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MPI_Neighbor_alltoallw, MPI_Ineighbor_alltoallw - All processes
send data of different types to, and receive data of different types from,
all processes
#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)
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
- sendbuf
- Starting address of send buffer.
- sendcounts
- Integer
array, where entry i specifies the number of elements 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 elements 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.
- recvbuf
- Address of receive buffer.
- request
- Request (handle, non-blocking only).
- IERROR
- Fortran only: Error status.
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 communications.
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 element 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 different amounts and types of data to different processes
in the communicator.
The MPI_IN_PLACE option for sendbuf is not meaningful
for this operation
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.
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.
MPI_Neighbor_alltoall
MPI_Neighbor_alltoallv
MPI_Cart_create
MPI_Graph_create
MPI_Dist_graph_create
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