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

      2: /*
      3:     The memory scalable AO application ordering routines. These store the
      4:   orderings on each processor for that processor's range of values
      5: */

      7:  #include <../src/vec/is/ao/aoimpl.h>

      9: typedef struct {
     10:   PetscInt    *app_loc;    /* app_loc[i] is the partner for the ith local PETSc slot */
     11:   PetscInt    *petsc_loc;  /* petsc_loc[j] is the partner for the jth local app slot */
     12:   PetscLayout map;         /* determines the local sizes of ao */
     13: } AO_MemoryScalable;

     15: /*
     16:        All processors ship the data to process 0 to be printed; note that this is not scalable because
     17:        process 0 allocates space for all the orderings entry across all the processes
     18: */
     19: PetscErrorCode AOView_MemoryScalable(AO ao,PetscViewer viewer)
     20: {
     21:   PetscErrorCode    ierr;
     22:   PetscMPIInt       rank,size;
     23:   AO_MemoryScalable *aomems = (AO_MemoryScalable*)ao->data;
     24:   PetscBool         iascii;
     25:   PetscMPIInt       tag_app,tag_petsc;
     26:   PetscLayout       map = aomems->map;
     27:   PetscInt          *app,*app_loc,*petsc,*petsc_loc,len,i,j;
     28:   MPI_Status        status;

     31:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
     32:   if (!iascii) SETERRQ1(PetscObjectComm((PetscObject)viewer),PETSC_ERR_SUP,"Viewer type %s not supported for AO MemoryScalable",((PetscObject)viewer)->type_name);

     34:   MPI_Comm_rank(PetscObjectComm((PetscObject)ao),&rank);
     35:   MPI_Comm_size(PetscObjectComm((PetscObject)ao),&size);

     37:   PetscObjectGetNewTag((PetscObject)ao,&tag_app);
     38:   PetscObjectGetNewTag((PetscObject)ao,&tag_petsc);

     40:   if (!rank) {
     41:     PetscViewerASCIIPrintf(viewer,"Number of elements in ordering %D\n",ao->N);
     42:     PetscViewerASCIIPrintf(viewer,  "PETSc->App  App->PETSc\n");

     44:     PetscMalloc2(map->N,&app,map->N,&petsc);
     45:     len  = map->n;
     46:     /* print local AO */
     47:     PetscViewerASCIIPrintf(viewer,"Process [%d]\n",rank);
     48:     for (i=0; i<len; i++) {
     49:       PetscViewerASCIIPrintf(viewer,"%3D  %3D    %3D  %3D\n",i,aomems->app_loc[i],i,aomems->petsc_loc[i]);
     50:     }

     52:     /* recv and print off-processor's AO */
     53:     for (i=1; i<size; i++) {
     54:       len       = map->range[i+1] - map->range[i];
     55:       app_loc   = app  + map->range[i];
     56:       petsc_loc = petsc+ map->range[i];
     57:       MPI_Recv(app_loc,(PetscMPIInt)len,MPIU_INT,i,tag_app,PetscObjectComm((PetscObject)ao),&status);
     58:       MPI_Recv(petsc_loc,(PetscMPIInt)len,MPIU_INT,i,tag_petsc,PetscObjectComm((PetscObject)ao),&status);
     59:       PetscViewerASCIIPrintf(viewer,"Process [%D]\n",i);
     60:       for (j=0; j<len; j++) {
     61:         PetscViewerASCIIPrintf(viewer,"%3D  %3D    %3D  %3D\n",map->range[i]+j,app_loc[j],map->range[i]+j,petsc_loc[j]);
     62:       }
     63:     }
     64:     PetscFree2(app,petsc);

     66:   } else {
     67:     /* send values */
     68:     MPI_Send((void*)aomems->app_loc,map->n,MPIU_INT,0,tag_app,PetscObjectComm((PetscObject)ao));
     69:     MPI_Send((void*)aomems->petsc_loc,map->n,MPIU_INT,0,tag_petsc,PetscObjectComm((PetscObject)ao));
     70:   }
     71:   PetscViewerFlush(viewer);
     72:   return(0);
     73: }

     75: PetscErrorCode AODestroy_MemoryScalable(AO ao)
     76: {
     77:   AO_MemoryScalable *aomems = (AO_MemoryScalable*)ao->data;
     78:   PetscErrorCode    ierr;

