Date: 2022-03-31T04:46:34+00:00

Actual source code: vscat.c

      1: #include "petscsf.h"
      2: #include "petscsystypes.h"
      3: #include "petscvec.h"
      4: #include <petsc/private/sfimpl.h>
      5: #include <../src/vec/is/sf/impls/basic/sfbasic.h>
      6: #include <../src/vec/is/sf/impls/basic/sfpack.h>
      7: #include <petsc/private/vecimpl.h>

      9: typedef enum {IS_INVALID, IS_GENERAL, IS_BLOCK, IS_STRIDE} ISTypeID;

     11: static inline PetscErrorCode ISGetTypeID_Private(IS is,ISTypeID *id)
     12: {
     13:   PetscBool      same;

     15:   *id  = IS_INVALID;
     16:   PetscObjectTypeCompare((PetscObject)is,ISGENERAL,&same);
     17:   if (same) {*id = IS_GENERAL; goto functionend;}
     18:   PetscObjectTypeCompare((PetscObject)is,ISBLOCK,&same);
     19:   if (same) {*id = IS_BLOCK; goto functionend;}
     20:   PetscObjectTypeCompare((PetscObject)is,ISSTRIDE,&same);
     21:   if (same) {*id = IS_STRIDE; goto functionend;}
     22: functionend:
     23:   return 0;
     24: }

     26: static PetscErrorCode VecScatterBegin_Internal(VecScatter sf,Vec x,Vec y,InsertMode addv,ScatterMode mode)
     27: {
     28:   PetscSF        wsf=NULL; /* either sf or its local part */
     29:   MPI_Op         mop=MPI_OP_NULL;
     30:   PetscMPIInt    size;
     31:   PetscMemType   xmtype=PETSC_MEMTYPE_HOST,ymtype=PETSC_MEMTYPE_HOST;

     33:   if (x != y) VecLockReadPush(x);
     34:   VecGetArrayReadAndMemType(x,&sf->vscat.xdata,&xmtype);
     35:   VecGetArrayAndMemType(y,&sf->vscat.ydata,&ymtype);
     36:   VecLockWriteSet_Private(y,PETSC_TRUE);

     38:   /* SCATTER_LOCAL indicates ignoring inter-process communication */
     39:   MPI_Comm_size(PetscObjectComm((PetscObject)sf),&size);
     40:   if ((mode & SCATTER_LOCAL) && size > 1) { /* Lazy creation of sf->vscat.lsf since SCATTER_LOCAL is uncommon */
     41:     if (!sf->vscat.lsf) PetscSFCreateLocalSF_Private(sf,&sf->vscat.lsf);
     42:     wsf = sf->vscat.lsf;
     43:   } else {
     44:     wsf = sf;
     45:   }

     47:   /* Note xdata/ydata is always recorded on sf (not lsf) above */
     48:   if (addv == INSERT_VALUES)   mop = MPI_REPLACE;
     49:   else if (addv == ADD_VALUES) mop = MPIU_SUM; /* Petsc defines its own MPI datatype and SUM operation for __float128 etc. */
     50:   else if (addv == MAX_VALUES) mop = MPIU_MAX;
     51:   else if (addv == MIN_VALUES) mop = MPIU_MIN;
     52:   else SETERRQ(PetscObjectComm((PetscObject)sf),PETSC_ERR_SUP,"Unsupported InsertMode %d in VecScatterBegin/End",addv);

     54:   if (mode & SCATTER_REVERSE) { /* REVERSE indicates leaves to root scatter. Note that x and y are swapped in input */
     55:     PetscSFReduceWithMemTypeBegin(wsf,sf->vscat.unit,xmtype,sf->vscat.xdata,ymtype,sf->vscat.ydata,mop);
     56:   } else { /* FORWARD indicates x to y scatter, where x is root and y is leaf */
     57:     PetscSFBcastWithMemTypeBegin(wsf,sf->vscat.unit,xmtype,sf->vscat.xdata,ymtype,sf->vscat.ydata,mop);
     58:   }
     59:   return 0;
     60: }

     62: static PetscErrorCode VecScatterEnd_Internal(VecScatter sf,Vec x,Vec y,InsertMode addv,ScatterMode mode)
     63: {
     64:   PetscSF        wsf=NULL;
     65:   MPI_Op         mop=MPI_OP_NULL;
     66:   PetscMPIInt    size;

     68:   /* SCATTER_LOCAL indicates ignoring inter-process communication */
     69:   MPI_Comm_size(PetscObjectComm((PetscObject)sf),&size);
     70:   wsf  = ((mode & SCATTER_LOCAL) && size > 1) ? sf->vscat.lsf : sf;

     72:   if (addv == INSERT_VALUES)   mop = MPI_REPLACE;
     73:   else if (addv == ADD_VALUES) mop = MPIU_SUM;
     74:   else if (addv == MAX_VALUES) mop = MPIU_MAX;
     75:   else if (addv == MIN_VALUES) mop = MPIU_MIN;
     76:   else SETERRQ(PetscObjectComm((PetscObject)sf),PETSC_ERR_SUP,"Unsupported InsertMode %d in VecScatterBegin/End",addv);

     78:   if (mode & SCATTER_REVERSE) { /* reverse scatter sends leaves to roots. Note that x and y are swapped in input */
     79:     PetscSFReduceEnd(wsf,sf->vscat.unit,sf->vscat.xdata,sf->vscat.ydata,mop);
     80:   } else { /* forward scatter sends roots to leaves, i.e., x to y */
     81:     PetscSFBcastEnd(wsf,sf->vscat.unit,sf->vscat.xdata,sf->vscat.ydata,mop);
     82:   }

     84:   VecRestoreArrayReadAndMemType(x,&sf->vscat.xdata);
     85:   if (x != y) VecLockReadPop(x);
     86:   VecRestoreArrayAndMemType(y,&sf->vscat.ydata);
     87:   VecLockWriteSet_Private(y,PETSC_FALSE);
     88:   return 0;
     89: }

     91: /* VecScatterRemap provides a light way to slightly modify a VecScatter. Suppose the input sf scatters
     92:    x[i] to y[j], tomap gives a plan to change vscat to scatter x[tomap[i]] to y[j]. Note that in SF,
     93:    x is roots. That means we need to change incoming stuffs such as bas->irootloc[].
     94:  */
     95: static PetscErrorCode VecScatterRemap_Internal(VecScatter sf,const PetscInt *tomap,const PetscInt *frommap)
     96: {
     97:   PetscInt       i,bs = sf->vscat.bs;
     98:   PetscMPIInt    size;
     99:   PetscBool      ident = PETSC_TRUE,isbasic,isneighbor;
    100:   PetscSFType    type;
    101:   PetscSF_Basic  *bas = NULL;

    103:   /* check if it is an identity map. If it is, do nothing */
    104:   if (tomap) {
    105:     for (i=0; i<sf->nroots*bs; i++) {if (i != tomap[i]) {ident = PETSC_FALSE; break; } }
    106:     if (ident) return 0;
    107:   }
    109:   if (!tomap) return 0;

    111:   MPI_Comm_size(PetscObjectComm((PetscObject)sf),&size);

    113:   /* Since the indices changed, we must also update the local SF. But we do not do it since
    114:      lsf is rarely used. We just destroy lsf and rebuild it on demand from updated sf.
    115:   */
    116:   if (sf->vscat.lsf) PetscSFDestroy(&sf->vscat.lsf);

    118:   PetscSFGetType(sf,&type);
    119:   PetscObjectTypeCompare((PetscObject)sf,PETSCSFBASIC,&isbasic);
    120:   PetscObjectTypeCompare((PetscObject)sf,PETSCSFNEIGHBOR,&isneighbor);

