Actual source code: sbaijov.c
petsc-3.10.5 2019-03-28
Report Typos and Errors

      2: /*
      3:    Routines to compute overlapping regions of a parallel MPI matrix.
      4:    Used for finding submatrices that were shared across processors.
      5: */
      6:  #include <../src/mat/impls/sbaij/mpi/mpisbaij.h>
      7:  #include <petscbt.h>

      9: static PetscErrorCode MatIncreaseOverlap_MPISBAIJ_Once(Mat,PetscInt,IS*);
     10: static PetscErrorCode MatIncreaseOverlap_MPISBAIJ_Local(Mat,PetscInt*,PetscInt,PetscInt*,PetscBT*);

     12: PetscErrorCode MatIncreaseOverlap_MPISBAIJ(Mat C,PetscInt is_max,IS is[],PetscInt ov)
     13: {
     15:   PetscInt       i,N=C->cmap->N, bs=C->rmap->bs,M=C->rmap->N,Mbs=M/bs,*nidx,isz,iov;
     16:   IS             *is_new,*is_row;
     17:   Mat            *submats;
     18:   Mat_MPISBAIJ   *c=(Mat_MPISBAIJ*)C->data;
     19:   Mat_SeqSBAIJ   *asub_i;
     20:   PetscBT        table;
     21:   PetscInt       *ai,brow,nz,nis,l,nmax,nstages_local,nstages,max_no,pos;
     22:   const PetscInt *idx;
     23:   PetscBool      flg;

     26:   PetscMalloc1(is_max,&is_new);
     27:   /* Convert the indices into block format */
     28:   ISCompressIndicesGeneral(N,C->rmap->n,bs,is_max,is,is_new);
     29:   if (ov < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"Negative overlap specified\n");

     31:   /* ----- previous non-scalable implementation ----- */
     32:   flg  = PETSC_FALSE;
     33:   PetscOptionsHasName(NULL,NULL, "-IncreaseOverlap_old", &flg);
     34:   if (flg) { /* previous non-scalable implementation */
     35:     printf("use previous non-scalable implementation...\n");
     36:     for (i=0; i<ov; ++i) {
     37:       MatIncreaseOverlap_MPISBAIJ_Once(C,is_max,is_new);
     38:     }
     39:   } else { /* implementation using modified BAIJ routines */

     41:     PetscMalloc1(Mbs+1,&nidx);
     42:     PetscBTCreate(Mbs,&table); /* for column search */

     44:     /* Create is_row */
     45:     PetscMalloc1(is_max,&is_row);
     46:     ISCreateStride(PETSC_COMM_SELF,Mbs,0,1,&is_row[0]);

     48:     for (i=1; i<is_max; i++) {
     49:       is_row[i]  = is_row[0]; /* reuse is_row[0] */
     50:     }

     52:     /* Allocate memory to hold all the submatrices - Modified from MatCreateSubMatrices_MPIBAIJ() */
     53:     PetscMalloc1(is_max+1,&submats);

     55:     /* Determine the number of stages through which submatrices are done */
     56:     nmax = 20*1000000 / (c->Nbs * sizeof(PetscInt));
     57:     if (!nmax) nmax = 1;
     58:     nstages_local = is_max/nmax + ((is_max % nmax) ? 1 : 0);

     60:     /* Make sure every processor loops through the nstages */
     61:     MPIU_Allreduce(&nstages_local,&nstages,1,MPIU_INT,MPI_MAX,PetscObjectComm((PetscObject)C));

     63:     for (iov=0; iov<ov; ++iov) {
     64:       /* 1) Get submats for column search */
     65:       for (i=0,pos=0; i<nstages; i++) {
     66:         if (pos+nmax <= is_max) max_no = nmax;
     67:         else if (pos == is_max) max_no = 0;
     68:         else                    max_no = is_max-pos;
     69:         c->ijonly = PETSC_TRUE; /* only matrix data structures are requested */
     70:         MatCreateSubMatrices_MPIBAIJ_local(C,max_no,is_row+pos,is_new+pos,MAT_INITIAL_MATRIX,submats+pos);
     71:         pos      += max_no;
     72:       }

