Actual source code: vscat.c
petsc-3.15.0 2021-03-30
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      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: PETSC_STATIC_INLINE PetscErrorCode ISGetTypeID_Private(IS is,ISTypeID *id)
     12: {
     14:   PetscBool      same;

     17:   *id  = IS_INVALID;
     18:   PetscObjectTypeCompare((PetscObject)is,ISGENERAL,&same);
     19:   if (same) {*id = IS_GENERAL; goto functionend;}
     20:   PetscObjectTypeCompare((PetscObject)is,ISBLOCK,&same);
     21:   if (same) {*id = IS_BLOCK; goto functionend;}
     22:   PetscObjectTypeCompare((PetscObject)is,ISSTRIDE,&same);
     23:   if (same) {*id = IS_STRIDE; goto functionend;}
     24: functionend:
     25:   return(0);
     26: }

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

     37:   if (x != y) {VecLockReadPush(x);}
     38:   if (sf->use_gpu_aware_mpi || sf->vscat.packongpu) {
     39:     VecGetArrayReadAndMemType(x,&sf->vscat.xdata,&xmtype);
     40:   } else {
     41:     VecGetArrayRead(x,&sf->vscat.xdata);
     42:   }

     44:   if (x != y) {
     45:     if (sf->use_gpu_aware_mpi || sf->vscat.packongpu) {VecGetArrayAndMemType(y,&sf->vscat.ydata,&ymtype);}
     46:     else {VecGetArray(y,&sf->vscat.ydata);}
     47:   } else {
     48:     sf->vscat.ydata = (PetscScalar *)sf->vscat.xdata;
     49:     ymtype          = xmtype;
     50:   }
     51:   VecLockWriteSet_Private(y,PETSC_TRUE);

     53:   /* SCATTER_LOCAL indicates ignoring inter-process communication */
     54:   MPI_Comm_size(PetscObjectComm((PetscObject)sf),&size);
     55:   if ((mode & SCATTER_LOCAL) && size > 1) { /* Lazy creation of sf->vscat.lsf since SCATTER_LOCAL is uncommon */
     56:     if (!sf->vscat.lsf) {PetscSFCreateLocalSF_Private(sf,&sf->vscat.lsf);}
     57:     wsf = sf->vscat.lsf;
     58:   } else {
     59:     wsf = sf;
     60:   }

     62:   /* Note xdata/ydata is always recorded on sf (not lsf) above */
     63:   if (addv == INSERT_VALUES)   mop = MPI_REPLACE;
     64:   else if (addv == ADD_VALUES) mop = MPIU_SUM; /* Petsc defines its own MPI datatype and SUM operation for __float128 etc. */
     65:   else if (addv == MAX_VALUES) mop = MPIU_MAX;
     66:   else if (addv == MIN_VALUES) mop = MPIU_MIN;
     67:   else SETERRQ1(PetscObjectComm((PetscObject)sf),PETSC_ERR_SUP,"Unsupported InsertMode %D in VecScatterBegin/End",addv);

     69:   if (mode & SCATTER_REVERSE) { /* REVERSE indicates leaves to root scatter. Note that x and y are swapped in input */
     70:     PetscSFReduceWithMemTypeBegin(wsf,sf->vscat.unit,xmtype,sf->vscat.xdata,ymtype,sf->vscat.ydata,mop);
     71:   } else { /* FORWARD indicates x to y scatter, where x is root and y is leaf */
     72:     PetscSFBcastWithMemTypeBegin(wsf,sf->vscat.unit,xmtype,sf->vscat.xdata,ymtype,sf->vscat.ydata,mop);
     73:   }
     74:   return(0);
     75: }

     77: static PetscErrorCode VecScatterEnd_Internal(VecScatter sf,Vec x,Vec y,InsertMode addv,ScatterMode mode)
     78: {
     80:   PetscSF        wsf=NULL;
     81:   MPI_Op         mop=MPI_OP_NULL;
     82:   PetscMPIInt    size;

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

     89:   if (addv == INSERT_VALUES)   mop = MPI_REPLACE;
     90:   else if (addv == ADD_VALUES) mop = MPIU_SUM;
     91:   else if (addv == MAX_VALUES) mop = MPIU_MAX;
     92:   else if (addv == MIN_VALUES) mop = MPIU_MIN;
     93:   else SETERRQ1(PetscObjectComm((PetscObject)sf),PETSC_ERR_SUP,"Unsupported InsertMode %D in VecScatterBegin/End",addv);

     95:   if (mode & SCATTER_REVERSE) { /* reverse scatter sends leaves to roots. Note that x and y are swapped in input */
     96:     PetscSFReduceEnd(wsf,sf->vscat.unit,sf->vscat.xdata,sf->vscat.ydata,mop);
     97:   } else { /* forward scatter sends roots to leaves, i.e., x to y */
     98:     PetscSFBcastEnd(wsf,sf->vscat.unit,sf->vscat.xdata,sf->vscat.ydata,mop);
     99:   }

    101:   if (x != y) {
    102:     if (sf->use_gpu_aware_mpi || sf->vscat.packongpu) {VecRestoreArrayReadAndMemType(x,&sf->vscat.xdata);}
    103:     else {VecRestoreArrayRead(x,&sf->vscat.xdata);}
    104:     VecLockReadPop(x);
    105:   }

    107:   if (sf->use_gpu_aware_mpi || sf->vscat.packongpu) {VecRestoreArrayAndMemType(y,&sf->vscat.ydata);}
    108:   else {VecRestoreArray(y,&sf->vscat.ydata);}
    109:   VecLockWriteSet_Private(y,PETSC_FALSE);

    111:   return(0);
    112: }

    114: /* VecScatterRemap provides a light way to slightly modify a VecScatter. Suppose the input sf scatters
    115:    x[i] to y[j], tomap gives a plan to change vscat to scatter x[tomap[i]] to y[j]. Note that in SF,
    116:    x is roots. That means we need to change incoming stuffs such as bas->irootloc[].
    117:  */
    118: static PetscErrorCode VecScatterRemap_Internal(VecScatter sf,const PetscInt *tomap,const PetscInt *frommap)
    119: {
    120:   PetscInt       i,bs = sf->vscat.bs;
    121:   PetscMPIInt    size;
    122:   PetscBool      ident = PETSC_TRUE,isbasic,isneighbor;
    123:   PetscSFType    type;
    124:   PetscSF_Basic  *bas = NULL;

    128:   /* check if it is an identity map. If it is, do nothing */
    129:   if (tomap) {
    130:     for (i=0; i<sf->nroots*bs; i++) {if (i != tomap[i]) {ident = PETSC_FALSE; break; } }
    131:     if (ident) return(0);
    132:   }
    133:   if (frommap) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Unable to remap the FROM in scatters yet");
    134:   if (!tomap) return(0);

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

    138:   /* Since the indices changed, we must also update the local SF. But we do not do it since
    139:      lsf is rarely used. We just destroy lsf and rebuild it on demand from updated sf.
    140:   */
    141:   if (sf->vscat.lsf) {PetscSFDestroy(&sf->vscat.lsf);}

    143:   PetscSFGetType(sf,&type);
    144:   PetscObjectTypeCompare((PetscObject)sf,PETSCSFBASIC,&isbasic);
    145:   PetscObjectTypeCompare((PetscObject)sf,PETSCSFNEIGHBOR,&isneighbor);
    146:   if (!isbasic && !isneighbor) SETERRQ1(PetscObjectComm((PetscObject)sf),PETSC_ERR_SUP,"VecScatterRemap on SF type %s is not supported",type);