    123:   PetscSFSetUp(sf); /* to bulid sf->irootloc if SetUp is not yet called */

    125:   /* Root indices are going to be remapped. This is tricky for SF. Root indices are used in sf->rremote,
    126:     sf->remote and bas->irootloc. The latter one is cheap to remap, but the former two are not.
    127:     To remap them, we have to do a bcast from roots to leaves, to let leaves know their updated roots.
    128:     Since VecScatterRemap is supposed to be a cheap routine to adapt a vecscatter by only changing where
    129:     x[] data is taken, we do not remap sf->rremote, sf->remote. The consequence is that operations
    130:     accessing them (such as PetscSFCompose) may get stale info. Considering VecScatter does not need
    131:     that complicated SF operations, we do not remap sf->rremote, sf->remote, instead we destroy them
    132:     so that code accessing them (if any) will crash (instead of get silent errors). Note that BcastAndOp/Reduce,
    133:     which are used by VecScatter and only rely on bas->irootloc, are updated and correct.
    134:   */
    135:   sf->remote = NULL;
    136:   PetscFree(sf->remote_alloc);
    137:   /* Not easy to free sf->rremote since it was allocated with PetscMalloc4(), so just give it crazy values */
    138:   for (i=0; i<sf->roffset[sf->nranks]; i++) sf->rremote[i] = PETSC_MIN_INT;

    140:   /* Indices in tomap[] are for each indivisual vector entry. But indices in sf are for each
    141:      block in the vector. So before the remapping, we have to expand indices in sf by bs, and
    142:      after the remapping, we have to shrink them back.
    143:    */
    144:   bas = (PetscSF_Basic*)sf->data;
    145:   for (i=0; i<bas->ioffset[bas->niranks]; i++) bas->irootloc[i] = tomap[bas->irootloc[i]*bs]/bs;
    146: #if defined(PETSC_HAVE_DEVICE)
    147:   /* Free the irootloc copy on device. We allocate a new copy and get the updated value on demand. See PetscSFLinkGetRootPackOptAndIndices() */
    148:   for (i=0; i<2; i++) PetscSFFree(sf,PETSC_MEMTYPE_DEVICE,bas->irootloc_d[i]);
    149: #endif
    150:   /* Destroy and then rebuild root packing optimizations since indices are changed */
    151:   PetscSFResetPackFields(sf);
    152:   PetscSFSetUpPackFields(sf);
    153:   return 0;
    154: }

    156: /* Given a parallel VecScatter context, return number of procs and vector entries involved in remote (i.e., off-process) communication

    158:   Input Parameters:
    159: + sf   - the context (must be a parallel vecscatter)
    160: - send  - true to select the send info (i.e., todata), otherwise to select the recv info (i.e., fromdata)

    162:   Output parameters:
    163: + num_procs   - number of remote processors
    164: - num_entries - number of vector entries to send or recv

    166:   .seealso: VecScatterGetRemote_Private(), VecScatterGetRemoteOrdered_Private()

    168:   Notes:
    169:   Sometimes PETSc internally needs to use the matrix-vector-multiply vecscatter context for other purposes. The client code
    170:   usually only uses MPI_Send/Recv. This group of subroutines provides info needed for such uses.
    171:  */
    172: PetscErrorCode VecScatterGetRemoteCount_Private(VecScatter sf,PetscBool send,PetscInt *num_procs,PetscInt *num_entries)
    173: {
    174:   PetscInt          nranks,remote_start;
    175:   PetscMPIInt       rank;
    176:   const PetscInt    *offset;
    177:   const PetscMPIInt *ranks;

    179:   PetscSFSetUp(sf);
    180:   MPI_Comm_rank(PetscObjectComm((PetscObject)sf),&rank);

    182:   /* This routine is mainly used for MatMult's Mvctx. In Mvctx, we scatter an MPI vector x to a sequential vector lvec.
    183:      Remember x is roots and lvec is leaves. 'send' means roots to leaves communication. If 'send' is true, we need to
    184:      get info about which ranks this processor needs to send to. In other words, we need to call PetscSFGetLeafRanks().
    185:      If send is false, we do the opposite, calling PetscSFGetRootRanks().
    186:   */
    187:   if (send) PetscSFGetLeafRanks(sf,&nranks,&ranks,&offset,NULL);
    188:   else PetscSFGetRootRanks(sf,&nranks,&ranks,&offset,NULL,NULL);
    189:   if (nranks) {
    190:     remote_start = (rank == ranks[0])? 1 : 0;
    191:     if (num_procs)   *num_procs   = nranks - remote_start;
    192:     if (num_entries) *num_entries = offset[nranks] - offset[remote_start];
    193:   } else {
    194:     if (num_procs)   *num_procs   = 0;
    195:     if (num_entries) *num_entries = 0;
    196:   }
    197:   return 0;
    198: }

    200: /* Given a parallel VecScatter context, return a plan that represents the remote communication.
    201:    Any output parameter can be NULL.

    203:   Input Parameters:
    204: + sf   - the context
    205: - send  - true to select the send info (i.e., todata), otherwise to select the recv info (i.e., fromdata)

    207:   Output parameters:
    208: + n        - number of remote processors
    209: . starts   - starting point in indices for each proc. ATTENTION: starts[0] is not necessarily zero.
    210:              Therefore, expressions like starts[i+1]-starts[i] and indices[starts[i]+j] work as
    211:              expected for a CSR structure but buf[starts[i]+j] may be out of range if buf was allocated
    212:              with length starts[n]-starts[0]. One should use buf[starts[i]-starts[0]+j] instead.
    213: . indices  - indices of entries to send/recv
    214: . procs    - ranks of remote processors
    215: - bs       - block size

    217:   .seealso: VecScatterRestoreRemote_Private(), VecScatterGetRemoteOrdered_Private()
    218:  */
    219: PetscErrorCode VecScatterGetRemote_Private(VecScatter sf,PetscBool send,PetscInt *n,const PetscInt **starts,const PetscInt **indices,const PetscMPIInt **procs,PetscInt *bs)
    220: {
    221:   PetscInt          nranks,remote_start;
    222:   PetscMPIInt       rank;
    223:   const PetscInt    *offset,*location;
    224:   const PetscMPIInt *ranks;

    226:   PetscSFSetUp(sf);
    227:   MPI_Comm_rank(PetscObjectComm((PetscObject)sf),&rank);

    229:   if (send) PetscSFGetLeafRanks(sf,&nranks,&ranks,&offset,&location);
    230:   else PetscSFGetRootRanks(sf,&nranks,&ranks,&offset,&location,NULL);

    232:   if (nranks) {
    233:     remote_start = (rank == ranks[0])? 1 : 0;
    234:     if (n)       *n       = nranks - remote_start;
    235:     if (starts)  *starts  = &offset[remote_start];
    236:     if (indices) *indices = location; /* not &location[offset[remote_start]]. Starts[0] may point to the middle of indices[] */
    237:     if (procs)   *procs   = &ranks[remote_start];
    238:   } else {
    239:     if (n)       *n       = 0;
    240:     if (starts)  *starts  = NULL;
    241:     if (indices) *indices = NULL;
    242:     if (procs)   *procs   = NULL;
    243:   }

    245:   if (bs) *bs = 1;
    246:   return 0;
    247: }

    249: /* Given a parallel VecScatter context, return a plan that represents the remote communication. Ranks of remote
    250:    processors returned in procs must be sorted in ascending order. Any output parameter can be NULL.

    252:   Input Parameters:
    253: + sf   - the context
    254: - send  - true to select the send info (i.e., todata), otherwise to select the recv info (i.e., fromdata)

    256:   Output parameters:
    257: + n        - number of remote processors
    258: . starts   - starting point in indices for each proc. ATTENTION: starts[0] is not necessarily zero.
    259:              Therefore, expressions like starts[i+1]-starts[i] and indices[starts[i]+j] work as
    260:              expected for a CSR structure but buf[starts[i]+j] may be out of range if buf was allocated
    261:              with length starts[n]-starts[0]. One should use buf[starts[i]-starts[0]+j] instead.
    262: . indices  - indices of entries to send/recv
    263: . procs    - ranks of remote processors
    264: - bs       - block size

    266:   .seealso: VecScatterRestoreRemoteOrdered_Private(), VecScatterGetRemote_Private()

    268:   Notes:
    269:   Output parameters like starts, indices must also be adapted according to the sorted ranks.
    270:  */
    271: PetscErrorCode VecScatterGetRemoteOrdered_Private(VecScatter sf,PetscBool send,PetscInt *n,const PetscInt **starts,const PetscInt **indices,const PetscMPIInt **procs,PetscInt *bs)
    272: {
    273:   VecScatterGetRemote_Private(sf,send,n,starts,indices,procs,bs);
    274:   if (PetscUnlikelyDebug(n && procs)) {
    275:     PetscInt i;
    276:     /* from back to front to also handle cases *n=0 */
    278:   }
    279:   return 0;
    280: }

    282: /* Given a parallel VecScatter context, restore the plan returned by VecScatterGetRemote_Private. This gives a chance for
    283:    an implementation to free memory allocated in the VecScatterGetRemote_Private call.