     74:       /* 2) Row search */
     75:       MatIncreaseOverlap_MPIBAIJ_Once(C,is_max,is_new);

     77:       /* 3) Column search */
     78:       for (i=0; i<is_max; i++) {
     79:         asub_i = (Mat_SeqSBAIJ*)submats[i]->data;
     80:         ai     = asub_i->i;;

     82:         /* put is_new obtained from MatIncreaseOverlap_MPIBAIJ() to table */
     83:         PetscBTMemzero(Mbs,table);

     85:         ISGetIndices(is_new[i],&idx);
     86:         ISGetLocalSize(is_new[i],&nis);
     87:         for (l=0; l<nis; l++) {
     88:           PetscBTSet(table,idx[l]);
     89:           nidx[l] = idx[l];
     90:         }
     91:         isz = nis;

     93:         /* add column entries to table */
     94:         for (brow=0; brow<Mbs; brow++) {
     95:           nz = ai[brow+1] - ai[brow];
     96:           if (nz) {
     97:             if (!PetscBTLookupSet(table,brow)) nidx[isz++] = brow;
     98:           }
     99:         }
    100:         ISRestoreIndices(is_new[i],&idx);
    101:         ISDestroy(&is_new[i]);

    103:         /* create updated is_new */
    104:         ISCreateGeneral(PETSC_COMM_SELF,isz,nidx,PETSC_COPY_VALUES,is_new+i);
    105:       }

    107:       /* Free tmp spaces */
    108:       for (i=0; i<is_max; i++) {
    109:         MatDestroy(&submats[i]);
    110:       }
    111:     }

    113:     PetscBTDestroy(&table);
    114:     PetscFree(submats);
    115:     ISDestroy(&is_row[0]);
    116:     PetscFree(is_row);
    117:     PetscFree(nidx);

    119:   }

    121:   for (i=0; i<is_max; i++) {ISDestroy(&is[i]);}
    122:   ISExpandIndicesGeneral(N,N,bs,is_max,is_new,is);

    124:   for (i=0; i<is_max; i++) {ISDestroy(&is_new[i]);}
    125:   PetscFree(is_new);
    126:   return(0);
    127: }

    129: typedef enum {MINE,OTHER} WhoseOwner;
    130: /*  data1, odata1 and odata2 are packed in the format (for communication):
    131:        data[0]          = is_max, no of is
    132:        data[1]          = size of is[0]
    133:         ...
    134:        data[is_max]     = size of is[is_max-1]
    135:        data[is_max + 1] = data(is[0])
    136:         ...
    137:        data[is_max+1+sum(size of is[k]), k=0,...,i-1] = data(is[i])
    138:         ...
    139:    data2 is packed in the format (for creating output is[]):
    140:        data[0]          = is_max, no of is
    141:        data[1]          = size of is[0]
    142:         ...
    143:        data[is_max]     = size of is[is_max-1]
    144:        data[is_max + 1] = data(is[0])
    145:         ...
    146:        data[is_max + 1 + Mbs*i) = data(is[i])
    147:         ...
    148: */
    149: static PetscErrorCode MatIncreaseOverlap_MPISBAIJ_Once(Mat C,PetscInt is_max,IS is[])
    150: {
    151:   Mat_MPISBAIJ   *c = (Mat_MPISBAIJ*)C->data;
    153:   PetscMPIInt    size,rank,tag1,tag2,*len_s,nrqr,nrqs,*id_r1,*len_r1,flag,len,*iwork;
    154:   const PetscInt *idx_i;
    155:   PetscInt       idx,isz,col,*n,*data1,**data1_start,*data2,*data2_i,*data,*data_i;
    156:   PetscInt       Mbs,i,j,k,*odata1,*odata2;
    157:   PetscInt       proc_id,**odata2_ptr,*ctable=0,*btable,len_max,len_est;
    158:   PetscInt       proc_end=0,len_unused,nodata2;
    159:   PetscInt       ois_max; /* max no of is[] in each of processor */
    160:   char           *t_p;
    161:   MPI_Comm       comm;
    162:   MPI_Request    *s_waits1,*s_waits2,r_req;
    163:   MPI_Status     *s_status,r_status;
    164:   PetscBT        *table;  /* mark indices of this processor's is[] */
    165:   PetscBT        table_i;
    166:   PetscBT        otable; /* mark indices of other processors' is[] */
    167:   PetscInt       bs=C->rmap->bs,Bn = c->B->cmap->n,Bnbs = Bn/bs,*Bowners;
    168:   IS             garray_local,garray_gl;