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

    150:   /* Root indices are going to be remapped. This is tricky for SF. Root indices are used in sf->rremote,
    151:     sf->remote and bas->irootloc. The latter one is cheap to remap, but the former two are not.
    152:     To remap them, we have to do a bcast from roots to leaves, to let leaves know their updated roots.
    153:     Since VecScatterRemap is supposed to be a cheap routine to adapt a vecscatter by only changing where
    154:     x[] data is taken, we do not remap sf->rremote, sf->remote. The consequence is that operations
    155:     accessing them (such as PetscSFCompose) may get stale info. Considering VecScatter does not need
    156:     that complicated SF operations, we do not remap sf->rremote, sf->remote, instead we destroy them
    157:     so that code accessing them (if any) will crash (instead of get silent errors). Note that BcastAndOp/Reduce,
    158:     which are used by VecScatter and only rely on bas->irootloc, are updated and correct.
    159:   */
    160:   sf->remote = NULL;
    161:   PetscFree(sf->remote_alloc);
    162:   /* Not easy to free sf->rremote since it was allocated with PetscMalloc4(), so just give it crazy values */
    163:   for (i=0; i<sf->roffset[sf->nranks]; i++) sf->rremote[i] = PETSC_MIN_INT;

    165:   /* Indices in tomap[] are for each indivisual vector entry. But indices in sf are for each
    166:      block in the vector. So before the remapping, we have to expand indices in sf by bs, and
    167:      after the remapping, we have to shrink them back.
    168:    */
    169:   bas = (PetscSF_Basic*)sf->data;
    170:   for (i=0; i<bas->ioffset[bas->niranks]; i++) bas->irootloc[i] = tomap[bas->irootloc[i]*bs]/bs;
    171: #if defined(PETSC_HAVE_DEVICE)
    172:   /* Free the irootloc copy on device. We allocate a new copy and get the updated value on demand. See PetscSFLinkGetRootPackOptAndIndices() */
    173:   for (i=0; i<2; i++) {PetscSFFree(sf,PETSC_MEMTYPE_DEVICE,bas->irootloc_d[i]);}
    174: #endif
    175:   /* Destroy and then rebuild root packing optimizations since indices are changed */
    176:   PetscSFResetPackFields(sf);
    177:   PetscSFSetUpPackFields(sf);
    178:   return(0);
    179: }

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

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

    187:   Output parameters:
    188: + num_procs   - number of remote processors
    189: - num_entries - number of vector entries to send or recv

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

    194:   Notes:
    195:   Sometimes PETSc internally needs to use the matrix-vector-multiply vecscatter context for other purposes. The client code
    196:   usually only uses MPI_Send/Recv. This group of subroutines provides info needed for such uses.
    197:  */
    198: PetscErrorCode VecScatterGetRemoteCount_Private(VecScatter sf,PetscBool send,PetscInt *num_procs,PetscInt *num_entries)
    199: {
    200:   PetscErrorCode    ierr;
    201:   PetscInt          nranks,remote_start;
    202:   PetscMPIInt       rank;
    203:   const PetscInt    *offset;
    204:   const PetscMPIInt *ranks;

    207:   PetscSFSetUp(sf);
    208:   MPI_Comm_rank(PetscObjectComm((PetscObject)sf),&rank);

    210:   /* This routine is mainly used for MatMult's Mvctx. In Mvctx, we scatter an MPI vector x to a sequential vector lvec.
    211:      Remember x is roots and lvec is leaves. 'send' means roots to leaves communication. If 'send' is true, we need to
    212:      get info about which ranks this processor needs to send to. In other words, we need to call PetscSFGetLeafRanks().
    213:      If send is false, we do the opposite, calling PetscSFGetRootRanks().
    214:   */
    215:   if (send) {PetscSFGetLeafRanks(sf,&nranks,&ranks,&offset,NULL);}
    216:   else {PetscSFGetRootRanks(sf,&nranks,&ranks,&offset,NULL,NULL);}
    217:   if (nranks) {
    218:     remote_start = (rank == ranks[0])? 1 : 0;
    219:     if (num_procs)   *num_procs   = nranks - remote_start;
    220:     if (num_entries) *num_entries = offset[nranks] - offset[remote_start];
    221:   } else {
    222:     if (num_procs)   *num_procs   = 0;
    223:     if (num_entries) *num_entries = 0;
    224:   }
    225:   return(0);
    226: }

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

    231:   Input Parameters:
    232: + sf   - the context
    233: - send  - true to select the send info (i.e., todata), otherwise to select the recv info (i.e., fromdata)

    235:   Output parameters:
    236: + n        - number of remote processors
    237: . starts   - starting point in indices for each proc. ATTENTION: starts[0] is not necessarily zero.
    238:              Therefore, expressions like starts[i+1]-starts[i] and indices[starts[i]+j] work as
    239:              expected for a CSR structure but buf[starts[i]+j] may be out of range if buf was allocated
    240:              with length starts[n]-starts[0]. One should use buf[starts[i]-starts[0]+j] instead.
    241: . indices  - indices of entries to send/recv
    242: . procs    - ranks of remote processors
    243: - bs       - block size

    245:   .seealso: VecScatterRestoreRemote_Private(), VecScatterGetRemoteOrdered_Private()
    246:  */
    247: PetscErrorCode VecScatterGetRemote_Private(VecScatter sf,PetscBool send,PetscInt *n,const PetscInt **starts,const PetscInt **indices,const PetscMPIInt **procs,PetscInt *bs)
    248: {
    249:   PetscErrorCode    ierr;
    250:   PetscInt          nranks,remote_start;
    251:   PetscMPIInt       rank;
    252:   const PetscInt    *offset,*location;
    253:   const PetscMPIInt *ranks;

    256:   PetscSFSetUp(sf);
    257:   MPI_Comm_rank(PetscObjectComm((PetscObject)sf),&rank);

    259:   if (send) {PetscSFGetLeafRanks(sf,&nranks,&ranks,&offset,&location);}
    260:   else {PetscSFGetRootRanks(sf,&nranks,&ranks,&offset,&location,NULL);}

    262:   if (nranks) {
    263:     remote_start = (rank == ranks[0])? 1 : 0;
    264:     if (n)       *n       = nranks - remote_start;
    265:     if (starts)  *starts  = &offset[remote_start];
    266:     if (indices) *indices = location; /* not &location[offset[remote_start]]. Starts[0] may point to the middle of indices[] */
    267:     if (procs)   *procs   = &ranks[remote_start];
    268:   } else {
    269:     if (n)       *n       = 0;
    270:     if (starts)  *starts  = NULL;
    271:     if (indices) *indices = NULL;
    272:     if (procs)   *procs   = NULL;
    273:   }

    275:   if (bs) *bs = 1;
    276:   return(0);
    277: }

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

    282:   Input Parameters:
    283: + sf   - the context
    284: - send  - true to select the send info (i.e., todata), otherwise to select the recv info (i.e., fromdata)

    286:   Output parameters:
    287: + n        - number of remote processors
    288: . starts   - starting point in indices for each proc. ATTENTION: starts[0] is not necessarily zero.
    289:              Therefore, expressions like starts[i+1]-starts[i] and indices[starts[i]+j] work as
    290:              expected for a CSR structure but buf[starts[i]+j] may be out of range if buf was allocated
    291:              with length starts[n]-starts[0]. One should use buf[starts[i]-starts[0]+j] instead.
    292: . indices  - indices of entries to send/recv
    293: . procs    - ranks of remote processors
    294: - bs       - block size

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

    298:   Notes:
    299:   Output parameters like starts, indices must also be adapted according to the sorted ranks.
    300:  */
    301: PetscErrorCode VecScatterGetRemoteOrdered_Private(VecScatter sf,PetscBool send,PetscInt *n,const PetscInt **starts,const PetscInt **indices,const PetscMPIInt **procs,PetscInt *bs)
    302: {