    285:   Input Parameters:
    286: + sf   - the context
    287: - send  - true to select the send info (i.e., todata), otherwise to select the recv info (i.e., fromdata)

    289:   Output parameters:
    290: + n        - number of remote processors
    291: . starts   - starting point in indices for each proc
    292: . indices  - indices of entries to send/recv
    293: . procs    - ranks of remote processors
    294: - bs       - block size

    296:   .seealso: VecScatterGetRemote_Private()
    297:  */
    298: PetscErrorCode VecScatterRestoreRemote_Private(VecScatter sf,PetscBool send,PetscInt *n,const PetscInt **starts,const PetscInt **indices,const PetscMPIInt **procs,PetscInt *bs)
    299: {
    300:   if (starts)   *starts  = NULL;
    301:   if (indices)  *indices = NULL;
    302:   if (procs)    *procs   = NULL;
    303:   return 0;
    304: }

    306: /* Given a parallel VecScatter context, restore the plan returned by VecScatterGetRemoteOrdered_Private. This gives a chance for
    307:    an implementation to free memory allocated in the VecScatterGetRemoteOrdered_Private call.

    309:   Input Parameters:
    310: + sf   - the context
    311: - send  - true to select the send info (i.e., todata), otherwise to select the recv info (i.e., fromdata)

    313:   Output parameters:
    314: + n        - number of remote processors
    315: . starts   - starting point in indices for each proc
    316: . indices  - indices of entries to send/recv
    317: . procs    - ranks of remote processors
    318: - bs       - block size

    320:   .seealso: VecScatterGetRemoteOrdered_Private()
    321:  */
    322: PetscErrorCode VecScatterRestoreRemoteOrdered_Private(VecScatter sf,PetscBool send,PetscInt *n,const PetscInt **starts,const PetscInt **indices,const PetscMPIInt **procs,PetscInt *bs)
    323: {
    324:   VecScatterRestoreRemote_Private(sf,send,n,starts,indices,procs,bs);
    325:   return 0;
    326: }

    328: /*@
    329:    VecScatterSetUp - Sets up the VecScatter to be able to actually scatter information between vectors

    331:    Collective on VecScatter

    333:    Input Parameter:
    334: .  sf - the scatter context

    336:    Level: intermediate

    338: .seealso: VecScatterCreate(), VecScatterCopy()
    339: @*/
    340: PetscErrorCode VecScatterSetUp(VecScatter sf)
    341: {
    342:   PetscSFSetUp(sf);
    343:   return 0;
    344: }

    346: /*@C
    347:   VecScatterSetType - Builds a vector scatter, for a particular vector scatter implementation.

    349:   Collective on VecScatter

    351:   Input Parameters:
    352: + sf - The VecScatter (SF) object
    353: - type - The name of the vector scatter type

    355:   Options Database Key:
    356: . -sf_type <type> - Sets the VecScatter (SF) type

    358:   Notes:
    359:   Use VecScatterDuplicate() to form additional vectors scatter of the same type as an existing vector scatter.

    361:   Level: intermediate

    363: .seealso: VecScatterGetType(), VecScatterCreate()
    364: @*/
    365: PetscErrorCode VecScatterSetType(VecScatter sf, VecScatterType type)
    366: {
    367:   PetscSFSetType(sf,type);
    368:   return 0;
    369: }

    371: /*@C
    372:   VecScatterGetType - Gets the vector scatter type name (as a string) from the VecScatter.

    374:   Not Collective

    376:   Input Parameter:
    377: . sf  - The vector scatter (SF)

    379:   Output Parameter:
    380: . type - The vector scatter type name

    382:   Level: intermediate

    384: .seealso: VecScatterSetType(), VecScatterCreate()
    385: @*/
    386: PetscErrorCode VecScatterGetType(VecScatter sf, VecScatterType *type)
    387: {
    388:   PetscSFGetType(sf,type);
    389:   return 0;
    390: }

    392: /*@C
    393:   VecScatterRegister -  Adds a new vector scatter component implementation

    395:   Not Collective

    397:   Input Parameters:
    398: + name        - The name of a new user-defined creation routine
    399: - create_func - The creation routine itself

    401:   Level: advanced

    403: .seealso: VecRegister()
    404: @*/
    405: PetscErrorCode VecScatterRegister(const char sname[], PetscErrorCode (*function)(VecScatter))
    406: {
    407:   PetscSFRegister(sname,function);
    408:   return 0;
    409: }

    411: /* ------------------------------------------------------------------*/
    412: /*@
    413:    VecScatterGetMerged - Returns true if the scatter is completed in the VecScatterBegin()
    414:       and the VecScatterEnd() does nothing

    416:    Not Collective

    418:    Input Parameter:
    419: .   sf - scatter context created with VecScatterCreate()

    421:    Output Parameter:
    422: .   flg - PETSC_TRUE if the VecScatterBegin/End() are all done during the VecScatterBegin()

    424:    Level: developer

    426: .seealso: VecScatterCreate(), VecScatterEnd(), VecScatterBegin()
    427: @*/
    428: PetscErrorCode  VecScatterGetMerged(VecScatter sf,PetscBool *flg)
    429: {
    431:   if (flg) *flg = sf->vscat.beginandendtogether;
    432:   return 0;
    433: }
    434: /*@C
    435:    VecScatterDestroy - Destroys a scatter context created by VecScatterCreate()

    437:    Collective on VecScatter

    439:    Input Parameter:
    440: .  sf - the scatter context

    442:    Level: intermediate

    444: .seealso: VecScatterCreate(), VecScatterCopy()
    445: @*/
    446: PetscErrorCode VecScatterDestroy(VecScatter *sf)
    447: {
    448:   PetscSFDestroy(sf);
    449:   return 0;
    450: }

    452: /*@
    453:    VecScatterCopy - Makes a copy of a scatter context.

    455:    Collective on VecScatter

    457:    Input Parameter:
    458: .  sf - the scatter context

    460:    Output Parameter:
    461: .  newsf - the context copy

    463:    Level: advanced

    465: .seealso: VecScatterCreate(), VecScatterDestroy()
    466: @*/
    467: PetscErrorCode  VecScatterCopy(VecScatter sf,VecScatter *newsf)
    468: {
    470:   PetscSFDuplicate(sf,PETSCSF_DUPLICATE_GRAPH,newsf);
    471:   PetscSFSetUp(*newsf);
    472:   return 0;
    473: }

    475: /*@C
    476:    VecScatterViewFromOptions - View from Options

    478:    Collective on VecScatter

    480:    Input Parameters:
    481: +  sf - the scatter context
    482: .  obj - Optional object
    483: -  name - command line option

    485:    Level: intermediate
    486: .seealso:  VecScatter, VecScatterView, PetscObjectViewFromOptions(), VecScatterCreate()
    487: @*/
    488: PetscErrorCode  VecScatterViewFromOptions(VecScatter sf,PetscObject obj,const char name[])
    489: {
    491:   PetscObjectViewFromOptions((PetscObject)sf,obj,name);
    492:   return 0;
    493: }

    495: /* ------------------------------------------------------------------*/
    496: /*@C
    497:    VecScatterView - Views a vector scatter context.

    499:    Collective on VecScatter

    501:    Input Parameters:
    502: +  sf - the scatter context
    503: -  viewer - the viewer for displaying the context

    505:    Level: intermediate

    507: @*/
    508: PetscErrorCode  VecScatterView(VecScatter sf,PetscViewer viewer)
    509: {
    510:   PetscSFView(sf,viewer);
    511:   return 0;
    512: }

    514: /*@C
    515:    VecScatterRemap - Remaps the "from" and "to" indices in a
    516:    vector scatter context. FOR EXPERTS ONLY!

