| 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(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> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, COMM, IERROR
void MPI::Comm::Alltoall(const void* sendbuf, int sendcount, const MPI::Datatype& sendtype, void* recvbuf, int recvcount, const MPI::Datatype& recvtype) const = 0
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,
MPI_Send(sendbuf+i· sendcount· extent(sendtype),sendcount,sendtype,i, ...),
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. No ``in place'' option is supported.
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 all-to-all 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.)
| MPI_ALLTOALLV(sendbuf, sendcounts, sdispls, sendtype, recvbuf, recvcounts, rdispls, recvtype, comm) | |
| IN sendbuf | starting address of send buffer (choice) |
| IN sendcounts | non-negative integer array equal to the group size specifying the number of elements to send to each processor |
| IN sdispls | integer array (of length group size). Entry j specifies the displacement (relative to sendbuf from which to take the outgoing data destined for process j |
| IN sendtype | data type of send buffer elements (handle) |
| OUT recvbuf | address of receive buffer (choice) |
| IN recvcounts | non-negative integer array equal to the group size specifying the number of elements that can be received from each processor |
| IN rdispls | integer array (of length group size). Entry i specifies the displacement (relative to recvbuf at which to place the incoming data from process i |
| IN recvtype | data type of receive buffer elements (handle) |
| IN comm | communicator (handle) |
int MPI_Alltoallv(void* sendbuf, int *sendcounts, int *sdispls, MPI_Datatype sendtype, void* recvbuf, int *recvcounts, int *rdispls, MPI_Datatype recvtype, MPI_Comm comm)
MPI_ALLTOALLV(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPE, RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPE, COMM, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPE, RECVCOUNTS(*), RDISPLS(*), RECVTYPE, COMM, IERROR
void MPI::Comm::Alltoallv(const void* sendbuf, const int sendcounts[], const int sdispls[], const MPI::Datatype& sendtype, void* recvbuf, const int recvcounts[], const int rdispls[], const MPI::Datatype& recvtype) const = 0
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 sendcount[j], sendtype at process i must be equal to the type signature associated with recvcount[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,
MPI_Send(sendbuf+displs[i]· extent(sendtype),sendcounts[i],sendtype,i,...),
and received a message from every other process with a call to
MPI_Recv(recvbuf+displs[i]· extent(recvtype),recvcounts[i],recvtype,i,...).
All arguments on all processes are significant. The argument comm must have identical values on all processes. No ``in place'' option is supported.
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.)
| MPI_ALLTOALLW(sendbuf, sendcounts, sdispls, sendtypes, recvbuf, recvcounts, rdispls, recvtypes, comm) | |
| IN sendbuf | starting address of send buffer (choice) |
| IN sendcounts | integer array equal to the group size specifying the number of elements to send to each processor (array of non-negative integers) |
| IN sdispls | integer array (of length group size). Entry j specifies the displacement in bytes (relative to sendbuf) from which to take the outgoing data destined for process j (array of integers) |
| IN sendtypes | array of datatypes (of length group size). Entry j specifies the type of data to send to process j (array of handles) |
| OUT recvbuf | address of receive buffer (choice) |
| IN recvcounts | integer array equal to the group size specifying the number of elements that can be received from each processor (array of non-negative integers) |
| IN rdispls | integer array (of length group size). Entry i specifies the displacement in bytes (relative to recvbuf) at which to place the incoming data from process i (array of integers) |
| IN recvtypes | array of datatypes (of length group size). Entry i specifies the type of data received from process i (array of handles) |
| IN comm | communicator (handle) |
int MPI_Alltoallw(void *sendbuf, int sendcounts[], int sdispls[], MPI_Datatype sendtypes[], void *recvbuf, int recvcounts[], int rdispls[], MPI_Datatype recvtypes[], MPI_Comm comm)
MPI_ALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES, RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPES(*), RECVCOUNTS(*), RDISPLS(*), RECVTYPES(*), COMM, IERROR
void MPI::Comm::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[]) const = 0
MPI_ALLTOALLW is the most general form of All-to-all. 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
MPI_Send(sendbuf+sdispls[i],sendcounts[i],sendtypes[i] ,i,...),
and received a message from every other process with a call to
MPI_Recv(recvbuf+rdispls[i],recvcounts[i],recvtypes[i] ,i,...).
All arguments on all processes are significant. The argument comm must describe the same communicator on all processes.
No ``in place'' option is supported. 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.)