xref: /petsc/src/mat/impls/aij/mpi/mpiov.c (revision 2c49b84a12866a53d6c320c2a0b3f6953a6d6501)
1 /*
2    Routines to compute overlapping regions of a parallel MPI matrix
3   and to find submatrices that were shared across processors.
4 */
5 #include <../src/mat/impls/aij/seq/aij.h>
6 #include <../src/mat/impls/aij/mpi/mpiaij.h>
7 #include <petscbt.h>
8 #include <petscsf.h>
9 
10 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Once(Mat,PetscInt,IS*);
11 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Local(Mat,PetscInt,char**,PetscInt*,PetscInt**,PetscTable*);
12 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Receive(Mat,PetscInt,PetscInt**,PetscInt**,PetscInt*);
13 extern PetscErrorCode MatGetRow_MPIAIJ(Mat,PetscInt,PetscInt*,PetscInt**,PetscScalar**);
14 extern PetscErrorCode MatRestoreRow_MPIAIJ(Mat,PetscInt,PetscInt*,PetscInt**,PetscScalar**);
15 
16 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Once_Scalable(Mat,PetscInt,IS*);
17 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Local_Scalable(Mat,PetscInt,IS*);
18 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Send_Scalable(Mat,PetscInt,PetscMPIInt,PetscMPIInt *,PetscInt *, PetscInt *,PetscInt **,PetscInt **);
19 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Receive_Scalable(Mat,PetscInt,IS*,PetscInt,PetscInt *);
20 
21 
22 PetscErrorCode MatIncreaseOverlap_MPIAIJ(Mat C,PetscInt imax,IS is[],PetscInt ov)
23 {
24   PetscErrorCode ierr;
25   PetscInt       i;
26 
27   PetscFunctionBegin;
28   if (ov < 0) SETERRQ(PetscObjectComm((PetscObject)C),PETSC_ERR_ARG_OUTOFRANGE,"Negative overlap specified");
29   for (i=0; i<ov; ++i) {
30     ierr = MatIncreaseOverlap_MPIAIJ_Once(C,imax,is);CHKERRQ(ierr);
31   }
32   PetscFunctionReturn(0);
33 }
34 
35 PetscErrorCode MatIncreaseOverlap_MPIAIJ_Scalable(Mat C,PetscInt imax,IS is[],PetscInt ov)
36 {
37   PetscErrorCode ierr;
38   PetscInt       i;
39 
40   PetscFunctionBegin;
41   if (ov < 0) SETERRQ(PetscObjectComm((PetscObject)C),PETSC_ERR_ARG_OUTOFRANGE,"Negative overlap specified");
42   for (i=0; i<ov; ++i) {
43     ierr = MatIncreaseOverlap_MPIAIJ_Once_Scalable(C,imax,is);CHKERRQ(ierr);
44   }
45   PetscFunctionReturn(0);
46 }
47 
48 
49 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Once_Scalable(Mat mat,PetscInt nidx,IS is[])
50 {
51   PetscErrorCode   ierr;
52   MPI_Comm         comm;
53   PetscInt        *length,length_i,tlength,*remoterows,nrrows,reducednrrows,*rrow_ranks,*rrow_isids,i,j,owner;
54   PetscInt         *tosizes,*tosizes_temp,*toffsets,*fromsizes,*todata,*fromdata;
55   PetscInt         nrecvrows,*sbsizes = 0,*sbdata = 0;
56   const PetscInt  *indices_i,**indices;
57   PetscLayout      rmap;
58   PetscMPIInt      rank,size,*toranks,*fromranks,nto,nfrom;
59   PetscSF          sf;
60   PetscSFNode     *remote;
61 
62   PetscFunctionBegin;
63   ierr = PetscObjectGetComm((PetscObject)mat,&comm);CHKERRQ(ierr);
64   ierr = MPI_Comm_rank(comm,&rank);CHKERRQ(ierr);
65   ierr = MPI_Comm_size(comm,&size);CHKERRQ(ierr);
66   /* get row map to determine where rows should be going */
67   ierr = MatGetLayouts(mat,&rmap,NULL);CHKERRQ(ierr);
68   /* retrieve IS data and put all together so that we
69    * can optimize communication
70    *  */
71   ierr = PetscCalloc2(nidx,(PetscInt ***)&indices,nidx,&length);CHKERRQ(ierr);
72   for (i=0,tlength=0; i<nidx; i++){
73     ierr = ISGetLocalSize(is[i],&length[i]);CHKERRQ(ierr);
74     tlength += length[i];
75     ierr = ISGetIndices(is[i],&indices[i]);CHKERRQ(ierr);
76   }
77   /* find these rows on remote processors */
78   ierr = PetscCalloc3(tlength,&remoterows,tlength,&rrow_ranks,tlength,&rrow_isids);CHKERRQ(ierr);
79   ierr = PetscCalloc3(size,&toranks,2*size,&tosizes,size,&tosizes_temp);CHKERRQ(ierr);
80   nrrows = 0;
81   for (i=0; i<nidx; i++){
82     length_i     = length[i];
83     indices_i    = indices[i];
84     for (j=0; j<length_i; j++){
85       owner = -1;
86       ierr = PetscLayoutFindOwner(rmap,indices_i[j],&owner);CHKERRQ(ierr);
87       /* remote processors */
88       if (owner != rank){
89         tosizes_temp[owner]++; /* number of rows to owner */
90         rrow_ranks[nrrows]  = owner; /* processor */
91         rrow_isids[nrrows]   = i; /* is id */
92         remoterows[nrrows++] = indices_i[j]; /* row */
93       }
94     }
95     ierr = ISRestoreIndices(is[i],&indices[i]);CHKERRQ(ierr);
96   }
97   ierr = PetscFree2(indices,length);CHKERRQ(ierr);
98   /* test if we need to exchange messages
99    * generally speaking, we do not need to exchange
100    * data when overlap is 1
101    * */
102   ierr = MPIU_Allreduce(&nrrows,&reducednrrows,1,MPIU_INT,MPIU_MAX,comm);CHKERRQ(ierr);
103   /* we do not have any messages
104    * It usually corresponds to overlap 1
105    * */
106   if (!reducednrrows){
107     ierr = PetscFree3(toranks,tosizes,tosizes_temp);CHKERRQ(ierr);
108     ierr = PetscFree3(remoterows,rrow_ranks,rrow_isids);CHKERRQ(ierr);
109     ierr = MatIncreaseOverlap_MPIAIJ_Local_Scalable(mat,nidx,is);CHKERRQ(ierr);
110     PetscFunctionReturn(0);
111   }
112   nto = 0;
113   /* send sizes and ranks for building a two-sided communcation */
114   for (i=0; i<size; i++){
115    if (tosizes_temp[i]){
116      tosizes[nto*2]  = tosizes_temp[i]*2; /* size */
117      tosizes_temp[i] = nto; /* a map from processor to index */
118      toranks[nto++]  = i; /* processor */
119    }
120   }
121   ierr = PetscCalloc1(nto+1,&toffsets);CHKERRQ(ierr);
122   for (i=0; i<nto; i++){
123     toffsets[i+1]  = toffsets[i]+tosizes[2*i]; /* offsets */
124     tosizes[2*i+1] = toffsets[i]; /* offsets to send */
125   }
126   /* send information to other processors */
127   ierr = PetscCommBuildTwoSided(comm,2,MPIU_INT,nto,toranks,tosizes,&nfrom,&fromranks,&fromsizes);CHKERRQ(ierr);
128   nrecvrows = 0;
129   for (i=0; i<nfrom; i++) nrecvrows += fromsizes[2*i];
130   ierr = PetscMalloc1(nrecvrows,&remote);CHKERRQ(ierr);
131   nrecvrows = 0;
132   for (i=0; i<nfrom; i++){
133     for (j=0; j<fromsizes[2*i]; j++){
134       remote[nrecvrows].rank    = fromranks[i];
135       remote[nrecvrows++].index = fromsizes[2*i+1]+j;
136     }
137   }
138   ierr = PetscSFCreate(comm,&sf);CHKERRQ(ierr);
139   ierr = PetscSFSetGraph(sf,nrecvrows,nrecvrows,NULL,PETSC_OWN_POINTER,remote,PETSC_OWN_POINTER);CHKERRQ(ierr);
140   /* use two-sided communication by default since OPENMPI has some bugs for one-sided one */
141   ierr = PetscSFSetType(sf,PETSCSFBASIC);CHKERRQ(ierr);
142   ierr = PetscSFSetFromOptions(sf);CHKERRQ(ierr);
143   /* message pair <no of is, row>  */
144   ierr = PetscCalloc2(2*nrrows,&todata,nrecvrows,&fromdata);CHKERRQ(ierr);
145   for (i=0; i<nrrows; i++){
146     owner = rrow_ranks[i]; /* processor */
147     j     = tosizes_temp[owner]; /* index */
148     todata[toffsets[j]++] = rrow_isids[i];
149     todata[toffsets[j]++] = remoterows[i];
150   }
151   ierr = PetscFree3(toranks,tosizes,tosizes_temp);CHKERRQ(ierr);
152   ierr = PetscFree3(remoterows,rrow_ranks,rrow_isids);CHKERRQ(ierr);
153   ierr = PetscFree(toffsets);CHKERRQ(ierr);
154   ierr = PetscSFBcastBegin(sf,MPIU_INT,todata,fromdata);CHKERRQ(ierr);
155   ierr = PetscSFBcastEnd(sf,MPIU_INT,todata,fromdata);CHKERRQ(ierr);
156   ierr = PetscSFDestroy(&sf);CHKERRQ(ierr);
157   /* send rows belonging to the remote so that then we could get the overlapping data back */
158   ierr = MatIncreaseOverlap_MPIAIJ_Send_Scalable(mat,nidx,nfrom,fromranks,fromsizes,fromdata,&sbsizes,&sbdata);CHKERRQ(ierr);
159   ierr = PetscFree2(todata,fromdata);CHKERRQ(ierr);
160   ierr = PetscFree(fromsizes);CHKERRQ(ierr);
161   ierr = PetscCommBuildTwoSided(comm,2,MPIU_INT,nfrom,fromranks,sbsizes,&nto,&toranks,&tosizes);CHKERRQ(ierr);
162   ierr = PetscFree(fromranks);CHKERRQ(ierr);
163   nrecvrows = 0;
164   for (i=0; i<nto; i++) nrecvrows += tosizes[2*i];
165   ierr = PetscCalloc1(nrecvrows,&todata);CHKERRQ(ierr);
166   ierr = PetscMalloc1(nrecvrows,&remote);CHKERRQ(ierr);
167   nrecvrows = 0;
168   for (i=0; i<nto; i++){
169     for (j=0; j<tosizes[2*i]; j++){
170       remote[nrecvrows].rank    = toranks[i];
171       remote[nrecvrows++].index = tosizes[2*i+1]+j;
172     }
173   }
174   ierr = PetscSFCreate(comm,&sf);CHKERRQ(ierr);
175   ierr = PetscSFSetGraph(sf,nrecvrows,nrecvrows,NULL,PETSC_OWN_POINTER,remote,PETSC_OWN_POINTER);CHKERRQ(ierr);
176   /* use two-sided communication by default since OPENMPI has some bugs for one-sided one */
177   ierr = PetscSFSetType(sf,PETSCSFBASIC);CHKERRQ(ierr);
178   ierr = PetscSFSetFromOptions(sf);CHKERRQ(ierr);
179   /* overlap communication and computation */
180   ierr = PetscSFBcastBegin(sf,MPIU_INT,sbdata,todata);CHKERRQ(ierr);
181   ierr = MatIncreaseOverlap_MPIAIJ_Local_Scalable(mat,nidx,is);CHKERRQ(ierr);
182   ierr = PetscSFBcastEnd(sf,MPIU_INT,sbdata,todata);CHKERRQ(ierr);
183   ierr = PetscSFDestroy(&sf);CHKERRQ(ierr);
184   ierr = PetscFree2(sbdata,sbsizes);CHKERRQ(ierr);
185   ierr = MatIncreaseOverlap_MPIAIJ_Receive_Scalable(mat,nidx,is,nrecvrows,todata);CHKERRQ(ierr);
186   ierr = PetscFree(toranks);CHKERRQ(ierr);
187   ierr = PetscFree(tosizes);CHKERRQ(ierr);
188   ierr = PetscFree(todata);CHKERRQ(ierr);
189   PetscFunctionReturn(0);
190 }
191 
192 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Receive_Scalable(Mat mat,PetscInt nidx, IS is[], PetscInt nrecvs, PetscInt *recvdata)
193 {
194   PetscInt         *isz,isz_i,i,j,is_id, data_size;
195   PetscInt          col,lsize,max_lsize,*indices_temp, *indices_i;
196   const PetscInt   *indices_i_temp;
197   PetscErrorCode    ierr;
198 
199   PetscFunctionBegin;
200   max_lsize = 0;
201   ierr = PetscMalloc1(nidx,&isz);CHKERRQ(ierr);
202   for (i=0; i<nidx; i++){
203     ierr = ISGetLocalSize(is[i],&lsize);CHKERRQ(ierr);
204     max_lsize = lsize>max_lsize ? lsize:max_lsize;
205     isz[i]    = lsize;
206   }
207   ierr = PetscMalloc1((max_lsize+nrecvs)*nidx,&indices_temp);CHKERRQ(ierr);
208   for (i=0; i<nidx; i++){
209     ierr = ISGetIndices(is[i],&indices_i_temp);CHKERRQ(ierr);
210     ierr = PetscMemcpy(indices_temp+i*(max_lsize+nrecvs),indices_i_temp, sizeof(PetscInt)*isz[i]);CHKERRQ(ierr);
211     ierr = ISRestoreIndices(is[i],&indices_i_temp);CHKERRQ(ierr);
212     ierr = ISDestroy(&is[i]);CHKERRQ(ierr);
213   }
214   /* retrieve information to get row id and its overlap */
215   for (i=0; i<nrecvs; ){
216     is_id      = recvdata[i++];
217     data_size  = recvdata[i++];
218     indices_i  = indices_temp+(max_lsize+nrecvs)*is_id;
219     isz_i      = isz[is_id];
220     for (j=0; j< data_size; j++){
221       col = recvdata[i++];
222       indices_i[isz_i++] = col;
223     }
224     isz[is_id] = isz_i;
225   }
226   /* remove duplicate entities */
227   for (i=0; i<nidx; i++){
228     indices_i  = indices_temp+(max_lsize+nrecvs)*i;
229     isz_i      = isz[i];
230     ierr = PetscSortRemoveDupsInt(&isz_i,indices_i);CHKERRQ(ierr);
231     ierr = ISCreateGeneral(PETSC_COMM_SELF,isz_i,indices_i,PETSC_COPY_VALUES,&is[i]);CHKERRQ(ierr);
232   }
233   ierr = PetscFree(isz);CHKERRQ(ierr);
234   ierr = PetscFree(indices_temp);CHKERRQ(ierr);
235   PetscFunctionReturn(0);
236 }
237 
238 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Send_Scalable(Mat mat,PetscInt nidx, PetscMPIInt nfrom,PetscMPIInt *fromranks,PetscInt *fromsizes, PetscInt *fromrows, PetscInt **sbrowsizes, PetscInt **sbrows)
239 {
240   PetscLayout       rmap,cmap;
241   PetscInt          i,j,k,l,*rows_i,*rows_data_ptr,**rows_data,max_fszs,rows_pos,*rows_pos_i;
242   PetscInt          is_id,tnz,an,bn,rstart,cstart,row,start,end,col,totalrows,*sbdata;
243   PetscInt         *indv_counts,indvc_ij,*sbsizes,*indices_tmp,*offsets;
244   const PetscInt   *gcols,*ai,*aj,*bi,*bj;
245   Mat               amat,bmat;
246   PetscMPIInt       rank;
247   PetscBool         done;
248   MPI_Comm          comm;
249   PetscErrorCode    ierr;
250 
251   PetscFunctionBegin;
252   ierr = PetscObjectGetComm((PetscObject)mat,&comm);CHKERRQ(ierr);
253   ierr = MPI_Comm_rank(comm,&rank);CHKERRQ(ierr);
254   ierr = MatMPIAIJGetSeqAIJ(mat,&amat,&bmat,&gcols);CHKERRQ(ierr);
255   /* Even if the mat is symmetric, we still assume it is not symmetric */
256   ierr = MatGetRowIJ(amat,0,PETSC_FALSE,PETSC_FALSE,&an,&ai,&aj,&done);CHKERRQ(ierr);
257   if (!done) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"can not get row IJ \n");
258   ierr = MatGetRowIJ(bmat,0,PETSC_FALSE,PETSC_FALSE,&bn,&bi,&bj,&done);CHKERRQ(ierr);
259   if (!done) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"can not get row IJ \n");
260   /* total number of nonzero values is used to estimate the memory usage in the next step */
261   tnz  = ai[an]+bi[bn];
262   ierr = MatGetLayouts(mat,&rmap,&cmap);CHKERRQ(ierr);
263   ierr = PetscLayoutGetRange(rmap,&rstart,NULL);CHKERRQ(ierr);
264   ierr = PetscLayoutGetRange(cmap,&cstart,NULL);CHKERRQ(ierr);
265   /* to find the longest message */
266   max_fszs = 0;
267   for (i=0; i<nfrom; i++) max_fszs = fromsizes[2*i]>max_fszs ? fromsizes[2*i]:max_fszs;
268   /* better way to estimate number of nonzero in the mat??? */
269   ierr = PetscCalloc5(max_fszs*nidx,&rows_data_ptr,nidx,&rows_data,nidx,&rows_pos_i,nfrom*nidx,&indv_counts,tnz,&indices_tmp);CHKERRQ(ierr);
270   for (i=0; i<nidx; i++) rows_data[i] = rows_data_ptr+max_fszs*i;
271   rows_pos  = 0;
272   totalrows = 0;
273   for (i=0; i<nfrom; i++){
274     ierr = PetscMemzero(rows_pos_i,sizeof(PetscInt)*nidx);CHKERRQ(ierr);
275     /* group data together */
276     for (j=0; j<fromsizes[2*i]; j+=2){
277       is_id                       = fromrows[rows_pos++];/* no of is */
278       rows_i                      = rows_data[is_id];
279       rows_i[rows_pos_i[is_id]++] = fromrows[rows_pos++];/* row */
280     }
281     /* estimate a space to avoid multiple allocations  */
282     for (j=0; j<nidx; j++){
283       indvc_ij = 0;
284       rows_i   = rows_data[j];
285       for (l=0; l<rows_pos_i[j]; l++){
286         row    = rows_i[l]-rstart;
287         start  = ai[row];
288         end    = ai[row+1];
289         for (k=start; k<end; k++){ /* Amat */
290           col = aj[k] + cstart;
291           indices_tmp[indvc_ij++] = col;/* do not count the rows from the original rank */
292         }
293         start = bi[row];
294         end   = bi[row+1];
295         for (k=start; k<end; k++) { /* Bmat */
296           col = gcols[bj[k]];
297           indices_tmp[indvc_ij++] = col;
298         }
299       }
300       ierr = PetscSortRemoveDupsInt(&indvc_ij,indices_tmp);CHKERRQ(ierr);
301       indv_counts[i*nidx+j] = indvc_ij;
302       totalrows            += indvc_ij;
303     }
304   }
305   /* message triple <no of is, number of rows, rows> */
306   ierr = PetscCalloc2(totalrows+nidx*nfrom*2,&sbdata,2*nfrom,&sbsizes);CHKERRQ(ierr);
307   totalrows = 0;
308   rows_pos  = 0;
309   /* use this code again */
310   for (i=0;i<nfrom;i++){
311     ierr = PetscMemzero(rows_pos_i,sizeof(PetscInt)*nidx);CHKERRQ(ierr);
312     for (j=0; j<fromsizes[2*i]; j+=2){
313       is_id                       = fromrows[rows_pos++];
314       rows_i                      = rows_data[is_id];
315       rows_i[rows_pos_i[is_id]++] = fromrows[rows_pos++];
316     }
317     /* add data  */
318     for (j=0; j<nidx; j++){
319       if (!indv_counts[i*nidx+j]) continue;
320       indvc_ij = 0;
321       sbdata[totalrows++] = j;
322       sbdata[totalrows++] = indv_counts[i*nidx+j];
323       sbsizes[2*i]       += 2;
324       rows_i              = rows_data[j];
325       for (l=0; l<rows_pos_i[j]; l++){
326         row   = rows_i[l]-rstart;
327         start = ai[row];
328         end   = ai[row+1];
329         for (k=start; k<end; k++){ /* Amat */
330           col = aj[k] + cstart;
331           indices_tmp[indvc_ij++] = col;
332         }
333         start = bi[row];
334         end   = bi[row+1];
335         for (k=start; k<end; k++) { /* Bmat */
336           col = gcols[bj[k]];
337           indices_tmp[indvc_ij++] = col;
338         }
339       }
340       ierr = PetscSortRemoveDupsInt(&indvc_ij,indices_tmp);CHKERRQ(ierr);
341       sbsizes[2*i]  += indvc_ij;
342       ierr = PetscMemcpy(sbdata+totalrows,indices_tmp,sizeof(PetscInt)*indvc_ij);CHKERRQ(ierr);
343       totalrows += indvc_ij;
344     }
345   }
346   ierr = PetscCalloc1(nfrom+1,&offsets);CHKERRQ(ierr);
347   for (i=0; i<nfrom; i++){
348     offsets[i+1]   = offsets[i] + sbsizes[2*i];
349     sbsizes[2*i+1] = offsets[i];
350   }
351   ierr = PetscFree(offsets);CHKERRQ(ierr);
352   if (sbrowsizes) *sbrowsizes = sbsizes;
353   if (sbrows) *sbrows = sbdata;
354   ierr = PetscFree5(rows_data_ptr,rows_data,rows_pos_i,indv_counts,indices_tmp);CHKERRQ(ierr);
355   ierr = MatRestoreRowIJ(amat,0,PETSC_FALSE,PETSC_FALSE,&an,&ai,&aj,&done);CHKERRQ(ierr);
356   ierr = MatRestoreRowIJ(bmat,0,PETSC_FALSE,PETSC_FALSE,&bn,&bi,&bj,&done);CHKERRQ(ierr);
357   PetscFunctionReturn(0);
358 }
359 
360 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Local_Scalable(Mat mat,PetscInt nidx, IS is[])
361 {
362   const PetscInt   *gcols,*ai,*aj,*bi,*bj, *indices;
