[pa[tmp2]];
2513       jmax    = sbuf1_i[0];
2514       ct1     = 2*jmax+1;
2515       ct2     = 0;
2516       rbuf2_i = rbuf2[tmp2];
2517       rbuf3_i = rbuf3[tmp2];
2518       for (j=1; j<=jmax; j++) {
2519         is_no  = sbuf1_i[2*j-1];
2520         max1   = sbuf1_i[2*j];
2521         lens_i = lens[is_no];
2522         if (!allcolumns[is_no]) cmap_i = cmap[is_no];
2523         rmap_i = rmap[is_no];
2524         for (k=0; k<max1; k++,ct1++) {
2525 #if defined(PETSC_USE_CTABLE)
2526           ierr = PetscTableFind(rmap_i,sbuf1_i[ct1]+1,&row);CHKERRQ(ierr);
2527           row--;
2528           if (row < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"row not found in table");
2529 #else
2530           row = rmap_i[sbuf1_i[ct1]]; /* the val in the new matrix to be */
2531 #endif
2532           max2 = rbuf2_i[ct1];
2533           for (l=0; l<max2; l++,ct2++) {
2534             if (!allcolumns[is_no]) {
2535 #if defined(PETSC_USE_CTABLE)
2536               ierr = PetscTableFind(cmap_i,rbuf3_i[ct2]+1,&tcol);CHKERRQ(ierr);
2537 #else
2538               tcol = cmap_i[rbuf3_i[ct2]];
2539 #endif
2540               if (tcol) lens_i[row]++;
2541             } else { /* allcolumns */
2542               lens_i[row]++; /* lens_i[row] += max2 ? */
2543             }
2544           }
2545         }
2546       }
2547     }
2548     }
2549     ierr = PetscFree(r_status3);CHKERRQ(ierr);
2550     ierr = PetscFree(r_waits3);CHKERRQ(ierr);
2551     if (nrqr) {ierr = MPI_Waitall(nrqr,s_waits3,s_status3);CHKERRQ(ierr);}
2552     ierr = PetscFree(s_status3);CHKERRQ(ierr);
2553     ierr = PetscFree(s_waits3);CHKERRQ(ierr);
2554 
2555     /* Create the submatrices */
2556     for (i=0; i<ismax; i++) {
2557       PetscInt    rbs,cbs;
2558 
2559       ierr = ISGetBlockSize(isrow[i],&rbs);CHKERRQ(ierr);
2560       ierr = ISGetBlockSize(iscol[i],&cbs);CHKERRQ(ierr);
2561 
2562       ierr = MatCreate(PETSC_COMM_SELF,submats+i);CHKERRQ(ierr);
2563       ierr = MatSetSizes(submats[i],nrow[i],ncol[i],PETSC_DETERMINE,PETSC_DETERMINE);CHKERRQ(ierr);
2564 
2565       ierr = MatSetBlockSizes(submats[i],rbs,cbs);CHKERRQ(ierr);
2566       ierr = MatSetType(submats[i],((PetscObject)A)->type_name);CHKERRQ(ierr);
2567       ierr = MatSeqAIJSetPreallocation(submats[i],0,lens[i]);CHKERRQ(ierr);
2568 
2569       /* create struct Mat_SubMat and attached it to submat */
2570       ierr = PetscNew(&smat_i);CHKERRQ(ierr);
2571       subc = (Mat_SeqAIJ*)submats[i]->data;
2572       subc->submatis1 = smat_i;
2573       smats[i]        = smat_i;
2574 
2575       smat_i->destroy          = submats[i]->ops->destroy;
2576       submats[i]->ops->destroy = MatDestroy_MPIAIJ_MatGetSubmatrices;
2577       submats[i]->factortype   = C->factortype;
2578 
2579       smat_i->id          = i;
2580       smat_i->nrqs        = nrqs;
2581       smat_i->nrqr        = nrqr;
2582       smat_i->rbuf1       = rbuf1;
2583       smat_i->rbuf2       = rbuf2;
2584       smat_i->rbuf3       = rbuf3;
2585       smat_i->sbuf2       = sbuf2;
2586       smat_i->req_source2 = req_source2;
2587 
2588       smat_i->sbuf1       = sbuf1;
2589       smat_i->ptr         = ptr;
2590       smat_i->tmp         = tmp;
2591       smat_i->ctr         = ctr;
2592 
2593       smat_i->pa           = pa;
2594       smat_i->req_size     = req_size;
2595       smat_i->req_source1  = req_source1;
2596 
2597       smat_i->allcolumns  = allcolumns[i];
2598       smat_i->row2proc    = row2proc[i];
2599       smat_i->rmap        = rmap[i];
2600       smat_i->cmap        = cmap[i];
2601     }
2602 
2603     if (ismax) {ierr = PetscFree(lens[0]);CHKERRQ(ierr);}
2604     ierr = PetscFree(lens);CHKERRQ(ierr);
2605     ierr = PetscFree(sbuf_aj[0]);CHKERRQ(ierr);
2606     ierr = PetscFree(sbuf_aj);CHKERRQ(ierr);
2607 
2608   } /* endof scall == MAT_INITIAL_MATRIX */
2609 
2610   /* Post recv matrix values */
2611   ierr = PetscObjectGetNewTag((PetscObject)C,&tag4);CHKERRQ(ierr);
2612   ierr = PetscMalloc1(nrqs+1,&rbuf4);CHKERRQ(ierr);
2613   ierr = PetscMalloc1(nrqs+1,&r_waits4);CHKERRQ(ierr);
2614   ierr = PetscMalloc1(nrqs+1,&r_status4);CHKERRQ(ierr);
2615   ierr = PetscMalloc1(nrqr+1,&s_status4);CHKERRQ(ierr);
