plucky (3) MPI_Alltoallv.openmpi.3.gz

Provided by: openmpi-doc_5.0.7-1_all bug

SYNTAX

   C Syntax
          #include <mpi.h>

          int MPI_Alltoallv(const void *sendbuf, const int sendcounts[],
               const int sdispls[], MPI_Datatype sendtype,
               void *recvbuf, const int recvcounts[],
               const int rdispls[], MPI_Datatype recvtype, MPI_Comm comm)

          int MPI_Ialltoallv(const void *sendbuf, const int sendcounts[],
               const int sdispls[], MPI_Datatype sendtype,
               void *recvbuf, const int recvcounts[],
               const int rdispls[], MPI_Datatype recvtype, MPI_Comm comm,
               MPI_Request *request)

          int MPI_Alltoallv_init(const void *sendbuf, const int sendcounts[],
               const int sdispls[], MPI_Datatype sendtype,
               void *recvbuf, const int recvcounts[],
               const int rdispls[], MPI_Datatype recvtype, MPI_Comm comm,
               MPI_Info info, MPI_Request *request)

   Fortran Syntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_ALLTOALLV(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPE,
               RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPE, COMM, IERROR)

               <type>  SENDBUF(*), RECVBUF(*)
               INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPE
               INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPE
               INTEGER COMM, IERROR

          MPI_IALLTOALLV(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPE,
               RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPE, COMM, REQUEST, IERROR)

               <type>  SENDBUF(*), RECVBUF(*)
               INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPE
               INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPE
               INTEGER COMM, REQUEST, IERROR

          MPI_ALLTOALLV_INIT(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPE,
               RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPE, COMM, INFO, REQUEST, IERROR)

               <type>  SENDBUF(*), RECVBUF(*)
               INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPE
               INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPE
               INTEGER COMM, INFO, REQUEST, IERROR

   Fortran 2008 Syntax
          USE mpi_f08
          MPI_Alltoallv(sendbuf, sendcounts, sdispls, sendtype, recvbuf, recvcounts,
                       rdispls, recvtype, comm, ierror)

               TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
               TYPE(*), DIMENSION(..) :: recvbuf
               INTEGER, INTENT(IN) :: sendcounts(*), sdispls(*), recvcounts(*),
               rdispls(*)
               TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
               TYPE(MPI_Comm), INTENT(IN) :: comm
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

          MPI_Ialltoallv(sendbuf, sendcounts, sdispls, sendtype, recvbuf, recvcounts,
                       rdispls, recvtype, comm, request, ierror)

               TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
               TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
               INTEGER, INTENT(IN), ASYNCHRONOUS :: sendcounts(*), sdispls(*),
               recvcounts(*), rdispls(*)
               TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
               TYPE(MPI_Comm), INTENT(IN) :: comm
               TYPE(MPI_Request), INTENT(OUT) :: request
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

          MPI_Alltoallv_init(sendbuf, sendcounts, sdispls, sendtype, recvbuf, recvcounts,
                               rdispls, recvtype, comm, info, request, ierror)

               TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
               TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
               INTEGER, INTENT(IN), ASYNCHRONOUS :: sendcounts(*), sdispls(*),
               recvcounts(*), rdispls(*)
               TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
               TYPE(MPI_Comm), INTENT(IN) :: comm
               TYPE(MPI_Info), INTENT(IN) :: info
               TYPE(MPI_Request), INTENT(OUT) :: request
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

sendbuf: Starting address of send buffer.

       • sendcounts: Integer array, where entry i specifies the number of elements to send to rank i.

       • sdispls: Integer array, where entry i specifies the displacement (offset  from  sendbuf,  in  units  of
         sendtype) from which to send data to rank i.

       • sendtype: Datatype of send buffer elements.

       • recvcounts: Integer array, where entry j specifies the number of elements to receive from rank j.

       • rdispls:  Integer  array,  where  entry  j specifies the displacement (offset from recvbuf, in units of
         recvtype) to which data from rank j should be written.

       • recvtype: Datatype of receive buffer elements.