363   PetscInt          tnz,an,bn,i,j,row,start,end,rstart,cstart,col,k,*indices_temp;
364   PetscInt          lsize,lsize_tmp,owner;
365   PetscMPIInt       rank;
366   Mat               amat,bmat;
367   PetscBool         done;
368   PetscLayout       cmap,rmap;
369   MPI_Comm          comm;
370   PetscErrorCode    ierr;
371 
372   PetscFunctionBegin;
373   ierr = PetscObjectGetComm((PetscObject)mat,&comm);CHKERRQ(ierr);
374   ierr = MPI_Comm_rank(comm,&rank);CHKERRQ(ierr);
375   ierr = MatMPIAIJGetSeqAIJ(mat,&amat,&bmat,&gcols);CHKERRQ(ierr);
376   ierr = MatGetRowIJ(amat,0,PETSC_FALSE,PETSC_FALSE,&an,&ai,&aj,&done);CHKERRQ(ierr);
377   if (!done) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"can not get row IJ \n");
378   ierr = MatGetRowIJ(bmat,0,PETSC_FALSE,PETSC_FALSE,&bn,&bi,&bj,&done);CHKERRQ(ierr);
379   if (!done) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"can not get row IJ \n");
380   /* is it a safe way to compute number of nonzero values ? */
381   tnz  = ai[an]+bi[bn];
382   ierr = MatGetLayouts(mat,&rmap,&cmap);CHKERRQ(ierr);
383   ierr = PetscLayoutGetRange(rmap,&rstart,NULL);CHKERRQ(ierr);
384   ierr = PetscLayoutGetRange(cmap,&cstart,NULL);CHKERRQ(ierr);
385   /* it is a better way to estimate memory than the old implementation
386    * where global size of matrix is used
387    * */
388   ierr = PetscMalloc1(tnz,&indices_temp);CHKERRQ(ierr);
389   for (i=0; i<nidx; i++) {
390     ierr = ISGetLocalSize(is[i],&lsize);CHKERRQ(ierr);
391     ierr = ISGetIndices(is[i],&indices);CHKERRQ(ierr);
392     lsize_tmp = 0;
393     for (j=0; j<lsize; j++) {
394       owner = -1;
395       row   = indices[j];
396       ierr = PetscLayoutFindOwner(rmap,row,&owner);CHKERRQ(ierr);
397       if (owner != rank) continue;
398       /* local number */
399       row  -= rstart;
400       start = ai[row];
401       end   = ai[row+1];
402       for (k=start; k<end; k++) { /* Amat */
403         col = aj[k] + cstart;
404         indices_temp[lsize_tmp++] = col;
405       }
406       start = bi[row];
407       end   = bi[row+1];
408       for (k=start; k<end; k++) { /* Bmat */
409         col = gcols[bj[k]];
410         indices_temp[lsize_tmp++] = col;
411       }
412     }
413    ierr = ISRestoreIndices(is[i],&indices);CHKERRQ(ierr);
414    ierr = ISDestroy(&is[i]);CHKERRQ(ierr);
415    ierr = PetscSortRemoveDupsInt(&lsize_tmp,indices_temp);CHKERRQ(ierr);
416    ierr = ISCreateGeneral(PETSC_COMM_SELF,lsize_tmp,indices_temp,PETSC_COPY_VALUES,&is[i]);CHKERRQ(ierr);
417   }
418   ierr = PetscFree(indices_temp);CHKERRQ(ierr);
419   ierr = MatRestoreRowIJ(amat,0,PETSC_FALSE,PETSC_FALSE,&an,&ai,&aj,&done);CHKERRQ(ierr);
420   ierr = MatRestoreRowIJ(bmat,0,PETSC_FALSE,PETSC_FALSE,&bn,&bi,&bj,&done);CHKERRQ(ierr);
421   PetscFunctionReturn(0);
422 }
423 
424 
425 /*
426   Sample message format:
427   If a processor A wants processor B to process some elements corresponding
428   to index sets is[1],is[5]
429   mesg [0] = 2   (no of index sets in the mesg)
430   -----------
431   mesg [1] = 1 => is[1]
432   mesg [2] = sizeof(is[1]);
433   -----------
434   mesg [3] = 5  => is[5]
435   mesg [4] = sizeof(is[5]);
436   -----------
437   mesg [5]
438   mesg [n]  datas[1]
439   -----------
440   mesg[n+1]
441   mesg[m]  data(is[5])
442   -----------
443 
444   Notes:
445   nrqs - no of requests sent (or to be sent out)
446   nrqr - no of requests recieved (which have to be or which have been processed
447 */
448 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Once(Mat C,PetscInt imax,IS is[])
449 {
450   Mat_MPIAIJ     *c = (Mat_MPIAIJ*)C->data;
451   PetscMPIInt    *w1,*w2,nrqr,*w3,*w4,*onodes1,*olengths1,*onodes2,*olengths2;
452   const PetscInt **idx,*idx_i;
453   PetscInt       *n,**data,len;
454 #if defined(PETSC_USE_CTABLE)
455   PetscTable     *table_data,table_data_i;
456   PetscInt       *tdata,tcount,tcount_max;
457 #else
458   PetscInt       *data_i,*d_p;
459 #endif
460   PetscErrorCode ierr;
461   PetscMPIInt    size,rank,tag1,tag2;
462   PetscInt       M,i,j,k,**rbuf,row,proc = 0,nrqs,msz,**outdat,**ptr;
463   PetscInt       *ctr,*pa,*tmp,*isz,*isz1,**xdata,**rbuf2;
464   PetscBT        *table;
465   MPI_Comm       comm;
466   MPI_Request    *s_waits1,*r_waits1,*s_waits2,*r_waits2;
467   MPI_Status     *s_status,*recv_status;
468   char           *t_p;
469 
470   PetscFunctionBegin;
471   ierr = PetscObjectGetComm((PetscObject)C,&comm);CHKERRQ(ierr);
472   size = c->size;
473   rank = c->rank;
474   M    = C->rmap->N;
475 
476   ierr = PetscObjectGetNewTag((PetscObject)C,&tag1);CHKERRQ(ierr);
477   ierr = PetscObjectGetNewTag((PetscObject)C,&tag2);CHKERRQ(ierr);
478 
479   ierr = PetscMalloc2(imax,&idx,imax,&n);CHKERRQ(ierr);
480 
481   for (i=0; i<imax; i++) {
482     ierr = ISGetIndices(is[i],&idx[i]);CHKERRQ(ierr);
483     ierr = ISGetLocalSize(is[i],&n[i]);CHKERRQ(ierr);
484   }
485 
486   /* evaluate communication - mesg to who,length of mesg, and buffer space
487      required. Based on this, buffers are allocated, and data copied into them  */
488   ierr = PetscMalloc4(size,&w1,size,&w2,size,&w3,size,&w4);CHKERRQ(ierr);
489   ierr = PetscMemzero(w1,size*sizeof(PetscMPIInt));CHKERRQ(ierr); /* initialise work vector*/
490   ierr = PetscMemzero(w2,size*sizeof(PetscMPIInt));CHKERRQ(ierr); /* initialise work vector*/
491   ierr = PetscMemzero(w3,size*sizeof(PetscMPIInt));CHKERRQ(ierr); /* initialise work vector*/
492   for (i=0; i<imax; i++) {
493     ierr  = PetscMemzero(w4,size*sizeof(PetscMPIInt));CHKERRQ(ierr); /* initialise work vector*/
494     idx_i = idx[i];
495     len   = n[i];
496     for (j=0; j<len; j++) {
497       row = idx_i[j];
498       if (row < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"Index set cannot have negative entries");
499       ierr = PetscLayoutFindOwner(C->rmap,row,&proc);CHKERRQ(ierr);
500       w4[proc]++;
501     }
502     for (j=0; j<size; j++) {
503       if (w4[j]) { w1[j] += w4[j]; w3[j]++;}
504     }
505   }
506 
507   nrqs     = 0;              /* no of outgoing messages */
508   msz      = 0;              /* total mesg length (for all proc */
509   w1[rank] = 0;              /* no mesg sent to intself */
510   w3[rank] = 0;
511   for (i=0; i<size; i++) {
512     if (w1[i])  {w2[i] = 1; nrqs++;} /* there exists a message to proc i */
513   }
514   /* pa - is list of processors to communicate with */
515   ierr = PetscMalloc1(nrqs+1,&pa);CHKERRQ(ierr);
516   for (i=0,j=0; i<size; i++) {
517     if (w1[i]) {pa[j] = i; j++;}
518   }
519 
520   /* Each message would have a header = 1 + 2*(no of IS) + data */
521   for (i=0; i<nrqs; i++) {
522     j      = pa[i];
523     w1[j] += w2[j] + 2*w3[j];
524     msz   += w1[j];
525   }
526 
527   /* Determine the number of messages to expect, their lengths, from from-ids */
528   ierr = PetscGatherNumberOfMessages(comm,w2,w1,&nrqr);CHKERRQ(ierr);
529   ierr = PetscGatherMessageLengths(comm,nrqs,nrqr,w1,&onodes1,&olengths1);CHKERRQ(ierr);
530 
531   /* Now post the Irecvs corresponding to these messages */
532   ierr = PetscPostIrecvInt(comm,tag1,nrqr,onodes1,olengths1,&rbuf,&r_waits1);CHKERRQ(ierr);
533 
534   /* Allocate Memory for outgoing messages */
535   ierr = PetscMalloc4(size,&outdat,size,&ptr,msz,&tmp,size,&ctr);CHKERRQ(ierr);
536   ierr = PetscMemzero(outdat,size*sizeof(PetscInt*));CHKERRQ(ierr);
537   ierr = PetscMemzero(ptr,size*sizeof(PetscInt*));CHKERRQ(ierr);
538 
539   {
540     PetscInt *iptr = tmp,ict  = 0;
541     for (i=0; i<nrqs; i++) {
542       j         = pa[i];
543       iptr     +=  ict;
544       outdat[j] = iptr;
545       ict       = w1[j];
546     }
547   }
548 
549   /* Form the outgoing messages */
550   /* plug in the headers */
551   for (i=0; i<nrqs; i++) {
552     j            = pa[i];
553     outdat[j][0] = 0;
554     ierr         = PetscMemzero(outdat[j]+1,2*w3[j]*sizeof(PetscInt));CHKERRQ(ierr);
555     ptr[j]       = outdat[j] + 2*w3[j] + 1;
556   }
557 
558   /* Memory for doing local proc's work */
559   {
560     PetscInt M_BPB_imax = 0;
561 #if defined(PETSC_USE_CTABLE)
562     ierr = PetscIntMultError((M/PETSC_BITS_PER_BYTE+1),imax, &M_BPB_imax);CHKERRQ(ierr);
563     ierr = PetscMalloc1(imax,&table_data);CHKERRQ(ierr);
564     for (i=0; i<imax; i++) {
565       ierr = PetscTableCreate(n[i]+1,M+1,&table_data[i]);CHKERRQ(ierr);
566     }
567     ierr = PetscCalloc4(imax,&table, imax,&data, imax,&isz, M_BPB_imax,&t_p);CHKERRQ(ierr);
568     for (i=0; i<imax; i++) {
569       table[i] = t_p + (M/PETSC_BITS_PER_BYTE+1)*i;
570     }
571 #else
572     PetscInt Mimax = 0;
573     ierr = PetscIntMultError(M,imax, &Mimax);CHKERRQ(ierr);
574     ierr = PetscIntMultError((M/PETSC_BITS_PER_BYTE+1),imax, &M_BPB_imax);CHKERRQ(ierr);
575     ierr = PetscCalloc5(imax,&table, imax,&data, imax,&isz, Mimax,&d_p, M_BPB_imax,&t_p);CHKERRQ(ierr);
576     for (i=0; i<imax; i++) {
577       table[i] = t_p + (M/PETSC_BITS_PER_BYTE+1)*i;
578       data[i]  = d_p + M*i;
579     }
580 #endif
581   }
582 
583   /* Parse the IS and update local tables and the outgoing buf with the data */
584   {
585     PetscInt n_i,isz_i,*outdat_j,ctr_j;
586     PetscBT  table_i;
587 
588     for (i=0; i<imax; i++) {
589       ierr    = PetscMemzero(ctr,size*sizeof(PetscInt));CHKERRQ(ierr);
590       n_i     = n[i];
591       table_i = table[i];
592       idx_i   = idx[i];
593 #if defined(PETSC_USE_CTABLE)
594       table_data_i = table_data[i];
595 #else
596       data_i  = data[i];
597 #endif
598       isz_i   = isz[i];
599       for (j=0; j<n_i; j++) {   /* parse the indices of each IS */
600         row  = idx_i[j];
601         ierr = PetscLayoutFindOwner(C->rmap,row,&proc);CHKERRQ(ierr);
602         if (proc != rank) { /* copy to the outgoing buffer */
603           ctr[proc]++;
604           *ptr[proc] = row;
605           ptr[proc]++;
606         } else if (!PetscBTLookupSet(table_i,row)) {
607 #if defined(PETSC_USE_CTABLE)
608           ierr = PetscTableAdd(table_data_i,row+1,isz_i+1,INSERT_VALUES);CHKERRQ(ierr);
609 #else
610           data_i[isz_i] = row; /* Update the local table */
611 #endif
612           isz_i++;
613         }
614       }
615       /* Update the headers for the current IS */
616       for (j=0; j<size; j++) { /* Can Optimise this loop by using pa[] */
617         if ((ctr_j = ctr[j])) {
618           outdat_j        = outdat[j];
619           k               = ++outdat_j[0];
620           outdat_j[2*k]   = ctr_j;
621           outdat_j[2*k-1] = i;
622         }
623       }
624       isz[i] = isz_i;
625     }
626   }
627 
628   /*  Now  post the sends */
629   ierr = PetscMalloc1(nrqs+1,&s_waits1);CHKERRQ(ierr);
630   for (i=0; i<nrqs; ++i) {
631     j    = pa[i];
632     ierr = MPI_Isend(outdat[j],w1[j],MPIU_INT,j,tag1,comm,s_waits1+i);CHKERRQ(ierr);
633   }
634 
635   /* No longer need the original indices */
636   for (i=0; i<imax; ++i) {
637     ierr = ISRestoreIndices(is[i],idx+i);CHKERRQ(ierr);
638   }
639   ierr = PetscFree2(idx,n);CHKERRQ(ierr);
640 
641   for (i=0; i<imax; ++i) {
642     ierr = ISDestroy(&is[i]);CHKERRQ(ierr);
643   }
644 
645   /* Do Local work */
646 #if defined(PETSC_USE_CTABLE)
647   ierr = MatIncreaseOverlap_MPIAIJ_Local(C,imax,table,isz,NULL,table_data);CHKERRQ(ierr);
648 #else
649   ierr = MatIncreaseOverlap_MPIAIJ_Local(C,imax,table,isz,data,NULL);CHKERRQ(ierr);
650 #endif
651 
652   /* Receive messages */
653   ierr = PetscMalloc1(nrqr+1,&recv_status);CHKERRQ(ierr);
654   if (nrqr) {ierr = MPI_Waitall(nrqr,r_waits1,recv_status);CHKERRQ(ierr);}
655 
656   ierr = PetscMalloc1(nrqs+1,&s_status);CHKERRQ(ierr);
657   if (nrqs) {ierr = MPI_Waitall(nrqs,s_waits1,s_status);CHKERRQ(ierr);}
658 
659   /* Phase 1 sends are complete - deallocate buffers */
660   ierr = PetscFree4(outdat,ptr,tmp,ctr);CHKERRQ(ierr);
661   ierr = PetscFree4(w1,w2,w3,w4);CHKERRQ(ierr);
662 
663   ierr = PetscMalloc1(nrqr+1,&xdata);CHKERRQ(ierr);
664   ierr = PetscMalloc1(nrqr+1,&isz1);CHKERRQ(ierr);
665   ierr = MatIncreaseOverlap_MPIAIJ_Receive(C,nrqr,rbuf,xdata,isz1);CHKERRQ(ierr);
666   ierr = PetscFree(rbuf[0]);CHKERRQ(ierr);
667   ierr = PetscFree(rbuf);CHKERRQ(ierr);
668 
669 
670   /* Send the data back */
671   /* Do a global reduction to know the buffer space req for incoming messages */
672   {
673     PetscMPIInt *rw1;
674 
675     ierr = PetscCalloc1(size,&rw1);CHKERRQ(ierr);
676 
677     for (i=0; i<nrqr; ++i) {
678       proc = recv_status[i].MPI_SOURCE;
679 
680       if (proc != onodes1[i]) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"MPI_SOURCE mismatch");
681       rw1[proc] = isz1[i];
682     }
683     ierr = PetscFree(onodes1);CHKERRQ(ierr);
684     ierr = PetscFree(olengths1);CHKERRQ(ierr);
685 
686     /* Determine the number of messages to expect, their lengths, from from-ids */
687     ierr = PetscGatherMessageLengths(comm,nrqr,nrqs,rw1,&onodes2,&olengths2);CHKERRQ(ierr);
688     ierr = PetscFree(rw1);CHKERRQ(ierr);
689   }
690   /* Now post the Irecvs corresponding to these messages */
691   ierr = PetscPostIrecvInt(comm,tag2,nrqs,onodes2,olengths2,&rbuf2,&r_waits2);CHKERRQ(ierr);
692 
693   /* Now  post the sends */
694   ierr = PetscMalloc1(nrqr+1,&s_waits2);CHKERRQ(ierr);
695   for (i=0; i<nrqr; ++i) {
696     j    = recv_status[i].MPI_SOURCE;
697     ierr = MPI_Isend(xdata[i],isz1[i],MPIU_INT,j,tag2,comm,s_waits2+i);CHKERRQ(ierr);
698   }
699 
700   /* receive work done on other processors */
701   {
702     PetscInt    is_no,ct1,max,*rbuf2_i,isz_i,jmax;
703     PetscMPIInt idex;
704     PetscBT     table_i;
705     MPI_Status  *status2;
706 
707     ierr = PetscMalloc1((PetscMax(nrqr,nrqs)+1),&status2);CHKERRQ(ierr);
708     for (i=0; i<nrqs; ++i) {
709       ierr = MPI_Waitany(nrqs,r_waits2,&idex,status2+i);CHKERRQ(ierr);
710       /* Process the message */
711       rbuf2_i = rbuf2[idex];
712       ct1     = 2*rbuf2_i[0]+1;
713       jmax    = rbuf2[idex][0];
714       for (j=1; j<=jmax; j++) {
715         max     = rbuf2_i[2*j];
716         is_no   = rbuf2_i[2*j-1];
717         isz_i   = isz[is_no];
718         table_i = table[is_no];
719 #if defined(PETSC_USE_CTABLE)
720         table_data_i = table_data[is_no];
721 #else
722         data_i  = data[is_no];
723 #endif
724         for (k=0; k<max; k++,ct1++) {
725           row = rbuf2_i[ct1];
726           if (!PetscBTLookupSet(table_i,row)) {
727 #if defined(PETSC_USE_CTABLE)
728             ierr = PetscTableAdd(table_data_i,row+1,isz_i+1,INSERT_VALUES);CHKERRQ(ierr);
729 #else
730             data_i[isz_i] = row;
731 #endif
732             isz_i++;
733           }
734         }
735         isz[is_no] = isz_i;
736       }
737     }
738 
739     if (nrqr) {ierr = MPI_Waitall(nrqr,s_waits2,status2);CHKERRQ(ierr);}
740     ierr = PetscFree(status2);CHKERRQ(ierr);
741   }
742 
743 #if defined(PETSC_USE_CTABLE)
744   tcount_max = 0;
745   for (i=0; i<imax; ++i) {
746     table_data_i = table_data[i];
747     ierr = PetscTableGetCount(table_data_i,&tcount);CHKERRQ(ierr);
748     if (tcount_max < tcount) tcount_max = tcount;
749   }
750   ierr = PetscMalloc1(tcount_max+1,&tdata);CHKERRQ(ierr);
751 #endif
752 
753   for (i=0; i<imax; ++i) {
754 #if defined(PETSC_USE_CTABLE)
755     PetscTablePosition tpos;
756     table_data_i = table_data[i];
757 
758     ierr = PetscTableGetHeadPosition(table_data_i,&tpos);CHKERRQ(ierr);
759     while (tpos) {
760       ierr = PetscTableGetNext(table_data_i,&tpos,&k,&j);CHKERRQ(ierr);
761       tdata[--j] = --k;
762     }
763     ierr = ISCreateGeneral(PETSC_COMM_SELF,isz[i],tdata,PETSC_COPY_VALUES,is+i);CHKERRQ(ierr);
764 #else
765     ierr = ISCreateGeneral(PETSC_COMM_SELF,isz[i],data[i],PETSC_COPY_VALUES,is+i);CHKERRQ(ierr);
766 #endif
767   }
768 
769   ierr = PetscFree(onodes2);CHKERRQ(ierr);
770   ierr = PetscFree(olengths2);CHKERRQ(ierr);
771 
772   ierr = PetscFree(pa);CHKERRQ(ierr);
773   ierr = PetscFree(rbuf2[0]);CHKERRQ(ierr);
774   ierr = PetscFree(rbuf2);CHKERRQ(ierr);
775   ierr = PetscFree(s_waits1);CHKERRQ(ierr);
776   ierr = PetscFree(r_waits1);CHKERRQ(ierr);
777   ierr = PetscFree(s_waits2);CHKERRQ(ierr);
778   ierr = PetscFree(r_waits2);CHKERRQ(ierr);
779   ierr = PetscFree(s_status);CHKERRQ(ierr);
780   ierr = PetscFree(recv_status);CHKERRQ(ierr);
781   ierr = PetscFree(xdata[0]);CHKERRQ(ierr);
782   ierr = PetscFree(xdata);CHKERRQ(ierr);
783   ierr = PetscFree(isz1);CHKERRQ(ierr);
784 #if defined(PETSC_USE_CTABLE)
785   for (i=0; i<imax; i++) {
786     ierr = PetscTableDestroy((PetscTable*)&table_data[i]);CHKERRQ(ierr);
787   }
788   ierr = PetscFree(table_data);CHKERRQ(ierr);
789   ierr = PetscFree(tdata);CHKERRQ(ierr);
790   ierr = PetscFree4(table,data,isz,t_p);CHKERRQ(ierr);
791 #else
792   ierr = PetscFree5(table,data,isz,d_p,t_p);CHKERRQ(ierr);
793 #endif
794   PetscFunctionReturn(0);
795 }
796 
797 /*
798    MatIncreaseOverlap_MPIAIJ_Local - Called by MatincreaseOverlap, to do
799        the work on the local processor.
800 
801      Inputs:
802       C      - MAT_MPIAIJ;
803       imax - total no of index sets processed at a time;
804       table  - an array of char - size = m bits.