    306:   VecScatterGetRemote_Private(sf,send,n,starts,indices,procs,bs);
    307:   if (PetscUnlikelyDebug(n && procs)) {
    308:     PetscInt i;
    309:     /* from back to front to also handle cases *n=0 */
    310:     for (i=*n-1; i>0; i--) { if ((*procs)[i-1] > (*procs)[i]) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"procs[] are not ordered"); }
    311:   }
    312:   return(0);
    313: }

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

    318:   Input Parameters:
    319: + sf   - the context
    320: - send  - true to select the send info (i.e., todata), otherwise to select the recv info (i.e., fromdata)

    322:   Output parameters:
    323: + n        - number of remote processors
    324: . starts   - starting point in indices for each proc
    325: . indices  - indices of entries to send/recv
    326: . procs    - ranks of remote processors
    327: - bs       - block size

    329:   .seealso: VecScatterGetRemote_Private()
    330:  */
    331: PetscErrorCode VecScatterRestoreRemote_Private(VecScatter sf,PetscBool send,PetscInt *n,const PetscInt **starts,const PetscInt **indices,const PetscMPIInt **procs,PetscInt *bs)
    332: {
    334:   if (starts)   *starts  = NULL;
    335:   if (indices)  *indices = NULL;
    336:   if (procs)    *procs   = NULL;
    337:   return(0);
    338: }

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

    343:   Input Parameters:
    344: + sf   - the context
    345: - send  - true to select the send info (i.e., todata), otherwise to select the recv info (i.e., fromdata)

    347:   Output parameters:
    348: + n        - number of remote processors
    349: . starts   - starting point in indices for each proc
    350: . indices  - indices of entries to send/recv
    351: . procs    - ranks of remote processors
    352: - bs       - block size

    354:   .seealso: VecScatterGetRemoteOrdered_Private()
    355:  */
    356: PetscErrorCode VecScatterRestoreRemoteOrdered_Private(VecScatter sf,PetscBool send,PetscInt *n,const PetscInt **starts,const PetscInt **indices,const PetscMPIInt **procs,PetscInt *bs)
    357: {
    360:   VecScatterRestoreRemote_Private(sf,send,n,starts,indices,procs,bs);
    361:   return(0);
    362: }

    364: /*@
    365:    VecScatterSetUp - Sets up the VecScatter to be able to actually scatter information between vectors

    367:    Collective on VecScatter

    369:    Input Parameter:
    370: .  sf - the scatter context

    372:    Level: intermediate

    374: .seealso: VecScatterCreate(), VecScatterCopy()
    375: @*/
    376: PetscErrorCode VecScatterSetUp(VecScatter sf)
    377: {
    380:   PetscSFSetUp(sf);
    381:   return(0);
    382: }

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

    387:   Collective on VecScatter

    389:   Input Parameters:
    390: + sf - The VecScatter (SF) object
    391: - type - The name of the vector scatter type

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

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

    399:   Level: intermediate

    401: .seealso: VecScatterGetType(), VecScatterCreate()
    402: @*/
    403: PetscErrorCode VecScatterSetType(VecScatter sf, VecScatterType type)
    404: {

    408:   PetscSFSetType(sf,type);
    409:   return(0);
    410: }

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

    415:   Not Collective

    417:   Input Parameter:
    418: . sf  - The vector scatter (SF)

    420:   Output Parameter:
    421: . type - The vector scatter type name

    423:   Level: intermediate

    425: .seealso: VecScatterSetType(), VecScatterCreate()
    426: @*/
    427: PetscErrorCode VecScatterGetType(VecScatter sf, VecScatterType *type)
    428: {
    431:   PetscSFGetType(sf,type);
    432:   return(0);
    433: }

    435: /*@C
    436:   VecScatterRegister -  Adds a new vector scatter component implementation

    438:   Not Collective

    440:   Input Parameters:
    441: + name        - The name of a new user-defined creation routine
    442: - create_func - The creation routine itself

    444:   Level: advanced

    446: .seealso: VecRegister()
    447: @*/
    448: PetscErrorCode VecScatterRegister(const char sname[], PetscErrorCode (*function)(VecScatter))
    449: {
    452:   PetscSFRegister(sname,function);
    453:   return(0);
    454: }

    456: /* ------------------------------------------------------------------*/
    457: /*@
    458:    VecScatterGetMerged - Returns true if the scatter is completed in the VecScatterBegin()
    459:       and the VecScatterEnd() does nothing

    461:    Not Collective

    463:    Input Parameter:
    464: .   sf - scatter context created with VecScatterCreate()

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

    469:    Level: developer

    471: .seealso: VecScatterCreate(), VecScatterEnd(), VecScatterBegin()
    472: @*/
    473: PetscErrorCode  VecScatterGetMerged(VecScatter sf,PetscBool *flg)
    474: {
    477:   if (flg) *flg = sf->vscat.beginandendtogether;
    478:   return(0);
    479: }
    480: /*@C
    481:    VecScatterDestroy - Destroys a scatter context created by VecScatterCreate()

    483:    Collective on VecScatter

    485:    Input Parameter:
    486: .  sf - the scatter context

    488:    Level: intermediate

    490: .seealso: VecScatterCreate(), VecScatterCopy()
    491: @*/
    492: PetscErrorCode VecScatterDestroy(VecScatter *sf)
    493: {

    497:   PetscSFDestroy(sf);
    498:   return(0);
    499: }

    501: /*@
    502:    VecScatterCopy - Makes a copy of a scatter context.

    504:    Collective on VecScatter

    506:    Input Parameter:
    507: .  sf - the scatter context

    509:    Output Parameter:
    510: .  newsf - the context copy

    512:    Level: advanced

    514: .seealso: VecScatterCreate(), VecScatterDestroy()
    515: @*/
    516: PetscErrorCode  VecScatterCopy(VecScatter sf,VecScatter *newsf)
    517: {

    522:   PetscSFDuplicate(sf,PETSCSF_DUPLICATE_GRAPH,newsf);
    523:   PetscSFSetUp(*newsf);
    524:   return(0);
    525: }

    527: /*@C
    528:    VecScatterViewFromOptions - View from Options

    530:    Collective on VecScatter

    532:    Input Parameters:
    533: +  sf - the scatter context
    534: .  obj - Optional object
    535: -  name - command line option

    537:    Level: intermediate
    538: .seealso:  VecScatter, VecScatterView, PetscObjectViewFromOptions(), VecScatterCreate()
    539: @*/
    540: PetscErrorCode  VecScatterViewFromOptions(VecScatter sf,PetscObject obj,const char name[])
    541: {

    546:   PetscObjectViewFromOptions((PetscObject)sf,obj,name);
    547:   return(0);
    548: }

    550: /* ------------------------------------------------------------------*/
    551: /*@C
    552:    VecScatterView - Views a vector scatter context.

    554:    Collective on VecScatter

    556:    Input Parameters:
    557: +  sf - the scatter context
    558: -  viewer - the viewer for displaying the context

    560:    Level: intermediate

    562: @*/
    563: PetscErrorCode  VecScatterView(VecScatter sf,PetscViewer viewer)
    564: {

    568:   PetscSFView(sf,viewer);
    569:   return(0);
    570: }

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

    576:    Collective on VecScatter

    578:    Input Parameters:
    579: +  sf    - vector scatter context
    580: .  tomap   - remapping plan for "to" indices (may be NULL).
    581: -  frommap - remapping plan for "from" indices (may be NULL)

    583:    Level: developer

    585:    Notes:
    586:      In the parallel case the todata contains indices from where the data is taken
    587:      (and then sent to others)! The fromdata contains indices from where the received
    588:      data is finally put locally.

