| MPI_ALLTOALL(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype, comm) | |
| IN sendbuf | starting address of send buffer (choice) |
| IN sendcount | number of elements sent to each process (non-negative integer) |
| IN sendtype | data type of send buffer elements (handle) |
| OUT recvbuf | address of receive buffer (choice) |
| IN recvcount | number of elements received from any process (non-negative integer) |
| IN recvtype | data type of receive buffer elements (handle) |
| IN comm | communicator (handle) |
int MPI_Alltoall(const void* sendbuf, int sendcount, MPI_Datatype sendtype, void* recvbuf, int recvcount, MPI_Datatype recvtype, MPI_Comm comm)
MPI_Alltoall(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_ALLTOALL(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT, RECVTYPE, COMM, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, COMM, IERROR
MPI_ALLTOALL is an extension of MPI_ALLGATHER to the case where each process sends distinct data to each of the receivers. The j-th block sent from process i is received by process j and is placed in the i-th block of recvbuf.
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. This implies that the amount of data sent must be equal to the amount of data received, pairwise between every pair of processes. As usual, however, the type maps may be different.
If comm is an intracommunicator, the outcome is as if each process executed a send to each process (itself included) with a call to,
and a receive from every other process with a call to,
All arguments on all processes are significant. The argument comm must have identical values on all processes.
The ``in place'' option for intracommunicators is specified by passing MPI_IN_PLACE to the argument sendbuf at all processes. In such a case, sendcount and sendtype are ignored. The data to be sent is taken from the recvbuf and replaced by the received data. Data sent and received must have the same type map as specified by recvcount and recvtype.
Rationale.
For large MPI_ALLTOALL instances,
allocating both send and receive buffers may consume too much memory.
The ``in place'' option effectively halves the application memory consumption
and is useful in situations where the data to be sent will not be used by the
sending process after the MPI_ALLTOALL exchange (e.g., in parallel
Fast Fourier Transforms).
( End of rationale.)
Advice
to implementors.
Users may opt to use the ``in place'' option in order to conserve memory.
Quality MPI implementations should thus strive to minimize system buffering.
( End of advice to implementors.)
If comm is an intercommunicator, then the outcome is as if
each process in group A sends a message to each process in group B,
and vice versa. The j-th send buffer of process i in group A should
be consistent with the i-th receive buffer of process j in group B,
and vice versa.
Advice to users.
When a complete exchange is executed on an intercommunication domain, then
the number of data items sent from processes in group A to processes
in group B need not equal the number of items sent in the reverse
direction. In particular, one can have unidirectional communication
by specifying sendcount = 0 in the reverse direction.
( End of advice to users.)
int MPI_Alltoallv(const void* sendbuf, const int sendcounts[], const int sdispls[], MPI_Datatype sendtype, void* recvbuf, const int recvcounts[], const int rdispls[], MPI_Datatype recvtype, MPI_Comm comm)
MPI_Alltoallv(sendbuf, sendcounts, sdispls, sendtype, recvbuf, recvcounts, rdispls, recvtype, comm, ierror)
TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
TYPE(*), DIMENSION(..) :: recvbuf
INTEGER, INTENT(IN) :: sendcounts(*), sdispls(*), recvcounts(*), rdispls(*)
TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_ALLTOALLV(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPE, RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPE, COMM, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPE, RECVCOUNTS(*), RDISPLS(*), RECVTYPE, COMM, IERROR
MPI_ALLTOALLV adds flexibility to MPI_ALLTOALL in that the location of data for the send is specified by sdispls and the location of the placement of the data on the receive side is specified by rdispls.
If comm is an intracommunicator, then the j-th block sent from process i is received by process j and is placed in the i-th block of recvbuf. These blocks need not all have the same size.
The type signature associated with sendcounts[j], sendtype at process i must be equal to the type signature associated with recvcounts[i], recvtype at process j. This implies that the amount of data sent must be equal to the amount of data received, pairwise between every pair of processes. Distinct type maps between sender and receiver are still allowed.
The outcome is as if each process sent a message to every other process with,
and received a message from every other process with a call to
All arguments on all processes are significant. The argument comm must have identical values on all processes.
