NAME

       MPI_Neighbor_alltoallw,  MPI_Ineighbor_alltoallw  -  All  processes  send data of different types to, and
       receive data of different types from, all processes

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Neighbor_alltoallw(const void *sendbuf, const int sendcounts[],
            const MPI_Aint sdispls[], const MPI_Datatype sendtypes[],
            void *recvbuf, const int recvcounts[], const MPI_Aint rdispls[],
            const MPI_Datatype recvtypes[], MPI_Comm comm)

       int MPI_Ineighbor_alltoallw(const void *sendbuf, const int sendcounts[],
            const MPI_Aint sdispls[], const MPI_Datatype sendtypes[],
            void *recvbuf, const int recvcounts[], const MPI_Aint rdispls[],
            const MPI_Datatype recvtypes[], MPI_Comm comm, MPI_Request *request)

Fortran Syntax

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_NEIGHBOR_ALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
            RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, IERROR)

            <type>    SENDBUF(*), RECVBUF(*)
            INTEGER   SENDCOUNTS(*), SENDTYPES(*)
            INTEGER   RECVCOUNTS(*), RECVTYPES(*)
            INTEGER(KIND=MPI_ADDRESS_KIND) SDISPLS(*), RDISPLS(*)
            INTEGER   COMM, IERROR

       MPI_INEIGHBOR_ALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
            RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, REQUEST, IERROR)

            <type>    SENDBUF(*), RECVBUF(*)
            INTEGER   SENDCOUNTS(*), SENDTYPES(*)
            INTEGER   RECVCOUNTS(*), RECVTYPES(*)
            INTEGER(KIND=MPI_ADDRESS_KIND) SDISPLS(*), RDISPLS(*)
            INTEGER   COMM, REQUEST, IERROR

Fortran 2008 Syntax

       USE mpi_f08
       MPI_Neighbor_alltoallw(sendbuf, sendcounts, sdispls, sendtypes, recvbuf,
                 recvcounts, rdispls, recvtypes, comm, ierror)

            TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
            TYPE(*), DIMENSION(..) :: recvbuf
            INTEGER, INTENT(IN) :: sendcounts(*), recvcounts(*)
            INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: sdispls(*), rdispls(*)
            TYPE(MPI_Datatype), INTENT(IN) :: sendtypes(*), recvtypes(*)
            TYPE(MPI_Comm), INTENT(IN) :: comm
            INTEGER, OPTIONAL, INTENT(OUT) :: ierror

       MPI_Ineighbor_alltoallw(sendbuf, sendcounts, sdispls, sendtypes, recvbuf,
                 recvcounts, rdispls, recvtypes, comm, request, ierror)

            TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
            TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
            INTEGER, INTENT(IN), ASYNCHRONOUS :: sendcounts(*), recvcounts(*)
            INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN), ASYNCHRONOUS ::
            sdispls(*), rdispls(*)
            TYPE(MPI_Datatype), INTENT(IN), ASYNCHRONOUS :: sendtypes(*),
            recvtypes(*)
            TYPE(MPI_Comm), INTENT(IN) :: comm
            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 neighbor i.

       sdispls     Integer array, where entry i specifies the displacement (in bytes, offset from sendbuf)  from
                   which to send data to neighbor i.

       sendtypes   Datatype array, where entry i specifies the datatype to use when sending data to neighbor i.

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

       rdispls     Integer  array,  where  entry j specifies the displacement (in bytes, offset from recvbuf) to
                   which data from neighbor j should be written.

       recvtypes   Datatype array, where entry j specifies the datatype to use when receiving data from neighbor
                   j.

       comm        Communicator over which data is to be exchanged.

OUTPUT PARAMETERS

       recvbuf     Address of receive buffer.

       request   Request (handle, non-blocking only).

       IERROR      Fortran only: Error status.

DESCRIPTION

       MPI_Neighbor_alltoallw  is  a  generalized  collective  operation in which all processes send data to and
       receive data from all neighbors. It adds flexibility to MPI_Neighbor_alltoallv by allowing  the  user  to
       specify  the  datatype  of  individual  data  blocks (in addition to displacement and element count). Its
       operation can be thought of in the following way, where each process performs 2n (n being the  number  of
       neighbors in the topology of communicator comm) independent point-to-point communications.  The neighbors
       and buffer layout are determined by the topology of comm.

               MPI_Cart_get(comm, maxdims, dims, periods, coords);
               for (dim = 0, i = 0 ; dim < dims ; ++dim) {
                   MPI_Cart_shift(comm, dim, 1, &r0, &r1);
                   MPI_Isend(sendbuf + sdispls[i]  * extent(sendtype),
                             sendcount, sendtypes[i], r0, ..., comm, ...);
                   MPI_Irecv(recvbuf + rdispls[i] * extent(recvtype),
                             recvcount, recvtypes[i], r0, ..., comm, ...);
                   ++i;
                   MPI_Isend(sendbuf + sdispls[i] * extent(sendtype),
                             sendcount, sendtypes[i], r1, ..., comm, &req[i]);
                   MPI_Irecv(recvbuf + rdispls[i] * extent(recvtype),
                             recvcount, recvtypes[i], r1, ..., comm, ...);
                   ++i;
               }

               MPI_Wait_all (...);

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

       Process j sends the k-th block of its local sendbuf to neighbor 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 and types of  data  to  different  processes  in  the
       communicator.

NOTES

       The MPI_IN_PLACE option for sendbuf is not meaningful for this operation

       The  specification  of  counts, types, 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 bytes.  Compare this to MPI_Neighbor_alltoallv, where
       these offsets are measured in units of sendtype and recvtype, respectively.

ERRORS

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

       Before  the  error  value  is  returned,  the current MPI error handler is called. By default, this error
       handler aborts the MPI job, except for I/O function  errors.  The  error  handler  may  be  changed  with
       MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values
       to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

SEE ALSO

       MPI_Neighbor_alltoall
       MPI_Neighbor_alltoallv
       MPI_Cart_create
       MPI_Graph_create
       MPI_Dist_graph_create