    590:      In the sequential case the todata contains indices from where the data is put
    591:      and the fromdata contains indices from where the data is taken from.
    592:      This is backwards from the paralllel case!

    594: @*/
    595: PetscErrorCode  VecScatterRemap(VecScatter sf,PetscInt tomap[],PetscInt frommap[])
    596: {
    597:   PetscInt               ierr;

    602:   VecScatterRemap_Internal(sf,tomap,frommap);
    603:   if (frommap) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Unable to remap the FROM in scatters yet");
    604:   /* Mark then vector lengths as unknown because we do not know the lengths of the remapped vectors */
    605:   sf->vscat.from_n = -1;
    606:   sf->vscat.to_n   = -1;
    607:   return(0);
    608: }

    610: /*@
    611:   VecScatterSetFromOptions - Configures the vector scatter from the options database.

    613:   Collective on VecScatter

    615:   Input Parameter:
    616: . sf - The vector scatter

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

    622:   Level: beginner

    625: .seealso: VecScatterCreate(), VecScatterDestroy(), VecScatterSetUp()
    626: @*/
    627: PetscErrorCode VecScatterSetFromOptions(VecScatter sf)
    628: {

    633:   PetscObjectOptionsBegin((PetscObject)sf);

    635:   sf->vscat.beginandendtogether = PETSC_FALSE;
    636:   PetscOptionsBool("-vecscatter_merge","Use combined (merged) vector scatter begin and end","VecScatterCreate",sf->vscat.beginandendtogether,&sf->vscat.beginandendtogether,NULL);
    637:   if (sf->vscat.beginandendtogether) {PetscInfo(sf,"Using combined (merged) vector scatter begin and end\n");}

    639:   sf->vscat.packongpu = PETSC_TRUE;
    640:   PetscOptionsBool("-vecscatter_packongpu","For GPU vectors, pack needed entries on GPU, then copy packed data to CPU, then do MPI","VecScatterCreate",sf->vscat.packongpu,&sf->vscat.packongpu,NULL);
    641:   if (sf->vscat.packongpu) {PetscInfo(sf,"For GPU vectors, pack needed entries on GPU, then copy packed data to CPU, then do MPI\n");}
    642:   PetscOptionsEnd();
    643:   return(0);
    644: }

    646: /* ---------------------------------------------------------------- */
    647: /*@
    648:    VecScatterCreate - Creates a vector scatter context.

    650:    Collective on Vec

    652:    Input Parameters:
    653: +  xin - a vector that defines the shape (parallel data layout of the vector)
    654:          of vectors from which we scatter
    655: .  yin - a vector that defines the shape (parallel data layout of the vector)
    656:          of vectors to which we scatter
    657: .  ix - the indices of xin to scatter (if NULL scatters all values)
    658: -  iy - the indices of yin to hold results (if NULL fills entire vector yin)

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

    663:    Options Database Keys:
    664: +  -vecscatter_view         - Prints detail of communications
    665: .  -vecscatter_view ::ascii_info    - Print less details about communication
    666: .  -vecscatter_merge        - VecScatterBegin() handles all of the communication, VecScatterEnd() is a nop
    667:                               eliminates the chance for overlap of computation and communication
    668: -  -vecscatter_packongpu    - For GPU vectors, pack needed entries on GPU, then copy packed data to CPU, then do MPI.
    669:                               Otherwise, we might copy a segment encompassing needed entries. Default is TRUE.

    671:     Level: intermediate

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

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

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

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

    695: .seealso: VecScatterDestroy(), VecScatterCreateToAll(), VecScatterCreateToZero(), PetscSFCreate()
    696: @*/
    697: PetscErrorCode VecScatterCreate(Vec x,IS ix,Vec y,IS iy,VecScatter *newsf)
    698: {
    700:   MPI_Comm       xcomm,ycomm,bigcomm;
    701:   Vec            xx,yy;
    702:   IS             ix_old=ix,iy_old=iy,ixx,iyy;
    703:   PetscMPIInt    xcommsize,ycommsize,rank,result;
    704:   PetscInt       i,n,N,nroots,nleaves,*ilocal,xstart,ystart,ixsize,iysize,xlen,ylen;
    705:   const PetscInt *xindices,*yindices;
    706:   PetscSFNode    *iremote;
    707:   PetscLayout    xlayout,ylayout;
    708:   ISTypeID       ixid,iyid;
    709:   PetscInt       bs,bsx,bsy,min,max,m[2],ixfirst,ixstep,iyfirst,iystep;
    710:   PetscBool      can_do_block_opt=PETSC_FALSE;
    711:   PetscSF        sf;

    715:   if (!ix && !iy) SETERRQ(PetscObjectComm((PetscObject)x),PETSC_ERR_SUP,"Cannot pass default in for both input and output indices");

    717:   /* Get comm from x and y */
    718:   PetscObjectGetComm((PetscObject)x,&xcomm);
    719:   MPI_Comm_size(xcomm,&xcommsize);
    720:   PetscObjectGetComm((PetscObject)y,&ycomm);
    721:   MPI_Comm_size(ycomm,&ycommsize);
    722:   if (xcommsize > 1 && ycommsize > 1) {
    723:     MPI_Comm_compare(xcomm,ycomm,&result);
    724:     if (result == MPI_UNEQUAL) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_NOTSAMECOMM,"VecScatterCreate: parallel vectors x and y must have identical/congruent/similar communicators");
    725:   }
    726:   bs = 1; /* default, no blocking */

    728:   /*
    729:    Let P and S stand for parallel and sequential vectors respectively. There are four combinations of vecscatters: PtoP, PtoS,
    730:    StoP and StoS. The assumption of VecScatterCreate(Vec x,IS ix,Vec y,IS iy,VecScatter *newctx) is: if x is parallel, then ix
    731:    contains global indices of x. If x is sequential, ix contains local indices of x. Similarily for y and iy.

    733:    SF builds around concepts of local leaves and remote roots. We treat source vector x as roots and destination vector y as
    734:    leaves. A PtoS scatter can be naturally mapped to SF. We transform PtoP and StoP to PtoS, and treat StoS as trivial PtoS.
    735:   */

    737:   /* NULL ix or iy in VecScatterCreate(x,ix,y,iy,newctx) has special meaning. Recover them for these cases */
    738:   if (!ix) {
    739:     if (xcommsize > 1 && ycommsize == 1) { /* PtoS: null ix means the whole x will be scattered to each seq y */
    740:       VecGetSize(x,&N);
    741:       ISCreateStride(PETSC_COMM_SELF,N,0,1,&ix);
    742:     } else { /* PtoP, StoP or StoS: null ix means the whole local part of x will be scattered */
    743:       VecGetLocalSize(x,&n);
    744:       VecGetOwnershipRange(x,&xstart,NULL);
    745:       ISCreateStride(PETSC_COMM_SELF,n,xstart,1,&ix);
    746:     }
    747:   }

    749:   if (!iy) {
    750:     if (xcommsize == 1 && ycommsize > 1) { /* StoP: null iy means the whole y will be scattered to from each seq x */
    751:       VecGetSize(y,&N);
    752:       ISCreateStride(PETSC_COMM_SELF,N,0,1,&iy);
    753:     } else { /* PtoP, StoP or StoS: null iy means the whole local part of y will be scattered to */
    754:       VecGetLocalSize(y,&n);
    755:       VecGetOwnershipRange(y,&ystart,NULL);
    756:       ISCreateStride(PETSC_COMM_SELF,n,ystart,1,&iy);
    757:     }
    758:   }