       • comm: Communicator over which data is to be exchanged.

       • info: Info (handle, persistent only)

OUTPUT PARAMETERS

recvbuf: Address of receive buffer.

       • request: Request (handle, non-blocking only).

       • ierror: Fortran only: Error status.

DESCRIPTION

       MPI_Alltoallv is a generalized collective operation in which all processes send data to and receive  data
       from  all  other  processes.  It adds flexibility to MPI_Alltoall by allowing the user to specify data to
       send and receive vector-style (via a displacement and element count).  The operation of this routine  can
       be thought of as follows, where each process performs 2n (n being the number of processes in communicator
       comm) independent point-to-point communications (including communication with itself).

          MPI_Comm_size(comm, &n);
          for (i = 0, i < n; i++)
              MPI_Send(sendbuf + sdispls[i] * extent(sendtype),
                  sendcounts[i], sendtype, i, ..., comm);
          for (i = 0, i < n; i++)
              MPI_Recv(recvbuf + rdispls[i] * extent(recvtype),
                  recvcounts[i], recvtype, i, ..., comm);

       Process j sends the k-th block of its local sendbuf to process k, which places the data in the j-th block
       of its local recvbuf.

       When  a pair of processes exchanges data, each may pass different element count and datatype arguments so
       long as the sender specifies the same amount of data to send  (in  bytes)  as  the  receiver  expects  to
       receive.

       Note  that  process  i  may send a different amount of data to process j than it receives from process j.
       Also, a process may send entirely different amounts of data to different processes in the communicator.

       WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR

       When the communicator is an inter-communicator, the gather operation occurs in two phases.  The  data  is
       gathered  from  all  the  members of the first group and received by all the members of the second group.
       Then the data is gathered from all the members of the second group and received by all the members of the
       first. The operation exhibits a symmetric, full-duplex behavior.

       The  first group defines the root process. The root process uses MPI_ROOT as the value of root. All other
       processes in the first group use MPI_PROC_NULL as the value of root. All processes in  the  second  group
       use the rank of the root process in the first group as the value of root.

       When  the communicator is an intra-communicator, these groups are the same, and the operation occurs in a
       single phase.

USE OF IN-PLACE OPTION

       When the communicator is an intracommunicator, you can perform  an  all-to-all  operation  in-place  (the
       output  buffer  is  used  as the input buffer). Use the variable MPI_IN_PLACE as the value of sendbuf. In
       this case, sendcounts, sdispls, and sendtype are ignored. The input data of each process is assumed to be
       in the area where that process would receive its own contribution to the receive buffer.

NOTES

       The specification of counts and displacements should not cause any location to be written more than once.

       All  arguments on all processes are significant. The comm argument, in particular, must describe the same
       communicator on all processes.

       The offsets of sdispls and rdispls are measured in units of sendtype and recvtype, respectively.  Compare
       this to MPI_Alltoallw, where these offsets are measured in bytes.

ERRORS

       Almost  all  MPI  routines  return  an  error  value; C routines as the return result of the function and
       Fortran routines in the last argument.

       Before the error value is returned, the current MPI  error  handler  associated  with  the  communication
       object  (e.g.,  communicator, window, file) is called.  If no communication object is associated with the
       MPI call, then the call is considered attached to MPI_COMM_SELF and will call the  associated  MPI  error
       handler.   When   MPI_COMM_SELF   is   not  initialized  (i.e.,  before  MPI_Init/MPI_Init_thread,  after
       MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial  error  handler.
       The  initial  error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
       the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info  key  to  MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.   If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
       error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is  called  for  all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called on a communicator, it acts as if MPI_Abort was called on  that  communicator.  If  called  on  a
         window  or file, acts as if MPI_Abort was called on a communicator containing the group of processes in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandlerMPI_File_create_errhandler then MPI_File_set_errhandlerMPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_initMPI_Win_create_errhandler then MPI_Win_set_errhandler

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

       See the Error Handling section of the MPI-3.1 standard for more information.

       SEE ALSO:MPI_AlltoallMPI_Alltoallw

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                                  MPI_ALLTOALLV(3)