Actual source code: sbaijov.c
petsc-3.7.1 2016-05-15
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      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*);

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

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

     33:   /* ----- previous non-scalable implementation ----- */
     34:   flg  = PETSC_FALSE;
     35:   PetscOptionsHasName(NULL,NULL, "-IncreaseOverlap_old", &flg);
     36:   if (flg) { /* previous non-scalable implementation */
     37:     printf("use previous non-scalable implementation...\n");
     38:     for (i=0; i<ov; ++i) {
     39:       MatIncreaseOverlap_MPISBAIJ_Once(C,is_max,is_new);
     40:     }
     41:   } else { /* implementation using modified BAIJ routines */

     43:     PetscMalloc1(Mbs+1,&nidx);
     44:     PetscBTCreate(Mbs,&table); /* for column search */
     45:     PetscMalloc2(is_max+1,&allcolumns,is_max+1,&allrows);

     47:     /* Create is_row */
     48:     PetscMalloc1(is_max,&is_row);
     49:     ISCreateStride(PETSC_COMM_SELF,Mbs,0,1,&is_row[0]);

     51:     allrows[0] = PETSC_TRUE;
     52:     for (i=1; i<is_max; i++) {
     53:       is_row[i]  = is_row[0]; /* reuse is_row[0] */
     54:       allrows[i] = PETSC_TRUE;
     55:     }

     57:     /* Allocate memory to hold all the submatrices - Modified from MatGetSubMatrices_MPIBAIJ() */
     58:     PetscMalloc1(is_max+1,&submats);

     60:     /* Check for special case: each processor gets entire matrix columns */
     61:     for (i=0; i<is_max; i++) {
     62:       ISIdentity(is_new[i],&flg);
     63:       ISGetLocalSize(is_new[i],&isz);
     64:       if (flg && isz == Mbs) {
     65:         allcolumns[i] = PETSC_TRUE;
     66:       } else {
     67:         allcolumns[i] = PETSC_FALSE;
     68:       }
     69:     }

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

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

     79:     for (iov=0; iov<ov; ++iov) {
     80:       /* 1) Get submats for column search */
     81:       for (i=0,pos=0; i<nstages; i++) {
     82:         if (pos+nmax <= is_max) max_no = nmax;
     83:         else if (pos == is_max) max_no = 0;
     84:         else                    max_no = is_max-pos;
     85:         c->ijonly = PETSC_TRUE;
     86:         MatGetSubMatrices_MPIBAIJ_local(C,max_no,is_row+pos,is_new+pos,MAT_INITIAL_MATRIX,allrows+pos,allcolumns+pos,submats+pos);
     87:         pos      += max_no;
     88:       }

     90:       /* 2) Row search */
     91:       MatIncreaseOverlap_MPIBAIJ_Once(C,is_max,is_new);

     93:       /* 3) Column search */
     94:       for (i=0; i<is_max; i++) {
     95:         asub_i = (Mat_SeqSBAIJ*)submats[i]->data;
     96:         ai     = asub_i->i;;

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

    101:         ISGetIndices(is_new[i],&idx);
    102:         ISGetLocalSize(is_new[i],&nis);
    103:         for (l=0; l<nis; l++) {
    104:           PetscBTSet(table,idx[l]);
    105:           nidx[l] = idx[l];
    106:         }
    107:         isz = nis;

    109:         /* add column entries to table */
    110:         for (brow=0; brow<Mbs; brow++) {
    111:           nz = ai[brow+1] - ai[brow];
    112:           if (nz) {
    113:             if (!PetscBTLookupSet(table,brow)) nidx[isz++] = brow;
    114:           }
    115:         }
    116:         ISRestoreIndices(is_new[i],&idx);
    117:         ISDestroy(&is_new[i]);

    119:         /* create updated is_new */
    120:         ISCreateGeneral(PETSC_COMM_SELF,isz,nidx,PETSC_COPY_VALUES,is_new+i);
    121:       }

