MPI_Neighbor_alltoall(3)

NAME
MPI_Neighbor_alltoall - Sends and Receivs data from all neighboring processes

SYNOPSIS
int MPI_Neighbor_alltoall(const void *sendbuf, int sendcount,
MPI_Datatype sendtype, void *recvbuf, int recvcount,
MPI_Datatype recvtype, MPI_Comm comm)
int MPI_Neighbor_alltoall_c(const void *sendbuf, MPI_Count sendcount,
MPI_Datatype sendtype, void *recvbuf,
MPI_Count recvcount, MPI_Datatype recvtype,
MPI_Comm comm)

INPUT PARAMETERS
sendbuf
    - starting address of send buffer (choice)
sendcount
    - number of elements sent to each neighbor (non-negative integer)
sendtype
    - data type of send buffer elements (handle)
recvcount
    - number of elements received from each neighbor (non-negative integer)
recvtype
    - data type of receive buffer elements (handle)
comm
    - communicator with topology structure (handle)

OUTPUT PARAMETERS
recvbuf
    - starting address of receive buffer (choice)

NOTES
In this function, each process i receives data items from each process j if an edge (j,i) exists in the topology graph or Cartesian topology. Similarly, each process i sends data items to all processes j where an edge (i,j) exists. This call is more general than MPI_NEIGHBOR_ALLGATHER in that different data items can be sent to each neighbor. The k-th block in send buffer is sent to the k-th neighboring process and the l-th block in the receive buffer is received from the l-th neighbor.

THREAD AND INTERRUPT SAFETY
This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.

NOTES FOR FORTRAN
All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement. All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.

ERRORS
All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. 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; however, MPI implementations will attempt to continue whenever possible.
MPI_SUCCESS
    - No error; MPI routine completed successfully.
MPI_ERR_BUFFER
    - Invalid buffer pointer. Usually a null buffer where one is not valid.
MPI_ERR_COMM
    - Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank ).
MPI_ERR_COUNT
    - Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
MPI_ERR_TYPE
    - Invalid datatype argument. Additionally, this error can occur if an uncommitted MPI_Datatype (see MPI_Type_commit ) is used in a communication call.
MPI_ERR_OTHER
    - Other error; use MPI_Error_string to get more information about this error code.