2616   for (i=0; i<nrqs; ++i) {
2617     ierr = PetscMalloc1(rbuf2[i][0]+1,&rbuf4[i]);CHKERRQ(ierr);
2618     ierr = MPI_Irecv(rbuf4[i],rbuf2[i][0],MPIU_SCALAR,req_source2[i],tag4,comm,r_waits4+i);CHKERRQ(ierr);
2619   }
2620 
2621   /* Allocate sending buffers for a->a, and send them off */
2622   ierr = PetscMalloc1(nrqr+1,&sbuf_aa);CHKERRQ(ierr);
2623   for (i=0,j=0; i<nrqr; i++) j += req_size[i];
2624   ierr = PetscMalloc1(j+1,&sbuf_aa[0]);CHKERRQ(ierr);
2625   for (i=1; i<nrqr; i++) sbuf_aa[i] = sbuf_aa[i-1] + req_size[i-1];
2626 
2627   ierr = PetscMalloc1(nrqr+1,&s_waits4);CHKERRQ(ierr);
2628   {
2629     PetscInt    nzA,nzB,*a_i = a->i,*b_i = b->i, *cworkB,lwrite;
2630     PetscInt    cstart = C->cmap->rstart,rstart = C->rmap->rstart,*bmap = c->garray;
2631     PetscInt    cend   = C->cmap->rend;
2632     PetscInt    *b_j   = b->j;
2633     PetscScalar *vworkA,*vworkB,*a_a = a->a,*b_a = b->a;
2634 
2635     for (i=0; i<nrqr; i++) {
2636       rbuf1_i   = rbuf1[i];
2637       sbuf_aa_i = sbuf_aa[i];
2638       ct1       = 2*rbuf1_i[0]+1;
2639       ct2       = 0;
2640       for (j=1,max1=rbuf1_i[0]; j<=max1; j++) {
2641         kmax = rbuf1_i[2*j];
2642         for (k=0; k<kmax; k++,ct1++) {
2643           row    = rbuf1_i[ct1] - rstart;
2644           nzA    = a_i[row+1] - a_i[row];     nzB = b_i[row+1] - b_i[row];
2645           ncols  = nzA + nzB;
2646           cworkB = b_j + b_i[row];
2647           vworkA = a_a + a_i[row];
2648           vworkB = b_a + b_i[row];
2649 
2650           /* load the column values for this row into vals*/
2651           vals = sbuf_aa_i+ct2;
2652 
2653           lwrite = 0;
2654           for (l=0; l<nzB; l++) {
2655             if ((bmap[cworkB[l]]) < cstart) vals[lwrite++] = vworkB[l];
2656           }
2657           for (l=0; l<nzA; l++) vals[lwrite++] = vworkA[l];
2658           for (l=0; l<nzB; l++) {
2659             if ((bmap[cworkB[l]]) >= cend) vals[lwrite++] = vworkB[l];
2660           }
2661 
2662           ct2 += ncols;
2663         }
2664       }
2665       ierr = MPI_Isend(sbuf_aa_i,req_size[i],MPIU_SCALAR,req_source1[i],tag4,comm,s_waits4+i);CHKERRQ(ierr);
2666     }
2667   }
2668 
2669   if (!ismax) {
2670     ierr = PetscFree(rbuf1[0]);CHKERRQ(ierr);
2671     ierr = PetscFree(rbuf1);CHKERRQ(ierr);
2672   }
2673 
2674   /* Assemble the matrices */
2675   /* First assemble the local rows */
2676   {
2677     PetscInt    ilen_row,*imat_ilen,*imat_j,*imat_i,old_row;
2678     PetscScalar *imat_a;
2679 
2680     for (i=0; i<ismax; i++) {
2681       row2proc_i = row2proc[i];
2682       subc      = (Mat_SeqAIJ*)submats[i]->data;
2683       imat_ilen = subc->ilen;
2684       imat_j    = subc->j;
2685       imat_i    = subc->i;
2686       imat_a    = subc->a;
2687 
2688       if (!allcolumns[i]) cmap_i = cmap[i];
2689       rmap_i = rmap[i];
2690       irow_i = irow[i];
2691       jmax   = nrow[i];
2692       for (j=0; j<jmax; j++) {
2693         row  = irow_i[j];
2694         proc = row2proc_i[j];
2695         if (proc == rank) {
2696           old_row = row;
2697 #if defined(PETSC_USE_CTABLE)
2698           ierr = PetscTableFind(rmap_i,row+1,&row);CHKERRQ(ierr);
2699           row--;
2700 #else
2701           row = rmap_i[row];
2702 #endif
2703           ilen_row = imat_ilen[row];
2704           ierr     = MatGetRow_MPIAIJ(C,old_row,&ncols,&cols,&vals);CHKERRQ(ierr);
2705           mat_i    = imat_i[row];
2706           mat_a    = imat_a + mat_i;
2707           mat_j    = imat_j + mat_i;
2708           if (!allcolumns[i]) {
2709             for (k=0; k<ncols; k++) {
2710 #if defined(PETSC_USE_CTABLE)
2711               ierr = PetscTableFind(cmap_i,cols[k]+1,&tcol);CHKERRQ(ierr);
2712 #else
2713               tcol = cmap_i[cols[k]];
2714 #endif
2715               if (tcol) {
2716                 *mat_j++ = tcol - 1;
2717                 *mat_a++ = vals[k];
2718                 ilen_row++;
2719               }
2720             }
2721           } else { /* allcolumns */
2722             for (k=0; k<ncols; k++) {
2723               *mat_j++ = cols[k];  /* global col index! */
2724               *mat_a++ = vals[k];
2725               ilen_row++;
2726             }
