| 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)
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.
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.)
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.
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)
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 a 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.
<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 (binding deprecated, see Section Deprecated since MPI-2.2
) }
Rationale.
The ``in place'' option for intracommunicators is specified by passing
MPI_IN_PLACE as
the value of recvbuf at the root. In such acase,
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.
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)
<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 (binding deprecated, see Section Deprecated since MPI-2.2
) }
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