805 
806      Output:
807       isz    - array containing the count of the solution elements corresponding
808                to each index set;
809       data or table_data  - pointer to the solutions
810 */
811 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Local(Mat C,PetscInt imax,PetscBT *table,PetscInt *isz,PetscInt **data,PetscTable *table_data)
812 {
813   Mat_MPIAIJ *c = (Mat_MPIAIJ*)C->data;
814   Mat        A  = c->A,B = c->B;
815   Mat_SeqAIJ *a = (Mat_SeqAIJ*)A->data,*b = (Mat_SeqAIJ*)B->data;
816   PetscInt   start,end,val,max,rstart,cstart,*ai,*aj;
817   PetscInt   *bi,*bj,*garray,i,j,k,row,isz_i;
818   PetscBT    table_i;
819 #if defined(PETSC_USE_CTABLE)
820   PetscTable         table_data_i;
821   PetscErrorCode     ierr;
822   PetscTablePosition tpos;
823   PetscInt           tcount,*tdata;
824 #else
825   PetscInt           *data_i;
826 #endif
827 
828   PetscFunctionBegin;
829   rstart = C->rmap->rstart;
830   cstart = C->cmap->rstart;
831   ai     = a->i;
832   aj     = a->j;
833   bi     = b->i;
834   bj     = b->j;
835   garray = c->garray;
836 
837   for (i=0; i<imax; i++) {
838 #if defined(PETSC_USE_CTABLE)
839     /* copy existing entries of table_data_i into tdata[] */
840     table_data_i = table_data[i];
841     ierr = PetscTableGetCount(table_data_i,&tcount);CHKERRQ(ierr);
842     if (tcount != isz[i]) SETERRQ3(PETSC_COMM_SELF,0," tcount %d != isz[%d] %d",tcount,i,isz[i]);
843 
844     ierr = PetscMalloc1(tcount,&tdata);CHKERRQ(ierr);
845     ierr = PetscTableGetHeadPosition(table_data_i,&tpos);CHKERRQ(ierr);
846     while (tpos) {
847       ierr = PetscTableGetNext(table_data_i,&tpos,&row,&j);CHKERRQ(ierr);
848       tdata[--j] = --row;
849       if (j > tcount - 1) SETERRQ2(PETSC_COMM_SELF,0," j %d >= tcount %d",j,tcount);
850     }
851 #else
852     data_i  = data[i];
853 #endif
854     table_i = table[i];
855     isz_i   = isz[i];
856     max     = isz[i];
857 
858     for (j=0; j<max; j++) {
859 #if defined(PETSC_USE_CTABLE)
860       row   = tdata[j] - rstart;
861 #else
862       row   = data_i[j] - rstart;
863 #endif
864       start = ai[row];
865       end   = ai[row+1];
866       for (k=start; k<end; k++) { /* Amat */
867         val = aj[k] + cstart;
868         if (!PetscBTLookupSet(table_i,val)) {
869 #if defined(PETSC_USE_CTABLE)
870           ierr = PetscTableAdd(table_data_i,val+1,isz_i+1,INSERT_VALUES);CHKERRQ(ierr);
871 #else
872           data_i[isz_i] = val;
873 #endif
874           isz_i++;
875         }
876       }
877       start = bi[row];
878       end   = bi[row+1];
879       for (k=start; k<end; k++) { /* Bmat */
880         val = garray[bj[k]];
881         if (!PetscBTLookupSet(table_i,val)) {
882 #if defined(PETSC_USE_CTABLE)
883           ierr = PetscTableAdd(table_data_i,val+1,isz_i+1,INSERT_VALUES);CHKERRQ(ierr);
884 #else
885           data_i[isz_i] = val;
886 #endif
887           isz_i++;
888         }
889       }
890     }
891     isz[i] = isz_i;
892 
893 #if defined(PETSC_USE_CTABLE)
894     ierr = PetscFree(tdata);CHKERRQ(ierr);
895 #endif
896   }
897   PetscFunctionReturn(0);
898 }
899 
900 /*
901       MatIncreaseOverlap_MPIAIJ_Receive - Process the recieved messages,
902          and return the output
903 
904          Input:
905            C    - the matrix
906            nrqr - no of messages being processed.
907            rbuf - an array of pointers to the recieved requests
908 
909          Output:
910            xdata - array of messages to be sent back
911            isz1  - size of each message
912 
913   For better efficiency perhaps we should malloc separately each xdata[i],
914 then if a remalloc is required we need only copy the data for that one row
915 rather then all previous rows as it is now where a single large chunck of
916 memory is used.
917 
918 */
919 static PetscErrorCode MatIncreaseOverlap_MPIAIJ_Receive(Mat C,PetscInt nrqr,PetscInt **rbuf,PetscInt **xdata,PetscInt * isz1)
920 {
921   Mat_MPIAIJ     *c = (Mat_MPIAIJ*)C->data;
922   Mat            A  = c->A,B = c->B;
923   Mat_SeqAIJ     *a = (Mat_SeqAIJ*)A->data,*b = (Mat_SeqAIJ*)B->data;
924   PetscErrorCode ierr;
925   PetscInt       rstart,cstart,*ai,*aj,*bi,*bj,*garray,i,j,k;
926   PetscInt       row,total_sz,ct,ct1,ct2,ct3,mem_estimate,oct2,l,start,end;
927   PetscInt       val,max1,max2,m,no_malloc =0,*tmp,new_estimate,ctr;
928   PetscInt       *rbuf_i,kmax,rbuf_0;
929   PetscBT        xtable;
930 
931   PetscFunctionBegin;
932   m      = C->rmap->N;
933   rstart = C->rmap->rstart;
934   cstart = C->cmap->rstart;
935   ai     = a->i;
936   aj     = a->j;
937   bi     = b->i;
938   bj     = b->j;
939   garray = c->garray;
940 
941 
942   for (i=0,ct=0,total_sz=0; i<nrqr; ++i) {
943     rbuf_i =  rbuf[i];
944     rbuf_0 =  rbuf_i[0];
945     ct    += rbuf_0;
946     for (j=1; j<=rbuf_0; j++) total_sz += rbuf_i[2*j];
947   }
948 
949   if (C->rmap->n) max1 = ct*(a->nz + b->nz)/C->rmap->n;
950   else max1 = 1;
951   mem_estimate = 3*((total_sz > max1 ? total_sz : max1)+1);
952   ierr         = PetscMalloc1(mem_estimate,&xdata[0]);CHKERRQ(ierr);
953   ++no_malloc;
954   ierr = PetscBTCreate(m,&xtable);CHKERRQ(ierr);
955   ierr = PetscMemzero(isz1,nrqr*sizeof(PetscInt));CHKERRQ(ierr);
956 
957   ct3 = 0;
958   for (i=0; i<nrqr; i++) { /* for easch mesg from proc i */
959     rbuf_i =  rbuf[i];
960     rbuf_0 =  rbuf_i[0];
961     ct1    =  2*rbuf_0+1;
962     ct2    =  ct1;
963     ct3   += ct1;
964     for (j=1; j<=rbuf_0; j++) { /* for each IS from proc i*/
965       ierr = PetscBTMemzero(m,xtable);CHKERRQ(ierr);
966       oct2 = ct2;
967       kmax = rbuf_i[2*j];
968       for (k=0; k<kmax; k++,ct1++) {
969         row = rbuf_i[ct1];
970         if (!PetscBTLookupSet(xtable,row)) {
971           if (!(ct3 < mem_estimate)) {
972             new_estimate = (PetscInt)(1.5*mem_estimate)+1;
973             ierr         = PetscMalloc1(new_estimate,&tmp);CHKERRQ(ierr);
974             ierr         = PetscMemcpy(tmp,xdata[0],mem_estimate*sizeof(PetscInt));CHKERRQ(ierr);
975             ierr         = PetscFree(xdata[0]);CHKERRQ(ierr);
976             xdata[0]     = tmp;
977             mem_estimate = new_estimate; ++no_malloc;
978             for (ctr=1; ctr<=i; ctr++) xdata[ctr] = xdata[ctr-1] + isz1[ctr-1];
979           }
980           xdata[i][ct2++] = row;
981           ct3++;
982         }
983       }
984       for (k=oct2,max2=ct2; k<max2; k++) {
985         row   = xdata[i][k] - rstart;
986         start = ai[row];
987         end   = ai[row+1];
988         for (l=start; l<end; l++) {
989           val = aj[l] + cstart;
990           if (!PetscBTLookupSet(xtable,val)) {
991             if (!(ct3 < mem_estimate)) {
992               new_estimate = (PetscInt)(1.5*mem_estimate)+1;
993               ierr         = PetscMalloc1(new_estimate,&tmp);CHKERRQ(ierr);
994               ierr         = PetscMemcpy(tmp,xdata[0],mem_estimate*sizeof(PetscInt));CHKERRQ(ierr);
995               ierr         = PetscFree(xdata[0]);CHKERRQ(ierr);
996               xdata[0]     = tmp;
997               mem_estimate = new_estimate; ++no_malloc;
998               for (ctr=1; ctr<=i; ctr++) xdata[ctr] = xdata[ctr-1] + isz1[ctr-1];
999             }
1000             xdata[i][ct2++] = val;
1001             ct3++;
1002           }
1003         }
1004         start = bi[row];
1005         end   = bi[row+1];
1006         for (l=start; l<end; l++) {
1007           val = garray[bj[l]];
1008           if (!PetscBTLookupSet(xtable,val)) {
1009             if (!(ct3 < mem_estimate)) {
1010               new_estimate = (PetscInt)(1.5*mem_estimate)+1;
1011               ierr         = PetscMalloc1(new_estimate,&tmp);CHKERRQ(ierr);
1012               ierr         = PetscMemcpy(tmp,xdata[0],mem_estimate*sizeof(PetscInt));CHKERRQ(ierr);
1013               ierr         = PetscFree(xdata[0]);CHKERRQ(ierr);
1014               xdata[0]     = tmp;
1015               mem_estimate = new_estimate; ++no_malloc;
1016               for (ctr =1; ctr <=i; ctr++) xdata[ctr] = xdata[ctr-1] + isz1[ctr-1];
1017             }
1018             xdata[i][ct2++] = val;
1019             ct3++;
1020           }
1021         }
1022       }
1023       /* Update the header*/
1024       xdata[i][2*j]   = ct2 - oct2; /* Undo the vector isz1 and use only a var*/
1025       xdata[i][2*j-1] = rbuf_i[2*j-1];
1026     }
1027     xdata[i][0] = rbuf_0;
1028     xdata[i+1]  = xdata[i] + ct2;
1029     isz1[i]     = ct2; /* size of each message */
1030   }
1031   ierr = PetscBTDestroy(&xtable);CHKERRQ(ierr);
1032   ierr = PetscInfo3(C,"Allocated %D bytes, required %D bytes, no of mallocs = %D\n",mem_estimate,ct3,no_malloc);CHKERRQ(ierr);
1033   PetscFunctionReturn(0);
1034 }
1035 /* -------------------------------------------------------------------------*/
1036 extern PetscErrorCode MatGetSubMatrices_MPIAIJ_Local(Mat,PetscInt,const IS[],const IS[],MatReuse,Mat*);
1037 extern PetscErrorCode MatAssemblyEnd_SeqAIJ(Mat,MatAssemblyType);
1038 /*
1039     Every processor gets the entire matrix
1040 */
1041 PetscErrorCode MatGetSubMatrix_MPIAIJ_All(Mat A,MatGetSubMatrixOption flag,MatReuse scall,Mat *Bin[])
1042 {
1043   Mat            B;
1044   Mat_MPIAIJ     *a = (Mat_MPIAIJ*)A->data;
1045   Mat_SeqAIJ     *b,*ad = (Mat_SeqAIJ*)a->A->data,*bd = (Mat_SeqAIJ*)a->B->data;
1046   PetscErrorCode ierr;
1047   PetscMPIInt    size,rank,*recvcounts = 0,*displs = 0;
1048   PetscInt       sendcount,i,*rstarts = A->rmap->range,n,cnt,j;
1049   PetscInt       m,*b_sendj,*garray = a->garray,*lens,*jsendbuf,*a_jsendbuf,*b_jsendbuf;
1050   MatScalar      *sendbuf,*recvbuf,*a_sendbuf,*b_sendbuf;
1051 
1052   PetscFunctionBegin;
1053   ierr = MPI_Comm_size(PetscObjectComm((PetscObject)A),&size);CHKERRQ(ierr);
1054   ierr = MPI_Comm_rank(PetscObjectComm((PetscObject)A),&rank);CHKERRQ(ierr);
1055 
1056   if (scall == MAT_INITIAL_MATRIX) {
1057     /* ----------------------------------------------------------------
1058          Tell every processor the number of nonzeros per row
1059     */
1060     ierr = PetscMalloc1(A->rmap->N,&lens);CHKERRQ(ierr);
1061     for (i=A->rmap->rstart; i<A->rmap->rend; i++) {
1062       lens[i] = ad->i[i-A->rmap->rstart+1] - ad->i[i-A->rmap->rstart] + bd->i[i-A->rmap->rstart+1] - bd->i[i-A->rmap->rstart];
1063     }
1064     ierr      = PetscMalloc2(size,&recvcounts,size,&displs);CHKERRQ(ierr);
1065     for (i=0; i<size; i++) {
1066       recvcounts[i] = A->rmap->range[i+1] - A->rmap->range[i];
1067       displs[i]     = A->rmap->range[i];
1068     }
1069 #if defined(PETSC_HAVE_MPI_IN_PLACE)
1070     ierr = MPI_Allgatherv(MPI_IN_PLACE,0,MPI_DATATYPE_NULL,lens,recvcounts,displs,MPIU_INT,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1071 #else
1072     sendcount = A->rmap->rend - A->rmap->rstart;
1073     ierr = MPI_Allgatherv(lens+A->rmap->rstart,sendcount,MPIU_INT,lens,recvcounts,displs,MPIU_INT,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1074 #endif
1075     /* ---------------------------------------------------------------
1076          Create the sequential matrix of the same type as the local block diagonal
1077     */
1078     ierr  = MatCreate(PETSC_COMM_SELF,&B);CHKERRQ(ierr);
1079     ierr  = MatSetSizes(B,A->rmap->N,A->cmap->N,PETSC_DETERMINE,PETSC_DETERMINE);CHKERRQ(ierr);
1080     ierr  = MatSetBlockSizesFromMats(B,A,A);CHKERRQ(ierr);
1081     ierr  = MatSetType(B,((PetscObject)a->A)->type_name);CHKERRQ(ierr);
1082     ierr  = MatSeqAIJSetPreallocation(B,0,lens);CHKERRQ(ierr);
1083     ierr  = PetscMalloc1(1,Bin);CHKERRQ(ierr);
1084     **Bin = B;
1085     b     = (Mat_SeqAIJ*)B->data;
1086 
1087     /*--------------------------------------------------------------------
1088        Copy my part of matrix column indices over
1089     */
1090     sendcount  = ad->nz + bd->nz;
1091     jsendbuf   = b->j + b->i[rstarts[rank]];
1092     a_jsendbuf = ad->j;
1093     b_jsendbuf = bd->j;
1094     n          = A->rmap->rend - A->rmap->rstart;
1095     cnt        = 0;
1096     for (i=0; i<n; i++) {
1097 
1098       /* put in lower diagonal portion */
1099       m = bd->i[i+1] - bd->i[i];
1100       while (m > 0) {
1101         /* is it above diagonal (in bd (compressed) numbering) */
1102         if (garray[*b_jsendbuf] > A->rmap->rstart + i) break;
1103         jsendbuf[cnt++] = garray[*b_jsendbuf++];
1104         m--;
1105       }
1106 
1107       /* put in diagonal portion */
1108       for (j=ad->i[i]; j<ad->i[i+1]; j++) {
1109         jsendbuf[cnt++] = A->rmap->rstart + *a_jsendbuf++;
1110       }
1111 
1112       /* put in upper diagonal portion */
1113       while (m-- > 0) {
1114         jsendbuf[cnt++] = garray[*b_jsendbuf++];
1115       }
1116     }
1117     if (cnt != sendcount) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Corrupted PETSc matrix: nz given %D actual nz %D",sendcount,cnt);
1118 
1119     /*--------------------------------------------------------------------
1120        Gather all column indices to all processors
1121     */
1122     for (i=0; i<size; i++) {
1123       recvcounts[i] = 0;
1124       for (j=A->rmap->range[i]; j<A->rmap->range[i+1]; j++) {
1125         recvcounts[i] += lens[j];
1126       }
1127     }
1128     displs[0] = 0;
1129     for (i=1; i<size; i++) {
1130       displs[i] = displs[i-1] + recvcounts[i-1];
1131     }
1132 #if defined(PETSC_HAVE_MPI_IN_PLACE)
1133     ierr = MPI_Allgatherv(MPI_IN_PLACE,0,MPI_DATATYPE_NULL,b->j,recvcounts,displs,MPIU_INT,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1134 #else
1135     ierr = MPI_Allgatherv(jsendbuf,sendcount,MPIU_INT,b->j,recvcounts,displs,MPIU_INT,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1136 #endif
1137     /*--------------------------------------------------------------------
1138         Assemble the matrix into useable form (note numerical values not yet set)
1139     */
1140     /* set the b->ilen (length of each row) values */
1141     ierr = PetscMemcpy(b->ilen,lens,A->rmap->N*sizeof(PetscInt));CHKERRQ(ierr);
1142     /* set the b->i indices */
1143     b->i[0] = 0;
1144     for (i=1; i<=A->rmap->N; i++) {
1145       b->i[i] = b->i[i-1] + lens[i-1];
1146     }
1147     ierr = PetscFree(lens);CHKERRQ(ierr);
1148     ierr = MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
1149     ierr = MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
1150 
1151   } else {
1152     B = **Bin;
1153     b = (Mat_SeqAIJ*)B->data;
1154   }
1155 
1156   /*--------------------------------------------------------------------
1157        Copy my part of matrix numerical values into the values location
1158   */
1159   if (flag == MAT_GET_VALUES) {
1160     sendcount = ad->nz + bd->nz;
1161     sendbuf   = b->a + b->i[rstarts[rank]];
1162     a_sendbuf = ad->a;
1163     b_sendbuf = bd->a;
1164     b_sendj   = bd->j;
1165     n         = A->rmap->rend - A->rmap->rstart;
1166     cnt       = 0;
1167     for (i=0; i<n; i++) {
1168 
1169       /* put in lower diagonal portion */
1170       m = bd->i[i+1] - bd->i[i];
1171       while (m > 0) {
1172         /* is it above diagonal (in bd (compressed) numbering) */
1173         if (garray[*b_sendj] > A->rmap->rstart + i) break;
1174         sendbuf[cnt++] = *b_sendbuf++;
1175         m--;
1176         b_sendj++;
1177       }
1178 
1179       /* put in diagonal portion */
1180       for (j=ad->i[i]; j<ad->i[i+1]; j++) {
1181         sendbuf[cnt++] = *a_sendbuf++;
1182       }
1183 
1184       /* put in upper diagonal portion */
1185       while (m-- > 0) {
1186         sendbuf[cnt++] = *b_sendbuf++;
1187         b_sendj++;
1188       }
1189     }
1190     if (cnt != sendcount) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Corrupted PETSc matrix: nz given %D actual nz %D",sendcount,cnt);
1191 
1192     /* -----------------------------------------------------------------
1193        Gather all numerical values to all processors
1194     */
1195     if (!recvcounts) {
1196       ierr = PetscMalloc2(size,&recvcounts,size,&displs);CHKERRQ(ierr);
1197     }
1198     for (i=0; i<size; i++) {
1199       recvcounts[i] = b->i[rstarts[i+1]] - b->i[rstarts[i]];
1200     }
1201     displs[0] = 0;
1202     for (i=1; i<size; i++) {
1203       displs[i] = displs[i-1] + recvcounts[i-1];
1204     }
1205     recvbuf = b->a;
1206 #if defined(PETSC_HAVE_MPI_IN_PLACE)
1207     ierr = MPI_Allgatherv(MPI_IN_PLACE,0,MPI_DATATYPE_NULL,recvbuf,recvcounts,displs,MPIU_SCALAR,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1208 #else
1209     ierr = MPI_Allgatherv(sendbuf,sendcount,MPIU_SCALAR,recvbuf,recvcounts,displs,MPIU_SCALAR,PetscObjectComm((PetscObject)A));CHKERRQ(ierr);
1210 #endif
1211   }  /* endof (flag == MAT_GET_VALUES) */
1212   ierr = PetscFree2(recvcounts,displs);CHKERRQ(ierr);
1213 
1214   if (A->symmetric) {
1215     ierr = MatSetOption(B,MAT_SYMMETRIC,PETSC_TRUE);CHKERRQ(ierr);
1216   } else if (A->hermitian) {
1217     ierr = MatSetOption(B,MAT_HERMITIAN,PETSC_TRUE);CHKERRQ(ierr);
1218   } else if (A->structurally_symmetric) {