2727           }
2728           ierr = MatRestoreRow_MPIAIJ(C,old_row,&ncols,&cols,&vals);CHKERRQ(ierr);
2729 
2730           imat_ilen[row] = ilen_row;
2731         }
2732       }
2733     }
2734   }
2735 
2736   /*   Now assemble the off proc rows*/
2737   {
2738     PetscInt    *sbuf1_i,*rbuf2_i,*rbuf3_i,*imat_ilen,ilen;
2739     PetscInt    *imat_j,*imat_i;
2740     PetscScalar *imat_a,*rbuf4_i;
2741 
2742     ierr    = MPI_Waitall(nrqs,r_waits4,r_status4);CHKERRQ(ierr);
2743     for (tmp2=0; tmp2<nrqs; tmp2++) {
2744       sbuf1_i = sbuf1[pa[tmp2]];
2745       jmax    = sbuf1_i[0];
2746       ct1     = 2*jmax + 1;
2747       ct2     = 0;
2748       rbuf2_i = rbuf2[tmp2];
2749       rbuf3_i = rbuf3[tmp2];
2750       rbuf4_i = rbuf4[tmp2];
2751       for (j=1; j<=jmax; j++) {
2752         is_no     = sbuf1_i[2*j-1];
2753         rmap_i    = rmap[is_no];
2754         if (!allcolumns[is_no]) cmap_i = cmap[is_no];
2755         subc      = (Mat_SeqAIJ*)submats[is_no]->data;
2756         imat_ilen = subc->ilen;
2757         imat_j    = subc->j;
2758         imat_i    = subc->i;
2759         imat_a    = subc->a;
2760         max1      = sbuf1_i[2*j];
2761         for (k=0; k<max1; k++,ct1++) {
2762           row = sbuf1_i[ct1];
2763 #if defined(PETSC_USE_CTABLE)
2764           ierr = PetscTableFind(rmap_i,row+1,&row);CHKERRQ(ierr);
2765           row--;
2766 #else
2767           row = rmap_i[row];
2768 #endif
2769           ilen  = imat_ilen[row];
2770           mat_i = imat_i[row];
2771           mat_a = imat_a + mat_i;
2772           mat_j = imat_j + mat_i;
2773           max2  = rbuf2_i[ct1];
2774           if (!allcolumns[is_no]) {
2775             for (l=0; l<max2; l++,ct2++) {
2776 
2777 #if defined(PETSC_USE_CTABLE)
2778               ierr = PetscTableFind(cmap_i,rbuf3_i[ct2]+1,&tcol);CHKERRQ(ierr);
2779 #else
2780               tcol = cmap_i[rbuf3_i[ct2]];
2781 #endif
2782               if (tcol) {
2783                 *mat_j++ = tcol - 1;
2784                 *mat_a++ = rbuf4_i[ct2];
2785                 ilen++;
2786               }
2787             }
2788           } else { /* allcolumns */
2789             for (l=0; l<max2; l++,ct2++) {
2790               *mat_j++ = rbuf3_i[ct2]; /* same global column index of C */
2791               *mat_a++ = rbuf4_i[ct2];
2792               ilen++;
2793             }
2794           }
2795           imat_ilen[row] = ilen;
2796         }
2797       }
2798     }
2799   }
2800 
2801   ierr = PetscFree(r_status4);CHKERRQ(ierr);
2802   ierr = PetscFree(r_waits4);CHKERRQ(ierr);
2803   if (nrqr) {ierr = MPI_Waitall(nrqr,s_waits4,s_status4);CHKERRQ(ierr);}
2804   ierr = PetscFree(s_waits4);CHKERRQ(ierr);
2805   ierr = PetscFree(s_status4);CHKERRQ(ierr);
2806 
2807   /* Restore the indices */
2808   for (i=0; i<ismax; i++) {
2809     ierr = ISRestoreIndices(isrow[i],irow+i);CHKERRQ(ierr);
2810     if (!allcolumns[i]) {
2811       ierr = ISRestoreIndices(iscol[i],icol+i);CHKERRQ(ierr);
2812     }
2813   }
2814 
2815   for (i=0; i<ismax; i++) {
2816     ierr = MatAssemblyBegin(submats[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
2817     ierr = MatAssemblyEnd(submats[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
2818   }
2819 
2820   /* Destroy allocated memory */
2821   if (!ismax) {
2822     ierr = PetscFree(pa);CHKERRQ(ierr);
2823 
2824     ierr = PetscFree4(sbuf1,ptr,tmp,ctr);CHKERRQ(ierr);
2825     for (i=0; i<nrqr; ++i) {
2826       ierr = PetscFree(sbuf2[i]);CHKERRQ(ierr);
2827     }
2828     for (i=0; i<nrqs; ++i) {
2829       ierr = PetscFree(rbuf3[i]);CHKERRQ(ierr);
2830     }
2831 
2832     ierr = PetscFree3(sbuf2,req_size,req_source1);CHKERRQ(ierr);
2833     ierr = PetscFree3(req_source2,rbuf2,rbuf3);CHKERRQ(ierr);
2834   }
2835 
2836   ierr = PetscFree(sbuf_aa[0]);CHKERRQ(ierr);
2837   ierr = PetscFree(sbuf_aa);CHKERRQ(ierr);
2838   ierr = PetscFree5(irow,icol,nrow,ncol,issorted);CHKERRQ(ierr);
2839 
2840   for (i=0; i<nrqs; ++i) {
2841     ierr = PetscFree(rbuf4[i]);CHKERRQ(ierr);
2842   }
2843   ierr = PetscFree(rbuf4);CHKERRQ(ierr);
2844 
2845   ierr = PetscFree2(cmap,rmap);CHKERRQ(ierr);
2846   ierr = PetscFree(row2proc);CHKERRQ(ierr);