    518:    Collective on VecScatter

    520:    Input Parameters:
    521: +  sf    - vector scatter context
    522: .  tomap   - remapping plan for "to" indices (may be NULL).
    523: -  frommap - remapping plan for "from" indices (may be NULL)

    525:    Level: developer

    527:    Notes:
    528:      In the parallel case the todata contains indices from where the data is taken
    529:      (and then sent to others)! The fromdata contains indices from where the received
    530:      data is finally put locally.

    532:      In the sequential case the todata contains indices from where the data is put
    533:      and the fromdata contains indices from where the data is taken from.
    534:      This is backwards from the paralllel case!

    536: @*/
    537: PetscErrorCode  VecScatterRemap(VecScatter sf,PetscInt tomap[],PetscInt frommap[])
    538: {
    541:   VecScatterRemap_Internal(sf,tomap,frommap);
    543:   /* Mark then vector lengths as unknown because we do not know the lengths of the remapped vectors */
    544:   sf->vscat.from_n = -1;
    545:   sf->vscat.to_n   = -1;
    546:   return 0;
    547: }

    549: /*@
    550:   VecScatterSetFromOptions - Configures the vector scatter from the options database.

    552:   Collective on VecScatter

    554:   Input Parameter:
    555: . sf - The vector scatter

    557:   Notes:
    558:     To see all options, run your program with the -help option, or consult the users manual.
    559:           Must be called before VecScatterSetUp() but before the vector scatter is used.

    561:   Level: beginner

    563: .seealso: VecScatterCreate(), VecScatterDestroy(), VecScatterSetUp()
    564: @*/
    565: PetscErrorCode VecScatterSetFromOptions(VecScatter sf)
    566: {

    570:   PetscObjectOptionsBegin((PetscObject)sf);

    572:   sf->vscat.beginandendtogether = PETSC_FALSE;
    573:   PetscOptionsBool("-vecscatter_merge","Use combined (merged) vector scatter begin and end","VecScatterCreate",sf->vscat.beginandendtogether,&sf->vscat.beginandendtogether,NULL);
    574:   if (sf->vscat.beginandendtogether) PetscInfo(sf,"Using combined (merged) vector scatter begin and end\n");
    575:   PetscOptionsEnd();
    576:   return 0;
    577: }

    579: /* ---------------------------------------------------------------- */
    580: /*@
    581:    VecScatterCreate - Creates a vector scatter context.

    583:    Collective on Vec

    585:    Input Parameters:
    586: +  xin - a vector that defines the shape (parallel data layout of the vector)
    587:          of vectors from which we scatter
    588: .  yin - a vector that defines the shape (parallel data layout of the vector)
    589:          of vectors to which we scatter
    590: .  ix - the indices of xin to scatter (if NULL scatters all values)
    591: -  iy - the indices of yin to hold results (if NULL fills entire vector yin)

    593:    Output Parameter:
    594: .  newsf - location to store the new scatter (SF) context

    596:    Options Database Keys:
    597: +  -vecscatter_view         - Prints detail of communications
    598: .  -vecscatter_view ::ascii_info    - Print less details about communication
    599: -  -vecscatter_merge        - VecScatterBegin() handles all of the communication, VecScatterEnd() is a nop
    600:                               eliminates the chance for overlap of computation and communication

    602:   Level: intermediate

    604:   Notes:
    605:    If both xin and yin are parallel, their communicator must be on the same
    606:    set of processes, but their process order can be different.
    607:    In calls to VecScatter() you can use different vectors than the xin and
    608:    yin you used above; BUT they must have the same parallel data layout, for example,
    609:    they could be obtained from VecDuplicate().
    610:    A VecScatter context CANNOT be used in two or more simultaneous scatters;
    611:    that is you cannot call a second VecScatterBegin() with the same scatter
    612:    context until the VecScatterEnd() has been called on the first VecScatterBegin().
    613:    In this case a separate VecScatter is needed for each concurrent scatter.

    615:    Currently the MPI_Send() use PERSISTENT versions.
    616:    (this unfortunately requires that the same in and out arrays be used for each use, this
    617:     is why  we always need to pack the input into the work array before sending
    618:     and unpack upon receiving instead of using MPI datatypes to avoid the packing/unpacking).

    620:    Both ix and iy cannot be NULL at the same time.

    622:    Use VecScatterCreateToAll() to create a vecscatter that copies an MPI vector to sequential vectors on all MPI ranks.
    623:    Use VecScatterCreateToZero() to create a vecscatter that copies an MPI vector to a sequential vector on MPI rank 0.
    624:    These special vecscatters have better performance than general ones.

    626: .seealso: VecScatterDestroy(), VecScatterCreateToAll(), VecScatterCreateToZero(), PetscSFCreate()
    627: @*/
    628: PetscErrorCode VecScatterCreate(Vec x,IS ix,Vec y,IS iy,VecScatter *newsf)
    629: {
    630:   MPI_Comm       xcomm,ycomm,bigcomm;
    631:   Vec            xx,yy;
    632:   IS             ix_old=ix,iy_old=iy,ixx,iyy;
    633:   PetscMPIInt    xcommsize,ycommsize,rank,result;
    634:   PetscInt       i,n,N,nroots,nleaves,*ilocal,xstart,ystart,ixsize,iysize,xlen,ylen;
    635:   const PetscInt *xindices,*yindices;
    636:   PetscSFNode    *iremote;
    637:   PetscLayout    xlayout,ylayout;
    638:   ISTypeID       ixid,iyid;
    639:   PetscInt       bs,bsx,bsy,min,max,m[2],ixfirst,ixstep,iyfirst,iystep;
    640:   PetscBool      can_do_block_opt=PETSC_FALSE;
    641:   PetscSF        sf;

    646:   /* Get comm from x and y */
    647:   PetscObjectGetComm((PetscObject)x,&xcomm);
    648:   MPI_Comm_size(xcomm,&xcommsize);
    649:   PetscObjectGetComm((PetscObject)y,&ycomm);
    650:   MPI_Comm_size(ycomm,&ycommsize);
    651:   if (xcommsize > 1 && ycommsize > 1) {
    652:     MPI_Comm_compare(xcomm,ycomm,&result);
    654:   }
    655:   bs = 1; /* default, no blocking */

    657:   /*
    658:    Let P and S stand for parallel and sequential vectors respectively. There are four combinations of vecscatters: PtoP, PtoS,
    659:    StoP and StoS. The assumption of VecScatterCreate(Vec x,IS ix,Vec y,IS iy,VecScatter *newctx) is: if x is parallel, then ix
    660:    contains global indices of x. If x is sequential, ix contains local indices of x. Similarily for y and iy.

    662:    SF builds around concepts of local leaves and remote roots. We treat source vector x as roots and destination vector y as
    663:    leaves. A PtoS scatter can be naturally mapped to SF. We transform PtoP and StoP to PtoS, and treat StoS as trivial PtoS.
    664:   */

    666:   /* NULL ix or iy in VecScatterCreate(x,ix,y,iy,newctx) has special meaning. Recover them for these cases */
    667:   if (!ix) {
    668:     if (xcommsize > 1 && ycommsize == 1) { /* PtoS: null ix means the whole x will be scattered to each seq y */
    669:       VecGetSize(x,&N);
    670:       ISCreateStride(PETSC_COMM_SELF,N,0,1,&ix);
    671:     } else { /* PtoP, StoP or StoS: null ix means the whole local part of x will be scattered */
    672:       VecGetLocalSize(x,&n);
    673:       VecGetOwnershipRange(x,&xstart,NULL);
    674:       ISCreateStride(PETSC_COMM_SELF,n,xstart,1,&ix);
    675:     }
    676:   }

    678:   if (!iy) {
    679:     if (xcommsize == 1 && ycommsize > 1) { /* StoP: null iy means the whole y will be scattered to from each seq x */
    680:       VecGetSize(y,&N);
    681:       ISCreateStride(PETSC_COMM_SELF,N,0,1,&iy);
    682:     } else { /* PtoP, StoP or StoS: null iy means the whole local part of y will be scattered to */
    683:       VecGetLocalSize(y,&n);
    684:       VecGetOwnershipRange(y,&ystart,NULL);
    685:       ISCreateStride(PETSC_COMM_SELF,n,ystart,1,&iy);
    686:     }
    687:   }