1219     ierr = MatSetOption(B,MAT_STRUCTURALLY_SYMMETRIC,PETSC_TRUE);CHKERRQ(ierr);
1220   }
1221   PetscFunctionReturn(0);
1222 }
1223 
1224 PetscErrorCode MatDestroy_MPIAIJ_MatGetSubmatrices(Mat C)
1225 {
1226   PetscErrorCode ierr;
1227   Mat_SeqAIJ     *c = (Mat_SeqAIJ*)C->data;
1228   Mat_SubMat     *submatj = c->submatis1;
1229   PetscInt       i;
1230 
1231   PetscFunctionBegin;
1232   if (!submatj->id) { /* delete data that are linked only to submats[id=0] */
1233     ierr = PetscFree4(submatj->sbuf1,submatj->ptr,submatj->tmp,submatj->ctr);CHKERRQ(ierr);
1234 
1235     for (i=0; i<submatj->nrqr; ++i) {
1236       ierr = PetscFree(submatj->sbuf2[i]);CHKERRQ(ierr);
1237     }
1238     ierr = PetscFree3(submatj->sbuf2,submatj->req_size,submatj->req_source1);CHKERRQ(ierr);
1239 
1240     if (submatj->rbuf1) {
1241       ierr = PetscFree(submatj->rbuf1[0]);CHKERRQ(ierr);
1242       ierr = PetscFree(submatj->rbuf1);CHKERRQ(ierr);
1243     }
1244 
1245     for (i=0; i<submatj->nrqs; ++i) {
1246       ierr = PetscFree(submatj->rbuf3[i]);CHKERRQ(ierr);
1247     }
1248     ierr = PetscFree3(submatj->req_source2,submatj->rbuf2,submatj->rbuf3);CHKERRQ(ierr);
1249     ierr = PetscFree(submatj->pa);CHKERRQ(ierr);
1250   }
1251 
1252 #if defined(PETSC_USE_CTABLE)
1253   ierr = PetscTableDestroy((PetscTable*)&submatj->rmap);CHKERRQ(ierr);
1254   if (submatj->cmap_loc) {ierr = PetscFree(submatj->cmap_loc);CHKERRQ(ierr);}
1255   ierr = PetscFree(submatj->rmap_loc);CHKERRQ(ierr);
1256 #else
1257   ierr = PetscFree(submatj->rmap);CHKERRQ(ierr);
1258 #endif
1259 
1260   if (!submatj->allcolumns) {
1261 #if defined(PETSC_USE_CTABLE)
1262     ierr = PetscTableDestroy((PetscTable*)&submatj->cmap);CHKERRQ(ierr);
1263 #else
1264     ierr = PetscFree(submatj->cmap);CHKERRQ(ierr);
1265 #endif
1266   }
1267   ierr = submatj->destroy(C);CHKERRQ(ierr);
1268   ierr = PetscFree(submatj->row2proc);CHKERRQ(ierr);
1269 
1270   ierr = PetscFree(submatj);CHKERRQ(ierr);
1271   PetscFunctionReturn(0);
1272 }
1273 
1274 PetscErrorCode MatGetSubMatrices_MPIAIJ_SingleIS_Local(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,PetscBool allcolumns,Mat *submats)
1275 {
1276   Mat_MPIAIJ     *c = (Mat_MPIAIJ*)C->data;
1277   Mat            submat,A = c->A,B = c->B;
1278   Mat_SeqAIJ     *a = (Mat_SeqAIJ*)A->data,*b = (Mat_SeqAIJ*)B->data,*subc;
1279   PetscInt       *ai=a->i,*aj=a->j,*bi=b->i,*bj=b->j,nzA,nzB;
1280   PetscInt       cstart = C->cmap->rstart,cend = C->cmap->rend,rstart = C->rmap->rstart,*bmap = c->garray;
1281   const PetscInt *icol,*irow;
1282   PetscInt       nrow,ncol,start;
1283   PetscErrorCode ierr;
1284   PetscMPIInt    rank,size,tag1,tag2,tag3,tag4,*w1,*w2,nrqr;
1285   PetscInt       **sbuf1,**sbuf2,i,j,k,l,ct1,ct2,ct3,**rbuf1,row,proc;
1286   PetscInt       nrqs=0,msz,**ptr,*req_size,*ctr,*pa,*tmp,tcol,*iptr;
1287   PetscInt       **rbuf3,*req_source1,*req_source2,**sbuf_aj,**rbuf2,max1,nnz;
1288   PetscInt       *lens,rmax,ncols,*cols,Crow;
1289 #if defined(PETSC_USE_CTABLE)
1290   PetscTable     cmap,rmap;
1291   PetscInt       *cmap_loc,*rmap_loc;
1292 #else
1293   PetscInt       *cmap,*rmap;
1294 #endif
1295   PetscInt       ctr_j,*sbuf1_j,*sbuf_aj_i,*rbuf1_i,kmax,*sbuf1_i,*rbuf2_i,*rbuf3_i;
1296   PetscInt       *cworkB,lwrite,*subcols,*row2proc;
1297   PetscScalar    *vworkA,*vworkB,*a_a = a->a,*b_a = b->a,*subvals=NULL;
1298   MPI_Request    *s_waits1,*r_waits1,*s_waits2,*r_waits2,*r_waits3;
1299   MPI_Request    *r_waits4,*s_waits3 = NULL,*s_waits4;
1300   MPI_Status     *r_status1,*r_status2,*s_status1,*s_status3 = NULL,*s_status2;
1301   MPI_Status     *r_status3 = NULL,*r_status4,*s_status4;
1302   MPI_Comm       comm;
1303   PetscScalar    **rbuf4,**sbuf_aa,*vals,*sbuf_aa_i,*rbuf4_i;
1304   PetscMPIInt    *onodes1,*olengths1,idex,end;
1305   Mat_SubMat     *smatis1;
1306   PetscBool      isrowsorted;
1307 
1308   PetscFunctionBegin;
1309   if (ismax != 1) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"This routine only works when all processes have ismax=1");
1310 
1311   ierr = PetscObjectGetComm((PetscObject)C,&comm);CHKERRQ(ierr);
1312   size = c->size;
1313   rank = c->rank;
1314 
1315   ierr = ISSorted(isrow[0],&isrowsorted);CHKERRQ(ierr);
1316   if (!isrowsorted) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"isrow[0] must be sorted");
1317 
1318   ierr = ISGetIndices(isrow[0],&irow);CHKERRQ(ierr);
1319   ierr = ISGetLocalSize(isrow[0],&nrow);CHKERRQ(ierr);
1320   if (allcolumns) {
1321     icol = NULL;
1322     ncol = C->cmap->N;
1323   } else {
1324     ierr = ISGetIndices(iscol[0],&icol);CHKERRQ(ierr);
1325     ierr = ISGetLocalSize(iscol[0],&ncol);CHKERRQ(ierr);
1326   }
1327 
1328   if (scall == MAT_INITIAL_MATRIX) {
1329     PetscInt *sbuf2_i,*cworkA,lwrite,ctmp;
1330 
1331     /* Get some new tags to keep the communication clean */
1332     tag1 = ((PetscObject)C)->tag;
1333     ierr = PetscObjectGetNewTag((PetscObject)C,&tag2);CHKERRQ(ierr);
1334     ierr = PetscObjectGetNewTag((PetscObject)C,&tag3);CHKERRQ(ierr);
1335 
1336     /* evaluate communication - mesg to who, length of mesg, and buffer space
1337      required. Based on this, buffers are allocated, and data copied into them */
1338     ierr = PetscCalloc2(size,&w1,size,&w2);CHKERRQ(ierr);
1339     ierr = PetscMalloc1(nrow,&row2proc);CHKERRQ(ierr);
1340 
1341     /* w1[proc] = num of rows owned by proc -- to be requested */
1342     proc = 0;
1343     nrqs = 0; /* num of outgoing messages */
1344     for (j=0; j<nrow; j++) {
1345       row  = irow[j]; /* sorted! */
1346       while (row >= C->rmap->range[proc+1]) proc++;
1347       w1[proc]++;
1348       row2proc[j] = proc; /* map row index to proc */
1349 
1350       if (proc != rank && !w2[proc]) {
1351         w2[proc] = 1; nrqs++;
1352       }
1353     }
1354     w1[rank] = 0;  /* rows owned by self will not be requested */
1355 
1356     ierr = PetscMalloc1(nrqs+1,&pa);CHKERRQ(ierr); /*(proc -array)*/
1357     for (proc=0,j=0; proc<size; proc++) {
1358       if (w1[proc]) { pa[j++] = proc;}
1359     }
1360 
1361     /* Each message would have a header = 1 + 2*(num of IS) + data (here,num of IS = 1) */
1362     msz = 0;              /* total mesg length (for all procs) */
1363     for (i=0; i<nrqs; i++) {
1364       proc      = pa[i];
1365       w1[proc] += 3;
1366       msz      += w1[proc];
1367     }
1368     ierr = PetscInfo2(0,"Number of outgoing messages %D Total message length %D\n",nrqs,msz);CHKERRQ(ierr);
1369 
1370     /* Determine nrqr, the number of messages to expect, their lengths, from from-ids */
1371     /* if w2[proc]=1, a message of length w1[proc] will be sent to proc; */
1372     ierr = PetscGatherNumberOfMessages(comm,w2,w1,&nrqr);CHKERRQ(ierr);
1373 
1374     /* Input: nrqs: nsend; nrqr: nrecv; w1: msg length to be sent;
1375        Output: onodes1: recv node-ids; olengths1: corresponding recv message length */
1376     ierr = PetscGatherMessageLengths(comm,nrqs,nrqr,w1,&onodes1,&olengths1);CHKERRQ(ierr);
1377 
1378     /* Now post the Irecvs corresponding to these messages */
1379     ierr = PetscPostIrecvInt(comm,tag1,nrqr,onodes1,olengths1,&rbuf1,&r_waits1);CHKERRQ(ierr);
1380 
1381     ierr = PetscFree(onodes1);CHKERRQ(ierr);
1382     ierr = PetscFree(olengths1);CHKERRQ(ierr);
1383 
1384     /* Allocate Memory for outgoing messages */
1385     ierr = PetscMalloc4(size,&sbuf1,size,&ptr,2*msz,&tmp,size,&ctr);CHKERRQ(ierr);
1386     ierr = PetscMemzero(sbuf1,size*sizeof(PetscInt*));CHKERRQ(ierr);
1387     ierr = PetscMemzero(ptr,size*sizeof(PetscInt*));CHKERRQ(ierr);
1388 
1389     /* subf1[pa[0]] = tmp, subf1[pa[i]] = subf1[pa[i-1]] + w1[pa[i-1]] */
1390     iptr = tmp;
1391     for (i=0; i<nrqs; i++) {
1392       proc        = pa[i];
1393       sbuf1[proc] = iptr;
1394       iptr       += w1[proc];
1395     }
1396 
1397     /* Form the outgoing messages */
1398     /* Initialize the header space */
1399     for (i=0; i<nrqs; i++) {
1400       proc      = pa[i];
1401       ierr      = PetscMemzero(sbuf1[proc],3*sizeof(PetscInt));CHKERRQ(ierr);
1402       ptr[proc] = sbuf1[proc] + 3;
1403     }
1404 
1405     /* Parse the isrow and copy data into outbuf */
1406     ierr = PetscMemzero(ctr,size*sizeof(PetscInt));CHKERRQ(ierr);
1407     for (j=0; j<nrow; j++) {  /* parse the indices of each IS */
1408       proc = row2proc[j];
1409       if (proc != rank) { /* copy to the outgoing buf*/
1410         *ptr[proc] = irow[j];
1411         ctr[proc]++; ptr[proc]++;
1412       }
1413     }
1414 
1415     /* Update the headers for the current IS */
1416     for (j=0; j<size; j++) { /* Can Optimise this loop too */
1417       if ((ctr_j = ctr[j])) {
1418         sbuf1_j        = sbuf1[j];
1419         k              = ++sbuf1_j[0];
1420         sbuf1_j[2*k]   = ctr_j;
1421         sbuf1_j[2*k-1] = 0;
1422       }
1423     }
1424 
1425     /* Now post the sends */
1426     ierr = PetscMalloc1(nrqs+1,&s_waits1);CHKERRQ(ierr);
1427     for (i=0; i<nrqs; ++i) {
1428       proc = pa[i];
1429       ierr = MPI_Isend(sbuf1[proc],w1[proc],MPIU_INT,proc,tag1,comm,s_waits1+i);CHKERRQ(ierr);
1430     }
1431 
1432     /* Post Receives to capture the buffer size */
1433     ierr = PetscMalloc4(nrqs+1,&r_status2,nrqr+1,&s_waits2,nrqs+1,&r_waits2,nrqr+1,&s_status2);CHKERRQ(ierr);
1434     ierr = PetscMalloc3(nrqs+1,&req_source2,nrqs+1,&rbuf2,nrqs+1,&rbuf3);CHKERRQ(ierr);
1435 
1436     rbuf2[0] = tmp + msz;
1437     for (i=1; i<nrqs; ++i) rbuf2[i] = rbuf2[i-1] + w1[pa[i-1]];
1438 
1439     for (i=0; i<nrqs; ++i) {
1440       proc = pa[i];
1441       ierr = MPI_Irecv(rbuf2[i],w1[proc],MPIU_INT,proc,tag2,comm,r_waits2+i);CHKERRQ(ierr);
1442     }
1443 
1444     ierr = PetscFree2(w1,w2);CHKERRQ(ierr);
1445 
1446     /* Send to other procs the buf size they should allocate */
1447     /* Receive messages*/
1448     ierr = PetscMalloc1(nrqr+1,&r_status1);CHKERRQ(ierr);
1449     ierr = PetscMalloc3(nrqr,&sbuf2,nrqr,&req_size,nrqr,&req_source1);CHKERRQ(ierr);
1450 
1451     ierr = MPI_Waitall(nrqr,r_waits1,r_status1);CHKERRQ(ierr);
1452     for (i=0; i<nrqr; ++i) {
1453       req_size[i] = 0;
1454       rbuf1_i        = rbuf1[i];
1455       start          = 2*rbuf1_i[0] + 1;
1456       ierr           = MPI_Get_count(r_status1+i,MPIU_INT,&end);CHKERRQ(ierr);
1457       ierr           = PetscMalloc1(end+1,&sbuf2[i]);CHKERRQ(ierr);
1458       sbuf2_i        = sbuf2[i];
1459       for (j=start; j<end; j++) {
1460         k            = rbuf1_i[j] - rstart;
1461         ncols        = ai[k+1] - ai[k] + bi[k+1] - bi[k];
1462         sbuf2_i[j]   = ncols;
1463         req_size[i] += ncols;
1464       }
1465       req_source1[i] = r_status1[i].MPI_SOURCE;
1466 
1467       /* form the header */
1468       sbuf2_i[0] = req_size[i];
1469       for (j=1; j<start; j++) sbuf2_i[j] = rbuf1_i[j];
1470 
1471       ierr = MPI_Isend(sbuf2_i,end,MPIU_INT,req_source1[i],tag2,comm,s_waits2+i);CHKERRQ(ierr);
1472     }
1473 
1474     ierr = PetscFree(r_status1);CHKERRQ(ierr);
1475     ierr = PetscFree(r_waits1);CHKERRQ(ierr);
1476 
1477     /* rbuf2 is received, Post recv column indices a->j */
1478     ierr = MPI_Waitall(nrqs,r_waits2,r_status2);CHKERRQ(ierr);
1479 
1480     ierr = PetscMalloc4(nrqs+1,&r_waits3,nrqr+1,&s_waits3,nrqs+1,&r_status3,nrqr+1,&s_status3);CHKERRQ(ierr);
1481     for (i=0; i<nrqs; ++i) {
1482       ierr = PetscMalloc1(rbuf2[i][0]+1,&rbuf3[i]);CHKERRQ(ierr);
1483       req_source2[i] = r_status2[i].MPI_SOURCE;
1484       ierr = MPI_Irecv(rbuf3[i],rbuf2[i][0],MPIU_INT,req_source2[i],tag3,comm,r_waits3+i);CHKERRQ(ierr);
1485     }
1486 
1487     /* Wait on sends1 and sends2 */
1488     ierr = PetscMalloc1(nrqs+1,&s_status1);CHKERRQ(ierr);
1489     ierr = MPI_Waitall(nrqs,s_waits1,s_status1);CHKERRQ(ierr);
1490     ierr = PetscFree(s_waits1);CHKERRQ(ierr);
1491     ierr = PetscFree(s_status1);CHKERRQ(ierr);
1492 
1493     ierr = MPI_Waitall(nrqr,s_waits2,s_status2);CHKERRQ(ierr);
1494     ierr = PetscFree4(r_status2,s_waits2,r_waits2,s_status2);CHKERRQ(ierr);
1495 
1496     /* Now allocate sending buffers for a->j, and send them off */
1497     ierr = PetscMalloc1(nrqr+1,&sbuf_aj);CHKERRQ(ierr);
1498     for (i=0,j=0; i<nrqr; i++) j += req_size[i];
1499     ierr = PetscMalloc1(j+1,&sbuf_aj[0]);CHKERRQ(ierr);
1500     for (i=1; i<nrqr; i++) sbuf_aj[i] = sbuf_aj[i-1] + req_size[i-1];
1501 
1502     for (i=0; i<nrqr; i++) { /* for each requested message */
1503       rbuf1_i   = rbuf1[i];
1504       sbuf_aj_i = sbuf_aj[i];
1505       ct1       = 2*rbuf1_i[0] + 1;
1506       ct2       = 0;
1507       /* max1=rbuf1_i[0]; if (max1 != 1) SETERRQ1(PETSC_COMM_SELF,0,"max1 %d != 1",max1); */
1508 
1509       kmax = rbuf1[i][2];
1510       for (k=0; k<kmax; k++,ct1++) { /* for each row */
1511         row    = rbuf1_i[ct1] - rstart;
1512         nzA    = ai[row+1] - ai[row];
1513         nzB    = bi[row+1] - bi[row];
1514         ncols  = nzA + nzB;
1515         cworkA = aj + ai[row]; cworkB = bj + bi[row];
1516 
1517         /* load the column indices for this row into cols*/
1518         cols = sbuf_aj_i + ct2;
1519 
1520         lwrite = 0;
1521         for (l=0; l<nzB; l++) {
1522           if ((ctmp = bmap[cworkB[l]]) < cstart) cols[lwrite++] = ctmp;
1523         }
1524         for (l=0; l<nzA; l++) cols[lwrite++] = cstart + cworkA[l];
1525         for (l=0; l<nzB; l++) {
1526           if ((ctmp = bmap[cworkB[l]]) >= cend) cols[lwrite++] = ctmp;
1527         }
1528 
1529         ct2 += ncols;
1530       }
1531       ierr = MPI_Isend(sbuf_aj_i,req_size[i],MPIU_INT,req_source1[i],tag3,comm,s_waits3+i);CHKERRQ(ierr);
1532     }
1533 
1534     /* create column map (cmap): global col of C -> local col of submat */
1535 #if defined(PETSC_USE_CTABLE)
1536     if (!allcolumns) {
1537       ierr = PetscTableCreate(ncol+1,C->cmap->N+1,&cmap);CHKERRQ(ierr);
1538       ierr = PetscCalloc1(C->cmap->n,&cmap_loc);CHKERRQ(ierr);
1539       for (j=0; j<ncol; j++) { /* use array cmap_loc[] for local col indices */
1540         if (icol[j] >= cstart && icol[j] <cend) {
1541           cmap_loc[icol[j] - cstart] = j+1;
1542         } else { /* use PetscTable for non-local col indices */
1543           ierr = PetscTableAdd(cmap,icol[j]+1,j+1,INSERT_VALUES);CHKERRQ(ierr);
1544         }
1545       }
1546     } else {
1547       cmap     = NULL;
1548       cmap_loc = NULL;
1549     }
1550     ierr = PetscCalloc1(C->rmap->n,&rmap_loc);CHKERRQ(ierr);
1551 #else
1552     if (!allcolumns) {
1553       ierr   = PetscCalloc1(C->cmap->N,&cmap);CHKERRQ(ierr);
1554       for (j=0; j<ncol; j++) cmap[icol[j]] = j+1;
1555     } else {
1556       cmap = NULL;
1557     }
1558 #endif
1559 
1560     /* Create lens for MatSeqAIJSetPreallocation() */
1561     ierr = PetscCalloc1(nrow,&lens);CHKERRQ(ierr);
1562 
1563     /* Compute lens from local part of C */
1564     for (j=0; j<nrow; j++) {
1565       row  = irow[j];
1566       proc = row2proc[j];
1567       if (proc == rank) {
1568         /* diagonal part A = c->A */
1569         ncols = ai[row-rstart+1] - ai[row-rstart];
1570         cols  = aj + ai[row-rstart];
1571         if (!allcolumns) {
1572           for (k=0; k<ncols; k++) {
1573 #if defined(PETSC_USE_CTABLE)
1574             tcol = cmap_loc[cols[k]];
1575 #else
1576             tcol = cmap[cols[k]+cstart];
1577 #endif
1578             if (tcol) lens[j]++;
1579           }
1580         } else { /* allcolumns */
1581           lens[j] = ncols;
1582         }
1583 
1584         /* off-diagonal part B = c->B */
1585         ncols = bi[row-rstart+1] - bi[row-rstart];
1586         cols  = bj + bi[row-rstart];
1587         if (!allcolumns) {
1588           for (k=0; k<ncols; k++) {
1589 #if defined(PETSC_USE_CTABLE)
1590             ierr = PetscTableFind(cmap,bmap[cols[k]]+1,&tcol);CHKERRQ(ierr);
1591 #else
1592             tcol = cmap[bmap[cols[k]]];
1593 #endif
1594             if (tcol) lens[j]++;
1595           }
1596         } else { /* allcolumns */
1597           lens[j] += ncols;
1598         }
1599       }
1600     }
1601 
1602     /* Create row map (rmap): global row of C -> local row of submat */
1603 #if defined(PETSC_USE_CTABLE)
1604     ierr = PetscTableCreate(nrow+1,C->rmap->N+1,&rmap);CHKERRQ(ierr);
1605     for (j=0; j<nrow; j++) {
1606       row  = irow[j];
1607       proc = row2proc[j];
1608       if (proc == rank) { /* a local row */
1609         rmap_loc[row - rstart] = j;
1610       } else {
1611         ierr = PetscTableAdd(rmap,irow[j]+1,j+1,INSERT_VALUES);CHKERRQ(ierr);
1612       }
1613     }
1614 #else
1615     ierr = PetscCalloc1(C->rmap->N,&rmap);CHKERRQ(ierr);
1616     for (j=0; j<nrow; j++) {
1617       rmap[irow[j]] = j;
1618     }
1619 #endif
1620 
1621     /* Update lens from offproc data */
1622     /* recv a->j is done */
1623     ierr    = MPI_Waitall(nrqs,r_waits3,r_status3);CHKERRQ(ierr);
1624     for (i=0; i<nrqs; i++) {
1625       proc    = pa[i];
1626       sbuf1_i = sbuf1[proc];
1627       /* jmax    = sbuf1_i[0]; if (jmax != 1) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"jmax !=1"); */