2847   ierr = PetscFree(smats);CHKERRQ(ierr);
2848   ierr = PetscFree(allcolumns);CHKERRQ(ierr);
2849   PetscFunctionReturn(0);
2850 }
2851 
2852 /*
2853  Permute A & B into C's *local* index space using rowemb,dcolemb for A and rowemb,ocolemb for B.
2854  Embeddings are supposed to be injections and the above implies that the range of rowemb is a subset
2855  of [0,m), dcolemb is in [0,n) and ocolemb is in [N-n).
2856  If pattern == DIFFERENT_NONZERO_PATTERN, C is preallocated according to A&B.
2857  After that B's columns are mapped into C's global column space, so that C is in the "disassembled"
2858  state, and needs to be "assembled" later by compressing B's column space.
2859 
2860  This function may be called in lieu of preallocation, so C should not be expected to be preallocated.
2861  Following this call, C->A & C->B have been created, even if empty.
2862  */
2863 PetscErrorCode MatSetSeqMats_MPIAIJ(Mat C,IS rowemb,IS dcolemb,IS ocolemb,MatStructure pattern,Mat A,Mat B)
2864 {
2865   /* If making this function public, change the error returned in this function away from _PLIB. */
2866   PetscErrorCode ierr;
2867   Mat_MPIAIJ     *aij;
2868   Mat_SeqAIJ     *Baij;
2869   PetscBool      seqaij,Bdisassembled;
2870   PetscInt       m,n,*nz,i,j,ngcol,col,rstart,rend,shift,count;
2871   PetscScalar    v;
2872   const PetscInt *rowindices,*colindices;
2873 
2874   PetscFunctionBegin;
2875   /* Check to make sure the component matrices (and embeddings) are compatible with C. */
2876   if (A) {
2877     ierr = PetscObjectTypeCompare((PetscObject)A,MATSEQAIJ,&seqaij);CHKERRQ(ierr);
2878     if (!seqaij) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Diagonal matrix is of wrong type");
2879     if (rowemb) {
2880       ierr = ISGetLocalSize(rowemb,&m);CHKERRQ(ierr);
2881       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);
2882     } else {
2883       if (C->rmap->n != A->rmap->n) {
2884 	SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Diag seq matrix is row-incompatible with the MPIAIJ matrix");
2885       }
2886     }
2887     if (dcolemb) {
2888       ierr = ISGetLocalSize(dcolemb,&n);CHKERRQ(ierr);
2889       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);
2890     } else {
2891       if (C->cmap->n != A->cmap->n) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Diag seq matrix is col-incompatible with the MPIAIJ matrix");
2892     }
2893   }
2894   if (B) {
2895     ierr = PetscObjectTypeCompare((PetscObject)B,MATSEQAIJ,&seqaij);CHKERRQ(ierr);
2896     if (!seqaij) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Off-diagonal matrix is of wrong type");
2897     if (rowemb) {
2898       ierr = ISGetLocalSize(rowemb,&m);CHKERRQ(ierr);
2899       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);
2900     } else {
2901       if (C->rmap->n != B->rmap->n) {
2902 	SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Off-diag seq matrix is row-incompatible with the MPIAIJ matrix");
2903       }
2904     }
2905     if (ocolemb) {
2906       ierr = ISGetLocalSize(ocolemb,&n);CHKERRQ(ierr);
2907       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);
2908     } else {
2909       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");
2910     }
2911   }
2912 
2913   aij    = (Mat_MPIAIJ*)(C->data);
2914   if (!aij->A) {
2915     /* Mimic parts of MatMPIAIJSetPreallocation() */
2916     ierr   = MatCreate(PETSC_COMM_SELF,&aij->A);CHKERRQ(ierr);
2917     ierr   = MatSetSizes(aij->A,C->rmap->n,C->cmap->n,C->rmap->n,C->cmap->n);CHKERRQ(ierr);
2918     ierr   = MatSetBlockSizesFromMats(aij->A,C,C);CHKERRQ(ierr);
2919     ierr   = MatSetType(aij->A,MATSEQAIJ);CHKERRQ(ierr);
2920     ierr   = PetscLogObjectParent((PetscObject)C,(PetscObject)aij->A);CHKERRQ(ierr);
2921   }
2922   if (A) {
2923     ierr   = MatSetSeqMat_SeqAIJ(aij->A,rowemb,dcolemb,pattern,A);CHKERRQ(ierr);
2924   } else {
2925     ierr = MatSetUp(aij->A);CHKERRQ(ierr);
2926   }
2927   if (B) { /* Destroy the old matrix or the column map, depending on the sparsity pattern. */
2928     /*
2929       If pattern == DIFFERENT_NONZERO_PATTERN, we reallocate B and
2930       need to "disassemble" B -- convert it to using C's global indices.