    171:   PetscObjectGetComm((PetscObject)C,&comm);
    172:   size = c->size;
    173:   rank = c->rank;
    174:   Mbs  = c->Mbs;

    176:   PetscObjectGetNewTag((PetscObject)C,&tag1);
    177:   PetscObjectGetNewTag((PetscObject)C,&tag2);

    179:   /* create tables used in
    180:      step 1: table[i] - mark c->garray of proc [i]
    181:      step 3: table[i] - mark indices of is[i] when whose=MINE
    182:              table[0] - mark incideces of is[] when whose=OTHER */
    183:   len  = PetscMax(is_max, size);
    184:   PetscMalloc2(len,&table,(Mbs/PETSC_BITS_PER_BYTE+1)*len,&t_p);
    185:   for (i=0; i<len; i++) {
    186:     table[i] = t_p  + (Mbs/PETSC_BITS_PER_BYTE+1)*i;
    187:   }

    189:   MPIU_Allreduce(&is_max,&ois_max,1,MPIU_INT,MPI_MAX,comm);

    191:   /* 1. Send this processor's is[] to other processors */
    192:   /*---------------------------------------------------*/
    193:   /* allocate spaces */
    194:   PetscMalloc1(is_max,&n);
    195:   len  = 0;
    196:   for (i=0; i<is_max; i++) {
    197:     ISGetLocalSize(is[i],&n[i]);
    198:     len += n[i];
    199:   }
    200:   if (!len) {
    201:     is_max = 0;
    202:   } else {
    203:     len += 1 + is_max; /* max length of data1 for one processor */
    204:   }

    207:   PetscMalloc1(size*len+1,&data1);
    208:   PetscMalloc1(size,&data1_start);
    209:   for (i=0; i<size; i++) data1_start[i] = data1 + i*len;

    211:   PetscMalloc4(size,&len_s,size,&btable,size,&iwork,size+1,&Bowners);

    213:   /* gather c->garray from all processors */
    214:   ISCreateGeneral(comm,Bnbs,c->garray,PETSC_COPY_VALUES,&garray_local);
    215:   ISAllGather(garray_local, &garray_gl);
    216:   ISDestroy(&garray_local);
    217:   MPI_Allgather(&Bnbs,1,MPIU_INT,Bowners+1,1,MPIU_INT,comm);

    219:   Bowners[0] = 0;
    220:   for (i=0; i<size; i++) Bowners[i+1] += Bowners[i];

    222:   if (is_max) {
    223:     /* hash table ctable which maps c->row to proc_id) */
    224:     PetscMalloc1(Mbs,&ctable);
    225:     for (proc_id=0,j=0; proc_id<size; proc_id++) {
    226:       for (; j<C->rmap->range[proc_id+1]/bs; j++) ctable[j] = proc_id;
    227:     }

    229:     /* hash tables marking c->garray */
    230:     ISGetIndices(garray_gl,&idx_i);
    231:     for (i=0; i<size; i++) {
    232:       table_i = table[i];
    233:       PetscBTMemzero(Mbs,table_i);
    234:       for (j = Bowners[i]; j<Bowners[i+1]; j++) { /* go through B cols of proc[i]*/
    235:         PetscBTSet(table_i,idx_i[j]);
    236:       }
    237:     }
    238:     ISRestoreIndices(garray_gl,&idx_i);
    239:   }  /* if (is_max) */
    240:   ISDestroy(&garray_gl);