1628       ct1     = 2 + 1;
1629       ct2     = 0;
1630       rbuf2_i = rbuf2[i]; /* received length of C->j */
1631       rbuf3_i = rbuf3[i]; /* received C->j */
1632 
1633       /* is_no  = sbuf1_i[2*j-1]; if (is_no != 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"is_no !=0"); */
1634       max1   = sbuf1_i[2];
1635       for (k=0; k<max1; k++,ct1++) {
1636 #if defined(PETSC_USE_CTABLE)
1637         ierr = PetscTableFind(rmap,sbuf1_i[ct1]+1,&row);CHKERRQ(ierr);
1638         row--;
1639         if (row < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"row not found in table");
1640 #else
1641         row = rmap[sbuf1_i[ct1]]; /* the row index in submat */
1642 #endif
1643         /* Now, store row index of submat in sbuf1_i[ct1] */
1644         sbuf1_i[ct1] = row;
1645 
1646         nnz = rbuf2_i[ct1];
1647         if (!allcolumns) {
1648           for (l=0; l<nnz; l++,ct2++) {
1649 #if defined(PETSC_USE_CTABLE)
1650             if (rbuf3_i[ct2] >= cstart && rbuf3_i[ct2] <cend) {
1651               tcol = cmap_loc[rbuf3_i[ct2] - cstart];
1652             } else {
1653               ierr = PetscTableFind(cmap,rbuf3_i[ct2]+1,&tcol);CHKERRQ(ierr);
1654             }
1655 #else
1656             tcol = cmap[rbuf3_i[ct2]]; /* column index in submat */
1657 #endif
1658             if (tcol) lens[row]++;
1659           }
1660         } else { /* allcolumns */
1661           lens[row] += nnz;
1662         }
1663       }
1664     }
1665     ierr = MPI_Waitall(nrqr,s_waits3,s_status3);CHKERRQ(ierr);
1666     ierr = PetscFree4(r_waits3,s_waits3,r_status3,s_status3);CHKERRQ(ierr);
1667 
1668     /* Create the submatrices */
1669     ierr = MatCreate(PETSC_COMM_SELF,&submat);CHKERRQ(ierr);
1670     ierr = MatSetSizes(submat,nrow,ncol,PETSC_DETERMINE,PETSC_DETERMINE);CHKERRQ(ierr);
1671 
1672     ierr = ISGetBlockSize(isrow[0],&i);CHKERRQ(ierr);
1673     ierr = ISGetBlockSize(iscol[0],&j);CHKERRQ(ierr);
1674     ierr = MatSetBlockSizes(submat,i,j);CHKERRQ(ierr);
1675     ierr = MatSetType(submat,((PetscObject)A)->type_name);CHKERRQ(ierr);
1676     ierr = MatSeqAIJSetPreallocation(submat,0,lens);CHKERRQ(ierr);
1677 
1678     /* create struct Mat_SubMat and attached it to submat */
1679     ierr = PetscNew(&smatis1);CHKERRQ(ierr);
1680     subc = (Mat_SeqAIJ*)submat->data;
1681     subc->submatis1 = smatis1;
1682 
1683     smatis1->id          = 0;
1684     smatis1->nrqs        = nrqs;
1685     smatis1->nrqr        = nrqr;
1686     smatis1->rbuf1       = rbuf1;
1687     smatis1->rbuf2       = rbuf2;
1688     smatis1->rbuf3       = rbuf3;
1689     smatis1->sbuf2       = sbuf2;
1690     smatis1->req_source2 = req_source2;
1691 
1692     smatis1->sbuf1       = sbuf1;
1693     smatis1->ptr         = ptr;
1694     smatis1->tmp         = tmp;
1695     smatis1->ctr         = ctr;
1696 
1697     smatis1->pa           = pa;
1698     smatis1->req_size     = req_size;
1699     smatis1->req_source1  = req_source1;
1700 
1701     smatis1->allcolumns  = allcolumns;
1702     smatis1->singleis    = PETSC_TRUE;
1703     smatis1->row2proc    = row2proc;
1704     smatis1->rmap        = rmap;
1705     smatis1->cmap        = cmap;
1706 #if defined(PETSC_USE_CTABLE)
1707     smatis1->rmap_loc    = rmap_loc;
1708     smatis1->cmap_loc    = cmap_loc;
1709 #endif
1710 
1711     smatis1->destroy     = submat->ops->destroy;
1712     submat->ops->destroy = MatDestroy_MPIAIJ_MatGetSubmatrices;
1713     submat->factortype   = C->factortype;
1714 
1715     /* compute rmax */
1716     rmax = 0;
1717     for (i=0; i<nrow; i++) rmax = PetscMax(rmax,lens[i]);
1718 
1719   } else { /* scall == MAT_REUSE_MATRIX */
1720     submat = submats[0];
1721     if (submat->rmap->n != nrow || submat->cmap->n != ncol) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Cannot reuse matrix. wrong size");
1722 
1723     subc    = (Mat_SeqAIJ*)submat->data;
1724     rmax    = subc->rmax;
1725     smatis1 = subc->submatis1;
1726     nrqs        = smatis1->nrqs;
1727     nrqr        = smatis1->nrqr;
1728     rbuf1       = smatis1->rbuf1;
1729     rbuf2       = smatis1->rbuf2;
1730     rbuf3       = smatis1->rbuf3;
1731     req_source2 = smatis1->req_source2;
1732 
1733     sbuf1     = smatis1->sbuf1;
1734     sbuf2     = smatis1->sbuf2;
1735     ptr       = smatis1->ptr;
1736     tmp       = smatis1->tmp;
1737     ctr       = smatis1->ctr;
1738 
1739     pa         = smatis1->pa;
1740     req_size   = smatis1->req_size;
1741     req_source1 = smatis1->req_source1;
1742 
1743     allcolumns = smatis1->allcolumns;
1744     row2proc   = smatis1->row2proc;
1745     rmap       = smatis1->rmap;
1746     cmap       = smatis1->cmap;
1747 #if defined(PETSC_USE_CTABLE)
1748     rmap_loc   = smatis1->rmap_loc;
1749     cmap_loc   = smatis1->cmap_loc;
1750 #endif
1751   }
1752 
1753   /* Post recv matrix values */
1754   ierr = PetscMalloc3(nrqs+1,&rbuf4, rmax,&subcols, rmax,&subvals);CHKERRQ(ierr);
1755   ierr = PetscMalloc4(nrqs+1,&r_waits4,nrqr+1,&s_waits4,nrqs+1,&r_status4,nrqr+1,&s_status4);CHKERRQ(ierr);
1756   ierr = PetscObjectGetNewTag((PetscObject)C,&tag4);CHKERRQ(ierr);
1757   for (i=0; i<nrqs; ++i) {
1758     ierr = PetscMalloc1(rbuf2[i][0]+1,&rbuf4[i]);CHKERRQ(ierr);
1759     ierr = MPI_Irecv(rbuf4[i],rbuf2[i][0],MPIU_SCALAR,req_source2[i],tag4,comm,r_waits4+i);CHKERRQ(ierr);
1760   }
1761 
1762   /* Allocate sending buffers for a->a, and send them off */
1763   ierr = PetscMalloc1(nrqr+1,&sbuf_aa);CHKERRQ(ierr);
1764   for (i=0,j=0; i<nrqr; i++) j += req_size[i];
1765   ierr = PetscMalloc1(j+1,&sbuf_aa[0]);CHKERRQ(ierr);
1766   for (i=1; i<nrqr; i++) sbuf_aa[i] = sbuf_aa[i-1] + req_size[i-1];
1767 
1768   for (i=0; i<nrqr; i++) {
1769     rbuf1_i   = rbuf1[i];
1770     sbuf_aa_i = sbuf_aa[i];
1771     ct1       = 2*rbuf1_i[0]+1;
1772     ct2       = 0;
1773     /* max1=rbuf1_i[0]; if (max1 != 1) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"max1 !=1"); */
1774 
1775     kmax = rbuf1_i[2];
1776     for (k=0; k<kmax; k++,ct1++) {
1777       row = rbuf1_i[ct1] - rstart;
1778       nzA = ai[row+1] - ai[row];
1779       nzB = bi[row+1] - bi[row];
1780       ncols  = nzA + nzB;
1781       cworkB = bj + bi[row];
1782       vworkA = a_a + ai[row];
1783       vworkB = b_a + bi[row];
1784 
1785       /* load the column values for this row into vals*/
1786       vals = sbuf_aa_i + ct2;
1787 
1788       lwrite = 0;
1789       for (l=0; l<nzB; l++) {
1790         if ((bmap[cworkB[l]]) < cstart) vals[lwrite++] = vworkB[l];
1791       }
1792       for (l=0; l<nzA; l++) vals[lwrite++] = vworkA[l];
1793       for (l=0; l<nzB; l++) {
1794         if ((bmap[cworkB[l]]) >= cend) vals[lwrite++] = vworkB[l];
1795       }
1796 
1797       ct2 += ncols;
1798     }
1799     ierr = MPI_Isend(sbuf_aa_i,req_size[i],MPIU_SCALAR,req_source1[i],tag4,comm,s_waits4+i);CHKERRQ(ierr);
1800   }
1801 
1802   /* Assemble submat */
1803   /* First assemble the local rows */
1804   for (j=0; j<nrow; j++) {
1805     row  = irow[j];
1806     proc = row2proc[j];
1807     if (proc == rank) {
1808       Crow = row - rstart;  /* local row index of C */
1809 #if defined(PETSC_USE_CTABLE)
1810       row = rmap_loc[Crow]; /* row index of submat */
1811 #else
1812       row = rmap[row];
1813 #endif
1814 
1815       if (allcolumns) {
1816         /* diagonal part A = c->A */
1817         ncols = ai[Crow+1] - ai[Crow];
1818         cols  = aj + ai[Crow];
1819         vals  = a->a + ai[Crow];
1820         i     = 0;
1821         for (k=0; k<ncols; k++) {
1822           subcols[i]   = cols[k] + cstart;
1823           subvals[i++] = vals[k];
1824         }
1825 
1826         /* off-diagonal part B = c->B */
1827         ncols = bi[Crow+1] - bi[Crow];
1828         cols  = bj + bi[Crow];
1829         vals  = b->a + bi[Crow];
1830         for (k=0; k<ncols; k++) {
1831           subcols[i]   = bmap[cols[k]];
1832           subvals[i++] = vals[k];
1833         }
1834 
1835         ierr = MatSetValues_SeqAIJ(submat,1,&row,i,subcols,subvals,INSERT_VALUES);CHKERRQ(ierr);
1836 
1837       } else { /* !allcolumns */
1838 #if defined(PETSC_USE_CTABLE)
1839         /* diagonal part A = c->A */
1840         ncols = ai[Crow+1] - ai[Crow];
1841         cols  = aj + ai[Crow];
1842         vals  = a->a + ai[Crow];
1843         i     = 0;
1844         for (k=0; k<ncols; k++) {
1845           tcol = cmap_loc[cols[k]];
1846           if (tcol) {
1847             subcols[i]   = --tcol;
1848             subvals[i++] = vals[k];
1849           }
1850         }
1851 
1852         /* off-diagonal part B = c->B */
1853         ncols = bi[Crow+1] - bi[Crow];
1854         cols  = bj + bi[Crow];
1855         vals  = b->a + bi[Crow];
1856         for (k=0; k<ncols; k++) {
1857           ierr = PetscTableFind(cmap,bmap[cols[k]]+1,&tcol);CHKERRQ(ierr);
1858           if (tcol) {
1859             subcols[i]   = --tcol;
1860             subvals[i++] = vals[k];
1861           }
1862         }
1863 #else
1864         /* diagonal part A = c->A */
1865         ncols = ai[Crow+1] - ai[Crow];
1866         cols  = aj + ai[Crow];
1867         vals  = a->a + ai[Crow];
1868         i     = 0;
1869         for (k=0; k<ncols; k++) {
1870           tcol = cmap[cols[k]+cstart];
1871           if (tcol) {
1872             subcols[i]   = --tcol;
1873             subvals[i++] = vals[k];
1874           }
1875         }
1876 
1877         /* off-diagonal part B = c->B */
1878         ncols = bi[Crow+1] - bi[Crow];
1879         cols  = bj + bi[Crow];
1880         vals  = b->a + bi[Crow];
1881         for (k=0; k<ncols; k++) {
1882           tcol = cmap[bmap[cols[k]]];
1883           if (tcol) {
1884             subcols[i]   = --tcol;
1885             subvals[i++] = vals[k];
1886           }
1887         }
1888 #endif
1889         ierr = MatSetValues_SeqAIJ(submat,1,&row,i,subcols,subvals,INSERT_VALUES);CHKERRQ(ierr);
1890       }
1891     }
1892   }
1893 
1894   /* Now assemble the off-proc rows */
1895   for (i=0; i<nrqs; i++) { /* for each requested message */
1896     /* recv values from other processes */
1897     ierr    = MPI_Waitany(nrqs,r_waits4,&idex,r_status4+i);CHKERRQ(ierr);
1898     proc    = pa[idex];
1899     sbuf1_i = sbuf1[proc];
1900     /* jmax    = sbuf1_i[0]; if (jmax != 1)SETERRQ1(PETSC_COMM_SELF,0,"jmax %d != 1",jmax); */
1901     ct1     = 2 + 1;
1902     ct2     = 0; /* count of received C->j */
1903     ct3     = 0; /* count of received C->j that will be inserted into submat */
1904     rbuf2_i = rbuf2[idex]; /* int** received length of C->j from other processes */
1905     rbuf3_i = rbuf3[idex]; /* int** received C->j from other processes */
1906     rbuf4_i = rbuf4[idex]; /* scalar** received C->a from other processes */
1907 
1908     /* is_no = sbuf1_i[2*j-1]; if (is_no != 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"is_no !=0"); */
1909     max1 = sbuf1_i[2];             /* num of rows */
1910     for (k=0; k<max1; k++,ct1++) { /* for each recved row */
1911       row = sbuf1_i[ct1]; /* row index of submat */
1912       if (!allcolumns) {
1913         idex = 0;
1914         if (scall == MAT_INITIAL_MATRIX) {
1915           nnz  = rbuf2_i[ct1]; /* num of C entries in this row */
1916           for (l=0; l<nnz; l++,ct2++) { /* for each recved column */
1917 #if defined(PETSC_USE_CTABLE)
1918             if (rbuf3_i[ct2] >= cstart && rbuf3_i[ct2] <cend) {
1919               tcol = cmap_loc[rbuf3_i[ct2] - cstart];
1920             } else {
1921               ierr = PetscTableFind(cmap,rbuf3_i[ct2]+1,&tcol);CHKERRQ(ierr);
1922             }
1923 #else
1924             tcol = cmap[rbuf3_i[ct2]];
1925 #endif
1926             if (tcol) {
1927               subcols[idex]   = --tcol;
1928               subvals[idex++] = rbuf4_i[ct2];
1929 
1930               /* We receive an entire column of C, but a subset of it needs to be inserted into submat.
1931                For reuse, we replace received C->j with index that should be inserted to submat */
1932               rbuf3_i[ct3++] = ct2;
1933             }
1934           }
1935           ierr = MatSetValues_SeqAIJ(submat,1,&row,idex,subcols,subvals,INSERT_VALUES);CHKERRQ(ierr);
1936 
1937         } else { /* scall == MAT_REUSE_MATRIX */
1938           submat = submats[0];
1939           subc   = (Mat_SeqAIJ*)submat->data;
1940 
1941           nnz = subc->i[row+1] - subc->i[row]; /* num of submat entries in this row */
1942           for (l=0; l<nnz; l++) {
1943             ct2 = rbuf3_i[ct3++]; /* index of rbuf4_i[] which needs to be inserted into submat */
1944             subvals[idex++] = rbuf4_i[ct2];
1945           }
1946 
1947           bj = subc->j + subc->i[row];
1948           ierr = MatSetValues_SeqAIJ(submat,1,&row,nnz,bj,subvals,INSERT_VALUES);CHKERRQ(ierr);
1949         }
1950       } else { /* allcolumns */
1951         nnz  = rbuf2_i[ct1]; /* num of C entries in this row */
1952         ierr = MatSetValues_SeqAIJ(submat,1,&row,nnz,rbuf3_i+ct2,rbuf4_i+ct2,INSERT_VALUES);CHKERRQ(ierr);
1953         ct2 += nnz;
1954       }
1955     }
1956   }
1957 
1958   /* sending a->a are done */
1959   ierr = MPI_Waitall(nrqr,s_waits4,s_status4);CHKERRQ(ierr);
1960   ierr = PetscFree4(r_waits4,s_waits4,r_status4,s_status4);CHKERRQ(ierr);
1961 
1962   ierr = MatAssemblyBegin(submat,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
1963   ierr = MatAssemblyEnd(submat,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
1964   submats[0] = submat;
1965 
1966   /* Restore the indices */
1967   ierr = ISRestoreIndices(isrow[0],&irow);CHKERRQ(ierr);
1968   if (!allcolumns) {
1969     ierr = ISRestoreIndices(iscol[0],&icol);CHKERRQ(ierr);
1970   }
1971 
1972   /* Destroy allocated memory */
1973   for (i=0; i<nrqs; ++i) {
1974     ierr = PetscFree3(rbuf4[i],subcols,subvals);CHKERRQ(ierr);
1975   }
1976   ierr = PetscFree3(rbuf4,subcols,subvals);CHKERRQ(ierr);
1977   ierr = PetscFree(sbuf_aa[0]);CHKERRQ(ierr);
1978   ierr = PetscFree(sbuf_aa);CHKERRQ(ierr);
1979 
1980   if (scall == MAT_INITIAL_MATRIX) {
1981     ierr = PetscFree(lens);CHKERRQ(ierr);
1982     ierr = PetscFree(sbuf_aj[0]);CHKERRQ(ierr);
1983     ierr = PetscFree(sbuf_aj);CHKERRQ(ierr);
1984   }
1985   PetscFunctionReturn(0);
1986 }
1987 
1988 PetscErrorCode MatGetSubMatrices_MPIAIJ_SingleIS(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[])
1989 {
1990   PetscErrorCode ierr;
1991   PetscInt       ncol;
1992   PetscBool      colflag,allcolumns=PETSC_FALSE;
1993 
1994   PetscFunctionBegin;
1995   /* Allocate memory to hold all the submatrices */
1996   if (scall == MAT_INITIAL_MATRIX) {
1997     ierr = PetscMalloc1(1,submat);CHKERRQ(ierr);
1998   }
1999 
2000   /* Check for special case: each processor gets entire matrix columns */
2001   ierr = ISIdentity(iscol[0],&colflag);CHKERRQ(ierr);
2002   ierr = ISGetLocalSize(iscol[0],&ncol);CHKERRQ(ierr);
2003   if (colflag && ncol == C->cmap->N) allcolumns = PETSC_TRUE;
2004 
2005   ierr = MatGetSubMatrices_MPIAIJ_SingleIS_Local(C,ismax,isrow,iscol,scall,allcolumns,*submat);CHKERRQ(ierr);
2006   PetscFunctionReturn(0);
2007 }
2008 
2009 PetscErrorCode MatGetSubMatrices_MPIAIJ(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[])
2010 {
2011   PetscErrorCode ierr;
2012   PetscInt       nmax,nstages,i,pos,max_no,nrow,ncol,in[2],out[2];
2013   PetscBool      rowflag,colflag,wantallmatrix=PETSC_FALSE;
2014   Mat_SeqAIJ     *subc;
2015   Mat_SubMat     *smat;
2016 
2017   PetscFunctionBegin;
2018   /* Check for special case: each processor has a single IS */
2019   if (C->submat_singleis) { /* flag is set in PCSetUp_ASM() to skip MPIU_Allreduce() */
2020     ierr = MatGetSubMatrices_MPIAIJ_SingleIS(C,ismax,isrow,iscol,scall,submat);CHKERRQ(ierr);
2021     C->submat_singleis = PETSC_FALSE; /* resume its default value in case C will be used for non-singlis */
2022     PetscFunctionReturn(0);
2023   }
2024 
2025   /* Collect global wantallmatrix and nstages */
2026   if (!C->cmap->N) nmax=20*1000000/sizeof(PetscInt);
2027   else nmax = 20*1000000 / (C->cmap->N * sizeof(PetscInt));
2028   if (!nmax) nmax = 1;
2029 
2030   if (scall == MAT_INITIAL_MATRIX) {
2031     /* Collect global wantallmatrix and nstages */
2032     if (ismax == 1 && C->rmap->N == C->cmap->N) {
2033       ierr = ISIdentity(*isrow,&rowflag);CHKERRQ(ierr);
2034       ierr = ISIdentity(*iscol,&colflag);CHKERRQ(ierr);
2035       ierr = ISGetLocalSize(*isrow,&nrow);CHKERRQ(ierr);
2036       ierr = ISGetLocalSize(*iscol,&ncol);CHKERRQ(ierr);
2037       if (rowflag && colflag && nrow == C->rmap->N && ncol == C->cmap->N) {
2038         wantallmatrix = PETSC_TRUE;
2039 
2040         ierr = PetscOptionsGetBool(((PetscObject)C)->options,((PetscObject)C)->prefix,"-use_fast_submatrix",&wantallmatrix,NULL);CHKERRQ(ierr);
2041       }
2042     }
2043 
2044     /* Determine the number of stages through which submatrices are done
2045        Each stage will extract nmax submatrices.
2046        nmax is determined by the matrix column dimension.