2931       To insert the values we take the safer, albeit more expensive, route of MatSetValues().
2932 
2933       If pattern == SUBSET_NONZERO_PATTERN, we do not "disassemble" B and do not reallocate;
2934       we MatZeroValues(B) first, so there may be a bunch of zeros that, perhaps, could be compacted out.
2935 
2936       TODO: Put B's values into aij->B's aij structure in place using the embedding ISs?
2937       At least avoid calling MatSetValues() and the implied searches?
2938     */
2939 
2940     if (B && pattern == DIFFERENT_NONZERO_PATTERN) {
2941 #if defined(PETSC_USE_CTABLE)
2942       ierr = PetscTableDestroy(&aij->colmap);CHKERRQ(ierr);
2943 #else
2944       ierr = PetscFree(aij->colmap);CHKERRQ(ierr);
2945       /* A bit of a HACK: ideally we should deal with case aij->B all in one code block below. */
2946       if (aij->B) {
2947         ierr = PetscLogObjectMemory((PetscObject)C,-aij->B->cmap->n*sizeof(PetscInt));CHKERRQ(ierr);
2948       }
2949 #endif
2950       ngcol = 0;
2951       if (aij->lvec) {
2952 	ierr = VecGetSize(aij->lvec,&ngcol);CHKERRQ(ierr);
2953       }
2954       if (aij->garray) {
2955 	ierr = PetscFree(aij->garray);CHKERRQ(ierr);
2956 	ierr = PetscLogObjectMemory((PetscObject)C,-ngcol*sizeof(PetscInt));CHKERRQ(ierr);
2957       }
2958       ierr = VecDestroy(&aij->lvec);CHKERRQ(ierr);
2959       ierr = VecScatterDestroy(&aij->Mvctx);CHKERRQ(ierr);
2960     }
2961     if (aij->B && B && pattern == DIFFERENT_NONZERO_PATTERN) {
2962       ierr = MatDestroy(&aij->B);CHKERRQ(ierr);
2963     }
2964     if (aij->B && B && pattern == SUBSET_NONZERO_PATTERN) {
2965       ierr = MatZeroEntries(aij->B);CHKERRQ(ierr);
2966     }
2967   }
2968   Bdisassembled = PETSC_FALSE;
2969   if (!aij->B) {
2970     ierr = MatCreate(PETSC_COMM_SELF,&aij->B);CHKERRQ(ierr);
2971     ierr = PetscLogObjectParent((PetscObject)C,(PetscObject)aij->B);CHKERRQ(ierr);
2972     ierr = MatSetSizes(aij->B,C->rmap->n,C->cmap->N,C->rmap->n,C->cmap->N);CHKERRQ(ierr);
2973     ierr = MatSetBlockSizesFromMats(aij->B,B,B);CHKERRQ(ierr);
2974     ierr = MatSetType(aij->B,MATSEQAIJ);CHKERRQ(ierr);
2975     Bdisassembled = PETSC_TRUE;
2976   }
2977   if (B) {
2978     Baij = (Mat_SeqAIJ*)(B->data);
2979     if (pattern == DIFFERENT_NONZERO_PATTERN) {
2980       ierr = PetscMalloc1(B->rmap->n,&nz);CHKERRQ(ierr);
2981       for (i=0; i<B->rmap->n; i++) {
2982 	nz[i] = Baij->i[i+1] - Baij->i[i];
2983       }
2984       ierr = MatSeqAIJSetPreallocation(aij->B,0,nz);CHKERRQ(ierr);
2985       ierr = PetscFree(nz);CHKERRQ(ierr);
2986     }
2987 
2988     ierr  = PetscLayoutGetRange(C->rmap,&rstart,&rend);CHKERRQ(ierr);
2989     shift = rend-rstart;
2990     count = 0;
2991     rowindices = NULL;
2992     colindices = NULL;
2993     if (rowemb) {
2994       ierr = ISGetIndices(rowemb,&rowindices);CHKERRQ(ierr);
2995     }
2996     if (ocolemb) {
2997       ierr = ISGetIndices(ocolemb,&colindices);CHKERRQ(ierr);
2998     }
2999     for (i=0; i<B->rmap->n; i++) {
3000       PetscInt row;
3001       row = i;
3002       if (rowindices) row = rowindices[i];
3003       for (j=Baij->i[i]; j<Baij->i[i+1]; j++) {
3004 	col  = Baij->j[count];
3005 	if (colindices) col = colindices[col];
3006 	if (Bdisassembled && col>=rstart) col += shift;
3007 	v    = Baij->a[count];
3008 	ierr = MatSetValues(aij->B,1,&row,1,&col,&v,INSERT_VALUES);CHKERRQ(ierr);
3009 	++count;
3010       }
3011     }
3012     /* No assembly for aij->B is necessary. */
3013     /* FIXME: set aij->B's nonzerostate correctly. */
3014   } else {
3015     ierr = MatSetUp(aij->B);CHKERRQ(ierr);