    760:   /* Do error checking immediately after we have non-empty ix, iy */
    761:   ISGetLocalSize(ix,&ixsize);
    762:   ISGetLocalSize(iy,&iysize);
    763:   VecGetSize(x,&xlen);
    764:   VecGetSize(y,&ylen);
    765:   if (ixsize != iysize) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Scatter sizes of ix and iy don't match locally");
    766:   ISGetMinMax(ix,&min,&max);
    767:   if (min < 0 || max >= xlen) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"Scatter indices in ix are out of range");
    768:   ISGetMinMax(iy,&min,&max);
    769:   if (min < 0 || max >= ylen) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"Scatter indices in iy are out of range");

    771:   /* Extract info about ix, iy for further test */
    772:   ISGetTypeID_Private(ix,&ixid);
    773:   ISGetTypeID_Private(iy,&iyid);
    774:   if (ixid == IS_BLOCK)       {ISGetBlockSize(ix,&bsx);}
    775:   else if (ixid == IS_STRIDE) {ISStrideGetInfo(ix,&ixfirst,&ixstep);}

    777:   if (iyid == IS_BLOCK)      {ISGetBlockSize(iy,&bsy);}
    778:   else if (iyid == IS_STRIDE) {ISStrideGetInfo(iy,&iyfirst,&iystep);}

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

    784:      We can optimize these scatters with MPI collectives. We can also avoid costly analysis used for general scatters.
    785:   */
    786:   if (xcommsize > 1 && ycommsize == 1) { /* Ranks do not diverge at this if-test */
    787:     PetscInt    pattern[2] = {0, 0}; /* A boolean array with pattern[0] for allgather-like (ToAll) and pattern[1] for gather-like (ToZero) */
    788:     PetscLayout map;

    790:     MPI_Comm_rank(xcomm,&rank);
    791:     VecGetLayout(x,&map);
    792:     if (!rank) {
    793:       if (ixid == IS_STRIDE && iyid == IS_STRIDE && ixsize == xlen && ixfirst == 0 && ixstep == 1 && iyfirst == 0 && iystep == 1) {
    794:         /* Rank 0 scatters the whole mpi x to seq y, so it is either a ToAll or a ToZero candidate in its view */
    795:         pattern[0] = pattern[1] = 1;
    796:       }
    797:     } else {
    798:       if (ixid == IS_STRIDE && iyid == IS_STRIDE && ixsize == xlen && ixfirst == 0 && ixstep == 1 && iyfirst == 0 && iystep == 1) {
    799:         /* Other ranks also scatter the whole mpi x to seq y, so it is a ToAll candidate in their view */
    800:         pattern[0] = 1;
    801:       } else if (ixsize == 0) {
    802:         /* Other ranks do nothing, so it is a ToZero candiate */
    803:         pattern[1] = 1;
    804:       }
    805:     }

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

    810:     if (pattern[0] || pattern[1]) {
    811:       PetscSFCreate(xcomm,&sf);
    812:       PetscSFSetFromOptions(sf);
    813:       PetscSFSetGraphWithPattern(sf,map,pattern[0] ? PETSCSF_PATTERN_ALLGATHER : PETSCSF_PATTERN_GATHER);
    814:       goto functionend; /* No further analysis needed. What a big win! */
    815:     }
    816:   }

    818:   /* Continue ...
    819:      Do block optimization by taking advantage of high level info available in ix, iy.
    820:      The block optimization is valid when all of the following conditions are met:
    821:      1) ix, iy are blocked or can be blocked (i.e., strided with step=1);
    822:      2) ix, iy have the same block size;
    823:      3) all processors agree on one block size;
    824:      4) no blocks span more than one process;
    825:    */
    826:   bigcomm = (xcommsize == 1) ? ycomm : xcomm;

    828:   /* Processors could go through different path in this if-else test */
    829:   m[0] = m[1] = PETSC_MPI_INT_MIN;
    830:   if (ixid == IS_BLOCK && iyid == IS_BLOCK) {
    831:     m[0] = PetscMax(bsx,bsy);
    832:     m[1] = -PetscMin(bsx,bsy);
    833:   } else if (ixid == IS_BLOCK  && iyid == IS_STRIDE && iystep==1 && iyfirst%bsx==0) {
    834:     m[0] = bsx;
    835:     m[1] = -bsx;
    836:   } else if (ixid == IS_STRIDE && iyid == IS_BLOCK  && ixstep==1 && ixfirst%bsy==0) {
    837:     m[0] = bsy;
    838:     m[1] = -bsy;
    839:   }
    840:   /* Get max and min of bsx,bsy over all processes in one allreduce */
    841:   MPIU_Allreduce(MPI_IN_PLACE,m,2,MPIU_INT,MPI_MAX,bigcomm);
    842:   max = m[0]; min = -m[1];

    844:   /* Since we used allreduce above, all ranks will have the same min and max. min==max
    845:      implies all ranks have the same bs. Do further test to see if local vectors are dividable
    846:      by bs on ALL ranks. If they are, we are ensured that no blocks span more than one processor.
    847:    */
    848:   if (min == max && min > 1) {
    849:     VecGetLocalSize(x,&xlen);
    850:     VecGetLocalSize(y,&ylen);
    851:     m[0] = xlen%min;
    852:     m[1] = ylen%min;
    853:     MPIU_Allreduce(MPI_IN_PLACE,m,2,MPIU_INT,MPI_LOR,bigcomm);
    854:     if (!m[0] && !m[1]) can_do_block_opt = PETSC_TRUE;
    855:   }

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

    861:      xx is a little special. If x is seq, then xx is the concatenation of seq x's on ycomm. In this way,
    862:      we can treat PtoP and StoP uniformly as PtoS.
    863:    */
    864:   if (can_do_block_opt) {
    865:     const PetscInt *indices;

    867:     /* Shrink x and ix */
    868:     bs   = min;
    869:     VecCreateMPIWithArray(bigcomm,1,xlen/bs,PETSC_DECIDE,NULL,&xx); /* We only care xx's layout */
    870:     if (ixid == IS_BLOCK) {
    871:       ISBlockGetIndices(ix,&indices);
    872:       ISBlockGetLocalSize(ix,&ixsize);
    873:       ISCreateGeneral(PETSC_COMM_SELF,ixsize,indices,PETSC_COPY_VALUES,&ixx);
    874:       ISBlockRestoreIndices(ix,&indices);
    875:     } else { /* ixid == IS_STRIDE */
    876:       ISGetLocalSize(ix,&ixsize);
    877:       ISCreateStride(PETSC_COMM_SELF,ixsize/bs,ixfirst/bs,1,&ixx);
    878:     }

    880:     /* Shrink y and iy */
    881:     VecCreateMPIWithArray(ycomm,1,ylen/bs,PETSC_DECIDE,NULL,&yy);
    882:     if (iyid == IS_BLOCK) {
    883:       ISBlockGetIndices(iy,&indices);
    884:       ISBlockGetLocalSize(iy,&iysize);
    885:       ISCreateGeneral(PETSC_COMM_SELF,iysize,indices,PETSC_COPY_VALUES,&iyy);
    886:       ISBlockRestoreIndices(iy,&indices);
    887:     } else { /* iyid == IS_STRIDE */
    888:       ISGetLocalSize(iy,&iysize);
    889:       ISCreateStride(PETSC_COMM_SELF,iysize/bs,iyfirst/bs,1,&iyy);
    890:     }
    891:   } else {
    892:     ixx = ix;
    893:     iyy = iy;
    894:     yy  = y;
    895:     if (xcommsize == 1) {VecCreateMPIWithArray(bigcomm,1,xlen,PETSC_DECIDE,NULL,&xx);} else xx = x;
    896:   }

    898:   /* Now it is ready to build SF with preprocessed (xx, yy) and (ixx, iyy) */
    899:   ISGetIndices(ixx,&xindices);
    900:   ISGetIndices(iyy,&yindices);
    901:   VecGetLayout(xx,&xlayout);