    242:   /* evaluate communication - mesg to who, length, and buffer space */
    243:   for (i=0; i<size; i++) len_s[i] = 0;

    245:   /* header of data1 */
    246:   for (proc_id=0; proc_id<size; proc_id++) {
    247:     iwork[proc_id]        = 0;
    248:     *data1_start[proc_id] = is_max;
    249:     data1_start[proc_id]++;
    250:     for (j=0; j<is_max; j++) {
    251:       if (proc_id == rank) {
    252:         *data1_start[proc_id] = n[j];
    253:       } else {
    254:         *data1_start[proc_id] = 0;
    255:       }
    256:       data1_start[proc_id]++;
    257:     }
    258:   }

    260:   for (i=0; i<is_max; i++) {
    261:     ISGetIndices(is[i],&idx_i);
    262:     for (j=0; j<n[i]; j++) {
    263:       idx                = idx_i[j];
    264:       *data1_start[rank] = idx; data1_start[rank]++; /* for local proccessing */
    265:       proc_end           = ctable[idx];
    266:       for (proc_id=0; proc_id<=proc_end; proc_id++) {  /* for others to process */
    267:         if (proc_id == rank) continue; /* done before this loop */
    268:         if (proc_id < proc_end && !PetscBTLookup(table[proc_id],idx)) continue; /* no need for sending idx to [proc_id] */
    269:         *data1_start[proc_id] = idx; data1_start[proc_id]++;
    270:         len_s[proc_id]++;
    271:       }
    272:     }
    273:     /* update header data */
    274:     for (proc_id=0; proc_id<size; proc_id++) {
    275:       if (proc_id== rank) continue;
    276:       *(data1 + proc_id*len + 1 + i) = len_s[proc_id] - iwork[proc_id];
    277:       iwork[proc_id]                 = len_s[proc_id];
    278:     }
    279:     ISRestoreIndices(is[i],&idx_i);
    280:   }

    282:   nrqs = 0; nrqr = 0;
    283:   for (i=0; i<size; i++) {
    284:     data1_start[i] = data1 + i*len;
    285:     if (len_s[i]) {
    286:       nrqs++;
    287:       len_s[i] += 1 + is_max; /* add no. of header msg */
    288:     }
    289:   }

    291:   for (i=0; i<is_max; i++) {
    292:     ISDestroy(&is[i]);
    293:   }
    294:   PetscFree(n);
    295:   PetscFree(ctable);

    297:   /* Determine the number of messages to expect, their lengths, from from-ids */
    298:   PetscGatherNumberOfMessages(comm,NULL,len_s,&nrqr);
    299:   PetscGatherMessageLengths(comm,nrqs,nrqr,len_s,&id_r1,&len_r1);

    301:   /*  Now  post the sends */
    302:   PetscMalloc2(size,&s_waits1,size,&s_waits2);
    303:   k    = 0;
    304:   for (proc_id=0; proc_id<size; proc_id++) {  /* send data1 to processor [proc_id] */
    305:     if (len_s[proc_id]) {
    306:       MPI_Isend(data1_start[proc_id],len_s[proc_id],MPIU_INT,proc_id,tag1,comm,s_waits1+k);
    307:       k++;
    308:     }
    309:   }

    311:   /* 2. Receive other's is[] and process. Then send back */
    312:   /*-----------------------------------------------------*/
    313:   len = 0;
    314:   for (i=0; i<nrqr; i++) {
    315:     if (len_r1[i] > len) len = len_r1[i];
    316:   }
    317:   PetscFree(len_r1);
    318:   PetscFree(id_r1);

    320:   for (proc_id=0; proc_id<size; proc_id++) len_s[proc_id] = iwork[proc_id] = 0;