    123:       /* Free tmp spaces */
    124:       for (i=0; i<is_max; i++) {
    125:         MatDestroy(&submats[i]);
    126:       }
    127:     }
    128:     PetscFree2(allcolumns,allrows);
    129:     PetscBTDestroy(&table);
    130:     PetscFree(submats);
    131:     ISDestroy(&is_row[0]);
    132:     PetscFree(is_row);
    133:     PetscFree(nidx);

    135:   }

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

    140:   for (i=0; i<is_max; i++) {ISDestroy(&is_new[i]);}
    141:   PetscFree(is_new);
    142:   return(0);
    143: }

    145: typedef enum {MINE,OTHER} WhoseOwner;
    146: /*  data1, odata1 and odata2 are packed in the format (for communication):
    147:        data[0]          = is_max, no of is
    148:        data[1]          = size of is[0]
    149:         ...
    150:        data[is_max]     = size of is[is_max-1]
    151:        data[is_max + 1] = data(is[0])
    152:         ...
    153:        data[is_max+1+sum(size of is[k]), k=0,...,i-1] = data(is[i])
    154:         ...
    155:    data2 is packed in the format (for creating output is[]):
    156:        data[0]          = is_max, no of is
    157:        data[1]          = size of is[0]
    158:         ...
    159:        data[is_max]     = size of is[is_max-1]
    160:        data[is_max + 1] = data(is[0])
    161:         ...
    162:        data[is_max + 1 + Mbs*i) = data(is[i])
    163:         ...
    164: */
    167: static PetscErrorCode MatIncreaseOverlap_MPISBAIJ_Once(Mat C,PetscInt is_max,IS is[])
    168: {
    169:   Mat_MPISBAIJ   *c = (Mat_MPISBAIJ*)C->data;
    171:   PetscMPIInt    size,rank,tag1,tag2,*len_s,nrqr,nrqs,*id_r1,*len_r1,flag,len,*iwork;
    172:   const PetscInt *idx_i;
    173:   PetscInt       idx,isz,col,*n,*data1,**data1_start,*data2,*data2_i,*data,*data_i;
    174:   PetscInt       Mbs,i,j,k,*odata1,*odata2;
    175:   PetscInt       proc_id,**odata2_ptr,*ctable=0,*btable,len_max,len_est;
    176:   PetscInt       proc_end=0,len_unused,nodata2;
    177:   PetscInt       ois_max; /* max no of is[] in each of processor */
    178:   char           *t_p;
    179:   MPI_Comm       comm;
    180:   MPI_Request    *s_waits1,*s_waits2,r_req;
    181:   MPI_Status     *s_status,r_status;
    182:   PetscBT        *table;  /* mark indices of this processor's is[] */
    183:   PetscBT        table_i;
    184:   PetscBT        otable; /* mark indices of other processors' is[] */
    185:   PetscInt       bs=C->rmap->bs,Bn = c->B->cmap->n,Bnbs = Bn/bs,*Bowners;
    186:   IS             garray_local,garray_gl;

    189:   PetscObjectGetComm((PetscObject)C,&comm);
    190:   size = c->size;
    191:   rank = c->rank;
    192:   Mbs  = c->Mbs;

    194:   PetscObjectGetNewTag((PetscObject)C,&tag1);
    195:   PetscObjectGetNewTag((PetscObject)C,&tag2);

    197:   /* create tables used in
    198:      step 1: table[i] - mark c->garray of proc [i]
    199:      step 3: table[i] - mark indices of is[i] when whose=MINE
    200:              table[0] - mark incideces of is[] when whose=OTHER */
    201:   len  = PetscMax(is_max, size);
    202:   PetscMalloc2(len,&table,(Mbs/PETSC_BITS_PER_BYTE+1)*len,&t_p);
    203:   for (i=0; i<len; i++) {
    204:     table[i] = t_p  + (Mbs/PETSC_BITS_PER_BYTE+1)*i;
    205:   }

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

    209:   /* 1. Send this processor's is[] to other processors */
    210:   /*---------------------------------------------------*/
    211:   /* allocate spaces */
    212:   PetscMalloc1(is_max,&n);
    213:   len  = 0;
    214:   for (i=0; i<is_max; i++) {
    215:     ISGetLocalSize(is[i],&n[i]);
    216:     len += n[i];
    217:   }
    218:   if (!len) {
    219:     is_max = 0;
    220:   } else {
    221:     len += 1 + is_max; /* max length of data1 for one processor */
    222:   }

