| MPI_SCATTER( sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype, root, comm) | |
| IN sendbuf | address of send buffer (choice, significant only at root) |
| IN sendcount | number of elements sent to each process (non-negative integer, significant only at root) |
| IN sendtype | data type of send buffer elements (significant only at root) (handle) |
| OUT recvbuf | address of receive buffer (choice) |
| IN recvcount | number of elements in receive buffer (non-negative integer) |
| IN recvtype | data type of receive buffer elements (handle) |
| IN root | rank of sending process (integer) |
| IN comm | communicator (handle) |
int MPI_Scatter(void* sendbuf, int sendcount, MPI_Datatype sendtype, void* recvbuf, int recvcount, MPI_Datatype recvtype, int root, MPI_Comm comm)
MPI_SCATTER(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT, RECVTYPE, ROOT, COMM, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, ROOT, COMM, IERROR
void MPI::Comm::Scatter(const void* sendbuf, int sendcount, const MPI::Datatype& sendtype, void* recvbuf, int recvcount, const MPI::Datatype& recvtype, int root) const = 0
MPI_SCATTER is the inverse operation to MPI_GATHER.
If comm is an intracommunicator, the outcome is as if the root executed n send operations,
MPI_Send(sendbuf+i· sendcount· extent(sendtype), sendcount, sendtype, i,...),
and each process executed a receive,
MPI_Recv(recvbuf, recvcount, recvtype, i,...).
An alternative description is that the root sends a message with MPI_Send(sendbuf, sendcount·n, sendtype, ...). This message is split into n equal segments, the i-th segment is sent to the i-th process in the group, and each process receives this message as above.
The send buffer is ignored for all non-root processes.
The type signature associated with sendcount, sendtype at the root must be equal to the type signature associated with recvcount, recvtype at all processes (however, the type maps may be different). This implies that the amount of data sent must be equal to the amount of data received, pairwise between each process and the root. Distinct type maps between sender and receiver are still allowed.
All arguments to the function are significant on process root, while on other processes, only arguments recvbuf, recvcount, recvtype, root, and comm are significant. The arguments root and comm must have identical values on all processes.
The specification of counts and types should not cause any location on the root to be read more than once.
Rationale.
Though not needed, the last restriction is imposed so as
to achieve symmetry with
MPI_GATHER, where the corresponding restriction (a multiple-write
restriction) is necessary.
( End of rationale.)
The ``in place'' option for intracommunicators is specified by passing
MPI_IN_PLACE as
the value of recvbuf at the root. In such case,
recvcount and recvtype are ignored, and root
``sends'' no data to itself. The scattered vector is still assumed to
contain n segments, where n is the group size; the root-th
segment, which root should ``send to itself,'' is not moved.
If comm is an intercommunicator, then the call involves all processes in the intercommunicator, but with one group (group A) defining the root process. All processes in the other group (group B) pass the same value in argument root, which is the rank of the root in group A. The root passes the value MPI_ROOT in root. All other processes in group A pass the value MPI_PROC_NULL in root. Data is scattered from the root to all processes in group B. The receive buffer arguments of the processes in group B must be consistent with the send buffer argument of the root.
| MPI_SCATTERV( sendbuf, sendcounts, displs, sendtype, recvbuf, recvcount, recvtype, root, comm) | |
| IN sendbuf | address of send buffer (choice, significant only at root) |
| IN sendcounts | non-negative integer array (of length group size) specifying the number of elements to send to each processor |
| IN displs | integer array (of length group size). Entry i specifies the displacement (relative to sendbuf from which to take the outgoing data to process i |
| IN sendtype | data type of send buffer elements (handle) |
| OUT recvbuf | address of receive buffer (choice) |
| IN recvcount | number of elements in receive buffer (non-negative integer) |
| IN recvtype | data type of receive buffer elements (handle) |
| IN root | rank of sending process (integer) |
| IN comm | communicator (handle) |
int MPI_Scatterv(void* sendbuf, int *sendcounts, int *displs, MPI_Datatype sendtype, void* recvbuf, int recvcount, MPI_Datatype recvtype, int root, MPI_Comm comm)
MPI_SCATTERV(SENDBUF, SENDCOUNTS, DISPLS, SENDTYPE, RECVBUF, RECVCOUNT, RECVTYPE, ROOT, COMM, IERROR)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), DISPLS(*), SENDTYPE, RECVCOUNT, RECVTYPE, ROOT, COMM, IERROR
void MPI::Comm::Scatterv(const void* sendbuf, const int sendcounts[], const int displs[], const MPI::Datatype& sendtype, void* recvbuf, int recvcount, const MPI::Datatype& recvtype, int root) const = 0
MPI_SCATTERV is the inverse operation to MPI_GATHERV.
MPI_SCATTERV extends the functionality of MPI_SCATTER by allowing a varying count of data to be sent to each process, since sendcounts is now an array. It also allows more flexibility as to where the data is taken from on the root, by providing an additional argument, displs.
If comm is an intracommunicator, the outcome is as if the root executed n send operations,
MPI_Send(sendbuf+displs[i]· extent(sendtype), sendcounts[i], sendtype, i,...),
and each process executed a receive,
MPI_Recv(recvbuf, recvcount, recvtype, i,...).
The send buffer is ignored for all non-root processes.
The type signature implied by sendcount[i], sendtype at the root must be equal to the type signature implied by recvcount, recvtype at process i (however, the type maps may be different). This implies that the amount of data sent must be equal to the amount of data received, pairwise between each process and the root. Distinct type maps between sender and receiver are still allowed.
All arguments to the function are significant on process root, while on other processes, only arguments recvbuf, recvcount, recvtype, root, and comm are significant. The arguments root and comm must have identical values on all processes.
The specification of counts, types, and displacements should not cause any location on the root to be read more than once. The ``in place'' option for intracommunicators is specified by passing MPI_IN_PLACE as the value of recvbuf at the root. In such case, recvcount and recvtype are ignored, and root ``sends'' no data to itself. The scattered vector is still assumed to contain n segments, where n is the group size; the root-th segment, which root should ``send to itself,'' is not moved.
If comm is an intercommunicator, then the call involves all processes in the intercommunicator, but with one group (group A) defining the root process. All processes in the other group (group B) pass the same value in argument root, which is the rank of the root in group A. The root passes the value MPI_ROOT in root. All other processes in group A pass the value MPI_PROC_NULL in root. Data is scattered from the root to all processes in group B. The receive buffer arguments of the processes in group B must be consistent with the send buffer argument of the root.