    322:   PetscMalloc1(len+1,&odata1);
    323:   PetscMalloc1(size,&odata2_ptr);
    324:   PetscBTCreate(Mbs,&otable);

    326:   len_max = ois_max*(Mbs+1); /* max space storing all is[] for each receive */
    327:   len_est = 2*len_max;       /* estimated space of storing is[] for all receiving messages */
    328:   PetscMalloc1(len_est+1,&odata2);
    329:   nodata2 = 0;               /* nodata2+1: num of PetscMalloc(,&odata2_ptr[]) called */

    331:   odata2_ptr[nodata2] = odata2;

    333:   len_unused = len_est; /* unused space in the array odata2_ptr[nodata2]-- needs to be >= len_max  */

    335:   k = 0;
    336:   while (k < nrqr) {
    337:     /* Receive messages */
    338:     MPI_Iprobe(MPI_ANY_SOURCE,tag1,comm,&flag,&r_status);
    339:     if (flag) {
    340:       MPI_Get_count(&r_status,MPIU_INT,&len);
    341:       proc_id = r_status.MPI_SOURCE;
    342:       MPI_Irecv(odata1,len,MPIU_INT,proc_id,r_status.MPI_TAG,comm,&r_req);
    343:       MPI_Wait(&r_req,&r_status);

    345:       /*  Process messages */
    346:       /*  make sure there is enough unused space in odata2 array */
    347:       if (len_unused < len_max) { /* allocate more space for odata2 */
    348:         PetscMalloc1(len_est+1,&odata2);

    350:         odata2_ptr[++nodata2] = odata2;

    352:         len_unused = len_est;
    353:       }

    355:       MatIncreaseOverlap_MPISBAIJ_Local(C,odata1,OTHER,odata2,&otable);
    356:       len  = 1 + odata2[0];
    357:       for (i=0; i<odata2[0]; i++) len += odata2[1 + i];

    359:       /* Send messages back */
    360:       MPI_Isend(odata2,len,MPIU_INT,proc_id,tag2,comm,s_waits2+k);
    361:       k++;
    362:       odata2        += len;
    363:       len_unused    -= len;
    364:       len_s[proc_id] = len; /* num of messages sending back to [proc_id] by this proc */
    365:     }
    366:   }
    367:   PetscFree(odata1);
    368:   PetscBTDestroy(&otable);

    370:   /* 3. Do local work on this processor's is[] */
    371:   /*-------------------------------------------*/
    372:   /* make sure there is enough unused space in odata2(=data) array */
    373:   len_max = is_max*(Mbs+1); /* max space storing all is[] for this processor */
    374:   if (len_unused < len_max) { /* allocate more space for odata2 */
    375:     PetscMalloc1(len_est+1,&odata2);

    377:     odata2_ptr[++nodata2] = odata2;
    378:   }

    380:   data = odata2;
    381:   MatIncreaseOverlap_MPISBAIJ_Local(C,data1_start[rank],MINE,data,table);
    382:   PetscFree(data1_start);

    384:   /* 4. Receive work done on other processors, then merge */
    385:   /*------------------------------------------------------*/
    386:   /* get max number of messages that this processor expects to recv */
    387:   MPIU_Allreduce(len_s,iwork,size,MPI_INT,MPI_MAX,comm);
    388:   PetscMalloc1(iwork[rank]+1,&data2);
    389:   PetscFree4(len_s,btable,iwork,Bowners);

    391:   k = 0;
    392:   while (k < nrqs) {
    393:     /* Receive messages */
    394:     MPI_Iprobe(MPI_ANY_SOURCE,tag2,comm,&flag,&r_status);
    395:     if (flag) {
    396:       MPI_Get_count(&r_status,MPIU_INT,&len);

    398:       proc_id = r_status.MPI_SOURCE;