     81:   PetscFree2(aomems->app_loc,aomems->petsc_loc);
     82:   PetscLayoutDestroy(&aomems->map);
     83:   PetscFree(aomems);
     84:   return(0);
     85: }

     87: /*
     88:    Input Parameters:
     89: +   ao - the application ordering context
     90: .   n  - the number of integers in ia[]
     91: .   ia - the integers; these are replaced with their mapped value
     92: -   maploc - app_loc or petsc_loc in struct "AO_MemoryScalable"

     94:    Output Parameter:
     95: .   ia - the mapped interges
     96:  */
     97: PetscErrorCode AOMap_MemoryScalable_private(AO ao,PetscInt n,PetscInt *ia,const PetscInt *maploc)
     98: {
     99:   PetscErrorCode    ierr;
    100:   AO_MemoryScalable *aomems = (AO_MemoryScalable*)ao->data;
    101:   MPI_Comm          comm;
    102:   PetscMPIInt       rank,size,tag1,tag2;
    103:   PetscInt          *owner,*start,*sizes,nsends,nreceives;
    104:   PetscInt          nmax,count,*sindices,*rindices,i,j,idx,lastidx,*sindices2,*rindices2;
    105:   const PetscInt    *owners = aomems->map->range;
    106:   MPI_Request       *send_waits,*recv_waits,*send_waits2,*recv_waits2;
    107:   MPI_Status        recv_status;
    108:   PetscMPIInt       nindices,source,widx;
    109:   PetscInt          *rbuf,*sbuf;
    110:   MPI_Status        *send_status,*send_status2;

    113:   PetscObjectGetComm((PetscObject)ao,&comm);
    114:   MPI_Comm_rank(comm,&rank);
    115:   MPI_Comm_size(comm,&size);

    117:   /*  first count number of contributors to each processor */
    118:   PetscMalloc2(2*size,&sizes,size,&start);
    119:   PetscMemzero(sizes,2*size*sizeof(PetscInt));
    120:   PetscCalloc1(n,&owner);

    122:   j       = 0;
    123:   lastidx = -1;
    124:   for (i=0; i<n; i++) {
    125:     if (ia[i] < 0) owner[i] = -1; /* mark negative entries (which are not to be mapped) with a special negative value */
    126:     if (ia[i] >= ao->N) owner[i] = -2; /* mark out of range entries with special negative value */
    127:     else {
    128:       /* if indices are NOT locally sorted, need to start search at the beginning */
    129:       if (lastidx > (idx = ia[i])) j = 0;
    130:       lastidx = idx;
    131:       for (; j<size; j++) {
    132:         if (idx >= owners[j] && idx < owners[j+1]) {
    133:           sizes[2*j]++;     /* num of indices to be sent */
    134:           sizes[2*j+1] = 1; /* send to proc[j] */
    135:           owner[i]     = j;
    136:           break;
    137:         }
    138:       }
    139:     }
    140:   }
    141:   sizes[2*rank]=sizes[2*rank+1]=0; /* do not receive from self! */
    142:   nsends        = 0;
    143:   for (i=0; i<size; i++) nsends += sizes[2*i+1];

    145:   /* inform other processors of number of messages and max length*/
    146:   PetscMaxSum(comm,sizes,&nmax,&nreceives);

    148:   /* allocate arrays */
    149:   PetscObjectGetNewTag((PetscObject)ao,&tag1);
    150:   PetscObjectGetNewTag((PetscObject)ao,&tag2);

    152:   PetscMalloc2(nreceives*nmax,&rindices,nreceives,&recv_waits);
    153:   PetscMalloc2(nsends*nmax,&rindices2,nsends,&recv_waits2);

    155:   PetscMalloc3(n,&sindices,nsends,&send_waits,nsends,&send_status);
    156:   PetscMalloc3(n,&sindices2,nreceives,&send_waits2,nreceives,&send_status2);

    158:   /* post 1st receives: receive others requests
    159:      since we don't know how long each individual message is we
    160:      allocate the largest needed buffer for each receive. Potentially
    161:      this is a lot of wasted space.
    162:   */
    163:   for (i=0,count=0; i<nreceives; i++) {
    164:     MPI_Irecv(rindices+nmax*i,nmax,MPIU_INT,MPI_ANY_SOURCE,tag1,comm,recv_waits+count++);
    165:   }