3016   }
3017   C->preallocated  = PETSC_TRUE;
3018   C->was_assembled = PETSC_FALSE;
3019   C->assembled     = PETSC_FALSE;
3020    /*
3021       C will need to be assembled so that aij->B can be compressed into local form in MatSetUpMultiply_MPIAIJ().
3022       Furthermore, its nonzerostate will need to be based on that of aij->A's and aij->B's.
3023    */
3024   PetscFunctionReturn(0);
3025 }
3026 
3027 /*
3028   B uses local indices with column indices ranging between 0 and N-n; they  must be interpreted using garray.
3029  */
3030 PetscErrorCode MatGetSeqMats_MPIAIJ(Mat C,Mat *A,Mat *B)
3031 {
3032   Mat_MPIAIJ *aij = (Mat_MPIAIJ*) (C->data);
3033 
3034   PetscFunctionBegin;
3035   PetscValidPointer(A,2);
3036   PetscValidPointer(B,3);
3037   /* FIXME: make sure C is assembled */
3038   *A = aij->A;
3039   *B = aij->B;
3040   /* Note that we don't incref *A and *B, so be careful! */
3041   PetscFunctionReturn(0);
3042 }
3043 
3044 /*
3045   Extract MPI submatrices encoded by pairs of IS that may live on subcomms of C.
3046   NOT SCALABLE due to the use of ISGetNonlocalIS() (see below).
3047 */
3048 PetscErrorCode MatGetSubMatricesMPI_MPIXAIJ(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[],
3049                                                  PetscErrorCode(*getsubmats_seq)(Mat,PetscInt,const IS[],const IS[],MatReuse,Mat**),
3050 					         PetscErrorCode(*getlocalmats)(Mat,Mat*,Mat*),
3051 					         PetscErrorCode(*setseqmat)(Mat,IS,IS,MatStructure,Mat),
3052 					         PetscErrorCode(*setseqmats)(Mat,IS,IS,IS,MatStructure,Mat,Mat))
3053 {
3054   PetscErrorCode ierr;
3055   PetscMPIInt    isize,flag;
3056   PetscInt       i,ii,cismax,ispar;
3057   Mat            *A,*B;
3058   IS             *isrow_p,*iscol_p,*cisrow,*ciscol,*ciscol_p;
3059 
3060   PetscFunctionBegin;
3061   if (!ismax) PetscFunctionReturn(0);
3062 
3063   for (i = 0, cismax = 0; i < ismax; ++i) {
3064     PetscMPIInt isize;
3065     ierr = MPI_Comm_compare(((PetscObject)isrow[i])->comm,((PetscObject)iscol[i])->comm,&flag);CHKERRQ(ierr);
3066     if (flag != MPI_IDENT) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Row and column index sets must have the same communicator");
3067     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm, &isize);CHKERRQ(ierr);
3068     if (isize > 1) ++cismax;
3069   }
3070 
3071   /*
3072      If cismax is zero on all C's ranks, then and only then can we use purely sequential matrix extraction.
3073      ispar counts the number of parallel ISs across C's comm.
3074   */
3075   ierr = MPIU_Allreduce(&cismax,&ispar,1,MPIU_INT,MPI_MAX,PetscObjectComm((PetscObject)C));CHKERRQ(ierr);
3076   if (!ispar) { /* Sequential ISs only across C's comm, so can call the sequential matrix extraction subroutine. */
3077     ierr = (*getsubmats_seq)(C,ismax,isrow,iscol,scall,submat);CHKERRQ(ierr);
3078     PetscFunctionReturn(0);
3079   }
3080 
3081   /* if (ispar) */
3082   /*
3083     Construct the "complements" -- the off-processor indices -- of the iscol ISs for parallel ISs only.
3084     These are used to extract the off-diag portion of the resulting parallel matrix.
3085     The row IS for the off-diag portion is the same as for the diag portion,
3086     so we merely alias (without increfing) the row IS, while skipping those that are sequential.
3087   */
3088   ierr = PetscMalloc2(cismax,&cisrow,cismax,&ciscol);CHKERRQ(ierr);
3089   ierr = PetscMalloc1(cismax,&ciscol_p);CHKERRQ(ierr);
3090   for (i = 0, ii = 0; i < ismax; ++i) {
3091     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm,&isize);CHKERRQ(ierr);
3092     if (isize > 1) {
3093       /*
3094 	 TODO: This is the part that's ***NOT SCALABLE***.
3095 	 To fix this we need to extract just the indices of C's nonzero columns
3096 	 that lie on the intersection of isrow[i] and ciscol[ii] -- the nonlocal
3097 	 part of iscol[i] -- without actually computing ciscol[ii]. This also has
3098 	 to be done without serializing on the IS list, so, most likely, it is best
3099 	 done by rewriting MatGetSubMatrices_MPIAIJ() directly.