    225:   PetscMalloc1(size*len+1,&data1);
    226:   PetscMalloc1(size,&data1_start);
    227:   for (i=0; i<size; i++) data1_start[i] = data1 + i*len;

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

    231:   /* gather c->garray from all processors */
    232:   ISCreateGeneral(comm,Bnbs,c->garray,PETSC_COPY_VALUES,&garray_local);
    233:   ISAllGather(garray_local, &garray_gl);
    234:   ISDestroy(&garray_local);
    235:   MPI_Allgather(&Bnbs,1,MPIU_INT,Bowners+1,1,MPIU_INT,comm);

    237:   Bowners[0] = 0;
    238:   for (i=0; i<size; i++) Bowners[i+1] += Bowners[i];

    240:   if (is_max) {
    241:     /* hash table ctable which maps c->row to proc_id) */
    242:     PetscMalloc1(Mbs,&ctable);
    243:     for (proc_id=0,j=0; proc_id<size; proc_id++) {
    244:       for (; j<C->rmap->range[proc_id+1]/bs; j++) ctable[j] = proc_id;
    245:     }

    247:     /* hash tables marking c->garray */
    248:     ISGetIndices(garray_gl,&idx_i);
    249:     for (i=0; i<size; i++) {
    250:       table_i = table[i];
    251:       PetscBTMemzero(Mbs,table_i);
    252:       for (j = Bowners[i]; j<Bowners[i+1]; j++) { /* go through B cols of proc[i]*/
    253:         PetscBTSet(table_i,idx_i[j]);
    254:       }
    255:     }
    256:     ISRestoreIndices(garray_gl,&idx_i);
    257:   }  /* if (is_max) */
    258:   ISDestroy(&garray_gl);

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

    263:   /* header of data1 */
    264:   for (proc_id=0; proc_id<size; proc_id++) {
    265:     iwork[proc_id]        = 0;
    266:     *data1_start[proc_id] = is_max;
    267:     data1_start[proc_id]++;
    268:     for (j=0; j<is_max; j++) {
    269:       if (proc_id == rank) {
    270:         *data1_start[proc_id] = n[j];
    271:       } else {
    272:         *data1_start[proc_id] = 0;
    273:       }
    274:       data1_start[proc_id]++;
    275:     }
    276:   }

    278:   for (i=0; i<is_max; i++) {
    279:     ISGetIndices(is[i],&idx_i);
    280:     for (j=0; j<n[i]; j++) {
    281:       idx                = idx_i[j];
    282:       *data1_start[rank] = idx; data1_start[rank]++; /* for local proccessing */
    283:       proc_end           = ctable[idx];
    284:       for (proc_id=0; proc_id<=proc_end; proc_id++) {  /* for others to process */
    285:         if (proc_id == rank) continue; /* done before this loop */
    286:         if (proc_id < proc_end && !PetscBTLookup(table[proc_id],idx)) continue; /* no need for sending idx to [proc_id] */
    287:         *data1_start[proc_id] = idx; data1_start[proc_id]++;
    288:         len_s[proc_id]++;
    289:       }
    290:     }
    291:     /* update header data */
    292:     for (proc_id=0; proc_id<size; proc_id++) {
    293:       if (proc_id== rank) continue;
    294:       *(data1 + proc_id*len + 1 + i) = len_s[proc_id] - iwork[proc_id];
    295:       iwork[proc_id]                 = len_s[proc_id];
    296:     }
    297:     ISRestoreIndices(is[i],&idx_i);
    298:   }

    300:   nrqs = 0; nrqr = 0;
    301:   for (i=0; i<size; i++) {
    302:     data1_start[i] = data1 + i*len;
    303:     if (len_s[i]) {
    304:       nrqs++;
    305:       len_s[i] += 1 + is_max; /* add no. of header msg */
    306:     }
    307:   }