    689:   /* Do error checking immediately after we have non-empty ix, iy */
    690:   ISGetLocalSize(ix,&ixsize);
    691:   ISGetLocalSize(iy,&iysize);
    692:   VecGetSize(x,&xlen);
    693:   VecGetSize(y,&ylen);
    695:   ISGetMinMax(ix,&min,&max);
    697:   ISGetMinMax(iy,&min,&max);

    700:   /* Extract info about ix, iy for further test */
    701:   ISGetTypeID_Private(ix,&ixid);
    702:   ISGetTypeID_Private(iy,&iyid);
    703:   if (ixid == IS_BLOCK)       ISGetBlockSize(ix,&bsx);
    704:   else if (ixid == IS_STRIDE) ISStrideGetInfo(ix,&ixfirst,&ixstep);

    706:   if (iyid == IS_BLOCK)      ISGetBlockSize(iy,&bsy);
    707:   else if (iyid == IS_STRIDE) ISStrideGetInfo(iy,&iyfirst,&iystep);

    709:   /* Check if a PtoS is special ToAll/ToZero scatters, which can be results of VecScatterCreateToAll/Zero.
    710:      ToAll means a whole MPI vector is copied to a seq vector on every process. ToZero means a whole MPI
    711:      vector is copied to a seq vector on rank 0 and other processes do nothing(i.e.,they input empty ix,iy).

    713:      We can optimize these scatters with MPI collectives. We can also avoid costly analysis used for general scatters.
    714:   */
    715:   if (xcommsize > 1 && ycommsize == 1) { /* Ranks do not diverge at this if-test */
    716:     PetscInt    pattern[2] = {0, 0}; /* A boolean array with pattern[0] for allgather-like (ToAll) and pattern[1] for gather-like (ToZero) */
    717:     PetscLayout map;

    719:     MPI_Comm_rank(xcomm,&rank);
    720:     VecGetLayout(x,&map);
    721:     if (rank == 0) {
    722:       if (ixid == IS_STRIDE && iyid == IS_STRIDE && ixsize == xlen && ixfirst == 0 && ixstep == 1 && iyfirst == 0 && iystep == 1) {
    723:         /* Rank 0 scatters the whole mpi x to seq y, so it is either a ToAll or a ToZero candidate in its view */
    724:         pattern[0] = pattern[1] = 1;
    725:       }
    726:     } else {
    727:       if (ixid == IS_STRIDE && iyid == IS_STRIDE && ixsize == xlen && ixfirst == 0 && ixstep == 1 && iyfirst == 0 && iystep == 1) {
    728:         /* Other ranks also scatter the whole mpi x to seq y, so it is a ToAll candidate in their view */
    729:         pattern[0] = 1;
    730:       } else if (ixsize == 0) {
    731:         /* Other ranks do nothing, so it is a ToZero candiate */
    732:         pattern[1] = 1;
    733:       }
    734:     }

    736:     /* One stone (the expensive allreduce) two birds: pattern[] tells if it is ToAll or ToZero */
    737:     MPIU_Allreduce(MPI_IN_PLACE,pattern,2,MPIU_INT,MPI_LAND,xcomm);

    739:     if (pattern[0] || pattern[1]) {
    740:       PetscSFCreate(xcomm,&sf);
    741:       PetscSFSetFromOptions(sf);
    742:       PetscSFSetGraphWithPattern(sf,map,pattern[0] ? PETSCSF_PATTERN_ALLGATHER : PETSCSF_PATTERN_GATHER);
    743:       goto functionend; /* No further analysis needed. What a big win! */
    744:     }
    745:   }

    747:   /* Continue ...
    748:      Do block optimization by taking advantage of high level info available in ix, iy.
    749:      The block optimization is valid when all of the following conditions are met:
    750:      1) ix, iy are blocked or can be blocked (i.e., strided with step=1);
    751:      2) ix, iy have the same block size;
    752:      3) all processors agree on one block size;
    753:      4) no blocks span more than one process;
    754:    */
    755:   bigcomm = (xcommsize == 1) ? ycomm : xcomm;

    757:   /* Processors could go through different path in this if-else test */
    758:   m[0] = m[1] = PETSC_MPI_INT_MIN;
    759:   if (ixid == IS_BLOCK && iyid == IS_BLOCK) {
    760:     m[0] = PetscMax(bsx,bsy);
    761:     m[1] = -PetscMin(bsx,bsy);
    762:   } else if (ixid == IS_BLOCK  && iyid == IS_STRIDE && iystep==1 && iyfirst%bsx==0) {
    763:     m[0] = bsx;
    764:     m[1] = -bsx;
    765:   } else if (ixid == IS_STRIDE && iyid == IS_BLOCK  && ixstep==1 && ixfirst%bsy==0) {
    766:     m[0] = bsy;
    767:     m[1] = -bsy;
    768:   }
    769:   /* Get max and min of bsx,bsy over all processes in one allreduce */
    770:   MPIU_Allreduce(MPI_IN_PLACE,m,2,MPIU_INT,MPI_MAX,bigcomm);
    771:   max = m[0]; min = -m[1];

    773:   /* Since we used allreduce above, all ranks will have the same min and max. min==max
    774:      implies all ranks have the same bs. Do further test to see if local vectors are dividable
    775:      by bs on ALL ranks. If they are, we are ensured that no blocks span more than one processor.
    776:    */
    777:   if (min == max && min > 1) {
    778:     VecGetLocalSize(x,&xlen);
    779:     VecGetLocalSize(y,&ylen);
    780:     m[0] = xlen%min;
    781:     m[1] = ylen%min;
    782:     MPIU_Allreduce(MPI_IN_PLACE,m,2,MPIU_INT,MPI_LOR,bigcomm);
    783:     if (!m[0] && !m[1]) can_do_block_opt = PETSC_TRUE;
    784:   }

    786:   /* If can_do_block_opt, then shrink x, y, ix and iy by bs to get xx, yy, ixx and iyy, whose indices
    787:      and layout are actually used in building SF. Suppose blocked ix representing {0,1,2,6,7,8} has
    788:      indices {0,2} and bs=3, then ixx = {0,2}; suppose strided iy={3,4,5,6,7,8}, then iyy={1,2}.

    790:      xx is a little special. If x is seq, then xx is the concatenation of seq x's on ycomm. In this way,
    791:      we can treat PtoP and StoP uniformly as PtoS.
    792:    */
    793:   if (can_do_block_opt) {
    794:     const PetscInt *indices;

    796:     /* Shrink x and ix */
    797:     bs   = min;
    798:     VecCreateMPIWithArray(bigcomm,1,xlen/bs,PETSC_DECIDE,NULL,&xx); /* We only care xx's layout */
    799:     if (ixid == IS_BLOCK) {
    800:       ISBlockGetIndices(ix,&indices);
    801:       ISBlockGetLocalSize(ix,&ixsize);
    802:       ISCreateGeneral(PETSC_COMM_SELF,ixsize,indices,PETSC_COPY_VALUES,&ixx);
    803:       ISBlockRestoreIndices(ix,&indices);
    804:     } else { /* ixid == IS_STRIDE */
    805:       ISGetLocalSize(ix,&ixsize);
    806:       ISCreateStride(PETSC_COMM_SELF,ixsize/bs,ixfirst/bs,1,&ixx);
    807:     }

    809:     /* Shrink y and iy */
    810:     VecCreateMPIWithArray(ycomm,1,ylen/bs,PETSC_DECIDE,NULL,&yy);
    811:     if (iyid == IS_BLOCK) {
    812:       ISBlockGetIndices(iy,&indices);
    813:       ISBlockGetLocalSize(iy,&iysize);
    814:       ISCreateGeneral(PETSC_COMM_SELF,iysize,indices,PETSC_COPY_VALUES,&iyy);
    815:       ISBlockRestoreIndices(iy,&indices);
    816:     } else { /* iyid == IS_STRIDE */
    817:       ISGetLocalSize(iy,&iysize);
    818:       ISCreateStride(PETSC_COMM_SELF,iysize/bs,iyfirst/bs,1,&iyy);
    819:     }
    820:   } else {
    821:     ixx = ix;
    822:     iyy = iy;
    823:     yy  = y;
    824:     if (xcommsize == 1) VecCreateMPIWithArray(bigcomm,1,xlen,PETSC_DECIDE,NULL,&xx); else xx = x;
    825:   }

    827:   /* Now it is ready to build SF with preprocessed (xx, yy) and (ixx, iyy) */
    828:   ISGetIndices(ixx,&xindices);
    829:   ISGetIndices(iyy,&yindices);
    830:   VecGetLayout(xx,&xlayout);

    832:   if (ycommsize > 1) {
    833:     /* PtoP or StoP */

    835:     /* Below is a piece of complex code with a very simple goal: move global index pairs (xindices[i], yindices[i]),
    836:        to owner process of yindices[i] according to ylayout, i = 0..n.

