MPI_Neighbor_alltoallw(3) Open MPI MPI_Neighbor_alltoallw(3)NAME
MPI_Neighbor_alltoallw, MPI_Ineighbor_alltoallw - All processes send
data of different types to, and receive data of different types from,
all processes
SYNTAXC Syntax
#include <mpi.h>
int MPI_Neighbor_alltoallw(const void *sendbuf, const int sendcounts[],
const int sdispls[], const MPI_Datatype sendtypes[],
void *recvbuf, const int recvcounts[], const int rdispls[],
const MPI_Datatype recvtypes[], MPI_Comm comm)
int MPI_Ineighbor_alltoallw(const void *sendbuf, const int sendcounts[],
const int sdispls[], const MPI_Datatype sendtypes[],
void *recvbuf, const int recvcounts[], const int rdispls[],
const MPI_Datatype recvtypes[], MPI_Comm comm, MPI_Request *request)
Fortran Syntax
INCLUDE 'mpif.h'
MPI_NEIGHBOR_ALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPES(*)
INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPES(*)
INTEGER COMM, IERROR
MPI_INEIGHBOR_ALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES,
RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, REQUEST, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPES(*)
INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPES(*)
INTEGER COMM, REQUEST, IERROR
INPUT PARAMETERS
sendbuf Starting address of send buffer.
sendcounts Integer array, where entry i specifies the number of ele‐
ments to send to neighbor i.
sdispls Integer array, where entry i specifies the displacement (in
bytes, offset from sendbuf) from which to send data to
neighbor i.
sendtypes Datatype array, where entry i specifies the datatype to use
when sending data to neighbor i.
recvcounts Integer array, where entry j specifies the number of ele‐
ments to receive from neighbor j.
rdispls Integer array, where entry j specifies the displacement (in
bytes, offset from recvbuf) to which data from neighbor j
should be written.
recvtypes Datatype array, where entry j specifies the datatype to use
when receiving data from neighbor j.
comm Communicator over which data is to be exchanged.
OUTPUT PARAMETERS
recvbuf Address of receive buffer.
request Request (handle, non-blocking only).
IERROR Fortran only: Error status.
DESCRIPTION
MPI_Neighbor_alltoallw is a generalized collective operation in which
all processes send data to and receive data from all neighbors. It adds
flexibility to MPI_Neighbor_alltoallv by allowing the user to specify
the datatype of individual data blocks (in addition to displacement and
element count). Its operation can be thought of in the following way,
where each process performs 2n (n being the number of neighbors in the
topology of communicator comm) independent point-to-point communica‐
tions. The neighbors and buffer layout are determined by the topology
of comm.
MPI_Cart_get(comm, maxdims, dims, periods, coords);
for (dim = 0, i = 0 ; dim < dims ; ++dim) {
MPI_Cart_shift(comm, dim, 1, &r0, &r1);
MPI_Isend(sendbuf + sdispls[i] * extent(sendtype),
sendcount, sendtypes[i], r0, ..., comm, ...);
MPI_Irecv(recvbuf + rdispls[i] * extent(recvtype),
recvcount, recvtypes[i], r0, ..., comm, ...);
++i;
MPI_Isend(sendbuf + sdispls[i] * extent(sendtype),
sendcount, sendtypes[i], r1, ..., comm, &req[i]);
MPI_Irecv(recvbuf + rdispls[i] * extent(recvtype),
recvcount, recvtypes[i], r1, ..., comm, ...);
++i;
}
MPI_Wait_all (...);
MPI_Comm_size(comm, &n);
for (i = 0, i < n; i++)
MPI_Send(sendbuf + sdispls[i], sendcounts[i],
sendtypes[i], i, ..., comm);
for (i = 0, i < n; i++)
MPI_Recv(recvbuf + rdispls[i], recvcounts[i],
recvtypes[i], i, ..., comm);
Process j sends the k-th block of its local sendbuf to neighbor k,
which places the data in the j-th block of its local recvbuf.
When a pair of processes exchanges data, each may pass different ele‐
ment count and datatype arguments so long as the sender specifies the
same amount of data to send (in bytes) as the receiver expects to
receive.
Note that process i may send a different amount of data to process j
than it receives from process j. Also, a process may send entirely dif‐
ferent amounts and types of data to different processes in the communi‐
cator.
NOTES
The MPI_IN_PLACE option for sendbuf is not meaningful for this opera‐
tion
The specification of counts, types, and displacements should not cause
any location to be written more than once.
All arguments on all processes are significant. The comm argument, in
particular, must describe the same communicator on all processes.
The offsets of sdispls and rdispls are measured in bytes. Compare this
to MPI_Neighbor_alltoallv, where these offsets are measured in units of
sendtype and recvtype, respectively.
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_alltoall
MPI_Neighbor_alltoallv
MPI_Cart_create
MPI_Graph_create
MPI_Dist_graph_create
1.7.4 Feb 04, 2014 MPI_Neighbor_alltoallw(3)
