NAME

       MPI_Neighbor_alltoall  -   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.

SYNOPSIS

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

INPUT PARAMETERS

       sendbuf
              - starting address of the 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 (handle)

OUTPUT PARAMETERS

       recvbuf
              - starting address of the receive buffer (choice)

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 guarentee that an MPI program can continue past an error; however,  MPI
       implementations will attempt to continue whenever possible.

                                                   11/12/2019                           MPI_Neighbor_alltoall(3)