    838:        I did it through a temp sf, but later I thought the old design was inefficient and also distorted log view.
    839:        We want to mape one VecScatterCreate() call to one PetscSFCreate() call. The old design mapped to three
    840:        PetscSFCreate() calls. This code is on critical path of VecScatterSetUp and is used by every VecScatterCreate.
    841:        So I commented it out and did another optimized implementation. The commented code is left here for reference.
    842:      */
    843: #if 0
    844:     const PetscInt *degree;
    845:     PetscSF        tmpsf;
    846:     PetscInt       inedges=0,*leafdata,*rootdata;

    848:     VecGetOwnershipRange(xx,&xstart,NULL);
    849:     VecGetLayout(yy,&ylayout);
    850:     VecGetOwnershipRange(yy,&ystart,NULL);

    852:     VecGetLocalSize(yy,&nroots);
    853:     ISGetLocalSize(iyy,&nleaves);
    854:     PetscMalloc2(nleaves,&iremote,nleaves*2,&leafdata);

    856:     for (i=0; i<nleaves; i++) {
    857:       PetscLayoutFindOwnerIndex(ylayout,yindices[i],&iremote[i].rank,&iremote[i].index);
    858:       leafdata[2*i]   = yindices[i];
    859:       leafdata[2*i+1] = (xcommsize > 1)? xindices[i] : xindices[i] + xstart;
    860:     }

    862:     PetscSFCreate(ycomm,&tmpsf);
    863:     PetscSFSetGraph(tmpsf,nroots,nleaves,NULL,PETSC_USE_POINTER,iremote,PETSC_USE_POINTER);

    865:     PetscSFComputeDegreeBegin(tmpsf,&degree);
    866:     PetscSFComputeDegreeEnd(tmpsf,&degree);

    868:     for (i=0; i<nroots; i++) inedges += degree[i];
    869:     PetscMalloc1(inedges*2,&rootdata);
    870:     PetscSFGatherBegin(tmpsf,MPIU_2INT,leafdata,rootdata);
    871:     PetscSFGatherEnd(tmpsf,MPIU_2INT,leafdata,rootdata);

    873:     PetscFree2(iremote,leafdata);
    874:     PetscSFDestroy(&tmpsf);

    876:     /* rootdata contains global index pairs (i, j). j's are owned by the current process, but i's can point to anywhere.
    877:        We convert j to local, and convert i to (rank, index). In the end, we get an PtoS suitable for building SF.
    878:      */
    879:     nleaves = inedges;
    880:     VecGetLocalSize(xx,&nroots);
    881:     PetscMalloc1(nleaves,&ilocal);
    882:     PetscMalloc1(nleaves,&iremote);

    884:     for (i=0; i<inedges; i++) {
    885:       ilocal[i] = rootdata[2*i] - ystart; /* covert y's global index to local index */
    886:       PetscLayoutFindOwnerIndex(xlayout,rootdata[2*i+1],&iremote[i].rank,&iremote[i].index); /* convert x's global index to (rank, index) */
    887:     }
    888:     PetscFree(rootdata);
    889: #else
    890:     PetscInt       j,k,n,disp,rlentotal,*sstart,*xindices_sorted,*yindices_sorted;
    891:     const PetscInt *yrange;
    892:     PetscMPIInt    nsend,nrecv,nreq,yrank,*sendto,*recvfrom,tag1,tag2;
    893:     PetscInt       *slens,*rlens,count;
    894:     PetscInt       *rxindices,*ryindices;
    895:     MPI_Request    *reqs,*sreqs,*rreqs;

    897:     /* Sorting makes code simpler, faster and also helps getting rid of many O(P) arrays, which hurt scalability at large scale
    898:        yindices_sorted - sorted yindices
    899:        xindices_sorted - xindices sorted along with yindces
    900:      */
    901:     ISGetLocalSize(ixx,&n); /*ixx, iyy have the same local size */
    902:     PetscMalloc2(n,&xindices_sorted,n,&yindices_sorted);
    903:     PetscArraycpy(xindices_sorted,xindices,n);
    904:     PetscArraycpy(yindices_sorted,yindices,n);
    905:     PetscSortIntWithArray(n,yindices_sorted,xindices_sorted);
    906:     VecGetOwnershipRange(xx,&xstart,NULL);
    907:     if (xcommsize == 1) {for (i=0; i<n; i++) xindices_sorted[i] += xstart;} /* Convert to global indices */

    909:     /*=============================================================================
    910:              Calculate info about messages I need to send
    911:       =============================================================================*/
    912:     /* nsend    - number of non-empty messages to send
    913:        sendto   - [nsend] ranks I will send messages to
    914:        sstart   - [nsend+1] sstart[i] is the start index in xsindices_sorted[] I send to rank sendto[i]
    915:        slens    - [ycommsize] I want to send slens[i] entries to rank i.
    916:      */
    917:     VecGetLayout(yy,&ylayout);
    918:     PetscLayoutGetRanges(ylayout,&yrange);
    919:     PetscCalloc1(ycommsize,&slens); /* The only O(P) array in this algorithm */

    921:     i = j = nsend = 0;
    922:     while (i < n) {
    923:       if (yindices_sorted[i] >= yrange[j+1]) { /* If i-th index is out of rank j's bound */
    924:         do {j++;} while (yindices_sorted[i] >= yrange[j+1] && j < ycommsize); /* Increase j until i-th index falls in rank j's bound */
    926:       }
    927:       i++;
    928:       if (!slens[j]++) nsend++;
    929:     }

    931:     PetscMalloc2(nsend+1,&sstart,nsend,&sendto);

    933:     sstart[0] = 0;
    934:     for (i=j=0; i<ycommsize; i++) {
    935:       if (slens[i]) {
    936:         sendto[j]   = (PetscMPIInt)i;
    937:         sstart[j+1] = sstart[j] + slens[i];
    938:         j++;
    939:       }
    940:     }

    942:     /*=============================================================================
    943:       Calculate the reverse info about messages I will recv
    944:       =============================================================================*/
    945:     /* nrecv     - number of messages I will recv
    946:        recvfrom  - [nrecv] ranks I recv from
    947:        rlens     - [nrecv] I will recv rlens[i] entries from rank recvfrom[i]
    948:        rlentotal - sum of rlens[]
    949:        rxindices - [rlentotal] recv buffer for xindices_sorted
    950:        ryindices - [rlentotal] recv buffer for yindices_sorted
    951:      */
    952:     PetscGatherNumberOfMessages_Private(ycomm,NULL,slens,&nrecv);
    953:     PetscGatherMessageLengths_Private(ycomm,nsend,nrecv,slens,&recvfrom,&rlens);
    954:     PetscFree(slens); /* Free the O(P) array ASAP */
    955:     rlentotal = 0; for (i=0; i<nrecv; i++) rlentotal += rlens[i];