The ``in place'' option for intracommunicators is specified by passing MPI_IN_PLACE to the argument sendbuf at all processes. In such a case, sendcounts, sdispls and sendtype are ignored. The data to be sent is taken from the recvbuf and replaced by the received data. Data sent and received must have the same type map as specified by the recvcounts array and the recvtype, and is taken from the locations of the receive buffer specified by rdispls.
Advice to users.
Specifying the ``in place'' option (which must be given on all processes)
implies that the same amount and type of data is sent and received between
any two processes in the group of the communicator.
Different pairs of processes can exchange different amounts of data.
Users must ensure that recvcounts[j] and recvtype on process
i match recvcounts[i] and recvtype on process j.
This symmetric exchange can be useful in applications where the data to be sent will
not be used by the sending process after the MPI_ALLTOALLV exchange.
( End of advice to users.)
If comm is an intercommunicator, then the outcome is as if
each process in group A sends a message to each process in group B,
and vice versa. The j-th send buffer of process i in group A should
be consistent with the i-th receive buffer of process j in group B,
and vice versa.
Rationale.
The definitions of MPI_ALLTOALL and MPI_ALLTOALLV give as much
flexibility as one would achieve by specifying n independent,
point-to-point communications, with two exceptions: all messages use the same
datatype, and messages are scattered from (or gathered to) sequential
storage.
( End of rationale.)
Advice
to implementors.
Although the discussion of collective communication in terms of
point-to-point operation implies that each message is transferred directly
from sender to receiver, implementations may use a tree communication
pattern. Messages can be forwarded by intermediate nodes where they
are split (for scatter) or concatenated (for gather), if this
is more efficient.
( End of advice to implementors.)
int MPI_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_Alltoallw(sendbuf, sendcounts, sdispls, sendtypes, recvbuf, recvcounts, rdispls, recvtypes, comm, ierror)
TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
TYPE(*), DIMENSION(..) :: recvbuf
INTEGER, INTENT(IN) :: sendcounts(*), sdispls(*), recvcounts(*), rdispls(*)
TYPE(MPI_Datatype), INTENT(IN) :: sendtypes(*)
TYPE(MPI_Datatype), INTENT(IN) :: recvtypes(*)
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_ALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES, RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPES(*), RECVCOUNTS(*), RDISPLS(*), RECVTYPES(*), COMM, IERROR
MPI_ALLTOALLW is the most general form of complete exchange. Like MPI_TYPE_CREATE_STRUCT, the most general type constructor, MPI_ALLTOALLW allows separate specification of count, displacement and datatype. In addition, to allow maximum flexibility, the displacement of blocks within the send and receive buffers is specified in bytes.
If comm is an intracommunicator, then the j-th block sent from process i is received by process j and is placed in the i-th block of recvbuf. These blocks need not all have the same size.
The type signature associated with sendcounts[j], sendtypes[j] at process i must be equal to the type signature associated with recvcounts[i], recvtypes[i] at process j. This implies that the amount of data sent must be equal to the amount of data received, pairwise between every pair of processes. Distinct type maps between sender and receiver are still allowed.
The outcome is as if each process sent a message to every other process with
and received a message from every other process with a call to
All arguments on all processes are significant. The argument comm must describe the same communicator on all processes.
Like for MPI_ALLTOALLV, the ``in place'' option for intracommunicators is specified by passing MPI_IN_PLACE to the argument sendbuf at all processes. In such a case, sendcounts, sdispls and sendtypes are ignored. The data to be sent is taken from the recvbuf and replaced by the received data. Data sent and received must have the same type map as specified by the recvcounts and recvtypes arrays, and is taken from the locations of the receive buffer specified by rdispls.
If comm is an intercommunicator, then the outcome is as if each process in group A sends a message to each process in group B, and vice versa. The j-th send buffer of process i in group A should be consistent with the i-th receive buffer of process j in group B, and vice versa.
Rationale.
The MPI_ALLTOALLW function generalizes several MPI functions by
carefully selecting the input arguments. For example, by making all but one
process have sendcounts[i] = 0, this achieves an MPI_SCATTERW
function.
( End of rationale.)