2047        If the original matrix has 20M columns, only one submatrix per stage is allowed, etc.
2048     */
2049     nstages = ismax/nmax + ((ismax % nmax) ? 1 : 0); /* local nstages */
2050 
2051     in[0] = -1*(PetscInt)wantallmatrix;
2052     in[1] = nstages;
2053     ierr = MPIU_Allreduce(in,out,2,MPIU_INT,MPI_MAX,PetscObjectComm((PetscObject)C));CHKERRQ(ierr);
2054     wantallmatrix = (PetscBool)(-out[0]);
2055     nstages       = out[1]; /* Make sure every processor loops through the global nstages */
2056 
2057   } else { /* MAT_REUSE_MATRIX */
2058     subc = (Mat_SeqAIJ*)((*submat)[0]->data);
2059     smat   = subc->submatis1;
2060     if (!smat) {
2061       /* smat is not generated by MatGetSubMatrix_MPIAIJ_All(...,MAT_INITIAL_MATRIX,...) */
2062       wantallmatrix = PETSC_TRUE;
2063     } else if (smat->singleis) {
2064       ierr = MatGetSubMatrices_MPIAIJ_SingleIS(C,ismax,isrow,iscol,scall,submat);CHKERRQ(ierr);
2065       PetscFunctionReturn(0);
2066     } else {
2067       nstages = smat->nstages;
2068     }
2069   }
2070 
2071   if (wantallmatrix) {
2072     ierr = MatGetSubMatrix_MPIAIJ_All(C,MAT_GET_VALUES,scall,submat);CHKERRQ(ierr);
2073     PetscFunctionReturn(0);
2074   }
2075 
2076   /* Allocate memory to hold all the submatrices and dummy submatrices */
2077   if (scall == MAT_INITIAL_MATRIX) {
2078     ierr = PetscCalloc1(ismax+nstages,submat);CHKERRQ(ierr);
2079   }
2080 
2081 #if 0
2082   PetscMPIInt rank;
2083   ierr = MPI_Comm_rank(PetscObjectComm((PetscObject)C),&rank);CHKERRQ(ierr);
2084   printf("[%d] reuse %d, ismax %d, CN %d, nstages %d, nmax %d\n",rank,scall,ismax,C->cmap->N,nstages,nmax);
2085 #endif
2086   for (i=0,pos=0; i<nstages; i++) {
2087     if (pos+nmax <= ismax) max_no = nmax;
2088     else if (pos == ismax) max_no = 0;
2089     else                   max_no = ismax-pos;
2090     /* if (!max_no) printf("[%d] max_no=0, %d-stage\n",rank,i); */
2091     ierr = MatGetSubMatrices_MPIAIJ_Local(C,max_no,isrow+pos,iscol+pos,scall,*submat+pos);CHKERRQ(ierr);
2092     pos += max_no;
2093   }
2094 
2095   if (scall == MAT_INITIAL_MATRIX) {
2096     /* save nstages for reuse */
2097     subc = (Mat_SeqAIJ*)((*submat)[0]->data);
2098     smat = subc->submatis1;
2099     if (!smat) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_NULL,"smat does not exit");
2100     smat->nstages = nstages;
2101   }
2102   PetscFunctionReturn(0);
2103 }
2104 
2105 /* -------------------------------------------------------------------------*/
2106 PetscErrorCode MatGetSubMatrices_MPIAIJ_Local(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submats)
2107 {
2108   Mat_MPIAIJ     *c = (Mat_MPIAIJ*)C->data;
2109   Mat            A  = c->A;
2110   Mat_SeqAIJ     *a = (Mat_SeqAIJ*)A->data,*b = (Mat_SeqAIJ*)c->B->data,*subc;
2111   const PetscInt **icol,**irow;
2112   PetscInt       *nrow,*ncol,start;
2113   PetscErrorCode ierr;
2114   PetscMPIInt    rank,size,tag0,tag2,tag3,tag4,*w1,*w2,*w3,*w4,nrqr;
2115   PetscInt       **sbuf1,**sbuf2,i,j,k,l,ct1,ct2,**rbuf1,row,proc=-1;
2116   PetscInt       nrqs=0,msz,**ptr=NULL,*req_size=NULL,*ctr=NULL,*pa,*tmp=NULL,tcol;
2117   PetscInt       **rbuf3=NULL,*req_source1=NULL,*req_source2,**sbuf_aj,**rbuf2=NULL,max1,max2;
2118   PetscInt       **lens,is_no,ncols,*cols,mat_i,*mat_j,tmp2,jmax;
2119 #if defined(PETSC_USE_CTABLE)
2120   PetscTable     *cmap,cmap_i=NULL,*rmap,rmap_i;
2121 #else
2122   PetscInt       **cmap,*cmap_i=NULL,**rmap,*rmap_i;
2123 #endif
2124   const PetscInt *irow_i;
2125   PetscInt       ctr_j,*sbuf1_j,*sbuf_aj_i,*rbuf1_i,kmax,*lens_i;
2126   MPI_Request    *s_waits1,*r_waits1,*s_waits2,*r_waits2,*r_waits3;
2127   MPI_Request    *r_waits4,*s_waits3,*s_waits4;
2128   MPI_Status     *r_status1,*r_status2,*s_status1,*s_status3,*s_status2;
2129   MPI_Status     *r_status3,*r_status4,*s_status4;
2130   MPI_Comm       comm;
2131   PetscScalar    **rbuf4,*rbuf4_i,**sbuf_aa,*vals,*mat_a,*imat_a,*sbuf_aa_i;
2132   PetscMPIInt    *onodes1,*olengths1,end;
2133   PetscInt       **row2proc,*row2proc_i,ilen_row,*imat_ilen,*imat_j,*imat_i,old_row;
2134   Mat_SubMat     *smat_i;
2135   PetscBool      *issorted,*allcolumns,colflag,iscsorted=PETSC_TRUE;
2136   PetscInt       *sbuf1_i,*rbuf2_i,*rbuf3_i,ilen;
2137 
2138   PetscFunctionBegin;
2139   ierr = PetscObjectGetComm((PetscObject)C,&comm);CHKERRQ(ierr);
2140   size = c->size;
2141   rank = c->rank;
2142 
2143   ierr = PetscMalloc4(ismax,&row2proc,ismax,&cmap,ismax,&rmap,ismax+1,&allcolumns);CHKERRQ(ierr);
2144   ierr = PetscMalloc5(ismax,&irow,ismax,&icol,ismax,&nrow,ismax,&ncol,ismax,&issorted);CHKERRQ(ierr);
2145 
2146   for (i=0; i<ismax; i++) {
2147     ierr = ISSorted(iscol[i],&issorted[i]);CHKERRQ(ierr);
2148     if (!issorted[i]) iscsorted = issorted[i];
2149 
2150     ierr = ISSorted(isrow[i],&issorted[i]);CHKERRQ(ierr);
2151 
2152     ierr = ISGetIndices(isrow[i],&irow[i]);CHKERRQ(ierr);
2153     ierr = ISGetLocalSize(isrow[i],&nrow[i]);CHKERRQ(ierr);
2154 
2155     /* Check for special case: allcolumn */
2156     ierr = ISIdentity(iscol[i],&colflag);CHKERRQ(ierr);
2157     ierr = ISGetLocalSize(iscol[i],&ncol[i]);CHKERRQ(ierr);
2158     if (colflag && ncol[i] == C->cmap->N) {
2159       allcolumns[i] = PETSC_TRUE;
2160       icol[i] = NULL;
2161     } else {
2162       allcolumns[i] = PETSC_FALSE;
2163       ierr = ISGetIndices(iscol[i],&icol[i]);CHKERRQ(ierr);
2164     }
2165   }
2166 
2167   if (scall == MAT_REUSE_MATRIX) {
2168     /* Assumes new rows are same length as the old rows */
2169     for (i=0; i<ismax; i++) {
2170       if (!submats[i]) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_ARG_NULL,"submats[%D] is null, cannot reuse",i);
2171       subc = (Mat_SeqAIJ*)(submats[i]->data);
2172       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");
2173 
2174       /* Initial matrix as if empty */
2175       ierr = PetscMemzero(subc->ilen,submats[i]->rmap->n*sizeof(PetscInt));CHKERRQ(ierr);
2176 
2177       smat_i   = subc->submatis1;
2178 
2179       nrqs        = smat_i->nrqs;
2180       nrqr        = smat_i->nrqr;
2181       rbuf1       = smat_i->rbuf1;
2182       rbuf2       = smat_i->rbuf2;
2183       rbuf3       = smat_i->rbuf3;
2184       req_source2 = smat_i->req_source2;
2185 
2186       sbuf1     = smat_i->sbuf1;
2187       sbuf2     = smat_i->sbuf2;
2188       ptr       = smat_i->ptr;
2189       tmp       = smat_i->tmp;
2190       ctr       = smat_i->ctr;
2191 
2192       pa          = smat_i->pa;
2193       req_size    = smat_i->req_size;
2194       req_source1 = smat_i->req_source1;
2195 
2196       allcolumns[i] = smat_i->allcolumns;
2197       row2proc[i]   = smat_i->row2proc;
2198       rmap[i]       = smat_i->rmap;
2199       cmap[i]       = smat_i->cmap;
2200     }
2201 
2202     if (!ismax){ /* Get dummy submatrices and retrieve struct submatis1 */
2203       if (!submats[0]) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_NULL,"submats are null, cannot reuse");
2204       subc = (Mat_SeqAIJ*)(submats[0]->data);
2205       smat_i   = subc->submatis1;
2206 
2207       nrqs        = smat_i->nrqs;
2208       nrqr        = smat_i->nrqr;
2209       rbuf1       = smat_i->rbuf1;
2210       rbuf2       = smat_i->rbuf2;
2211       rbuf3       = smat_i->rbuf3;
2212       req_source2 = smat_i->req_source2;
2213 
2214       sbuf1       = smat_i->sbuf1;
2215       sbuf2       = smat_i->sbuf2;
2216       ptr         = smat_i->ptr;
2217       tmp         = smat_i->tmp;
2218       ctr         = smat_i->ctr;
2219 
2220       pa          = smat_i->pa;
2221       req_size    = smat_i->req_size;
2222       req_source1 = smat_i->req_source1;
2223 
2224       allcolumns[0] = PETSC_TRUE;
2225     }
2226   } else { /* scall == MAT_INITIAL_MATRIX */
2227     /* Get some new tags to keep the communication clean */
2228     ierr = PetscObjectGetNewTag((PetscObject)C,&tag2);CHKERRQ(ierr);
2229     ierr = PetscObjectGetNewTag((PetscObject)C,&tag3);CHKERRQ(ierr);
2230 
2231     /* evaluate communication - mesg to who, length of mesg, and buffer space
2232      required. Based on this, buffers are allocated, and data copied into them*/
2233     ierr = PetscCalloc4(size,&w1,size,&w2,size,&w3,size,&w4);CHKERRQ(ierr);   /* mesg size, initialize work vectors */
2234 
2235     for (i=0; i<ismax; i++) {
2236       jmax   = nrow[i];
2237       irow_i = irow[i];
2238 
2239       ierr   = PetscMalloc1(jmax,&row2proc_i);CHKERRQ(ierr);
2240       row2proc[i] = row2proc_i;
2241 
2242       if (issorted[i]) proc = 0;
2243       for (j=0; j<jmax; j++) {
2244         if (!issorted[i]) proc = 0;
2245         row = irow_i[j];
2246         while (row >= C->rmap->range[proc+1]) proc++;
2247         w4[proc]++;
2248         row2proc_i[j] = proc; /* map row index to proc */
2249       }
2250       for (j=0; j<size; j++) {
2251         if (w4[j]) { w1[j] += w4[j];  w3[j]++; w4[j] = 0;}
2252       }
2253     }
2254 
2255     nrqs     = 0;              /* no of outgoing messages */
2256     msz      = 0;              /* total mesg length (for all procs) */
2257     w1[rank] = 0;              /* no mesg sent to self */
2258     w3[rank] = 0;
2259     for (i=0; i<size; i++) {
2260       if (w1[i])  { w2[i] = 1; nrqs++;} /* there exists a message to proc i */
2261     }
2262     ierr = PetscMalloc1(nrqs+1,&pa);CHKERRQ(ierr); /*(proc -array)*/
2263     for (i=0,j=0; i<size; i++) {
2264       if (w1[i]) { pa[j] = i; j++; }
2265     }
2266 
2267     /* Each message would have a header = 1 + 2*(no of IS) + data */
2268     for (i=0; i<nrqs; i++) {
2269       j      = pa[i];
2270       w1[j] += w2[j] + 2* w3[j];
2271       msz   += w1[j];
2272     }
2273     ierr = PetscInfo2(0,"Number of outgoing messages %D Total message length %D\n",nrqs,msz);CHKERRQ(ierr);
2274 
2275     /* Determine the number of messages to expect, their lengths, from from-ids */
2276     ierr = PetscGatherNumberOfMessages(comm,w2,w1,&nrqr);CHKERRQ(ierr);
2277     ierr = PetscGatherMessageLengths(comm,nrqs,nrqr,w1,&onodes1,&olengths1);CHKERRQ(ierr);
2278 
2279     /* Now post the Irecvs corresponding to these messages */
2280     tag0 = ((PetscObject)C)->tag;
2281     ierr = PetscPostIrecvInt(comm,tag0,nrqr,onodes1,olengths1,&rbuf1,&r_waits1);CHKERRQ(ierr);
2282 
2283     ierr = PetscFree(onodes1);CHKERRQ(ierr);
2284     ierr = PetscFree(olengths1);CHKERRQ(ierr);
2285 
2286     /* Allocate Memory for outgoing messages */
2287     ierr = PetscMalloc4(size,&sbuf1,size,&ptr,2*msz,&tmp,size,&ctr);CHKERRQ(ierr);
2288     ierr = PetscMemzero(sbuf1,size*sizeof(PetscInt*));CHKERRQ(ierr);
2289     ierr = PetscMemzero(ptr,size*sizeof(PetscInt*));CHKERRQ(ierr);
2290 
2291     {
2292       PetscInt *iptr = tmp;
2293       k    = 0;
2294       for (i=0; i<nrqs; i++) {
2295         j        = pa[i];
2296         iptr    += k;
2297         sbuf1[j] = iptr;
2298         k        = w1[j];
2299       }
2300     }
2301 
2302     /* Form the outgoing messages. Initialize the header space */
2303     for (i=0; i<nrqs; i++) {
2304       j           = pa[i];
2305       sbuf1[j][0] = 0;
2306       ierr        = PetscMemzero(sbuf1[j]+1,2*w3[j]*sizeof(PetscInt));CHKERRQ(ierr);
2307       ptr[j]      = sbuf1[j] + 2*w3[j] + 1;
2308     }
2309 
2310     /* Parse the isrow and copy data into outbuf */
2311     for (i=0; i<ismax; i++) {
2312       row2proc_i = row2proc[i];
2313       ierr   = PetscMemzero(ctr,size*sizeof(PetscInt));CHKERRQ(ierr);
2314       irow_i = irow[i];
2315       jmax   = nrow[i];
2316       for (j=0; j<jmax; j++) {  /* parse the indices of each IS */
2317         proc = row2proc_i[j];
2318         if (proc != rank) { /* copy to the outgoing buf*/
2319           ctr[proc]++;
2320           *ptr[proc] = irow_i[j];
2321           ptr[proc]++;
2322         }
2323       }
2324       /* Update the headers for the current IS */
2325       for (j=0; j<size; j++) { /* Can Optimise this loop too */
2326         if ((ctr_j = ctr[j])) {
2327           sbuf1_j        = sbuf1[j];
2328           k              = ++sbuf1_j[0];
2329           sbuf1_j[2*k]   = ctr_j;
2330           sbuf1_j[2*k-1] = i;
2331         }
2332       }
2333     }
2334 
2335     /*  Now  post the sends */
2336     ierr = PetscMalloc1(nrqs+1,&s_waits1);CHKERRQ(ierr);
2337     for (i=0; i<nrqs; ++i) {
2338       j    = pa[i];
2339       ierr = MPI_Isend(sbuf1[j],w1[j],MPIU_INT,j,tag0,comm,s_waits1+i);CHKERRQ(ierr);
2340     }
2341 
2342     /* Post Receives to capture the buffer size */
2343     ierr = PetscMalloc1(nrqs+1,&r_waits2);CHKERRQ(ierr);
2344     ierr = PetscMalloc3(nrqs+1,&req_source2,nrqs+1,&rbuf2,nrqs+1,&rbuf3);CHKERRQ(ierr);
2345     rbuf2[0] = tmp + msz;
2346     for (i=1; i<nrqs; ++i) {
2347       rbuf2[i] = rbuf2[i-1]+w1[pa[i-1]];
2348     }
2349     for (i=0; i<nrqs; ++i) {
2350       j    = pa[i];
2351       ierr = MPI_Irecv(rbuf2[i],w1[j],MPIU_INT,j,tag2,comm,r_waits2+i);CHKERRQ(ierr);
2352     }
2353 
2354     /* Send to other procs the buf size they should allocate */
2355     /* Receive messages*/
2356     ierr = PetscMalloc1(nrqr+1,&s_waits2);CHKERRQ(ierr);
2357     ierr = PetscMalloc1(nrqr+1,&r_status1);CHKERRQ(ierr);
2358     ierr = PetscMalloc3(nrqr,&sbuf2,nrqr,&req_size,nrqr,&req_source1);CHKERRQ(ierr);
2359     {
2360       PetscInt   *sAi = a->i,*sBi = b->i,id,rstart = C->rmap->rstart;
2361       PetscInt   *sbuf2_i;
2362 
2363       ierr = MPI_Waitall(nrqr,r_waits1,r_status1);CHKERRQ(ierr);
2364       for (i=0; i<nrqr; ++i) {
2365         req_size[i] = 0;
2366         rbuf1_i        = rbuf1[i];
2367         start          = 2*rbuf1_i[0] + 1;
2368         ierr           = MPI_Get_count(r_status1+i,MPIU_INT,&end);CHKERRQ(ierr);
2369         ierr           = PetscMalloc1(end+1,&sbuf2[i]);CHKERRQ(ierr);
2370         sbuf2_i        = sbuf2[i];
2371         for (j=start; j<end; j++) {
2372           id              = rbuf1_i[j] - rstart;
2373           ncols           = sAi[id+1] - sAi[id] + sBi[id+1] - sBi[id];
2374           sbuf2_i[j]      = ncols;
2375           req_size[i] += ncols;
2376         }
2377         req_source1[i] = r_status1[i].MPI_SOURCE;
2378         /* form the header */
2379         sbuf2_i[0] = req_size[i];
2380         for (j=1; j<start; j++) sbuf2_i[j] = rbuf1_i[j];
2381 
2382         ierr = MPI_Isend(sbuf2_i,end,MPIU_INT,req_source1[i],tag2,comm,s_waits2+i);CHKERRQ(ierr);
2383       }
2384     }
2385     ierr = PetscFree(r_status1);CHKERRQ(ierr);
2386     ierr = PetscFree(r_waits1);CHKERRQ(ierr);
2387     ierr = PetscFree4(w1,w2,w3,w4);CHKERRQ(ierr);
2388 
2389     /* Receive messages*/
2390     ierr = PetscMalloc1(nrqs+1,&r_waits3);CHKERRQ(ierr);
2391     ierr = PetscMalloc1(nrqs+1,&r_status2);CHKERRQ(ierr);
2392 
2393     ierr = MPI_Waitall(nrqs,r_waits2,r_status2);CHKERRQ(ierr);
2394     for (i=0; i<nrqs; ++i) {
2395       ierr = PetscMalloc1(rbuf2[i][0]+1,&rbuf3[i]);CHKERRQ(ierr);
2396       req_source2[i] = r_status2[i].MPI_SOURCE;
2397       ierr = MPI_Irecv(rbuf3[i],rbuf2[i][0],MPIU_INT,req_source2[i],tag3,comm,r_waits3+i);CHKERRQ(ierr);
2398     }
2399     ierr = PetscFree(r_status2);CHKERRQ(ierr);
2400     ierr = PetscFree(r_waits2);CHKERRQ(ierr);
2401 
2402     /* Wait on sends1 and sends2 */
2403     ierr = PetscMalloc1(nrqs+1,&s_status1);CHKERRQ(ierr);
2404     ierr = PetscMalloc1(nrqr+1,&s_status2);CHKERRQ(ierr);
2405 
2406     if (nrqs) {ierr = MPI_Waitall(nrqs,s_waits1,s_status1);CHKERRQ(ierr);}
2407     if (nrqr) {ierr = MPI_Waitall(nrqr,s_waits2,s_status2);CHKERRQ(ierr);}
2408     ierr = PetscFree(s_status1);CHKERRQ(ierr);
2409     ierr = PetscFree(s_status2);CHKERRQ(ierr);
2410     ierr = PetscFree(s_waits1);CHKERRQ(ierr);
2411     ierr = PetscFree(s_waits2);CHKERRQ(ierr);
2412 
2413     /* Now allocate sending buffers for a->j, and send them off */
2414     ierr = PetscMalloc1(nrqr+1,&sbuf_aj);CHKERRQ(ierr);
2415     for (i=0,j=0; i<nrqr; i++) j += req_size[i];
2416     ierr = PetscMalloc1(j+1,&sbuf_aj[0]);CHKERRQ(ierr);
2417     for (i=1; i<nrqr; i++) sbuf_aj[i] = sbuf_aj[i-1] + req_size[i-1];
2418 
2419     ierr = PetscMalloc1(nrqr+1,&s_waits3);CHKERRQ(ierr);
2420     {
2421       PetscInt nzA,nzB,*a_i = a->i,*b_i = b->i,lwrite;
2422       PetscInt *cworkA,*cworkB,cstart = C->cmap->rstart,rstart = C->rmap->rstart,*bmap = c->garray;
2423       PetscInt cend = C->cmap->rend;
2424       PetscInt *a_j = a->j,*b_j = b->j,ctmp;
2425 
2426       for (i=0; i<nrqr; i++) {
2427         rbuf1_i   = rbuf1[i];
2428         sbuf_aj_i = sbuf_aj[i];
2429         ct1       = 2*rbuf1_i[0] + 1;
2430         ct2       = 0;
2431         for (j=1,max1=rbuf1_i[0]; j<=max1; j++) {
2432           kmax = rbuf1[i][2*j];
2433           for (k=0; k<kmax; k++,ct1++) {
2434             row    = rbuf1_i[ct1] - rstart;
2435             nzA    = a_i[row+1] - a_i[row]; nzB = b_i[row+1] - b_i[row];
2436             ncols  = nzA + nzB;
2437             cworkA = a_j + a_i[row]; cworkB = b_j + b_i[row];
2438 
2439             /* load the column indices for this row into cols */
2440             cols = sbuf_aj_i + ct2;
2441 
2442             lwrite = 0;
2443             for (l=0; l<nzB; l++) {
2444               if ((ctmp = bmap[cworkB[l]]) < cstart) cols[lwrite++] = ctmp;
2445             }
2446             for (l=0; l<nzA; l++) cols[lwrite++] = cstart + cworkA[l];
2447             for (l=0; l<nzB; l++) {
2448               if ((ctmp = bmap[cworkB[l]]) >= cend) cols[lwrite++] = ctmp;
2449             }
2450 
2451             ct2 += ncols;
2452           }
2453         }
2454         ierr = MPI_Isend(sbuf_aj_i,req_size[i],MPIU_INT,req_source1[i],tag3,comm,s_waits3+i);CHKERRQ(ierr);
2455       }
2456     }
2457     ierr = PetscMalloc2(nrqs+1,&r_status3,nrqr+1,&s_status3);CHKERRQ(ierr);
2458 
2459     /* create col map: global col of C -> local col of submatrices */
2460     {
2461       const PetscInt *icol_i;
