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

       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

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