NAME

       MPI_Neighbor_allgatherv,  MPI_Ineighbor_allgatherv - Gathers and distributes data from and
       to all neighbors. Each process may contribute a different amount of data.

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Neighbor_allgatherv(const void *sendbuf, int sendcount,
            MPI_Datatype sendtype, void *recvbuf, const int recvcounts[],
            const int displs[], MPI_Datatype recvtype, MPI_Comm comm)

       int MPI_Ineighbor_allgatherv(const void *sendbuf, int sendcount,
            MPI_Datatype sendtype, void *recvbuf, const int recvcounts[],
            const int displs[], MPI_Datatype recvtype, MPI_Comm comm,
               MPI_Request *request)

Fortran Syntax

       INCLUDE 'mpif.h'
       MPI_NEIGHBOR_ALLGATHERV(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF,
                 RECVCOUNT, DISPLS, RECVTYPE, COMM, IERROR)
            <type>    SENDBUF(*), RECVBUF(*)
            INTEGER   SENDCOUNT, SENDTYPE, RECVCOUNT(*),
            INTEGER   DISPLS(*), RECVTYPE, COMM, IERROR

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

       recvcount Integer array (of length group size) containing the number of elements that  are
                 received from each neighbor.

       displs    Integer  array  (of  length  group  size).  Entry  i  specifies the displacement
                 (relative to recvbuf) at which to place the incoming data from neighbor i.

       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_allgatherv is similar to MPI_Neighbor_allgather in that all processes  gather
       data from all neighbors, except that each process can send a different amount of data. The
       block of data sent from the jth neighbor is received by every neighbor and placed  in  the
       jth  block of the buffer. The neighbors and buffer layout is determined by the topology of
       comm.  recvbuf.

       The type signature associated with sendcount, sendtype, at process j must be equal to  the
       type  signature  associated  with  the  corresponding  entry  in recvcounts on neighboring
       processes.

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.

SEE ALSO

       MPI_Neighbor_allgather MPI_Cart_create MPI_Graph_create MPI_Dist_graph_create