    309:   for (i=0; i<is_max; i++) {
    310:     ISDestroy(&is[i]);
    311:   }
    312:   PetscFree(n);
    313:   PetscFree(ctable);

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

    319:   /*  Now  post the sends */
    320:   PetscMalloc2(size,&s_waits1,size,&s_waits2);
    321:   k    = 0;
    322:   for (proc_id=0; proc_id<size; proc_id++) {  /* send data1 to processor [proc_id] */
    323:     if (len_s[proc_id]) {
    324:       MPI_Isend(data1_start[proc_id],len_s[proc_id],MPIU_INT,proc_id,tag1,comm,s_waits1+k);
    325:       k++;
    326:     }
    327:   }

    329:   /* 2. Receive other's is[] and process. Then send back */
    330:   /*-----------------------------------------------------*/
    331:   len = 0;
    332:   for (i=0; i<nrqr; i++) {
    333:     if (len_r1[i] > len) len = len_r1[i];
    334:   }
    335:   PetscFree(len_r1);
    336:   PetscFree(id_r1);

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

    340:   PetscMalloc1(len+1,&odata1);
    341:   PetscMalloc1(size,&odata2_ptr);
    342:   PetscBTCreate(Mbs,&otable);

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

    349:   odata2_ptr[nodata2] = odata2;

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

    353:   k = 0;
    354:   while (k < nrqr) {
    355:     /* Receive messages */
    356:     MPI_Iprobe(MPI_ANY_SOURCE,tag1,comm,&flag,&r_status);
    357:     if (flag) {
    358:       MPI_Get_count(&r_status,MPIU_INT,&len);
    359:       proc_id = r_status.MPI_SOURCE;
    360:       MPI_Irecv(odata1,len,MPIU_INT,proc_id,r_status.MPI_TAG,comm,&r_req);
    361:       MPI_Wait(&r_req,&r_status);

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

    368:         odata2_ptr[++nodata2] = odata2;

    370:         len_unused = len_est;
    371:       }

    373:       MatIncreaseOverlap_MPISBAIJ_Local(C,odata1,OTHER,odata2,&otable);
    374:       len  = 1 + odata2[0];
    375:       for (i=0; i<odata2[0]; i++) len += odata2[1 + i];

    377:       /* Send messages back */
    378:       MPI_Isend(odata2,len,MPIU_INT,proc_id,tag2,comm,s_waits2+k);
    379:       k++;
    380:       odata2        += len;
    381:       len_unused    -= len;
    382:       len_s[proc_id] = len; /* num of messages sending back to [proc_id] by this proc */
    383:     }
    384:   }
    385:   PetscFree(odata1);
    386:   PetscBTDestroy(&otable);

    388:   /* 3. Do local work on this processor's is[] */
    389:   /*-------------------------------------------*/
    390:   /* make sure there is enough unused space in odata2(=data) array */
    391:   len_max = is_max*(Mbs+1); /* max space storing all is[] for this processor */
    392:   if (len_unused < len_max) { /* allocate more space for odata2 */
    393:     PetscMalloc1(len_est+1,&odata2);

    395:     odata2_ptr[++nodata2] = odata2;
    396:   }

    398:   data = odata2;
    399:   MatIncreaseOverlap_MPISBAIJ_Local(C,data1_start[rank],MINE,data,table);
    400:   PetscFree(data1_start);

    402:   /* 4. Receive work done on other processors, then merge */
    403:   /*------------------------------------------------------*/
    404:   /* get max number of messages that this processor expects to recv */
    405:   MPIU_Allreduce(len_s,iwork,size,MPI_INT,MPI_MAX,comm);
    406:   PetscMalloc1(iwork[rank]+1,&data2);
    407:   PetscFree4(len_s,btable,iwork,Bowners);

    409:   k = 0;
    410:   while (k < nrqs) {
    411:     /* Receive messages */
    412:     MPI_Iprobe(MPI_ANY_SOURCE,tag2,comm,&flag,&r_status);
    413:     if (flag) {
    414:       MPI_Get_count(&r_status,MPIU_INT,&len);

    416:       proc_id = r_status.MPI_SOURCE;