2462 #if defined(PETSC_USE_CTABLE)
2463       for (i=0; i<ismax; i++) {
2464         if (!allcolumns[i]) {
2465           ierr = PetscTableCreate(ncol[i]+1,C->cmap->N+1,&cmap[i]);CHKERRQ(ierr);
2466 
2467           jmax   = ncol[i];
2468           icol_i = icol[i];
2469           cmap_i = cmap[i];
2470           for (j=0; j<jmax; j++) {
2471             ierr = PetscTableAdd(cmap[i],icol_i[j]+1,j+1,INSERT_VALUES);CHKERRQ(ierr);
2472           }
2473         } else cmap[i] = NULL;
2474       }
2475 #else
2476       for (i=0; i<ismax; i++) {
2477         if (!allcolumns[i]) {
2478           ierr   = PetscCalloc1(C->cmap->N,&cmap[i]);CHKERRQ(ierr);
2479           jmax   = ncol[i];
2480           icol_i = icol[i];
2481           cmap_i = cmap[i];
2482           for (j=0; j<jmax; j++) {
2483             cmap_i[icol_i[j]] = j+1;
2484           }
2485         } else cmap[i] = NULL;
2486       }
2487 #endif
2488     }
2489 
2490     /* Create lens which is required for MatCreate... */
2491     for (i=0,j=0; i<ismax; i++) j += nrow[i];
2492     ierr = PetscMalloc1(ismax,&lens);CHKERRQ(ierr);
2493 
2494     if (ismax) {
2495       ierr = PetscCalloc1(j,&lens[0]);CHKERRQ(ierr);
2496     }
2497     for (i=1; i<ismax; i++) lens[i] = lens[i-1] + nrow[i-1];
2498 
2499     /* Update lens from local data */
2500     for (i=0; i<ismax; i++) {
2501       row2proc_i = row2proc[i];
2502       jmax = nrow[i];
2503       if (!allcolumns[i]) cmap_i = cmap[i];
2504       irow_i = irow[i];
2505       lens_i = lens[i];
2506       for (j=0; j<jmax; j++) {
2507         row = irow_i[j];
2508         proc = row2proc_i[j];
2509         if (proc == rank) {
2510           ierr = MatGetRow_MPIAIJ(C,row,&ncols,&cols,0);CHKERRQ(ierr);
2511           if (!allcolumns[i]) {
2512             for (k=0; k<ncols; k++) {
2513 #if defined(PETSC_USE_CTABLE)
2514               ierr = PetscTableFind(cmap_i,cols[k]+1,&tcol);CHKERRQ(ierr);
2515 #else
2516               tcol = cmap_i[cols[k]];
2517 #endif
2518               if (tcol) lens_i[j]++;
2519             }
2520           } else { /* allcolumns */
2521             lens_i[j] = ncols;
2522           }
2523           ierr = MatRestoreRow_MPIAIJ(C,row,&ncols,&cols,0);CHKERRQ(ierr);
2524         }
2525       }
2526     }
2527 
2528     /* Create row map: global row of C -> local row of submatrices */
2529 #if defined(PETSC_USE_CTABLE)
2530     for (i=0; i<ismax; i++) {
2531       ierr   = PetscTableCreate(nrow[i]+1,C->rmap->N+1,&rmap[i]);CHKERRQ(ierr);
2532       irow_i = irow[i];
2533       jmax   = nrow[i];
2534       for (j=0; j<jmax; j++) {
2535       ierr = PetscTableAdd(rmap[i],irow_i[j]+1,j+1,INSERT_VALUES);CHKERRQ(ierr);
2536       }
2537     }
2538 #else
2539     for (i=0; i<ismax; i++) {
2540       ierr   = PetscCalloc1(C->rmap->N,&rmap[i]);CHKERRQ(ierr);
2541       rmap_i = rmap[i];
2542       irow_i = irow[i];
2543       jmax   = nrow[i];
2544       for (j=0; j<jmax; j++) {
2545         rmap_i[irow_i[j]] = j;
2546       }
2547     }
2548 #endif
2549 
2550     /* Update lens from offproc data */
2551     {
2552       PetscInt *rbuf2_i,*rbuf3_i,*sbuf1_i;
2553 
2554       ierr    = MPI_Waitall(nrqs,r_waits3,r_status3);CHKERRQ(ierr);
2555       for (tmp2=0; tmp2<nrqs; tmp2++) {
2556         sbuf1_i = sbuf1[pa[tmp2]];
2557         jmax    = sbuf1_i[0];
2558         ct1     = 2*jmax+1;
2559         ct2     = 0;
2560         rbuf2_i = rbuf2[tmp2];
2561         rbuf3_i = rbuf3[tmp2];
2562         for (j=1; j<=jmax; j++) {
2563           is_no  = sbuf1_i[2*j-1];
2564           max1   = sbuf1_i[2*j];
2565           lens_i = lens[is_no];
2566           if (!allcolumns[is_no]) cmap_i = cmap[is_no];
2567           rmap_i = rmap[is_no];
2568           for (k=0; k<max1; k++,ct1++) {
2569 #if defined(PETSC_USE_CTABLE)
2570             ierr = PetscTableFind(rmap_i,sbuf1_i[ct1]+1,&row);CHKERRQ(ierr);
2571             row--;
2572             if (row < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"row not found in table");
2573 #else
2574             row = rmap_i[sbuf1_i[ct1]]; /* the val in the new matrix to be */
2575 #endif
2576             max2 = rbuf2_i[ct1];
2577             for (l=0; l<max2; l++,ct2++) {
2578               if (!allcolumns[is_no]) {
2579 #if defined(PETSC_USE_CTABLE)
2580                 ierr = PetscTableFind(cmap_i,rbuf3_i[ct2]+1,&tcol);CHKERRQ(ierr);
2581 #else
2582                 tcol = cmap_i[rbuf3_i[ct2]];
2583 #endif
2584                 if (tcol) lens_i[row]++;
2585               } else { /* allcolumns */
2586                 lens_i[row]++; /* lens_i[row] += max2 ? */
2587               }
2588             }
2589           }
2590         }
2591       }
2592     }
2593     ierr = PetscFree(r_waits3);CHKERRQ(ierr);
2594     if (nrqr) {ierr = MPI_Waitall(nrqr,s_waits3,s_status3);CHKERRQ(ierr);}
2595     ierr = PetscFree2(r_status3,s_status3);CHKERRQ(ierr);
2596     ierr = PetscFree(s_waits3);CHKERRQ(ierr);
2597 
2598     /* Create the submatrices */
2599     for (i=0; i<ismax; i++) {
2600       PetscInt    rbs,cbs;
2601 
2602       ierr = ISGetBlockSize(isrow[i],&rbs);CHKERRQ(ierr);
2603       ierr = ISGetBlockSize(iscol[i],&cbs);CHKERRQ(ierr);
2604 
2605       ierr = MatCreate(PETSC_COMM_SELF,submats+i);CHKERRQ(ierr);
2606       ierr = MatSetSizes(submats[i],nrow[i],ncol[i],PETSC_DETERMINE,PETSC_DETERMINE);CHKERRQ(ierr);
2607 
2608       ierr = MatSetBlockSizes(submats[i],rbs,cbs);CHKERRQ(ierr);
2609       ierr = MatSetType(submats[i],((PetscObject)A)->type_name);CHKERRQ(ierr);
2610       ierr = MatSeqAIJSetPreallocation(submats[i],0,lens[i]);CHKERRQ(ierr);
2611 
2612       /* create struct Mat_SubMat and attached it to submat */
2613       ierr = PetscNew(&smat_i);CHKERRQ(ierr);
2614       subc = (Mat_SeqAIJ*)submats[i]->data;
2615       subc->submatis1 = smat_i;
2616 
2617       smat_i->destroy          = submats[i]->ops->destroy;
2618       submats[i]->ops->destroy = MatDestroy_MPIAIJ_MatGetSubmatrices;
2619       submats[i]->factortype   = C->factortype;
2620 
2621       smat_i->id          = i;
2622       smat_i->nrqs        = nrqs;
2623       smat_i->nrqr        = nrqr;
2624       smat_i->rbuf1       = rbuf1;
2625       smat_i->rbuf2       = rbuf2;
2626       smat_i->rbuf3       = rbuf3;
2627       smat_i->sbuf2       = sbuf2;
2628       smat_i->req_source2 = req_source2;
2629 
2630       smat_i->sbuf1       = sbuf1;
2631       smat_i->ptr         = ptr;
2632       smat_i->tmp         = tmp;
2633       smat_i->ctr         = ctr;
2634 
2635       smat_i->pa           = pa;
2636       smat_i->req_size     = req_size;
2637       smat_i->req_source1  = req_source1;
2638 
2639       smat_i->allcolumns  = allcolumns[i];
2640       smat_i->singleis    = PETSC_FALSE;
2641       smat_i->row2proc    = row2proc[i];
2642       smat_i->rmap        = rmap[i];
2643       smat_i->cmap        = cmap[i];
2644     }
2645 
2646     if (!ismax) { /* Create dummy submats[0] for reuse struct subc */
2647       ierr = MatCreate(PETSC_COMM_SELF,&submats[0]);CHKERRQ(ierr);
2648       ierr = MatSetSizes(submats[0],0,0,PETSC_DETERMINE,PETSC_DETERMINE);CHKERRQ(ierr);
2649       ierr = MatSetType(submats[0],((PetscObject)A)->type_name);CHKERRQ(ierr);
2650       ierr = MatSeqAIJSetPreallocation(submats[0],0,NULL);CHKERRQ(ierr);
2651 
2652       /* create struct Mat_SubMat and attached it to submat */
2653       ierr = PetscNew(&smat_i);CHKERRQ(ierr);
2654       subc = (Mat_SeqAIJ*)submats[0]->data;
2655       subc->submatis1 = smat_i;
2656 
2657       smat_i->destroy          = submats[0]->ops->destroy;
2658       submats[0]->ops->destroy = MatDestroy_MPIAIJ_MatGetSubmatrices;
2659       submats[0]->factortype   = C->factortype;
2660 
2661       smat_i->id          = i;
2662       smat_i->nrqs        = nrqs;
2663       smat_i->nrqr        = nrqr;
2664       smat_i->rbuf1       = rbuf1;
2665       smat_i->rbuf2       = rbuf2;
2666       smat_i->rbuf3       = rbuf3;
2667       smat_i->sbuf2       = sbuf2;
2668       smat_i->req_source2 = req_source2;
2669 
2670       smat_i->sbuf1       = sbuf1;
2671       smat_i->ptr         = ptr;
2672       smat_i->tmp         = tmp;
2673       smat_i->ctr         = ctr;
2674 
2675       smat_i->pa           = pa;
2676       smat_i->req_size     = req_size;
2677       smat_i->req_source1  = req_source1;
2678 
2679       smat_i->allcolumns  = PETSC_TRUE;
2680       smat_i->singleis    = PETSC_FALSE;
2681       smat_i->row2proc    = NULL;
2682       smat_i->rmap        = NULL;
2683       smat_i->cmap        = NULL;
2684     }
2685 
2686     if (ismax) {ierr = PetscFree(lens[0]);CHKERRQ(ierr);}
2687     ierr = PetscFree(lens);CHKERRQ(ierr);
2688     ierr = PetscFree(sbuf_aj[0]);CHKERRQ(ierr);
2689     ierr = PetscFree(sbuf_aj);CHKERRQ(ierr);
2690 
2691   } /* endof scall == MAT_INITIAL_MATRIX */
2692 
2693   /* Post recv matrix values */
2694   ierr = PetscObjectGetNewTag((PetscObject)C,&tag4);CHKERRQ(ierr);
2695   ierr = PetscMalloc1(nrqs+1,&rbuf4);CHKERRQ(ierr);
2696   ierr = PetscMalloc1(nrqs+1,&r_waits4);CHKERRQ(ierr);
2697   ierr = PetscMalloc1(nrqs+1,&r_status4);CHKERRQ(ierr);
2698   ierr = PetscMalloc1(nrqr+1,&s_status4);CHKERRQ(ierr);
2699   for (i=0; i<nrqs; ++i) {
2700     ierr = PetscMalloc1(rbuf2[i][0]+1,&rbuf4[i]);CHKERRQ(ierr);
2701     ierr = MPI_Irecv(rbuf4[i],rbuf2[i][0],MPIU_SCALAR,req_source2[i],tag4,comm,r_waits4+i);CHKERRQ(ierr);
2702   }
2703 
2704   /* Allocate sending buffers for a->a, and send them off */
2705   ierr = PetscMalloc1(nrqr+1,&sbuf_aa);CHKERRQ(ierr);
2706   for (i=0,j=0; i<nrqr; i++) j += req_size[i];
2707   ierr = PetscMalloc1(j+1,&sbuf_aa[0]);CHKERRQ(ierr);
2708   for (i=1; i<nrqr; i++) sbuf_aa[i] = sbuf_aa[i-1] + req_size[i-1];
2709 
2710   ierr = PetscMalloc1(nrqr+1,&s_waits4);CHKERRQ(ierr);
2711   {
2712     PetscInt    nzA,nzB,*a_i = a->i,*b_i = b->i, *cworkB,lwrite;
2713     PetscInt    cstart = C->cmap->rstart,rstart = C->rmap->rstart,*bmap = c->garray;
2714     PetscInt    cend   = C->cmap->rend;
2715     PetscInt    *b_j   = b->j;
2716     PetscScalar *vworkA,*vworkB,*a_a = a->a,*b_a = b->a;
2717 
2718     for (i=0; i<nrqr; i++) {
2719       rbuf1_i   = rbuf1[i];
2720       sbuf_aa_i = sbuf_aa[i];
2721       ct1       = 2*rbuf1_i[0]+1;
2722       ct2       = 0;
2723       for (j=1,max1=rbuf1_i[0]; j<=max1; j++) {
2724         kmax = rbuf1_i[2*j];
2725         for (k=0; k<kmax; k++,ct1++) {
2726           row    = rbuf1_i[ct1] - rstart;
2727           nzA    = a_i[row+1] - a_i[row];     nzB = b_i[row+1] - b_i[row];
2728           ncols  = nzA + nzB;
2729           cworkB = b_j + b_i[row];
2730           vworkA = a_a + a_i[row];
2731           vworkB = b_a + b_i[row];
2732 
2733           /* load the column values for this row into vals*/
2734           vals = sbuf_aa_i+ct2;
2735 
2736           lwrite = 0;
2737           for (l=0; l<nzB; l++) {
2738             if ((bmap[cworkB[l]]) < cstart) vals[lwrite++] = vworkB[l];
2739           }
2740           for (l=0; l<nzA; l++) vals[lwrite++] = vworkA[l];
2741           for (l=0; l<nzB; l++) {
2742             if ((bmap[cworkB[l]]) >= cend) vals[lwrite++] = vworkB[l];
2743           }
2744 
2745           ct2 += ncols;
2746         }
2747       }
2748       ierr = MPI_Isend(sbuf_aa_i,req_size[i],MPIU_SCALAR,req_source1[i],tag4,comm,s_waits4+i);CHKERRQ(ierr);
2749     }
2750   }
2751 
2752   /* Assemble the matrices */
2753   /* First assemble the local rows */
2754   for (i=0; i<ismax; i++) {
2755     row2proc_i = row2proc[i];
2756     subc      = (Mat_SeqAIJ*)submats[i]->data;
2757     imat_ilen = subc->ilen;
2758     imat_j    = subc->j;
2759     imat_i    = subc->i;
2760     imat_a    = subc->a;
2761 
2762     if (!allcolumns[i]) cmap_i = cmap[i];
2763     rmap_i = rmap[i];
2764     irow_i = irow[i];
2765     jmax   = nrow[i];
2766     for (j=0; j<jmax; j++) {
2767       row  = irow_i[j];
2768       proc = row2proc_i[j];
2769       if (proc == rank) {
2770         old_row = row;
2771 #if defined(PETSC_USE_CTABLE)
2772         ierr = PetscTableFind(rmap_i,row+1,&row);CHKERRQ(ierr);
2773         row--;
2774 #else
2775         row = rmap_i[row];
2776 #endif
2777         ilen_row = imat_ilen[row];
2778         ierr     = MatGetRow_MPIAIJ(C,old_row,&ncols,&cols,&vals);CHKERRQ(ierr);
2779         mat_i    = imat_i[row];
2780         mat_a    = imat_a + mat_i;
2781         mat_j    = imat_j + mat_i;
2782         if (!allcolumns[i]) {
2783           for (k=0; k<ncols; k++) {
2784 #if defined(PETSC_USE_CTABLE)
2785             ierr = PetscTableFind(cmap_i,cols[k]+1,&tcol);CHKERRQ(ierr);
2786 #else
2787             tcol = cmap_i[cols[k]];
2788 #endif
2789             if (tcol) {
2790               *mat_j++ = tcol - 1;
2791               *mat_a++ = vals[k];
2792               ilen_row++;
2793             }
2794           }
2795         } else { /* allcolumns */
2796           for (k=0; k<ncols; k++) {
2797             *mat_j++ = cols[k];  /* global col index! */
2798             *mat_a++ = vals[k];
2799             ilen_row++;
2800           }
2801         }
2802         ierr = MatRestoreRow_MPIAIJ(C,old_row,&ncols,&cols,&vals);CHKERRQ(ierr);
2803 
2804         imat_ilen[row] = ilen_row;
2805       }
2806     }
2807   }
2808 
2809   /* Now assemble the off proc rows */
2810   ierr    = MPI_Waitall(nrqs,r_waits4,r_status4);CHKERRQ(ierr);
2811   for (tmp2=0; tmp2<nrqs; tmp2++) {
2812     sbuf1_i = sbuf1[pa[tmp2]];
2813     jmax    = sbuf1_i[0];
2814     ct1     = 2*jmax + 1;
2815     ct2     = 0;
2816     rbuf2_i = rbuf2[tmp2];
2817     rbuf3_i = rbuf3[tmp2];
2818     rbuf4_i = rbuf4[tmp2];
2819     for (j=1; j<=jmax; j++) {
2820       is_no     = sbuf1_i[2*j-1];
2821       rmap_i    = rmap[is_no];
2822       if (!allcolumns[is_no]) cmap_i = cmap[is_no];
2823       subc      = (Mat_SeqAIJ*)submats[is_no]->data;
2824       imat_ilen = subc->ilen;
2825       imat_j    = subc->j;
2826       imat_i    = subc->i;
2827       imat_a    = subc->a;
2828       max1      = sbuf1_i[2*j];
2829       for (k=0; k<max1; k++,ct1++) {
2830         row = sbuf1_i[ct1];
2831 #if defined(PETSC_USE_CTABLE)
2832         ierr = PetscTableFind(rmap_i,row+1,&row);CHKERRQ(ierr);
2833         row--;
2834 #else
2835         row = rmap_i[row];
2836 #endif
2837         ilen  = imat_ilen[row];
2838         mat_i = imat_i[row];
2839         mat_a = imat_a + mat_i;
2840         mat_j = imat_j + mat_i;
2841         max2  = rbuf2_i[ct1];
2842         if (!allcolumns[is_no]) {
2843           for (l=0; l<max2; l++,ct2++) {
2844 #if defined(PETSC_USE_CTABLE)
2845             ierr = PetscTableFind(cmap_i,rbuf3_i[ct2]+1,&tcol);CHKERRQ(ierr);
2846 #else
2847             tcol = cmap_i[rbuf3_i[ct2]];
2848 #endif
2849             if (tcol) {
2850               *mat_j++ = tcol - 1;
2851               *mat_a++ = rbuf4_i[ct2];
2852               ilen++;
2853             }
2854           }
2855         } else { /* allcolumns */
2856           for (l=0; l<max2; l++,ct2++) {
2857             *mat_j++ = rbuf3_i[ct2]; /* same global column index of C */
2858             *mat_a++ = rbuf4_i[ct2];
2859             ilen++;
2860           }
2861         }
2862         imat_ilen[row] = ilen;
2863       }
2864     }
2865   }
2866 
2867   if (!iscsorted) { /* sort column indices of the rows */
2868     for (i=0; i<ismax; i++) {
2869       subc      = (Mat_SeqAIJ*)submats[i]->data;
2870       imat_j    = subc->j;
2871       imat_i    = subc->i;
2872       imat_a    = subc->a;
2873       imat_ilen = subc->ilen;
2874 
2875       if (allcolumns[i]) continue;
2876       jmax = nrow[i];
2877       for (j=0; j<jmax; j++) {
2878         mat_i = imat_i[j];
2879         mat_a = imat_a + mat_i;
2880         mat_j = imat_j + mat_i;
2881         ierr  = PetscSortIntWithScalarArray(imat_ilen[j],mat_j,mat_a);CHKERRQ(ierr);
2882       }
2883     }
2884   }
2885 
2886   ierr = PetscFree(r_status4);CHKERRQ(ierr);
2887   ierr = PetscFree(r_waits4);CHKERRQ(ierr);
2888   if (nrqr) {ierr = MPI_Waitall(nrqr,s_waits4,s_status4);CHKERRQ(ierr);}
2889   ierr = PetscFree(s_waits4);CHKERRQ(ierr);
2890   ierr = PetscFree(s_status4);CHKERRQ(ierr);
2891 
2892   /* Restore the indices */
2893   for (i=0; i<ismax; i++) {
2894     ierr = ISRestoreIndices(isrow[i],irow+i);CHKERRQ(ierr);
2895     if (!allcolumns[i]) {
2896       ierr = ISRestoreIndices(iscol[i],icol+i);CHKERRQ(ierr);
2897     }
2898   }
2899 
2900   for (i=0; i<ismax; i++) {
2901     ierr = MatAssemblyBegin(submats[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
2902     ierr = MatAssemblyEnd(submats[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
2903   }
2904   if (!ismax) { /* a dummy matrix */
2905     ierr = MatAssemblyBegin(submats[0],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
2906     ierr = MatAssemblyEnd(submats[0],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
2907   }
2908 
2909   /* Destroy allocated memory */
2910   ierr = PetscFree(sbuf_aa[0]);CHKERRQ(ierr);
2911   ierr = PetscFree(sbuf_aa);CHKERRQ(ierr);
2912   ierr = PetscFree5(irow,icol,nrow,ncol,issorted);CHKERRQ(ierr);
2913 
2914   for (i=0; i<nrqs; ++i) {
2915     ierr = PetscFree(rbuf4[i]);CHKERRQ(ierr);
2916   }
2917   ierr = PetscFree(rbuf4);CHKERRQ(ierr);
2918 
2919   ierr = PetscFree4(row2proc,cmap,rmap,allcolumns);CHKERRQ(ierr);
2920   PetscFunctionReturn(0);
2921 }
2922 
2923 /*
2924  Permute A & B into C's *local* index space using rowemb,dcolemb for A and rowemb,ocolemb for B.
2925  Embeddings are supposed to be injections and the above implies that the range of rowemb is a subset
2926  of [0,m), dcolemb is in [0,n) and ocolemb is in [N-n).
2927  If pattern == DIFFERENT_NONZERO_PATTERN, C is preallocated according to A&B.
2928  After that B's columns are mapped into C's global column space, so that C is in the "disassembled"
2929  state, and needs to be "assembled" later by compressing B's column space.