    903:   if (ycommsize > 1) {
    904:     /* PtoP or StoP */

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

    909:        I did it through a temp sf, but later I thought the old design was inefficient and also distorted log view.
    910:        We want to mape one VecScatterCreate() call to one PetscSFCreate() call. The old design mapped to three
    911:        PetscSFCreate() calls. This code is on critical path of VecScatterSetUp and is used by every VecScatterCreate.
    912:        So I commented it out and did another optimized implementation. The commented code is left here for reference.
    913:      */
    914: #if 0
    915:     const PetscInt *degree;
    916:     PetscSF        tmpsf;
    917:     PetscInt       inedges=0,*leafdata,*rootdata;

    919:     VecGetOwnershipRange(xx,&xstart,NULL);
    920:     VecGetLayout(yy,&ylayout);
    921:     VecGetOwnershipRange(yy,&ystart,NULL);

    923:     VecGetLocalSize(yy,&nroots);
    924:     ISGetLocalSize(iyy,&nleaves);
    925:     PetscMalloc2(nleaves,&iremote,nleaves*2,&leafdata);

    927:     for (i=0; i<nleaves; i++) {
    928:       PetscLayoutFindOwnerIndex(ylayout,yindices[i],&iremote[i].rank,&iremote[i].index);
    929:       leafdata[2*i]   = yindices[i];
    930:       leafdata[2*i+1] = (xcommsize > 1)? xindices[i] : xindices[i] + xstart;
    931:     }

    933:     PetscSFCreate(ycomm,&tmpsf);
    934:     PetscSFSetGraph(tmpsf,nroots,nleaves,NULL,PETSC_USE_POINTER,iremote,PETSC_USE_POINTER);

    936:     PetscSFComputeDegreeBegin(tmpsf,&degree);
    937:     PetscSFComputeDegreeEnd(tmpsf,&degree);

    939:     for (i=0; i<nroots; i++) inedges += degree[i];
    940:     PetscMalloc1(inedges*2,&rootdata);
    941:     PetscSFGatherBegin(tmpsf,MPIU_2INT,leafdata,rootdata);
    942:     PetscSFGatherEnd(tmpsf,MPIU_2INT,leafdata,rootdata);

    944:     PetscFree2(iremote,leafdata);
    945:     PetscSFDestroy(&tmpsf);

    947:     /* rootdata contains global index pairs (i, j). j's are owned by the current process, but i's can point to anywhere.
    948:        We convert j to local, and convert i to (rank, index). In the end, we get an PtoS suitable for building SF.
    949:      */
    950:     nleaves = inedges;
    951:     VecGetLocalSize(xx,&nroots);
    952:     PetscMalloc1(nleaves,&ilocal);
    953:     PetscMalloc1(nleaves,&iremote);

    955:     for (i=0; i<inedges; i++) {
    956:       ilocal[i] = rootdata[2*i] - ystart; /* covert y's global index to local index */
    957:       PetscLayoutFindOwnerIndex(xlayout,rootdata[2*i+1],&iremote[i].rank,&iremote[i].index); /* convert x's global index to (rank, index) */
    958:     }
    959:     PetscFree(rootdata);
    960: #else
    961:     PetscInt       j,k,n,disp,rlentotal,*sstart,*xindices_sorted,*yindices_sorted;
    962:     const PetscInt *yrange;
    963:     PetscMPIInt    nsend,nrecv,nreq,count,yrank,*slens,*rlens,*sendto,*recvfrom,tag1,tag2;
    964:     PetscInt       *rxindices,*ryindices;
    965:     MPI_Request    *reqs,*sreqs,*rreqs;

    967:     /* Sorting makes code simpler, faster and also helps getting rid of many O(P) arrays, which hurt scalability at large scale
    968:        yindices_sorted - sorted yindices
    969:        xindices_sorted - xindices sorted along with yindces
    970:      */
    971:     ISGetLocalSize(ixx,&n); /*ixx, iyy have the same local size */
    972:     PetscMalloc2(n,&xindices_sorted,n,&yindices_sorted);
    973:     PetscArraycpy(xindices_sorted,xindices,n);
    974:     PetscArraycpy(yindices_sorted,yindices,n);
    975:     PetscSortIntWithArray(n,yindices_sorted,xindices_sorted);
    976:     VecGetOwnershipRange(xx,&xstart,NULL);
    977:     if (xcommsize == 1) {for (i=0; i<n; i++) xindices_sorted[i] += xstart;} /* Convert to global indices */

    979:     /*=============================================================================
    980:              Calculate info about messages I need to send
    981:       =============================================================================*/
    982:     /* nsend    - number of non-empty messages to send
    983:        sendto   - [nsend] ranks I will send messages to
    984:        sstart   - [nsend+1] sstart[i] is the start index in xsindices_sorted[] I send to rank sendto[i]
    985:        slens    - [ycommsize] I want to send slens[i] entries to rank i.
    986:      */
    987:     VecGetLayout(yy,&ylayout);
    988:     PetscLayoutGetRanges(ylayout,&yrange);
    989:     PetscCalloc1(ycommsize,&slens); /* The only O(P) array in this algorithm */

    991:     i = j = nsend = 0;
    992:     while (i < n) {
    993:       if (yindices_sorted[i] >= yrange[j+1]) { /* If i-th index is out of rank j's bound */
    994:         do {j++;} while (yindices_sorted[i] >= yrange[j+1] && j < ycommsize); /* Increase j until i-th index falls in rank j's bound */
    995:         if (j == ycommsize) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Index %D not owned by any process, upper bound %D",yindices_sorted[i],yrange[ycommsize]);
    996:       }
    997:       i++;
    998:       if (!slens[j]++) nsend++;
    999:     }

    1001:     PetscMalloc2(nsend+1,&sstart,nsend,&sendto);

    1003:     sstart[0] = 0;
    1004:     for (i=j=0; i<ycommsize; i++) {
    1005:       if (slens[i]) {
    1006:         sendto[j]   = (PetscMPIInt)i;
    1007:         sstart[j+1] = sstart[j] + slens[i];
    1008:         j++;
    1009:       }
    1010:     }

    1012:     /*=============================================================================
    1013:       Calculate the reverse info about messages I will recv
    1014:       =============================================================================*/
    1015:     /* nrecv     - number of messages I will recv
    1016:        recvfrom  - [nrecv] ranks I recv from
    1017:        rlens     - [nrecv] I will recv rlens[i] entries from rank recvfrom[i]
    1018:        rlentotal - sum of rlens[]
    1019:        rxindices - [rlentotal] recv buffer for xindices_sorted
    1020:        ryindices - [rlentotal] recv buffer for yindices_sorted
    1021:      */
    1022:     PetscGatherNumberOfMessages(ycomm,NULL,slens,&nrecv);
    1023:     PetscGatherMessageLengths(ycomm,nsend,nrecv,slens,&recvfrom,&rlens);
    1024:     PetscFree(slens); /* Free the O(P) array ASAP */
    1025:     rlentotal = 0; for (i=0; i<nrecv; i++) rlentotal += rlens[i];

    1027:     /*=============================================================================
    1028:       Communicate with processors in recvfrom[] to populate rxindices and ryindices
    1029:       ============================================================================*/
    1030:     PetscCommGetNewTag(ycomm,&tag1);
    1031:     PetscCommGetNewTag(ycomm,&tag2);
    1032:     PetscMalloc2(rlentotal,&rxindices,rlentotal,&ryindices);
    1033:     PetscMPIIntCast((nsend+nrecv)*2,&nreq);
    1034:     PetscMalloc1(nreq,&reqs);
    1035:     sreqs = reqs;
    1036:     rreqs = reqs + nsend*2;