    167:   /* do 1st sends:
    168:       1) starts[i] gives the starting index in svalues for stuff going to
    169:          the ith processor
    170:   */
    171:   start[0] = 0;
    172:   for (i=1; i<size; i++) start[i] = start[i-1] + sizes[2*i-2];
    173:   for (i=0; i<n; i++) {
    174:     j = owner[i];
    175:     if (j == -1) continue; /* do not remap negative entries in ia[] */
    176:     else if (j == -2) { /* out of range entries get mapped to -1 */
    177:       ia[i] = -1;
    178:       continue;
    179:     } else if (j != rank) {
    180:       sindices[start[j]++]  = ia[i];
    181:     } else { /* compute my own map */
    182:       ia[i] = maploc[ia[i]-owners[rank]];
    183:     }
    184:   }

    186:   start[0] = 0;
    187:   for (i=1; i<size; i++) start[i] = start[i-1] + sizes[2*i-2];
    188:   for (i=0,count=0; i<size; i++) {
    189:     if (sizes[2*i+1]) {
    190:       /* send my request to others */
    191:       MPI_Isend(sindices+start[i],sizes[2*i],MPIU_INT,i,tag1,comm,send_waits+count);
    192:       /* post receive for the answer of my request */
    193:       MPI_Irecv(sindices2+start[i],sizes[2*i],MPIU_INT,i,tag2,comm,recv_waits2+count);
    194:       count++;
    195:     }
    196:   }
    197:   if (nsends != count) SETERRQ2(comm,PETSC_ERR_SUP,"nsends %d != count %d",nsends,count);

    199:   /* wait on 1st sends */
    200:   if (nsends) {
    201:     MPI_Waitall(nsends,send_waits,send_status);
    202:   }

    204:   /* 1st recvs: other's requests */
    205:   for (j=0; j< nreceives; j++) {
    206:     MPI_Waitany(nreceives,recv_waits,&widx,&recv_status); /* idx: index of handle for operation that completed */
    207:     MPI_Get_count(&recv_status,MPIU_INT,&nindices);
    208:     rbuf   = rindices+nmax*widx; /* global index */
    209:     source = recv_status.MPI_SOURCE;

    211:     /* compute mapping */
    212:     sbuf = rbuf;
    213:     for (i=0; i<nindices; i++) sbuf[i] = maploc[rbuf[i]-owners[rank]];

    215:     /* send mapping back to the sender */
    216:     MPI_Isend(sbuf,nindices,MPIU_INT,source,tag2,comm,send_waits2+widx);
    217:   }

    219:   /* wait on 2nd sends */
    220:   if (nreceives) {
    221:     MPI_Waitall(nreceives,send_waits2,send_status2);
    222:   }

    224:   /* 2nd recvs: for the answer of my request */
    225:   for (j=0; j< nsends; j++) {
    226:     MPI_Waitany(nsends,recv_waits2,&widx,&recv_status);
    227:     MPI_Get_count(&recv_status,MPIU_INT,&nindices);
    228:     source = recv_status.MPI_SOURCE;
    229:     /* pack output ia[] */
    230:     rbuf  = sindices2+start[source];
    231:     count = 0;
    232:     for (i=0; i<n; i++) {
    233:       if (source == owner[i]) ia[i] = rbuf[count++];
    234:     }
    235:   }

    237:   /* free arrays */
    238:   PetscFree2(sizes,start);
    239:   PetscFree(owner);
    240:   PetscFree2(rindices,recv_waits);
    241:   PetscFree2(rindices2,recv_waits2);
    242:   PetscFree3(sindices,send_waits,send_status);
    243:   PetscFree3(sindices2,send_waits2,send_status2);
    244:   return(0);
    245: }

    247: PetscErrorCode AOPetscToApplication_MemoryScalable(AO ao,PetscInt n,PetscInt *ia)
    248: {
    249:   PetscErrorCode    ierr;
    250:   AO_MemoryScalable *aomems  = (AO_MemoryScalable*)ao->data;
    251:   PetscInt          *app_loc = aomems->app_loc;

    254:   AOMap_MemoryScalable_private(ao,n,ia,app_loc);
    255:   return(0);
    256: }

    258: PetscErrorCode AOApplicationToPetsc_MemoryScalable(AO ao,PetscInt n,PetscInt *ia)
    259: {
    260:   PetscErrorCode    ierr;
    261:   AO_MemoryScalable *aomems    = (AO_MemoryScalable*)ao->data;
    262:   PetscInt          *petsc_loc = aomems->petsc_loc;