2930 
2931  This function may be called in lieu of preallocation, so C should not be expected to be preallocated.
2932  Following this call, C->A & C->B have been created, even if empty.
2933  */
2934 PetscErrorCode MatSetSeqMats_MPIAIJ(Mat C,IS rowemb,IS dcolemb,IS ocolemb,MatStructure pattern,Mat A,Mat B)
2935 {
2936   /* If making this function public, change the error returned in this function away from _PLIB. */
2937   PetscErrorCode ierr;
2938   Mat_MPIAIJ     *aij;
2939   Mat_SeqAIJ     *Baij;
2940   PetscBool      seqaij,Bdisassembled;
2941   PetscInt       m,n,*nz,i,j,ngcol,col,rstart,rend,shift,count;
2942   PetscScalar    v;
2943   const PetscInt *rowindices,*colindices;
2944 
2945   PetscFunctionBegin;
2946   /* Check to make sure the component matrices (and embeddings) are compatible with C. */
2947   if (A) {
2948     ierr = PetscObjectTypeCompare((PetscObject)A,MATSEQAIJ,&seqaij);CHKERRQ(ierr);
2949     if (!seqaij) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Diagonal matrix is of wrong type");
2950     if (rowemb) {
2951       ierr = ISGetLocalSize(rowemb,&m);CHKERRQ(ierr);
2952       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);
2953     } else {
2954       if (C->rmap->n != A->rmap->n) {
2955 	SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Diag seq matrix is row-incompatible with the MPIAIJ matrix");
2956       }
2957     }
2958     if (dcolemb) {
2959       ierr = ISGetLocalSize(dcolemb,&n);CHKERRQ(ierr);
2960       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);
2961     } else {
2962       if (C->cmap->n != A->cmap->n) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Diag seq matrix is col-incompatible with the MPIAIJ matrix");
2963     }
2964   }
2965   if (B) {
2966     ierr = PetscObjectTypeCompare((PetscObject)B,MATSEQAIJ,&seqaij);CHKERRQ(ierr);
2967     if (!seqaij) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Off-diagonal matrix is of wrong type");
2968     if (rowemb) {
2969       ierr = ISGetLocalSize(rowemb,&m);CHKERRQ(ierr);
2970       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);
2971     } else {
2972       if (C->rmap->n != B->rmap->n) {
2973 	SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Off-diag seq matrix is row-incompatible with the MPIAIJ matrix");
2974       }
2975     }
2976     if (ocolemb) {
2977       ierr = ISGetLocalSize(ocolemb,&n);CHKERRQ(ierr);
2978       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);
2979     } else {
2980       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");
2981     }
2982   }
2983 
2984   aij    = (Mat_MPIAIJ*)(C->data);
2985   if (!aij->A) {
2986     /* Mimic parts of MatMPIAIJSetPreallocation() */
2987     ierr   = MatCreate(PETSC_COMM_SELF,&aij->A);CHKERRQ(ierr);
2988     ierr   = MatSetSizes(aij->A,C->rmap->n,C->cmap->n,C->rmap->n,C->cmap->n);CHKERRQ(ierr);
2989     ierr   = MatSetBlockSizesFromMats(aij->A,C,C);CHKERRQ(ierr);
2990     ierr   = MatSetType(aij->A,MATSEQAIJ);CHKERRQ(ierr);
2991     ierr   = PetscLogObjectParent((PetscObject)C,(PetscObject)aij->A);CHKERRQ(ierr);
2992   }
2993   if (A) {
2994     ierr   = MatSetSeqMat_SeqAIJ(aij->A,rowemb,dcolemb,pattern,A);CHKERRQ(ierr);
2995   } else {
2996     ierr = MatSetUp(aij->A);CHKERRQ(ierr);
2997   }
2998   if (B) { /* Destroy the old matrix or the column map, depending on the sparsity pattern. */
2999     /*
3000       If pattern == DIFFERENT_NONZERO_PATTERN, we reallocate B and
3001       need to "disassemble" B -- convert it to using C's global indices.
3002       To insert the values we take the safer, albeit more expensive, route of MatSetValues().
3003 
3004       If pattern == SUBSET_NONZERO_PATTERN, we do not "disassemble" B and do not reallocate;
3005       we MatZeroValues(B) first, so there may be a bunch of zeros that, perhaps, could be compacted out.
3006 
3007       TODO: Put B's values into aij->B's aij structure in place using the embedding ISs?
3008       At least avoid calling MatSetValues() and the implied searches?
3009     */
3010 
3011     if (B && pattern == DIFFERENT_NONZERO_PATTERN) {
3012 #if defined(PETSC_USE_CTABLE)
3013       ierr = PetscTableDestroy(&aij->colmap);CHKERRQ(ierr);
3014 #else
3015       ierr = PetscFree(aij->colmap);CHKERRQ(ierr);
3016       /* A bit of a HACK: ideally we should deal with case aij->B all in one code block below. */
3017       if (aij->B) {
3018         ierr = PetscLogObjectMemory((PetscObject)C,-aij->B->cmap->n*sizeof(PetscInt));CHKERRQ(ierr);
3019       }
3020 #endif
3021       ngcol = 0;
3022       if (aij->lvec) {
3023 	ierr = VecGetSize(aij->lvec,&ngcol);CHKERRQ(ierr);
3024       }
3025       if (aij->garray) {
3026 	ierr = PetscFree(aij->garray);CHKERRQ(ierr);
3027 	ierr = PetscLogObjectMemory((PetscObject)C,-ngcol*sizeof(PetscInt));CHKERRQ(ierr);
3028       }
3029       ierr = VecDestroy(&aij->lvec);CHKERRQ(ierr);
3030       ierr = VecScatterDestroy(&aij->Mvctx);CHKERRQ(ierr);
3031     }
3032     if (aij->B && B && pattern == DIFFERENT_NONZERO_PATTERN) {
3033       ierr = MatDestroy(&aij->B);CHKERRQ(ierr);
3034     }
3035     if (aij->B && B && pattern == SUBSET_NONZERO_PATTERN) {
3036       ierr = MatZeroEntries(aij->B);CHKERRQ(ierr);
3037     }
3038   }
3039   Bdisassembled = PETSC_FALSE;
3040   if (!aij->B) {
3041     ierr = MatCreate(PETSC_COMM_SELF,&aij->B);CHKERRQ(ierr);
3042     ierr = PetscLogObjectParent((PetscObject)C,(PetscObject)aij->B);CHKERRQ(ierr);
3043     ierr = MatSetSizes(aij->B,C->rmap->n,C->cmap->N,C->rmap->n,C->cmap->N);CHKERRQ(ierr);
3044     ierr = MatSetBlockSizesFromMats(aij->B,B,B);CHKERRQ(ierr);
3045     ierr = MatSetType(aij->B,MATSEQAIJ);CHKERRQ(ierr);
3046     Bdisassembled = PETSC_TRUE;
3047   }
3048   if (B) {
3049     Baij = (Mat_SeqAIJ*)(B->data);
3050     if (pattern == DIFFERENT_NONZERO_PATTERN) {
3051       ierr = PetscMalloc1(B->rmap->n,&nz);CHKERRQ(ierr);
3052       for (i=0; i<B->rmap->n; i++) {
3053 	nz[i] = Baij->i[i+1] - Baij->i[i];
3054       }
3055       ierr = MatSeqAIJSetPreallocation(aij->B,0,nz);CHKERRQ(ierr);
3056       ierr = PetscFree(nz);CHKERRQ(ierr);
3057     }
3058 
3059     ierr  = PetscLayoutGetRange(C->rmap,&rstart,&rend);CHKERRQ(ierr);
3060     shift = rend-rstart;
3061     count = 0;
3062     rowindices = NULL;
3063     colindices = NULL;
3064     if (rowemb) {
3065       ierr = ISGetIndices(rowemb,&rowindices);CHKERRQ(ierr);
3066     }
3067     if (ocolemb) {
3068       ierr = ISGetIndices(ocolemb,&colindices);CHKERRQ(ierr);
3069     }
3070     for (i=0; i<B->rmap->n; i++) {
3071       PetscInt row;
3072       row = i;
3073       if (rowindices) row = rowindices[i];
3074       for (j=Baij->i[i]; j<Baij->i[i+1]; j++) {
3075 	col  = Baij->j[count];
3076 	if (colindices) col = colindices[col];
3077 	if (Bdisassembled && col>=rstart) col += shift;
3078 	v    = Baij->a[count];
3079 	ierr = MatSetValues(aij->B,1,&row,1,&col,&v,INSERT_VALUES);CHKERRQ(ierr);
3080 	++count;
3081       }
3082     }
3083     /* No assembly for aij->B is necessary. */
3084     /* FIXME: set aij->B's nonzerostate correctly. */
3085   } else {
3086     ierr = MatSetUp(aij->B);CHKERRQ(ierr);
3087   }
3088   C->preallocated  = PETSC_TRUE;
3089   C->was_assembled = PETSC_FALSE;
3090   C->assembled     = PETSC_FALSE;
3091    /*
3092       C will need to be assembled so that aij->B can be compressed into local form in MatSetUpMultiply_MPIAIJ().
3093       Furthermore, its nonzerostate will need to be based on that of aij->A's and aij->B's.
3094    */
3095   PetscFunctionReturn(0);
3096 }
3097 
3098 /*
3099   B uses local indices with column indices ranging between 0 and N-n; they  must be interpreted using garray.
3100  */
3101 PetscErrorCode MatGetSeqMats_MPIAIJ(Mat C,Mat *A,Mat *B)
3102 {
3103   Mat_MPIAIJ *aij = (Mat_MPIAIJ*) (C->data);
3104 
3105   PetscFunctionBegin;
3106   PetscValidPointer(A,2);
3107   PetscValidPointer(B,3);
3108   /* FIXME: make sure C is assembled */
3109   *A = aij->A;
3110   *B = aij->B;
3111   /* Note that we don't incref *A and *B, so be careful! */
3112   PetscFunctionReturn(0);
3113 }
3114 
3115 /*
3116   Extract MPI submatrices encoded by pairs of IS that may live on subcomms of C.
3117   NOT SCALABLE due to the use of ISGetNonlocalIS() (see below).
3118 */
3119 PetscErrorCode MatGetSubMatricesMPI_MPIXAIJ(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[],
3120                                                  PetscErrorCode(*getsubmats_seq)(Mat,PetscInt,const IS[],const IS[],MatReuse,Mat**),
3121 					         PetscErrorCode(*getlocalmats)(Mat,Mat*,Mat*),
3122 					         PetscErrorCode(*setseqmat)(Mat,IS,IS,MatStructure,Mat),
3123 					         PetscErrorCode(*setseqmats)(Mat,IS,IS,IS,MatStructure,Mat,Mat))
3124 {
3125   PetscErrorCode ierr;
3126   PetscMPIInt    isize,flag;
3127   PetscInt       i,ii,cismax,ispar;
3128   Mat            *A,*B;
3129   IS             *isrow_p,*iscol_p,*cisrow,*ciscol,*ciscol_p;
3130 
3131   PetscFunctionBegin;
3132   if (!ismax) PetscFunctionReturn(0);
3133 
3134   for (i = 0, cismax = 0; i < ismax; ++i) {
3135     PetscMPIInt isize;
3136     ierr = MPI_Comm_compare(((PetscObject)isrow[i])->comm,((PetscObject)iscol[i])->comm,&flag);CHKERRQ(ierr);
3137     if (flag != MPI_IDENT) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Row and column index sets must have the same communicator");
3138     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm, &isize);CHKERRQ(ierr);
3139     if (isize > 1) ++cismax;
3140   }
3141 
3142   /*
3143      If cismax is zero on all C's ranks, then and only then can we use purely sequential matrix extraction.
3144      ispar counts the number of parallel ISs across C's comm.
3145   */
3146   ierr = MPIU_Allreduce(&cismax,&ispar,1,MPIU_INT,MPI_MAX,PetscObjectComm((PetscObject)C));CHKERRQ(ierr);
3147   if (!ispar) { /* Sequential ISs only across C's comm, so can call the sequential matrix extraction subroutine. */
3148     ierr = (*getsubmats_seq)(C,ismax,isrow,iscol,scall,submat);CHKERRQ(ierr);
3149     PetscFunctionReturn(0);
3150   }
3151 
3152   /* if (ispar) */
3153   /*
3154     Construct the "complements" -- the off-processor indices -- of the iscol ISs for parallel ISs only.
3155     These are used to extract the off-diag portion of the resulting parallel matrix.
3156     The row IS for the off-diag portion is the same as for the diag portion,
3157     so we merely alias (without increfing) the row IS, while skipping those that are sequential.
3158   */
3159   ierr = PetscMalloc2(cismax,&cisrow,cismax,&ciscol);CHKERRQ(ierr);
3160   ierr = PetscMalloc1(cismax,&ciscol_p);CHKERRQ(ierr);
3161   for (i = 0, ii = 0; i < ismax; ++i) {
3162     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm,&isize);CHKERRQ(ierr);
3163     if (isize > 1) {
3164       /*
3165 	 TODO: This is the part that's ***NOT SCALABLE***.
3166 	 To fix this we need to extract just the indices of C's nonzero columns
3167 	 that lie on the intersection of isrow[i] and ciscol[ii] -- the nonlocal
3168 	 part of iscol[i] -- without actually computing ciscol[ii]. This also has
3169 	 to be done without serializing on the IS list, so, most likely, it is best
3170 	 done by rewriting MatGetSubMatrices_MPIAIJ() directly.
3171       */
3172       ierr = ISGetNonlocalIS(iscol[i],&(ciscol[ii]));CHKERRQ(ierr);
3173       /* Now we have to
3174 	 (a) make sure ciscol[ii] is sorted, since, even if the off-proc indices
3175 	     were sorted on each rank, concatenated they might no longer be sorted;
3176 	 (b) Use ISSortPermutation() to construct ciscol_p, the mapping from the
3177 	     indices in the nondecreasing order to the original index positions.
3178 	 If ciscol[ii] is strictly increasing, the permutation IS is NULL.
3179       */
3180       ierr = ISSortPermutation(ciscol[ii],PETSC_FALSE,ciscol_p+ii);CHKERRQ(ierr);
3181       ierr = ISSort(ciscol[ii]);CHKERRQ(ierr);
3182       ++ii;
3183     }
3184   }
3185   ierr = PetscMalloc2(ismax,&isrow_p,ismax,&iscol_p);CHKERRQ(ierr);
3186   for (i = 0, ii = 0; i < ismax; ++i) {
3187     PetscInt       j,issize;
3188     const PetscInt *indices;
3189 
3190     /*
3191        Permute the indices into a nondecreasing order. Reject row and col indices with duplicates.
3192      */
3193     ierr = ISSortPermutation(isrow[i],PETSC_FALSE,isrow_p+i);CHKERRQ(ierr);
3194     ierr = ISSort(isrow[i]);CHKERRQ(ierr);
3195     ierr = ISGetLocalSize(isrow[i],&issize);CHKERRQ(ierr);
3196     ierr = ISGetIndices(isrow[i],&indices);CHKERRQ(ierr);
3197     for (j = 1; j < issize; ++j) {
3198       if (indices[j] == indices[j-1]) {
3199 	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]);
3200       }
3201     }
3202     ierr = ISRestoreIndices(isrow[i],&indices);CHKERRQ(ierr);
3203 
3204 
3205     ierr = ISSortPermutation(iscol[i],PETSC_FALSE,iscol_p+i);CHKERRQ(ierr);
3206     ierr = ISSort(iscol[i]);CHKERRQ(ierr);
3207     ierr = ISGetLocalSize(iscol[i],&issize);CHKERRQ(ierr);
3208     ierr = ISGetIndices(iscol[i],&indices);CHKERRQ(ierr);
3209     for (j = 1; j < issize; ++j) {
3210       if (indices[j-1] == indices[j]) {
3211 	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]);
3212       }
3213     }
3214     ierr = ISRestoreIndices(iscol[i],&indices);CHKERRQ(ierr);
3215     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm,&isize);CHKERRQ(ierr);
3216     if (isize > 1) {
3217       cisrow[ii] = isrow[i];
3218       ++ii;
3219     }
3220   }
3221   /*
3222     Allocate the necessary arrays to hold the resulting parallel matrices as well as the intermediate
3223     array of sequential matrices underlying the resulting parallel matrices.
3224     Which arrays to allocate is based on the value of MatReuse scall and whether ISs are sorted and/or
3225     contain duplicates.
3226 
3227     There are as many diag matrices as there are original index sets. There are only as many parallel
3228     and off-diag matrices, as there are parallel (comm size > 1) index sets.
3229 
3230     ARRAYS that can hold Seq matrices get allocated in any event -- either here or by getsubmats_seq():
3231     - If the array of MPI matrices already exists and is being reused, we need to allocate the array
3232       and extract the underlying seq matrices into it to serve as placeholders, into which getsubmats_seq
3233       will deposite the extracted diag and off-diag parts. Thus, we allocate the A&B arrays and fill them
3234       with A[i] and B[ii] extracted from the corresponding MPI submat.
3235     - However, if the rows, A's column indices or B's column indices are not sorted, the extracted A[i] & B[ii]
3236       will have a different order from what getsubmats_seq expects.  To handle this case -- indicated
3237       by a nonzero isrow_p[i], iscol_p[i], or ciscol_p[ii] -- we duplicate A[i] --> AA[i], B[ii] --> BB[ii]
3238       (retrieve composed AA[i] or BB[ii]) and reuse them here. AA[i] and BB[ii] are then used to permute its
3239       values into A[i] and B[ii] sitting inside the corresponding submat.
3240     - If no reuse is taking place then getsubmats_seq will allocate the A&B arrays and create the corresponding
3241       A[i], B[ii], AA[i] or BB[ii] matrices.
3242   */
3243   /* Parallel matrix array is allocated here only if no reuse is taking place. If reused, it is passed in by the caller. */
3244   if (scall == MAT_INITIAL_MATRIX) {
3245     ierr = PetscMalloc1(ismax,submat);CHKERRQ(ierr);
3246   }
3247 
3248   /* Now obtain the sequential A and B submatrices separately. */
3249   /* scall=MAT_REUSE_MATRIX is not handled yet, because getsubmats_seq() requires reuse of A and B */
3250   ierr = (*getsubmats_seq)(C,ismax,isrow,iscol,MAT_INITIAL_MATRIX,&A);CHKERRQ(ierr);
3251   ierr = (*getsubmats_seq)(C,cismax,cisrow,ciscol,MAT_INITIAL_MATRIX,&B);CHKERRQ(ierr);
3252 
3253   /*
3254     If scall == MAT_REUSE_MATRIX AND the permutations are NULL, we are done, since the sequential
3255     matrices A & B have been extracted directly into the parallel matrices containing them, or
3256     simply into the sequential matrix identical with the corresponding A (if isize == 1).
3257     Note that in that case colmap doesn't need to be rebuilt, since the matrices are expected
3258     to have the same sparsity pattern.
3259     Otherwise, A and/or B have to be properly embedded into C's index spaces and the correct colmap
3260     must be constructed for C. This is done by setseqmat(s).
3261   */
3262   for (i = 0, ii = 0; i < ismax; ++i) {
3263     /*
3264        TODO: cache ciscol, permutation ISs and maybe cisrow? What about isrow & iscol?
3265        That way we can avoid sorting and computing permutations when reusing.
3266        To this end:
3267         - remove the old cache, if it exists, when extracting submatrices with MAT_INITIAL_MATRIX
3268 	- if caching arrays to hold the ISs, make and compose a container for them so that it can
3269 	  be destroyed upon destruction of C (use PetscContainerUserDestroy() to clear out the contents).
3270     */
3271     MatStructure pattern;
3272     pattern = DIFFERENT_NONZERO_PATTERN;
3273 
3274     ierr = MPI_Comm_size(((PetscObject)isrow[i])->comm,&isize);CHKERRQ(ierr);
3275     /* Construct submat[i] from the Seq pieces A (and B, if necessary). */
3276     if (isize > 1) {
3277       if (scall == MAT_INITIAL_MATRIX) {
3278 	ierr = MatCreate(((PetscObject)isrow[i])->comm,(*submat)+i);CHKERRQ(ierr);
3279 	ierr = MatSetSizes((*submat)[i],A[i]->rmap->n,A[i]->cmap->n,PETSC_DETERMINE,PETSC_DETERMINE);CHKERRQ(ierr);
3280 	ierr = MatSetType((*submat)[i],MATMPIAIJ);CHKERRQ(ierr);
3281 	ierr = PetscLayoutSetUp((*submat)[i]->rmap);CHKERRQ(ierr);
3282 	ierr = PetscLayoutSetUp((*submat)[i]->cmap);CHKERRQ(ierr);
3283       }
3284       /*
3285 	For each parallel isrow[i], insert the extracted sequential matrices into the parallel matrix.
3286       */
3287       {
3288 	Mat AA,BB;
3289         AA = A[i];
3290         BB = B[ii];
3291 	if (AA || BB) {
3292 	  ierr = setseqmats((*submat)[i],isrow_p[i],iscol_p[i],ciscol_p[ii],pattern,AA,BB);CHKERRQ(ierr);
3293 	  ierr = MatAssemblyBegin((*submat)[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
3294 	  ierr = MatAssemblyEnd((*submat)[i],MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
3295 	}
3296 
3297         ierr = MatDestroy(&AA);CHKERRQ(ierr);
3298         ierr = MatDestroy(&BB);CHKERRQ(ierr);
3299       }
3300       ierr = ISDestroy(ciscol+ii);CHKERRQ(ierr);
3301       ierr = ISDestroy(ciscol_p+ii);CHKERRQ(ierr);
3302       ++ii;
3303     } else { /* if (isize == 1) */
3304       if (scall == MAT_REUSE_MATRIX) {
3305         ierr = MatDestroy(&(*submat)[i]);CHKERRQ(ierr);
3306       }
3307       if (isrow_p[i] || iscol_p[i]) {
3308         ierr = MatDuplicate(A[i],MAT_DO_NOT_COPY_VALUES,(*submat)+i);CHKERRQ(ierr);
3309         ierr = setseqmat((*submat)[i],isrow_p[i],iscol_p[i],pattern,A[i]);CHKERRQ(ierr);
3310 	/* Otherwise A is extracted straight into (*submats)[i]. */
3311 	/* TODO: Compose A[i] on (*submat([i] for future use, if ((isrow_p[i] || iscol_p[i]) && MAT_INITIAL_MATRIX). */
3312 	ierr = MatDestroy(A+i);CHKERRQ(ierr);
3313       } else (*submat)[i] = A[i];
3314     }
3315     ierr = ISDestroy(&isrow_p[i]);CHKERRQ(ierr);
3316     ierr = ISDestroy(&iscol_p[i]);CHKERRQ(ierr);
3317   }
3318   ierr = PetscFree2(cisrow,ciscol);CHKERRQ(ierr);
3319   ierr = PetscFree2(isrow_p,iscol_p);CHKERRQ(ierr);
3320   ierr = PetscFree(ciscol_p);CHKERRQ(ierr);
3321   ierr = PetscFree(A);CHKERRQ(ierr);
3322   ierr = PetscFree(B);CHKERRQ(ierr);
3323   PetscFunctionReturn(0);
3324 }
3325 
3326 PetscErrorCode MatGetSubMatricesMPI_MPIAIJ(Mat C,PetscInt ismax,const IS isrow[],const IS iscol[],MatReuse scall,Mat *submat[])
3327 {
3328   PetscErrorCode ierr;
3329 
3330   PetscFunctionBegin;
3331   ierr = MatGetSubMatricesMPI_MPIXAIJ(C,ismax,isrow,iscol,scall,submat,MatGetSubMatrices_MPIAIJ,MatGetSeqMats_MPIAIJ,MatSetSeqMat_SeqAIJ,MatSetSeqMats_MPIAIJ);CHKERRQ(ierr);
3332   PetscFunctionReturn(0);
3333 }
3334