    1038:     for (i=disp=0; i<nrecv; i++) {
    1039:       count = rlens[i];
    1040:       MPI_Irecv(rxindices+disp,count,MPIU_INT,recvfrom[i],tag1,ycomm,rreqs+i);
    1041:       MPI_Irecv(ryindices+disp,count,MPIU_INT,recvfrom[i],tag2,ycomm,rreqs+nrecv+i);
    1042:       disp += rlens[i];
    1043:     }

    1045:     for (i=0; i<nsend; i++) {
    1046:       PetscMPIIntCast(sstart[i+1]-sstart[i],&count);
    1047:       MPI_Isend(xindices_sorted+sstart[i],count,MPIU_INT,sendto[i],tag1,ycomm,sreqs+i);
    1048:       MPI_Isend(yindices_sorted+sstart[i],count,MPIU_INT,sendto[i],tag2,ycomm,sreqs+nsend+i);
    1049:     }
    1050:     MPI_Waitall(nreq,reqs,MPI_STATUS_IGNORE);

    1052:     /* Transform VecScatter into SF */
    1053:     nleaves = rlentotal;
    1054:     PetscMalloc1(nleaves,&ilocal);
    1055:     PetscMalloc1(nleaves,&iremote);
    1056:     MPI_Comm_rank(ycomm,&yrank);
    1057:     for (i=disp=0; i<nrecv; i++) {
    1058:       for (j=0; j<rlens[i]; j++) {
    1059:         k               = disp + j; /* k-th index pair */
    1060:         ilocal[k]       = ryindices[k] - yrange[yrank]; /* Convert y's global index to local index */
    1061:         PetscLayoutFindOwnerIndex(xlayout,rxindices[k],&rank,&iremote[k].index); /* Convert x's global index to (rank, index) */
    1062:         iremote[k].rank = rank;
    1063:       }
    1064:       disp += rlens[i];
    1065:     }

    1067:     PetscFree2(sstart,sendto);
    1068:     PetscFree(slens);
    1069:     PetscFree(rlens);
    1070:     PetscFree(recvfrom);
    1071:     PetscFree(reqs);
    1072:     PetscFree2(rxindices,ryindices);
    1073:     PetscFree2(xindices_sorted,yindices_sorted);
    1074: #endif
    1075:   } else {
    1076:     /* PtoS or StoS */
    1077:     ISGetLocalSize(iyy,&nleaves);
    1078:     PetscMalloc1(nleaves,&ilocal);
    1079:     PetscMalloc1(nleaves,&iremote);
    1080:     PetscArraycpy(ilocal,yindices,nleaves);
    1081:     for (i=0; i<nleaves; i++) {
    1082:       PetscLayoutFindOwnerIndex(xlayout,xindices[i],&rank,&iremote[i].index);
    1083:       iremote[i].rank = rank;
    1084:     }
    1085:   }

    1087:   /* MUST build SF on xx's comm, which is not necessarily identical to yy's comm.
    1088:      In SF's view, xx contains the roots (i.e., the remote) and iremote[].rank are ranks in xx's comm.
    1089:      yy contains leaves, which are local and can be thought as part of PETSC_COMM_SELF. */
    1090:   PetscSFCreate(PetscObjectComm((PetscObject)xx),&sf);
    1091:   PetscSFSetFromOptions(sf);
    1092:   VecGetLocalSize(xx,&nroots);
    1093:   PetscSFSetGraph(sf,nroots,nleaves,ilocal,PETSC_OWN_POINTER,iremote,PETSC_OWN_POINTER); /* Give ilocal/iremote to petsc and no need to free them here */

    1095:   /* Free memory no longer needed */
    1096:   ISRestoreIndices(ixx,&xindices);
    1097:   ISRestoreIndices(iyy,&yindices);
    1098:   if (can_do_block_opt) {
    1099:     VecDestroy(&xx);
    1100:     VecDestroy(&yy);
    1101:     ISDestroy(&ixx);
    1102:     ISDestroy(&iyy);
    1103:   } else if (xcommsize == 1) {
    1104:     VecDestroy(&xx);
    1105:   }

    1107: functionend:
    1108:   sf->vscat.bs = bs;
    1109:   if (sf->vscat.bs > 1) {
    1110:     MPI_Type_contiguous(sf->vscat.bs,MPIU_SCALAR,&sf->vscat.unit);
    1111:     MPI_Type_commit(&sf->vscat.unit);
    1112:   } else {
    1113:     sf->vscat.unit = MPIU_SCALAR;
    1114:   }
    1115:   VecGetLocalSize(x,&sf->vscat.from_n);
    1116:   VecGetLocalSize(y,&sf->vscat.to_n);
    1117:   if (!ix_old) {ISDestroy(&ix);} /* We created helper ix, iy. Free them */
    1118:   if (!iy_old) {ISDestroy(&iy);}

    1120:   /* Set default */
    1121:   VecScatterSetFromOptions(sf);

    1123:   *newsf = sf;
    1124:   return(0);
    1125: }

    1127: /*@C
    1128:       VecScatterCreateToAll - Creates a vector and a scatter context that copies all
    1129:           vector values to each processor

    1131:   Collective on Vec

    1133:   Input Parameter:
    1134: .  vin  - input MPIVEC

    1136:   Output Parameter:
    1137: +  ctx - scatter context
    1138: -  vout - output SEQVEC that is large enough to scatter into

    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: $        VecScatterCreateToAll(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:     Do NOT create a vector and then pass it in as the final argument vout! vout is created by this routine
    1157:   automatically (unless you pass NULL in for that argument if you do not need it).

    1159: .seealso VecScatterCreate(), VecScatterCreateToZero(), VecScatterBegin(), VecScatterEnd()

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

    1166:   PetscInt       N;
    1167:   IS             is;
    1168:   Vec            tmp;
    1169:   Vec            *tmpv;
    1170:   PetscBool      tmpvout = PETSC_FALSE;

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

    1184:   /* Create seq vec on each proc, with the same size of the original mpi vec */
    1185:   VecGetSize(vin,&N);
    1186:   VecCreateSeq(PETSC_COMM_SELF,N,tmpv);
    1187:   VecSetFromOptions(*tmpv);
    1188:   /* Create the VecScatter ctx with the communication info */
    1189:   ISCreateStride(PETSC_COMM_SELF,N,0,1,&is);
    1190:   VecScatterCreate(vin,is,*tmpv,is,ctx);
    1191:   ISDestroy(&is);
    1192:   if (tmpvout) {VecDestroy(tmpv);}
    1193:   return(0);
    1194: }

    1197: /*@C
    1198:       VecScatterCreateToZero - Creates an output vector and a scatter context used to
    1199:               copy all vector values into the output vector on the zeroth processor

    1201:   Collective on Vec

    1203:   Input Parameter:
    1204: .  vin  - input MPIVEC

    1206:   Output Parameter:
    1207: +  ctx - scatter context
    1208: -  vout - output SEQVEC that is large enough to scatter into on processor 0 and
    1209:           of length zero on all other processors

    1211:   Level: intermediate

    1213:    Note: vout may be NULL [PETSC_NULL_VEC from fortran] if you do not
    1214:    need to have it created

    1216:    Usage:
    1217: $        VecScatterCreateToZero(vin,&ctx,&vout);
    1218: $
    1219: $        // scatter as many times as you need
    1220: $        VecScatterBegin(ctx,vin,vout,INSERT_VALUES,SCATTER_FORWARD);
    1221: $        VecScatterEnd(ctx,vin,vout,INSERT_VALUES,SCATTER_FORWARD);
    1222: $
    1223: $        // destroy scatter context and local vector when no longer needed
    1224: $        VecScatterDestroy(&ctx);
    1225: $        VecDestroy(&vout);

    1227: .seealso VecScatterCreate(), VecScatterCreateToAll(), VecScatterBegin(), VecScatterEnd()

    1229:     Do NOT create a vector and then pass it in as the final argument vout! vout is created by this routine
    1230:   automatically (unless you pass NULL in for that argument if you do not need it).