3100       */
3101       ierr = ISGetNonlocalIS(iscol[i],&(ciscol[ii]));CHKERRQ(ierr);
3102       /* Now we have to
3103 	 (a) make sure ciscol[ii] is sorted, since, even if the off-proc indices
3104 	     were sorted on each rank, concatenated they might no longer be sorted;
3105 	 (b) Use ISSortPermutation() to construct ciscol_p, the mapping from the
3106 	     indices in the nondecreasing order to the original index positions.
3107 	 If ciscol[ii] is strictly increasing, the permutation IS is NULL.
3108       */
3109       ierr = ISSortPermutation(ciscol[ii],PETSC_FALSE,ciscol_p+ii);CHKERRQ(ierr);
3110       ierr = ISSort(ciscol[ii]);CHKERRQ(ierr);
3111       ++ii;
3112     }
3113   }
3114   ierr = PetscMalloc2(ismax,&isrow_p,ismax,&iscol_p);CHKERRQ(ierr);
3115   for (i = 0, ii = 0; i < ismax; ++i) {
3116     PetscInt       j,issize;
3117     const PetscInt *indices;
3118 
3119     /*
3120        Permute the indices into a nondecreasing order. Reject row and col indices with duplicates.
3121      */
3122     ierr = ISSortPermutation(isrow[i],PETSC_FALSE,isrow_p+i);CHKERRQ(ierr);
3123     ierr = ISSort(isrow[i]);CHKERRQ(ierr);
3124     ierr = ISGetLocalSize(isrow[i],&issize);CHKERRQ(ierr);
3125     ierr = ISGetIndices(isrow[i],&indices);CHKERRQ(ierr);
3126     for (j = 1; j < issize; ++j) {
3127       if (indices[j] == indices[j-1]) {
3128 	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]);
3129       }
3130     }
3131     ierr = ISRestoreIndices(isrow[i],&indices);CHKERRQ(ierr);
3132 
3133 
3134     ierr = ISSortPermutation(iscol[i],PETSC_FALSE,iscol_p+i);CHKERRQ(ierr);
3135     ierr = ISSort(iscol[i]);CHKERRQ(ierr);
3136     ierr = ISGetLocalSize(iscol[i],&issize);CHKERRQ(ierr);
3137     ierr = ISGetIndices(iscol[i],&indices);CHKERRQ(ierr);
3138     for (j = 1; j < issize; ++j) {
3139       if (indices[j-1] == indices[j]) {
3140 	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]);
3141       }
3142     }
3143     ierr = ISRestoreIndices(iscol[i],&indices);CHKERRQ(ierr);
3144     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm,&isize);CHKERRQ(ierr);
3145     if (isize > 1) {
3146       cisrow[ii] = isrow[i];
3147       ++ii;
3148     }
3149   }
3150   /*
3151     Allocate the necessary arrays to hold the resulting parallel matrices as well as the intermediate
3152     array of sequential matrices underlying the resulting parallel matrices.
3153     Which arrays to allocate is based on the value of MatReuse scall and whether ISs are sorted and/or
3154     contain duplicates.
3155 
3156     There are as many diag matrices as there are original index sets. There are only as many parallel
3157     and off-diag matrices, as there are parallel (comm size > 1) index sets.
3158 
3159     ARRAYS that can hold Seq matrices get allocated in any event -- either here or by getsubmats_seq():
3160     - If the array of MPI matrices already exists and is being reused, we need to allocate the array
3161       and extract the underlying seq matrices into it to serve as placeholders, into which getsubmats_seq
3162       will deposite the extracted diag and off-diag parts. Thus, we allocate the A&B arrays and fill them
3163       with A[i] and B[ii] extracted from the corresponding MPI submat.
3164     - However, if the rows, A's column indices or B's column indices are not sorted, the extracted A[i] & B[ii]
3165       will have a different order from what getsubmats_seq expects.  To handle this case -- indicated
3166       by a nonzero isrow_p[i], iscol_p[i], or ciscol_p[ii] -- we duplicate A[i] --> AA[i], B[ii] --> BB[ii]
3167       (retrieve composed AA[i] or BB[ii]) and reuse them here. AA[i] and BB[ii] are then used to permute its
3168       values into A[i] and B[ii] sitting inside the corresponding submat.
3169     - If no reuse is taking place then getsubmats_seq will allocate the A&B arrays and create the corresponding
3170       A[i], B[ii], AA[i] or BB[ii] matrices.
3171   */
3172   /* Parallel matrix array is allocated here only if no reuse is taking place. If reused, it is passed in by the caller. */
3173   if (scall == MAT_INITIAL_MATRIX) {
3174     ierr = PetscMalloc1(ismax,submat);CHKERRQ(ierr);
3175   }
3176 
3177   /* Now obtain the sequential A and B submatrices separately. */
3178   /* scall=MAT_REUSE_MATRIX is not handled yet, because getsubmats_seq() requires reuse of A and B */
3179   ierr = (*getsubmats_seq)(C,ismax,isrow,iscol,MAT_INITIAL_MATRIX,&A);CHKERRQ(ierr);
3180   ierr = (*getsubmats_seq)(C,cismax,cisrow,ciscol,MAT_INITIAL_MATRIX,&B);CHKERRQ(ierr);
3181 
3182   /*
3183     If scall == MAT_REUSE_MATRIX AND the permutations are NULL, we are done, since the sequential
3184     matrices A & B have been extracted directly into the parallel matrices containing them, or
3185     simply into the sequential matrix identical with the corresponding A (if isize == 1).