    265:   AOMap_MemoryScalable_private(ao,n,ia,petsc_loc);
    266:   return(0);
    267: }

    269: static struct _AOOps AOOps_MemoryScalable = {
    270:   AOView_MemoryScalable,
    271:   AODestroy_MemoryScalable,
    272:   AOPetscToApplication_MemoryScalable,
    273:   AOApplicationToPetsc_MemoryScalable,
    274:   0,
    275:   0,
    276:   0,
    277:   0
    278: };

    280: PetscErrorCode  AOCreateMemoryScalable_private(MPI_Comm comm,PetscInt napp,const PetscInt from_array[],const PetscInt to_array[],AO ao, PetscInt *aomap_loc)
    281: {
    282:   PetscErrorCode    ierr;
    283:   AO_MemoryScalable *aomems = (AO_MemoryScalable*)ao->data;
    284:   PetscLayout       map     = aomems->map;
    285:   PetscInt          n_local = map->n,i,j;
    286:   PetscMPIInt       rank,size,tag;
    287:   PetscInt          *owner,*start,*sizes,nsends,nreceives;
    288:   PetscInt          nmax,count,*sindices,*rindices,idx,lastidx;
    289:   PetscInt          *owners = aomems->map->range;
    290:   MPI_Request       *send_waits,*recv_waits;
    291:   MPI_Status        recv_status;
    292:   PetscMPIInt       nindices,widx;
    293:   PetscInt          *rbuf;
    294:   PetscInt          n=napp,ip,ia;
    295:   MPI_Status        *send_status;

    298:   PetscMemzero(aomap_loc,n_local*sizeof(PetscInt));

    300:   MPI_Comm_rank(comm,&rank);
    301:   MPI_Comm_size(comm,&size);

    303:   /*  first count number of contributors (of from_array[]) to each processor */
    304:   PetscCalloc1(2*size,&sizes);
    305:   PetscMalloc1(n,&owner);

    307:   j       = 0;
    308:   lastidx = -1;
    309:   for (i=0; i<n; i++) {
    310:     /* if indices are NOT locally sorted, need to start search at the beginning */
    311:     if (lastidx > (idx = from_array[i])) j = 0;
    312:     lastidx = idx;
    313:     for (; j<size; j++) {
    314:       if (idx >= owners[j] && idx < owners[j+1]) {
    315:         sizes[2*j]  += 2; /* num of indices to be sent - in pairs (ip,ia) */
    316:         sizes[2*j+1] = 1; /* send to proc[j] */
    317:         owner[i]      = j;
    318:         break;
    319:       }
    320:     }
    321:   }
    322:   sizes[2*rank]=sizes[2*rank+1]=0; /* do not receive from self! */
    323:   nsends        = 0;
    324:   for (i=0; i<size; i++) nsends += sizes[2*i+1];

    326:   /* inform other processors of number of messages and max length*/
    327:   PetscMaxSum(comm,sizes,&nmax,&nreceives);

    329:   /* allocate arrays */
    330:   PetscObjectGetNewTag((PetscObject)ao,&tag);
    331:   PetscMalloc2(nreceives*nmax,&rindices,nreceives,&recv_waits);
    332:   PetscMalloc3(2*n,&sindices,nsends,&send_waits,nsends,&send_status);
    333:   PetscMalloc1(size,&start);

    335:   /* post receives: */
    336:   for (i=0; i<nreceives; i++) {
    337:     MPI_Irecv(rindices+nmax*i,nmax,MPIU_INT,MPI_ANY_SOURCE,tag,comm,recv_waits+i);
    338:   }

    340:   /* do sends:
    341:       1) starts[i] gives the starting index in svalues for stuff going to
    342:          the ith processor
    343:   */
    344:   start[0] = 0;
    345:   for (i=1; i<size; i++) start[i] = start[i-1] + sizes[2*i-2];
    346:   for (i=0; i<n; i++) {
    347:     j = owner[i];
    348:     if (j != rank) {
    349:       ip                   = from_array[i];
    350:       ia                   = to_array[i];
    351:       sindices[start[j]++] = ip;
    352:       sindices[start[j]++] = ia;
    353:     } else { /* compute my own map */
    354:       ip            = from_array[i] - owners[rank];
    355:       ia            = to_array[i];
    356:       aomap_loc[ip] = ia;
    357:     }
    358:   }