    400:       MPI_Irecv(data2,len,MPIU_INT,proc_id,r_status.MPI_TAG,comm,&r_req);
    401:       MPI_Wait(&r_req,&r_status);
    402:       if (len > 1+is_max) { /* Add data2 into data */
    403:         data2_i = data2 + 1 + is_max;
    404:         for (i=0; i<is_max; i++) {
    405:           table_i = table[i];
    406:           data_i  = data + 1 + is_max + Mbs*i;
    407:           isz     = data[1+i];
    408:           for (j=0; j<data2[1+i]; j++) {
    409:             col = data2_i[j];
    410:             if (!PetscBTLookupSet(table_i,col)) data_i[isz++] = col;
    411:           }
    412:           data[1+i] = isz;
    413:           if (i < is_max - 1) data2_i += data2[1+i];
    414:         }
    415:       }
    416:       k++;
    417:     }
    418:   }
    419:   PetscFree(data2);
    420:   PetscFree2(table,t_p);

    422:   /* phase 1 sends are complete */
    423:   PetscMalloc1(size,&s_status);
    424:   if (nrqs) {MPI_Waitall(nrqs,s_waits1,s_status);}
    425:   PetscFree(data1);

    427:   /* phase 2 sends are complete */
    428:   if (nrqr) {MPI_Waitall(nrqr,s_waits2,s_status);}
    429:   PetscFree2(s_waits1,s_waits2);
    430:   PetscFree(s_status);

    432:   /* 5. Create new is[] */
    433:   /*--------------------*/
    434:   for (i=0; i<is_max; i++) {
    435:     data_i = data + 1 + is_max + Mbs*i;
    436:     ISCreateGeneral(PETSC_COMM_SELF,data[1+i],data_i,PETSC_COPY_VALUES,is+i);
    437:   }
    438:   for (k=0; k<=nodata2; k++) {
    439:     PetscFree(odata2_ptr[k]);
    440:   }
    441:   PetscFree(odata2_ptr);
    442:   return(0);
    443: }

    445: /*
    446:    MatIncreaseOverlap_MPISBAIJ_Local - Called by MatIncreaseOverlap, to do
    447:        the work on the local processor.

    449:      Inputs:
    450:       C      - MAT_MPISBAIJ;
    451:       data   - holds is[]. See MatIncreaseOverlap_MPISBAIJ_Once() for the format.
    452:       whose  - whose is[] to be processed,
    453:                MINE:  this processor's is[]
    454:                OTHER: other processor's is[]
    455:      Output:
    456:        nidx  - whose = MINE:
    457:                      holds input and newly found indices in the same format as data
    458:                whose = OTHER:
    459:                      only holds the newly found indices
    460:        table - table[i]: mark the indices of is[i], i=0,...,is_max. Used only in the case 'whose=MINE'.
    461: */
    462: /* Would computation be reduced by swapping the loop 'for each is' and 'for each row'? */
    463: static PetscErrorCode MatIncreaseOverlap_MPISBAIJ_Local(Mat C,PetscInt *data,PetscInt whose,PetscInt *nidx,PetscBT *table)
    464: {
    465:   Mat_MPISBAIJ   *c = (Mat_MPISBAIJ*)C->data;
    466:   Mat_SeqSBAIJ   *a = (Mat_SeqSBAIJ*)(c->A)->data;
    467:   Mat_SeqBAIJ    *b = (Mat_SeqBAIJ*)(c->B)->data;
    469:   PetscInt       row,mbs,Mbs,*nidx_i,col,col_max,isz,isz0,*ai,*aj,*bi,*bj,*garray,rstart,l;
    470:   PetscInt       a_start,a_end,b_start,b_end,i,j,k,is_max,*idx_i,n;
    471:   PetscBT        table0;  /* mark the indices of input is[] for look up */
    472:   PetscBT        table_i; /* poits to i-th table. When whose=OTHER, a single table is used for all is[] */

    475:   Mbs    = c->Mbs; mbs = a->mbs;
    476:   ai     = a->i; aj = a->j;
    477:   bi     = b->i; bj = b->j;
    478:   garray = c->garray;
    479:   rstart = c->rstartbs;
    480:   is_max = data[0];