    418:       MPI_Irecv(data2,len,MPIU_INT,proc_id,r_status.MPI_TAG,comm,&r_req);
    419:       MPI_Wait(&r_req,&r_status);
    420:       if (len > 1+is_max) { /* Add data2 into data */
    421:         data2_i = data2 + 1 + is_max;
    422:         for (i=0; i<is_max; i++) {
    423:           table_i = table[i];
    424:           data_i  = data + 1 + is_max + Mbs*i;
    425:           isz     = data[1+i];
    426:           for (j=0; j<data2[1+i]; j++) {
    427:             col = data2_i[j];
    428:             if (!PetscBTLookupSet(table_i,col)) data_i[isz++] = col;
    429:           }
    430:           data[1+i] = isz;
    431:           if (i < is_max - 1) data2_i += data2[1+i];
    432:         }
    433:       }
    434:       k++;
    435:     }
    436:   }
    437:   PetscFree(data2);
    438:   PetscFree2(table,t_p);

    440:   /* phase 1 sends are complete */
    441:   PetscMalloc1(size,&s_status);
    442:   if (nrqs) {MPI_Waitall(nrqs,s_waits1,s_status);}
    443:   PetscFree(data1);

    445:   /* phase 2 sends are complete */
    446:   if (nrqr) {MPI_Waitall(nrqr,s_waits2,s_status);}
    447:   PetscFree2(s_waits1,s_waits2);
    448:   PetscFree(s_status);

    450:   /* 5. Create new is[] */
    451:   /*--------------------*/
    452:   for (i=0; i<is_max; i++) {
    453:     data_i = data + 1 + is_max + Mbs*i;
    454:     ISCreateGeneral(PETSC_COMM_SELF,data[1+i],data_i,PETSC_COPY_VALUES,is+i);
    455:   }
    456:   for (k=0; k<=nodata2; k++) {
    457:     PetscFree(odata2_ptr[k]);
    458:   }
    459:   PetscFree(odata2_ptr);
    460:   return(0);
    461: }

    465: /*
    466:    MatIncreaseOverlap_MPISBAIJ_Local - Called by MatIncreaseOverlap, to do
    467:        the work on the local processor.

    469:      Inputs:
    470:       C      - MAT_MPISBAIJ;
    471:       data   - holds is[]. See MatIncreaseOverlap_MPISBAIJ_Once() for the format.
    472:       whose  - whose is[] to be processed,
    473:                MINE:  this processor's is[]
    474:                OTHER: other processor's is[]
    475:      Output:
    476:        nidx  - whose = MINE:
    477:                      holds input and newly found indices in the same format as data
    478:                whose = OTHER:
    479:                      only holds the newly found indices
    480:        table - table[i]: mark the indices of is[i], i=0,...,is_max. Used only in the case 'whose=MINE'.
    481: */
    482: /* Would computation be reduced by swapping the loop 'for each is' and 'for each row'? */
    483: static PetscErrorCode MatIncreaseOverlap_MPISBAIJ_Local(Mat C,PetscInt *data,PetscInt whose,PetscInt *nidx,PetscBT *table)
    484: {
    485:   Mat_MPISBAIJ   *c = (Mat_MPISBAIJ*)C->data;
    486:   Mat_SeqSBAIJ   *a = (Mat_SeqSBAIJ*)(c->A)->data;
    487:   Mat_SeqBAIJ    *b = (Mat_SeqBAIJ*)(c->B)->data;
    489:   PetscInt       row,mbs,Mbs,*nidx_i,col,col_max,isz,isz0,*ai,*aj,*bi,*bj,*garray,rstart,l;
    490:   PetscInt       a_start,a_end,b_start,b_end,i,j,k,is_max,*idx_i,n;
    491:   PetscBT        table0;  /* mark the indices of input is[] for look up */
    492:   PetscBT        table_i; /* poits to i-th table. When whose=OTHER, a single table is used for all is[] */

    495:   Mbs    = c->Mbs; mbs = a->mbs;
    496:   ai     = a->i; aj = a->j;
    497:   bi     = b->i; bj = b->j;
    498:   garray = c->garray;
    499:   rstart = c->rstartbs;
    500:   is_max = data[0];

