Actual source code: sbaijov.c

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

     24:   PetscMalloc1(is_max,&is_new);
     25:   /* Convert the indices into block format */
     26:   ISCompressIndicesGeneral(N,C->rmap->n,bs,is_max,is,is_new);

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

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

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

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

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

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

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

     61:     for (iov=0; iov<ov; ++iov) {
     62:       /* 1) Get submats for column search */
     63:       for (i=0,pos=0; i<nstages; i++) {
     64:         if (pos+nmax <= is_max) max_no = nmax;
     65:         else if (pos == is_max) max_no = 0;
     66:         else                    max_no = is_max-pos;
     67:         c->ijonly = PETSC_TRUE; /* only matrix data structures are requested */
     68:         /* The resulting submatrices should be BAIJ, not SBAIJ, hence we change this value to trigger that */
     69:         PetscStrcpy(((PetscObject)c->A)->type_name,MATSEQBAIJ);
     70:         MatCreateSubMatrices_MPIBAIJ_local(C,max_no,is_row+pos,is_new+pos,MAT_INITIAL_MATRIX,submats+pos);
     71:         PetscStrcpy(((PetscObject)c->A)->type_name,MATSEQSBAIJ);
     72:         pos      += max_no;
     73:       }

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

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

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

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

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

    104:         /* create updated is_new */
    105:         ISCreateGeneral(PETSC_COMM_SELF,isz,nidx,PETSC_COPY_VALUES,is_new+i);
    106:       }

    108:       /* Free tmp spaces */
    109:       for (i=0; i<is_max; i++) {
    110:         MatDestroy(&submats[i]);
    111:       }
    112:     }

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

    120:   }

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

    125:   for (i=0; i<is_max; i++) ISDestroy(&is_new[i]);
    126:   PetscFree(is_new);
    127:   return 0;
    128: }

    130: typedef enum {MINE,OTHER} WhoseOwner;
    131: /*  data1, odata1 and odata2 are packed in the format (for communication):
    132:        data[0]          = is_max, no of is
    133:        data[1]          = size of is[0]
    134:         ...
    135:        data[is_max]     = size of is[is_max-1]
    136:        data[is_max + 1] = data(is[0])
    137:         ...
    138:        data[is_max+1+sum(size of is[k]), k=0,...,i-1] = data(is[i])
    139:         ...
    140:    data2 is packed in the format (for creating output is[]):
    141:        data[0]          = is_max, no of is
    142:        data[1]          = size of is[0]
    143:         ...
    144:        data[is_max]     = size of is[is_max-1]
    145:        data[is_max + 1] = data(is[0])
    146:         ...
    147:        data[is_max + 1 + Mbs*i) = data(is[i])
    148:         ...
    149: */
    150: static PetscErrorCode MatIncreaseOverlap_MPISBAIJ_Once(Mat C,PetscInt is_max,IS is[])
    151: {
    152:   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=NULL,*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;

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

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

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

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

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

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

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

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

    217:   Bowners[0] = 0;
    218:   for (i=0; i<size; i++) Bowners[i+1] += Bowners[i];

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

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

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

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

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

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

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

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

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

    309:   /* 2. Receive other's is[] and process. Then send back */
    310:   /*-----------------------------------------------------*/
    311:   len = 0;
    312:   for (i=0; i<nrqr; i++) {
    313:     if (len_r1[i] > len) len = len_r1[i];
    314:   }
    315:   PetscFree(len_r1);
    316:   PetscFree(id_r1);

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

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

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

    329:   odata2_ptr[nodata2] = odata2;

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

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

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

    348:         odata2_ptr[++nodata2] = odata2;

    350:         len_unused = len_est;
    351:       }

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

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

    368:   /* 3. Do local work on this processor's is[] */
    369:   /*-------------------------------------------*/
    370:   /* make sure there is enough unused space in odata2(=data) array */
    371:   len_max = is_max*(Mbs+1); /* max space storing all is[] for this processor */
    372:   if (len_unused < len_max) { /* allocate more space for odata2 */
    373:     PetscMalloc1(len_est+1,&odata2);

    375:     odata2_ptr[++nodata2] = odata2;
    376:   }

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

    382:   /* 4. Receive work done on other processors, then merge */
    383:   /*------------------------------------------------------*/
    384:   /* get max number of messages that this processor expects to recv */
    385:   MPIU_Allreduce(len_s,iwork,size,MPI_INT,MPI_MAX,comm);
    386:   PetscMalloc1(iwork[rank]+1,&data2);
    387:   PetscFree4(len_s,btable,iwork,Bowners);

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

    396:       proc_id = r_status.MPI_SOURCE;

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

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

    425:   /* phase 2 sends are complete */
    426:   if (nrqr) MPI_Waitall(nrqr,s_waits2,s_status);
    427:   PetscFree2(s_waits1,s_waits2);
    428:   PetscFree(s_status);

    430:   /* 5. Create new is[] */
    431:   /*--------------------*/
    432:   for (i=0; i<is_max; i++) {
    433:     data_i = data + 1 + is_max + Mbs*i;
    434:     ISCreateGeneral(PETSC_COMM_SELF,data[1+i],data_i,PETSC_COPY_VALUES,is+i);
    435:   }
    436:   for (k=0; k<=nodata2; k++) {
    437:     PetscFree(odata2_ptr[k]);
    438:   }
    439:   PetscFree(odata2_ptr);
    440:   return 0;
    441: }

    443: /*
    444:    MatIncreaseOverlap_MPISBAIJ_Local - Called by MatIncreaseOverlap, to do
    445:        the work on the local processor.

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

    471:   Mbs    = c->Mbs; mbs = a->mbs;
    472:   ai     = a->i; aj = a->j;
    473:   bi     = b->i; bj = b->j;
    474:   garray = c->garray;
    475:   rstart = c->rstartbs;
    476:   is_max = data[0];

    478:   PetscBTCreate(Mbs,&table0);

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

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

    501:     isz0 = 0; col_max = 0;
    502:     for (j=0; j<n; j++) {
    503:       col = idx_i[j];
    505:       if (!PetscBTLookupSet(table_i,col)) {
    506:         PetscBTSet(table0,col);
    507:         if (whose == MINE) nidx_i[isz0] = col;
    508:         if (col_max < col) col_max = col;
    509:         isz0++;
    510:       }
    511:     }

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

    551:     if (i < is_max - 1) {
    552:       idx_i  += n;   /* ptr to input is[i+1] array */
    553:       nidx_i += isz; /* ptr to output is[i+1] array */
    554:     }
    555:     nidx[1+i] = isz; /* size of new is[i] */
    556:   } /* for each is */
    557:   PetscBTDestroy(&table0);
    558:   return 0;
    559: }