    360:   start[0] = 0;
    361:   for (i=1; i<size; i++) start[i] = start[i-1] + sizes[2*i-2];
    362:   for (i=0,count=0; i<size; i++) {
    363:     if (sizes[2*i+1]) {
    364:       MPI_Isend(sindices+start[i],sizes[2*i],MPIU_INT,i,tag,comm,send_waits+count);
    365:       count++;
    366:     }
    367:   }
    368:   if (nsends != count) SETERRQ2(comm,PETSC_ERR_SUP,"nsends %d != count %d",nsends,count);

    370:   /* wait on sends */
    371:   if (nsends) {
    372:     MPI_Waitall(nsends,send_waits,send_status);
    373:   }

    375:   /* recvs */
    376:   count=0;
    377:   for (j= nreceives; j>0; j--) {
    378:     MPI_Waitany(nreceives,recv_waits,&widx,&recv_status);
    379:     MPI_Get_count(&recv_status,MPIU_INT,&nindices);
    380:     rbuf = rindices+nmax*widx; /* global index */

    382:     /* compute local mapping */
    383:     for (i=0; i<nindices; i+=2) { /* pack aomap_loc */
    384:       ip            = rbuf[i] - owners[rank]; /* local index */
    385:       ia            = rbuf[i+1];
    386:       aomap_loc[ip] = ia;
    387:     }
    388:     count++;
    389:   }

    391:   PetscFree(start);
    392:   PetscFree3(sindices,send_waits,send_status);
    393:   PetscFree2(rindices,recv_waits);
    394:   PetscFree(owner);
    395:   PetscFree(sizes);
    396:   return(0);
    397: }

    399: PETSC_EXTERN PetscErrorCode AOCreate_MemoryScalable(AO ao)
    400: {
    401:   PetscErrorCode    ierr;
    402:   IS                isapp=ao->isapp,ispetsc=ao->ispetsc;
    403:   const PetscInt    *mypetsc,*myapp;
    404:   PetscInt          napp,n_local,N,i,start,*petsc,*lens,*disp;
    405:   MPI_Comm          comm;
    406:   AO_MemoryScalable *aomems;
    407:   PetscLayout       map;
    408:   PetscMPIInt       size,rank;

    411:   if (!isapp) SETERRQ(PetscObjectComm((PetscObject)ao),PETSC_ERR_ARG_WRONGSTATE,"AOSetIS() must be called before AOSetType()");
    412:   /* create special struct aomems */
    413:   PetscNewLog(ao,&aomems);
    414:   ao->data = (void*) aomems;
    415:   PetscMemcpy(ao->ops,&AOOps_MemoryScalable,sizeof(struct _AOOps));
    416:   PetscObjectChangeTypeName((PetscObject)ao,AOMEMORYSCALABLE);

    418:   /* transmit all local lengths of isapp to all processors */
    419:   PetscObjectGetComm((PetscObject)isapp,&comm);
    420:   MPI_Comm_size(comm, &size);
    421:   MPI_Comm_rank(comm, &rank);
    422:   PetscMalloc2(size,&lens,size,&disp);
    423:   ISGetLocalSize(isapp,&napp);
    424:   MPI_Allgather(&napp, 1, MPIU_INT, lens, 1, MPIU_INT, comm);

    426:   N = 0;
    427:   for (i = 0; i < size; i++) {
    428:     disp[i] = N;
    429:     N      += lens[i];
    430:   }

    432:   /* If ispetsc is 0 then use "natural" numbering */
    433:   if (napp) {
    434:     if (!ispetsc) {
    435:       start = disp[rank];
    436:       PetscMalloc1(napp+1, &petsc);
    437:       for (i=0; i<napp; i++) petsc[i] = start + i;
    438:     } else {
    439:       ISGetIndices(ispetsc,&mypetsc);
    440:       petsc = (PetscInt*)mypetsc;
    441:     }
    442:   } else {
    443:     petsc = NULL;
    444:   }

    446:   /* create a map with global size N - used to determine the local sizes of ao - shall we use local napp instead of N? */
    447:   PetscLayoutCreate(comm,&map);
    448:   map->bs = 1;
    449:   map->N  = N;
    450:   PetscLayoutSetUp(map);

    452:   ao->N       = N;
    453:   ao->n       = map->n;
    454:   aomems->map = map;

