MPI_Neighbor_allgather(3) Open MPI MPI_Neighbor_allgather(3)NAME
MPI_Neighbor_allgather, MPI_Ineighbor_allgather - Gathers and distrib‐
utes data from and to all neighbors
SYNTAXC 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
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_NEIGHBOR_ALLGATHER(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
RECVTYPE, COMM, REQUEST, IERROR)
<type> SENDBUF (*), RECVBUF (*)
INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, COMM,
INTEGER 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).
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).
DESCRIPTIONMPI_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 topol‐
ogy, 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 gen‐
erally 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 neigh‐
borhood collective communication behaves like a point-to-point communi‐
cation 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 opera‐
tion.
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_allgatherv MPI_Cart_create MPI_Garph_create
MPI_Dist_graph_create
MPI_Gather
1.7.4 Feb 04, 2014 MPI_Neighbor_allgather(3)
