Ubuntu Manpage: MPI_Neighbor_allgather, MPI_Ineighbor_allgather - Gathers and distributes data from and to all neighbors

Provided by: openmpi-doc_4.1.6-7ubuntu2_all

NAME

       MPI_Neighbor_allgather, MPI_Ineighbor_allgather - Gathers and distributes data from and to all neighbors

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Neighbor_allgather(const void *sendbuf, int  sendcount,
            MPI_Datatype sendtype, void *recvbuf, int recvcount,
             MPI_Datatype recvtype, MPI_Comm comm)

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

Fortran Syntax

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_NEIGHBOR_ALLGATHER(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
                 RECVTYPE, COMM, IERROR)
            <type>    SENDBUF (*), RECVBUF (*)
            INTEGER   SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, COMM,
            INTEGER   IERROR

       MPI_INEIGHBOR_ALLGATHER(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
                 RECVTYPE, COMM, REQUEST, IERROR)
            <type>    SENDBUF (*), RECVBUF (*)
            INTEGER   SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, COMM,
            INTEGER   REQUEST, IERROR

Fortran 2008 Syntax

       USE mpi_f08
       MPI_Neighbor_allgather(sendbuf, sendcount, sendtype, recvbuf, recvcount,
                 recvtype, comm, ierror)
            TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
            TYPE(*), DIMENSION(..) :: recvbuf
            INTEGER, INTENT(IN) :: sendcount, recvcount
            TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
            TYPE(MPI_Comm), INTENT(IN) :: comm
            INTEGER, OPTIONAL, INTENT(OUT) :: ierror

       MPI_Ineighbor_allgather(sendbuf, sendcount, sendtype, recvbuf, recvcount,
                 recvtype, comm, request, ierror)
            TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
            TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
            INTEGER, INTENT(IN) :: sendcount, recvcount
            TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
            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 (choice).

       sendcount Number of elements in send buffer (integer).

       sendtype  Datatype of send buffer elements (handle).

       recvbuf   Starting address of recv buffer (choice).

       recvcount Number of elements received from any process (integer).

       recvtype  Datatype of receive buffer elements (handle).

       comm      Communicator (handle).

OUTPUT PARAMETERS

       recvbuf   Address of receive buffer (choice).

       request   Request (handle, non-blocking only).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       MPI_Neighbor_allgather  is  similar  to MPI_Allgather, except that only the neighboring processes receive
       the result, instead of all processes. The neighbors and buffer layout is determined by  the  topology  of
       comm.

       The  type  signature associated with sendcount, sendtype at a process must be equal to the type signature
       associated with recvcount, recvtype at any other process.

NEIGHBOR ORDERING

For a distributed graph topology, created with MPI_Dist_graph_create, the sequence of neighbors in the
send and receive buffers at each process is defined as the sequence returned by MPI_Dist_graph_neighbors
for destinations and sources, respectively. For a general graph topology, created with MPI_Graph_create,
the order of neighbors in the send and receive buffers is defined as the sequence of neighbors as
returned by MPI_Graph_neighbors. Note that general graph topologies should generally be replaced by the
distributed graph topologies.

For a Cartesian topology, created with MPI_Cart_create, the sequence of neighbors in the send and receive
buffers at each process is defined by order of the dimensions, first the neighbor in the negative
direction and then in the positive direction with displacement 1. The numbers of sources and destinations
in the communication routines are 2*ndims with ndims defined in MPI_Cart_create. If a neighbor does not
exist, i.e., at the border of a Cartesian topology in the case of a non-periodic virtual grid dimension
(i.e., periods[...]==false), then this neighbor is defined to be MPI_PROC_NULL.

If a neighbor in any of the functions is MPI_PROC_NULL, then the neighborhood collective communication
behaves like a point-to-point communication with MPI_PROC_NULL in this direction. That is, the buffer is
still part of the sequence of neighbors but it is neither communicated nor updated.

NOTES

       The MPI_IN_PLACE option for sendbuf is not meaningful for this operation.

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.