    482:   PetscBTCreate(Mbs,&table0);

    484:   nidx[0] = is_max;
    485:   idx_i   = data + is_max + 1; /* ptr to input is[0] array */
    486:   nidx_i  = nidx + is_max + 1; /* ptr to output is[0] array */
    487:   for (i=0; i<is_max; i++) { /* for each is */
    488:     isz = 0;
    489:     n   = data[1+i]; /* size of input is[i] */

    491:     /* initialize and set table_i(mark idx and nidx) and table0(only mark idx) */
    492:     if (whose == MINE) { /* process this processor's is[] */
    493:       table_i = table[i];
    494:       nidx_i  = nidx + 1+ is_max + Mbs*i;
    495:     } else {            /* process other processor's is[] - only use one temp table */
    496:       table_i = table[0];
    497:     }
    498:     PetscBTMemzero(Mbs,table_i);
    499:     PetscBTMemzero(Mbs,table0);
    500:     if (n==0) {
    501:       nidx[1+i] = 0;  /* size of new is[i] */
    502:       continue;
    503:     }

    505:     isz0 = 0; col_max = 0;
    506:     for (j=0; j<n; j++) {
    507:       col = idx_i[j];
    508:       if (col >= Mbs) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"index col %D >= Mbs %D",col,Mbs);
    509:       if (!PetscBTLookupSet(table_i,col)) {
    510:         PetscBTSet(table0,col);
    511:         if (whose == MINE) nidx_i[isz0] = col;
    512:         if (col_max < col) col_max = col;
    513:         isz0++;
    514:       }
    515:     }

    517:     if (whose == MINE) isz = isz0;
    518:     k = 0;  /* no. of indices from input is[i] that have been examined */
    519:     for (row=0; row<mbs; row++) {
    520:       a_start = ai[row]; a_end = ai[row+1];
    521:       b_start = bi[row]; b_end = bi[row+1];
    522:       if (PetscBTLookup(table0,row+rstart)) { /* row is on input is[i]:
    523:                                                 do row search: collect all col in this row */
    524:         for (l = a_start; l<a_end ; l++) { /* Amat */
    525:           col = aj[l] + rstart;
    526:           if (!PetscBTLookupSet(table_i,col)) nidx_i[isz++] = col;
    527:         }
    528:         for (l = b_start; l<b_end ; l++) { /* Bmat */
    529:           col = garray[bj[l]];
    530:           if (!PetscBTLookupSet(table_i,col)) nidx_i[isz++] = col;
    531:         }
    532:         k++;
    533:         if (k >= isz0) break; /* for (row=0; row<mbs; row++) */
    534:       } else { /* row is not on input is[i]:
    535:                   do col serach: add row onto nidx_i if there is a col in nidx_i */
    536:         for (l = a_start; l<a_end; l++) {  /* Amat */
    537:           col = aj[l] + rstart;
    538:           if (col > col_max) break;
    539:           if (PetscBTLookup(table0,col)) {
    540:             if (!PetscBTLookupSet(table_i,row+rstart)) nidx_i[isz++] = row+rstart;
    541:             break; /* for l = start; l<end ; l++) */
    542:           }
    543:         }
    544:         for (l = b_start; l<b_end; l++) {  /* Bmat */
    545:           col = garray[bj[l]];
    546:           if (col > col_max) break;
    547:           if (PetscBTLookup(table0,col)) {
    548:             if (!PetscBTLookupSet(table_i,row+rstart)) nidx_i[isz++] = row+rstart;
    549:             break; /* for l = start; l<end ; l++) */
    550:           }
    551:         }
    552:       }
    553:     }

    555:     if (i < is_max - 1) {
    556:       idx_i  += n;   /* ptr to input is[i+1] array */
    557:       nidx_i += isz; /* ptr to output is[i+1] array */
    558:     }
    559:     nidx[1+i] = isz; /* size of new is[i] */
    560:   } /* for each is */
    561:   PetscBTDestroy(&table0);
    562:   return(0);
    563: }