    502:   PetscBTCreate(Mbs,&table0);

    504:   nidx[0] = is_max;
    505:   idx_i   = data + is_max + 1; /* ptr to input is[0] array */
    506:   nidx_i  = nidx + is_max + 1; /* ptr to output is[0] array */
    507:   for (i=0; i<is_max; i++) { /* for each is */
    508:     isz = 0;
    509:     n   = data[1+i]; /* size of input is[i] */

    511:     /* initialize and set table_i(mark idx and nidx) and table0(only mark idx) */
    512:     if (whose == MINE) { /* process this processor's is[] */
    513:       table_i = table[i];
    514:       nidx_i  = nidx + 1+ is_max + Mbs*i;
    515:     } else {            /* process other processor's is[] - only use one temp table */
    516:       table_i = table[0];
    517:     }
    518:     PetscBTMemzero(Mbs,table_i);
    519:     PetscBTMemzero(Mbs,table0);
    520:     if (n==0) {
    521:       nidx[1+i] = 0;  /* size of new is[i] */
    522:       continue;
    523:     }

    525:     isz0 = 0; col_max = 0;
    526:     for (j=0; j<n; j++) {
    527:       col = idx_i[j];
    528:       if (col >= Mbs) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"index col %D >= Mbs %D",col,Mbs);
    529:       if (!PetscBTLookupSet(table_i,col)) {
    530:         PetscBTSet(table0,col);
    531:         if (whose == MINE) nidx_i[isz0] = col;
    532:         if (col_max < col) col_max = col;
    533:         isz0++;
    534:       }
    535:     }

    537:     if (whose == MINE) isz = isz0;
    538:     k = 0;  /* no. of indices from input is[i] that have been examined */
    539:     for (row=0; row<mbs; row++) {
    540:       a_start = ai[row]; a_end = ai[row+1];
    541:       b_start = bi[row]; b_end = bi[row+1];
    542:       if (PetscBTLookup(table0,row+rstart)) { /* row is on input is[i]:
    543:                                                 do row search: collect all col in this row */
    544:         for (l = a_start; l<a_end ; l++) { /* Amat */
    545:           col = aj[l] + rstart;
    546:           if (!PetscBTLookupSet(table_i,col)) nidx_i[isz++] = col;
    547:         }
    548:         for (l = b_start; l<b_end ; l++) { /* Bmat */
    549:           col = garray[bj[l]];
    550:           if (!PetscBTLookupSet(table_i,col)) nidx_i[isz++] = col;
    551:         }
    552:         k++;
    553:         if (k >= isz0) break; /* for (row=0; row<mbs; row++) */
    554:       } else { /* row is not on input is[i]:
    555:                   do col serach: add row onto nidx_i if there is a col in nidx_i */
    556:         for (l = a_start; l<a_end; l++) {  /* Amat */
    557:           col = aj[l] + rstart;
    558:           if (col > col_max) break;
    559:           if (PetscBTLookup(table0,col)) {
    560:             if (!PetscBTLookupSet(table_i,row+rstart)) nidx_i[isz++] = row+rstart;
    561:             break; /* for l = start; l<end ; l++) */
    562:           }
    563:         }
    564:         for (l = b_start; l<b_end; l++) {  /* Bmat */
    565:           col = garray[bj[l]];
    566:           if (col > col_max) break;
    567:           if (PetscBTLookup(table0,col)) {
    568:             if (!PetscBTLookupSet(table_i,row+rstart)) nidx_i[isz++] = row+rstart;
    569:             break; /* for l = start; l<end ; l++) */
    570:           }
    571:         }
    572:       }
    573:     }

    575:     if (i < is_max - 1) {
    576:       idx_i  += n;   /* ptr to input is[i+1] array */
    577:       nidx_i += isz; /* ptr to output is[i+1] array */
    578:     }
    579:     nidx[1+i] = isz; /* size of new is[i] */
    580:   } /* for each is */
    581:   PetscBTDestroy(&table0);
    582:   return(0);
    583: }