    1232: @*/
    1233: PetscErrorCode  VecScatterCreateToZero(Vec vin,VecScatter *ctx,Vec *vout)
    1234: {

    1237:   PetscInt       N;
    1238:   PetscMPIInt    rank;
    1239:   IS             is;
    1240:   Vec            tmp;
    1241:   Vec            *tmpv;
    1242:   PetscBool      tmpvout = PETSC_FALSE;

    1248:   if (vout) {
    1250:     tmpv = vout;
    1251:   } else {
    1252:     tmpvout = PETSC_TRUE;
    1253:     tmpv    = &tmp;
    1254:   }

    1256:   /* Create vec on each proc, with the same size of the original mpi vec (all on process 0)*/
    1257:   VecGetSize(vin,&N);
    1258:   MPI_Comm_rank(PetscObjectComm((PetscObject)vin),&rank);
    1259:   if (rank) N = 0;
    1260:   VecCreateSeq(PETSC_COMM_SELF,N,tmpv);
    1261:   VecSetFromOptions(*tmpv);
    1262:   /* Create the VecScatter ctx with the communication info */
    1263:   ISCreateStride(PETSC_COMM_SELF,N,0,1,&is);
    1264:   VecScatterCreate(vin,is,*tmpv,is,ctx);
    1265:   ISDestroy(&is);
    1266:   if (tmpvout) {VecDestroy(tmpv);}
    1267:   return(0);
    1268: }

    1270: /*@
    1271:    VecScatterBegin - Begins a generalized scatter from one vector to
    1272:    another. Complete the scattering phase with VecScatterEnd().

    1274:    Neighbor-wise Collective on VecScatter

    1276:    Input Parameters:
    1277: +  sf - scatter context generated by VecScatterCreate()
    1278: .  x - the vector from which we scatter
    1279: .  y - the vector to which we scatter
    1280: .  addv - either ADD_VALUES, MAX_VALUES, MIN_VALUES or INSERT_VALUES, with INSERT_VALUES mode any location
    1281:           not scattered to retains its old value; i.e. the vector is NOT first zeroed.
    1282: -  mode - the scattering mode, usually SCATTER_FORWARD.  The available modes are:
    1283:     SCATTER_FORWARD or SCATTER_REVERSE

    1286:    Level: intermediate

    1288:    Options Database: See VecScatterCreate()

    1290:    Notes:
    1291:    The vectors x and y need not be the same vectors used in the call
    1292:    to VecScatterCreate(), but x must have the same parallel data layout
    1293:    as that passed in as the x to VecScatterCreate(), similarly for the y.
    1294:    Most likely they have been obtained from VecDuplicate().

    1296:    You cannot change the values in the input vector between the calls to VecScatterBegin()
    1297:    and VecScatterEnd().

    1299:    If you use SCATTER_REVERSE the two arguments x and y should be reversed, from
    1300:    the SCATTER_FORWARD.

    1302:    y[iy[i]] = x[ix[i]], for i=0,...,ni-1

    1304:    This scatter is far more general than the conventional
    1305:    scatter, since it can be a gather or a scatter or a combination,
    1306:    depending on the indices ix and iy.  If x is a parallel vector and y
    1307:    is sequential, VecScatterBegin() can serve to gather values to a
    1308:    single processor.  Similarly, if y is parallel and x sequential, the
    1309:    routine can scatter from one processor to many processors.

    1312: .seealso: VecScatterCreate(), VecScatterEnd()
    1313: @*/
    1314: PetscErrorCode  VecScatterBegin(VecScatter sf,Vec x,Vec y,InsertMode addv,ScatterMode mode)
    1315: {
    1317:   PetscInt       to_n,from_n;

    1323:   if (PetscDefined(USE_DEBUG)) {
    1324:     /*
    1325:      Error checking to make sure these vectors match the vectors used
    1326:      to create the vector scatter context. -1 in the from_n and to_n indicate the
    1327:      vector lengths are unknown (for example with mapped scatters) and thus
    1328:      no error checking is performed.
    1329:      */
    1330:     if (sf->vscat.from_n >= 0 && sf->vscat.to_n >= 0) {
    1331:       VecGetLocalSize(x,&from_n);
    1332:       VecGetLocalSize(y,&to_n);
    1333:       if (mode & SCATTER_REVERSE) {
    1334:         if (to_n != sf->vscat.from_n) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Vector wrong size %D for scatter %D (scatter reverse and vector to != sf from size)",to_n,sf->vscat.from_n);
    1335:         if (from_n != sf->vscat.to_n) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Vector wrong size %D for scatter %D (scatter reverse and vector from != sf to size)",from_n,sf->vscat.to_n);
    1336:       } else {
    1337:         if (to_n != sf->vscat.to_n) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Vector wrong size %D for scatter %D (scatter forward and vector to != sf to size)",to_n,sf->vscat.to_n);
    1338:         if (from_n != sf->vscat.from_n) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Vector wrong size %D for scatter %D (scatter forward and vector from != sf from size)",from_n,sf->vscat.from_n);
    1339:       }
    1340:     }
    1341:   }

    1343:   sf->vscat.logging = PETSC_TRUE;
    1344:   PetscLogEventBegin(VEC_ScatterBegin,sf,x,y,0);
    1345:   VecScatterBegin_Internal(sf,x,y,addv,mode);
    1346:   if (sf->vscat.beginandendtogether) {
    1347:     VecScatterEnd_Internal(sf,x,y,addv,mode);
    1348:   }
    1349:   PetscLogEventEnd(VEC_ScatterBegin,sf,x,y,0);
    1350:   sf->vscat.logging = PETSC_FALSE;
    1351:   return(0);
    1352: }

    1354: /*@
    1355:    VecScatterEnd - Ends a generalized scatter from one vector to another.  Call
    1356:    after first calling VecScatterBegin().

    1358:    Neighbor-wise Collective on VecScatter

    1360:    Input Parameters:
    1361: +  sf - scatter context generated by VecScatterCreate()
    1362: .  x - the vector from which we scatter
    1363: .  y - the vector to which we scatter
    1364: .  addv - one of ADD_VALUES, MAX_VALUES, MIN_VALUES or INSERT_VALUES
    1365: -  mode - the scattering mode, usually SCATTER_FORWARD.  The available modes are:
    1366:      SCATTER_FORWARD, SCATTER_REVERSE

    1368:    Level: intermediate

    1370:    Notes:
    1371:    If you use SCATTER_REVERSE the arguments x and y should be reversed, from the SCATTER_FORWARD.

    1373:    y[iy[i]] = x[ix[i]], for i=0,...,ni-1

    1375: .seealso: VecScatterBegin(), VecScatterCreate()
    1376: @*/
    1377: PetscErrorCode  VecScatterEnd(VecScatter sf,Vec x,Vec y,InsertMode addv,ScatterMode mode)
    1378: {

    1385:   if (!sf->vscat.beginandendtogether) {
    1386:     sf->vscat.logging = PETSC_TRUE;
    1387:     PetscLogEventBegin(VEC_ScatterEnd,sf,x,y,0);
    1388:     VecScatterEnd_Internal(sf,x,y,addv,mode);
    1389:     PetscLogEventEnd(VEC_ScatterEnd,sf,x,y,0);
    1390:     sf->vscat.logging = PETSC_FALSE;
    1391:   }
    1392:   return(0);
    1393: }