3186     Note that in that case colmap doesn't need to be rebuilt, since the matrices are expected
3187     to have the same sparsity pattern.
3188     Otherwise, A and/or B have to be properly embedded into C's index spaces and the correct colmap
3189     must be constructed for C. This is done by setseqmat(s).
3190   */
3191   for (i = 0, ii = 0; i < ismax; ++i) {
3192     /*
3193        TODO: cache ciscol, permutation ISs and maybe cisrow? What about isrow & iscol?
3194        That way we can avoid sorting and computing permutations when reusing.
3195        To this end:
3196         - remove the old cache, if it exists, when extracting submatrices with MAT_INITIAL_MATRIX
3197 	- if caching arrays to hold the ISs, make and compose a container for them so that it can
3198 	  be destroyed upon destruction of C (use PetscContainerUserDestroy() to clear out the contents).
3199     */
3200     MatStructure pattern;
3201     pattern = DIFFERENT_NONZERO_PATTERN;
3202 
3203     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm,&isize);CHKERRQ(ierr);
3204     /* Construct submat[i] from the Seq pieces A (and B, if necessary). */
3205     if (isize > 1) {
3206       if (scall == MAT_INITIAL_MATRIX) {
3207 	ierr = MatCreate(((PetscObject)isrow[i])->comm,(*submat)+i);CHKERRQ(ierr);
3208 	ierr = MatSetSizes((*submat)[i],A[i]->rmap->n,A[i]->cmap->n,PETSC_DETERMINE,PETSC_DETERMINE);CHKERRQ(ierr);
3209 	ierr = MatSetType((*submat)[i],MATMPIAIJ);CHKERRQ(ierr);
3210 	ierr = PetscLayoutSetUp((*submat)[i]->rmap);CHKERRQ(ierr);
3211 	ierr = PetscLayoutSetUp((*submat)[i]->cmap);CHKERRQ(ierr);
3212       }
3213       /*
3214 	For each parallel isrow[i], insert the extracted sequential matrices into the parallel matrix.
3215       */
3216       {
3217 	Mat AA,BB;
3218         AA = A[i];
3219         BB = B[ii];
3220 	if (AA || BB) {
3221 	  ierr = setseqmats((*submat)[i],isrow_p[i],iscol_p[i],ciscol_p[ii],pattern,AA,BB);CHKERRQ(ierr);
3222 	  ierr = MatAssemblyBegin((*submat)[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
3223 	  ierr = MatAssemblyEnd((*submat)[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
3224 	}
3225 
3226         ierr = MatDestroy(&AA);CHKERRQ(ierr);
3227         ierr = MatDestroy(&BB);CHKERRQ(ierr);
3228       }
3229       ierr = ISDestroy(ciscol+ii);CHKERRQ(ierr);
3230       ierr = ISDestroy(ciscol_p+ii);CHKERRQ(ierr);
3231       ++ii;
3232     } else { /* if (isize == 1) */
3233       if (scall == MAT_REUSE_MATRIX) {
3234         ierr = MatDestroy(&(*submat)[i]);CHKERRQ(ierr);
3235       }
3236       if (isrow_p[i] || iscol_p[i]) {
3237         ierr = MatDuplicate(A[i],MAT_DO_NOT_COPY_VALUES,(*submat)+i);CHKERRQ(ierr);
3238         ierr = setseqmat((*submat)[i],isrow_p[i],iscol_p[i],pattern,A[i]);CHKERRQ(ierr);
3239 	/* Otherwise A is extracted straight into (*submats)[i]. */
3240 	/* TODO: Compose A[i] on (*submat([i] for future use, if ((isrow_p[i] || iscol_p[i]) && MAT_INITIAL_MATRIX). */
3241 	ierr = MatDestroy(A+i);CHKERRQ(ierr);
3242       } else (*submat)[i] = A[i];
3243     }
3244     ierr = ISDestroy(&isrow_p[i]);CHKERRQ(ierr);
3245     ierr = ISDestroy(&iscol_p[i]);CHKERRQ(ierr);
3246   }
3247   ierr = PetscFree2(cisrow,ciscol);CHKERRQ(ierr);
3248   ierr = PetscFree2(isrow_p,iscol_p);CHKERRQ(ierr);
3249   ierr = PetscFree(ciscol_p);CHKERRQ(ierr);
3250   ierr = PetscFree(A);CHKERRQ(ierr);
3251   ierr = PetscFree(B);CHKERRQ(ierr);
3252   PetscFunctionReturn(0);
3253 }
3254 
3255 PetscErrorCode MatGetSubMatricesMPI_MPIAIJ(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[])
3256 {
3257   PetscErrorCode ierr;
3258 
3259   PetscFunctionBegin;
3260   ierr = MatGetSubMatricesMPI_MPIXAIJ(C,ismax,isrow,iscol,scall,submat,MatGetSubMatrices_MPIAIJ,MatGetSeqMats_MPIAIJ,MatSetSeqMat_SeqAIJ,MatSetSeqMats_MPIAIJ);CHKERRQ(ierr);
3261   PetscFunctionReturn(0);
3262 }
3263