    456:   /* create distributed indices app_loc: petsc->app and petsc_loc: app->petsc */
    457:   n_local = map->n;
    458:   PetscMalloc2(n_local, &aomems->app_loc,n_local,&aomems->petsc_loc);
    459:   PetscLogObjectMemory((PetscObject)ao,2*n_local*sizeof(PetscInt));
    460:   PetscMemzero(aomems->app_loc,n_local*sizeof(PetscInt));
    461:   PetscMemzero(aomems->petsc_loc,n_local*sizeof(PetscInt));
    462:   ISGetIndices(isapp,&myapp);

    464:   AOCreateMemoryScalable_private(comm,napp,petsc,myapp,ao,aomems->app_loc);
    465:   AOCreateMemoryScalable_private(comm,napp,myapp,petsc,ao,aomems->petsc_loc);

    467:   ISRestoreIndices(isapp,&myapp);
    468:   if (napp) {
    469:     if (ispetsc) {
    470:       ISRestoreIndices(ispetsc,&mypetsc);
    471:     } else {
    472:       PetscFree(petsc);
    473:     }
    474:   }
    475:   PetscFree2(lens,disp);
    476:   return(0);
    477: }

    479: /*@C
    480:    AOCreateMemoryScalable - Creates a memory scalable application ordering using two integer arrays.

    482:    Collective on MPI_Comm

    484:    Input Parameters:
    485: +  comm - MPI communicator that is to share AO
    486: .  napp - size of integer arrays
    487: .  myapp - integer array that defines an ordering
    488: -  mypetsc - integer array that defines another ordering (may be NULL to
    489:              indicate the natural ordering, that is 0,1,2,3,...)

    491:    Output Parameter:
    492: .  aoout - the new application ordering

    494:    Level: beginner

    496:     Notes:
    497:     The arrays myapp and mypetsc must contain the all the integers 0 to napp-1 with no duplicates; that is there cannot be any "holes"
    498:            in the indices. Use AOCreateMapping() or AOCreateMappingIS() if you wish to have "holes" in the indices.
    499:            Comparing with AOCreateBasic(), this routine trades memory with message communication.

    501: .keywords: AO, create

    503: .seealso: AOCreateMemoryScalableIS(), AODestroy(), AOPetscToApplication(), AOApplicationToPetsc()
    504: @*/
    505: PetscErrorCode AOCreateMemoryScalable(MPI_Comm comm,PetscInt napp,const PetscInt myapp[],const PetscInt mypetsc[],AO *aoout)
    506: {
    508:   IS             isapp,ispetsc;
    509:   const PetscInt *app=myapp,*petsc=mypetsc;

    512:   ISCreateGeneral(comm,napp,app,PETSC_USE_POINTER,&isapp);
    513:   if (mypetsc) {
    514:     ISCreateGeneral(comm,napp,petsc,PETSC_USE_POINTER,&ispetsc);
    515:   } else {
    516:     ispetsc = NULL;
    517:   }
    518:   AOCreateMemoryScalableIS(isapp,ispetsc,aoout);
    519:   ISDestroy(&isapp);
    520:   if (mypetsc) {
    521:     ISDestroy(&ispetsc);
    522:   }
    523:   return(0);
    524: }

    526: /*@C
    527:    AOCreateMemoryScalableIS - Creates a memory scalable application ordering using two index sets.

    529:    Collective on IS

    531:    Input Parameters:
    532: +  isapp - index set that defines an ordering
    533: -  ispetsc - index set that defines another ordering (may be NULL to use the
    534:              natural ordering)

    536:    Output Parameter:
    537: .  aoout - the new application ordering

    539:    Level: beginner

    541:     Notes:
    542:     The index sets isapp and ispetsc must contain the all the integers 0 to napp-1 (where napp is the length of the index sets) with no duplicates;
    543:            that is there cannot be any "holes".
    544:            Comparing with AOCreateBasicIS(), this routine trades memory with message communication.
    545: .keywords: AO, create

    547: .seealso: AOCreateMemoryScalable(),  AODestroy()
    548: @*/
    549: PetscErrorCode  AOCreateMemoryScalableIS(IS isapp,IS ispetsc,AO *aoout)
    550: {
    552:   MPI_Comm       comm;
    553:   AO             ao;

    556:   PetscObjectGetComm((PetscObject)isapp,&comm);
    557:   AOCreate(comm,&ao);
    558:   AOSetIS(ao,isapp,ispetsc);
    559:   AOSetType(ao,AOMEMORYSCALABLE);
    560:   AOViewFromOptions(ao,NULL,"-ao_view");
    561:   *aoout = ao;
    562:   return(0);
    563: }