    957:     /*=============================================================================
    958:       Communicate with processors in recvfrom[] to populate rxindices and ryindices
    959:       ============================================================================*/
    960:     PetscCommGetNewTag(ycomm,&tag1);
    961:     PetscCommGetNewTag(ycomm,&tag2);
    962:     PetscMalloc2(rlentotal,&rxindices,rlentotal,&ryindices);
    963:     PetscMPIIntCast((nsend+nrecv)*2,&nreq);
    964:     PetscMalloc1(nreq,&reqs);
    965:     sreqs = reqs;
    966:     rreqs = reqs + nsend*2;

    968:     for (i=disp=0; i<nrecv; i++) {
    969:       count = rlens[i];
    970:       MPIU_Irecv(rxindices+disp,count,MPIU_INT,recvfrom[i],tag1,ycomm,rreqs+i);
    971:       MPIU_Irecv(ryindices+disp,count,MPIU_INT,recvfrom[i],tag2,ycomm,rreqs+nrecv+i);
    972:       disp += rlens[i];
    973:     }

    975:     for (i=0; i<nsend; i++) {
    976:       count = sstart[i+1]-sstart[i];
    977:       MPIU_Isend(xindices_sorted+sstart[i],count,MPIU_INT,sendto[i],tag1,ycomm,sreqs+i);
    978:       MPIU_Isend(yindices_sorted+sstart[i],count,MPIU_INT,sendto[i],tag2,ycomm,sreqs+nsend+i);
    979:     }
    980:     MPI_Waitall(nreq,reqs,MPI_STATUS_IGNORE);

    982:     /* Transform VecScatter into SF */
    983:     nleaves = rlentotal;
    984:     PetscMalloc1(nleaves,&ilocal);
    985:     PetscMalloc1(nleaves,&iremote);
    986:     MPI_Comm_rank(ycomm,&yrank);
    987:     for (i=disp=0; i<nrecv; i++) {
    988:       for (j=0; j<rlens[i]; j++) {
    989:         k               = disp + j; /* k-th index pair */
    990:         ilocal[k]       = ryindices[k] - yrange[yrank]; /* Convert y's global index to local index */
    991:         PetscLayoutFindOwnerIndex(xlayout,rxindices[k],&rank,&iremote[k].index); /* Convert x's global index to (rank, index) */
    992:         iremote[k].rank = rank;
    993:       }
    994:       disp += rlens[i];
    995:     }

    997:     PetscFree2(sstart,sendto);
    998:     PetscFree(rlens);
    999:     PetscFree(recvfrom);
    1000:     PetscFree(reqs);
    1001:     PetscFree2(rxindices,ryindices);
    1002:     PetscFree2(xindices_sorted,yindices_sorted);
    1003: #endif
    1004:   } else {
    1005:     /* PtoS or StoS */
    1006:     ISGetLocalSize(iyy,&nleaves);
    1007:     PetscMalloc1(nleaves,&ilocal);
    1008:     PetscMalloc1(nleaves,&iremote);
    1009:     PetscArraycpy(ilocal,yindices,nleaves);
    1010:     for (i=0; i<nleaves; i++) {
    1011:       PetscLayoutFindOwnerIndex(xlayout,xindices[i],&rank,&iremote[i].index);
    1012:       iremote[i].rank = rank;
    1013:     }
    1014:   }

    1016:   /* MUST build SF on xx's comm, which is not necessarily identical to yy's comm.
    1017:      In SF's view, xx contains the roots (i.e., the remote) and iremote[].rank are ranks in xx's comm.
    1018:      yy contains leaves, which are local and can be thought as part of PETSC_COMM_SELF. */
    1019:   PetscSFCreate(PetscObjectComm((PetscObject)xx),&sf);
    1020:   sf->allow_multi_leaves = PETSC_TRUE;
    1021:   PetscSFSetFromOptions(sf);
    1022:   VecGetLocalSize(xx,&nroots);
    1023:   PetscSFSetGraph(sf,nroots,nleaves,ilocal,PETSC_OWN_POINTER,iremote,PETSC_OWN_POINTER); /* Give ilocal/iremote to petsc and no need to free them here */

    1025:   /* Free memory no longer needed */
    1026:   ISRestoreIndices(ixx,&xindices);
    1027:   ISRestoreIndices(iyy,&yindices);
    1028:   if (can_do_block_opt) {
    1029:     VecDestroy(&xx);
    1030:     VecDestroy(&yy);
    1031:     ISDestroy(&ixx);
    1032:     ISDestroy(&iyy);
    1033:   } else if (xcommsize == 1) {
    1034:     VecDestroy(&xx);
    1035:   }

    1037: functionend:
    1038:   sf->vscat.bs = bs;
    1039:   if (sf->vscat.bs > 1) {
    1040:     MPI_Type_contiguous(sf->vscat.bs,MPIU_SCALAR,&sf->vscat.unit);
    1041:     MPI_Type_commit(&sf->vscat.unit);
    1042:   } else {
    1043:     sf->vscat.unit = MPIU_SCALAR;
    1044:   }
    1045:   VecGetLocalSize(x,&sf->vscat.from_n);
    1046:   VecGetLocalSize(y,&sf->vscat.to_n);
    1047:   if (!ix_old) ISDestroy(&ix); /* We created helper ix, iy. Free them */
    1048:   if (!iy_old) ISDestroy(&iy);

    1050:   /* Set default */
    1051:   VecScatterSetFromOptions(sf);

    1053:   *newsf = sf;
    1054:   return 0;
    1055: }

    1057: /*@C
    1058:       VecScatterCreateToAll - Creates a vector and a scatter context that copies all
    1059:           vector values to each processor

    1061:   Collective on Vec

    1063:   Input Parameter:
    1064: .  vin  - input MPIVEC

    1066:   Output Parameters:
    1067: +  ctx - scatter context
    1068: -  vout - output SEQVEC that is large enough to scatter into

    1070:   Level: intermediate

    1072:    Note: vout may be NULL [PETSC_NULL_VEC from fortran] if you do not
    1073:    need to have it created

    1075:    Usage:
    1076: $        VecScatterCreateToAll(vin,&ctx,&vout);
    1077: $
    1078: $        // scatter as many times as you need
    1079: $        VecScatterBegin(ctx,vin,vout,INSERT_VALUES,SCATTER_FORWARD);
    1080: $        VecScatterEnd(ctx,vin,vout,INSERT_VALUES,SCATTER_FORWARD);
    1081: $
    1082: $        // destroy scatter context and local vector when no longer needed
    1083: $        VecScatterDestroy(&ctx);
    1084: $        VecDestroy(&vout);

    1086:     Do NOT create a vector and then pass it in as the final argument vout! vout is created by this routine
    1087:   automatically (unless you pass NULL in for that argument if you do not need it).

    1089: .seealso VecScatterCreate(), VecScatterCreateToZero(), VecScatterBegin(), VecScatterEnd()

    1091: @*/
    1092: PetscErrorCode  VecScatterCreateToAll(Vec vin,VecScatter *ctx,Vec *vout)
    1093: {
    1094:   PetscInt       N;
    1095:   IS             is;
    1096:   Vec            tmp;
    1097:   Vec            *tmpv;
    1098:   PetscBool      tmpvout = PETSC_FALSE;
    1099:   VecType        roottype;

    1104:   if (vout) {
    1106:     tmpv = vout;
    1107:   } else {
    1108:     tmpvout = PETSC_TRUE;
    1109:     tmpv    = &tmp;
    1110:   }

    1112:   /* Create seq vec on each proc, with the same size of the original vec */
    1113:   VecGetSize(vin,&N);
    1114:   VecGetRootType_Private(vin,&roottype);
    1115:   VecCreate(PETSC_COMM_SELF,tmpv);
    1116:   VecSetSizes(*tmpv,N,PETSC_DECIDE);
    1117:   VecSetType(*tmpv,roottype);
    1118:   /* Create the VecScatter ctx with the communication info */
    1119:   ISCreateStride(PETSC_COMM_SELF,N,0,1,&is);
    1120:   VecScatterCreate(vin,is,*tmpv,is,ctx);
    1121:   ISDestroy(&is);
    1122:   if (tmpvout) VecDestroy(tmpv);
    1123:   return 0;
    1124: }

    1126: /*@C
    1127:       VecScatterCreateToZero - Creates an output vector and a scatter context used to
    1128:               copy all vector values into the output vector on the zeroth processor

    1130:   Collective on Vec

    1132:   Input Parameter:
    1133: .  vin  - input MPIVEC

    1135:   Output Parameters:
    1136: +  ctx - scatter context
    1137: -  vout - output SEQVEC that is large enough to scatter into on processor 0 and
    1138:           of length zero on all other processors

    1140:   Level: intermediate

    1142:    Note: vout may be NULL [PETSC_NULL_VEC from fortran] if you do not
    1143:    need to have it created

    1145:    Usage:
    1146: $        VecScatterCreateToZero(vin,&ctx,&vout);
    1147: $
    1148: $        // scatter as many times as you need
    1149: $        VecScatterBegin(ctx,vin,vout,INSERT_VALUES,SCATTER_FORWARD);
    1150: $        VecScatterEnd(ctx,vin,vout,INSERT_VALUES,SCATTER_FORWARD);
    1151: $
    1152: $        // destroy scatter context and local vector when no longer needed
    1153: $        VecScatterDestroy(&ctx);
    1154: $        VecDestroy(&vout);

    1156: .seealso VecScatterCreate(), VecScatterCreateToAll(), VecScatterBegin(), VecScatterEnd()

    1158:     Do NOT create a vector and then pass it in as the final argument vout! vout is created by this routine
    1159:   automatically (unless you pass NULL in for that argument if you do not need it).

    1161: @*/
    1162: PetscErrorCode  VecScatterCreateToZero(Vec vin,VecScatter *ctx,Vec *vout)
    1163: {

    1165:   PetscInt       N;
    1166:   PetscMPIInt    rank;
    1167:   IS             is;
    1168:   Vec            tmp;
    1169:   Vec            *tmpv;
    1170:   PetscBool      tmpvout = PETSC_FALSE;
    1171:   VecType        roottype;

    1176:   if (vout) {
    1178:     tmpv = vout;
    1179:   } else {
    1180:     tmpvout = PETSC_TRUE;
    1181:     tmpv    = &tmp;
    1182:   }

    1184:   /* Create vec on each proc, with the same size of the original vec all on process 0 */
    1185:   VecGetSize(vin,&N);
    1186:   MPI_Comm_rank(PetscObjectComm((PetscObject)vin),&rank);
    1187:   if (rank) N = 0;
    1188:   VecGetRootType_Private(vin,&roottype);
    1189:   VecCreate(PETSC_COMM_SELF,tmpv);
    1190:   VecSetSizes(*tmpv,N,PETSC_DECIDE);
    1191:   VecSetType(*tmpv,roottype);
    1192:   /* Create the VecScatter ctx with the communication info */
    1193:   ISCreateStride(PETSC_COMM_SELF,N,0,1,&is);
    1194:   VecScatterCreate(vin,is,*tmpv,is,ctx);
    1195:   ISDestroy(&is);
    1196:   if (tmpvout) VecDestroy(tmpv);
    1197:   return 0;
    1198: }

    1200: /*@
    1201:    VecScatterBegin - Begins a generalized scatter from one vector to
    1202:    another. Complete the scattering phase with VecScatterEnd().

    1204:    Neighbor-wise Collective on VecScatter

    1206:    Input Parameters:
    1207: +  sf - scatter context generated by VecScatterCreate()
    1208: .  x - the vector from which we scatter
    1209: .  y - the vector to which we scatter
    1210: .  addv - either ADD_VALUES, MAX_VALUES, MIN_VALUES or INSERT_VALUES, with INSERT_VALUES mode any location
    1211:           not scattered to retains its old value; i.e. the vector is NOT first zeroed.
    1212: -  mode - the scattering mode, usually SCATTER_FORWARD.  The available modes are:
    1213:     SCATTER_FORWARD or SCATTER_REVERSE

    1215:    Level: intermediate

    1217:    Options Database: See VecScatterCreate()

    1219:    Notes:
    1220:    The vectors x and y need not be the same vectors used in the call
    1221:    to VecScatterCreate(), but x must have the same parallel data layout
    1222:    as that passed in as the x to VecScatterCreate(), similarly for the y.
    1223:    Most likely they have been obtained from VecDuplicate().

    1225:    You cannot change the values in the input vector between the calls to VecScatterBegin()
    1226:    and VecScatterEnd().

    1228:    If you use SCATTER_REVERSE the two arguments x and y should be reversed, from
    1229:    the SCATTER_FORWARD.

    1231:    y[iy[i]] = x[ix[i]], for i=0,...,ni-1

    1233:    This scatter is far more general than the conventional
    1234:    scatter, since it can be a gather or a scatter or a combination,
    1235:    depending on the indices ix and iy.  If x is a parallel vector and y
    1236:    is sequential, VecScatterBegin() can serve to gather values to a
    1237:    single processor.  Similarly, if y is parallel and x sequential, the
    1238:    routine can scatter from one processor to many processors.

    1240: .seealso: VecScatterCreate(), VecScatterEnd()
    1241: @*/
    1242: PetscErrorCode  VecScatterBegin(VecScatter sf,Vec x,Vec y,InsertMode addv,ScatterMode mode)
    1243: {
    1244:   PetscInt       to_n,from_n;

    1249:   if (PetscDefined(USE_DEBUG)) {
    1250:     /*
    1251:      Error checking to make sure these vectors match the vectors used
    1252:      to create the vector scatter context. -1 in the from_n and to_n indicate the
    1253:      vector lengths are unknown (for example with mapped scatters) and thus
    1254:      no error checking is performed.
    1255:      */
    1256:     if (sf->vscat.from_n >= 0 && sf->vscat.to_n >= 0) {
    1257:       VecGetLocalSize(x,&from_n);
    1258:       VecGetLocalSize(y,&to_n);
    1259:       if (mode & SCATTER_REVERSE) {
    1262:       } else {
    1265:       }
    1266:     }
    1267:   }

    1269:   sf->vscat.logging = PETSC_TRUE;
    1270:   PetscLogEventBegin(VEC_ScatterBegin,sf,x,y,0);
    1271:   VecScatterBegin_Internal(sf,x,y,addv,mode);
    1272:   if (sf->vscat.beginandendtogether) {
    1273:     VecScatterEnd_Internal(sf,x,y,addv,mode);
    1274:   }
    1275:   PetscLogEventEnd(VEC_ScatterBegin,sf,x,y,0);
    1276:   sf->vscat.logging = PETSC_FALSE;
    1277:   return 0;
    1278: }

    1280: /*@
    1281:    VecScatterEnd - Ends a generalized scatter from one vector to another.  Call
    1282:    after first calling VecScatterBegin().

    1284:    Neighbor-wise Collective on VecScatter

    1286:    Input Parameters:
    1287: +  sf - scatter context generated by VecScatterCreate()
    1288: .  x - the vector from which we scatter
    1289: .  y - the vector to which we scatter
    1290: .  addv - one of ADD_VALUES, MAX_VALUES, MIN_VALUES or INSERT_VALUES
    1291: -  mode - the scattering mode, usually SCATTER_FORWARD.  The available modes are:
    1292:      SCATTER_FORWARD, SCATTER_REVERSE

    1294:    Level: intermediate

    1296:    Notes:
    1297:    If you use SCATTER_REVERSE the arguments x and y should be reversed, from the SCATTER_FORWARD.

    1299:    y[iy[i]] = x[ix[i]], for i=0,...,ni-1

    1301: .seealso: VecScatterBegin(), VecScatterCreate()
    1302: @*/
    1303: PetscErrorCode  VecScatterEnd(VecScatter sf,Vec x,Vec y,InsertMode addv,ScatterMode mode)
    1304: {
    1308:   if (!sf->vscat.beginandendtogether) {
    1309:     sf->vscat.logging = PETSC_TRUE;
    1310:     PetscLogEventBegin(VEC_ScatterEnd,sf,x,y,0);
    1311:     VecScatterEnd_Internal(sf,x,y,addv,mode);
    1312:     PetscLogEventEnd(VEC_ScatterEnd,sf,x,y,0);
    1313:     sf->vscat.logging = PETSC_FALSE;
    1314:   }
    1315:   return 0;
    1316: }