| MPI_GATHER( sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype, root, comm) | |
| IN sendbuf | starting address of send buffer (choice) |
| IN sendcount | number of elements in send buffer (non-negative integer) |
| IN sendtype | data type of send buffer elements (handle) |
| OUT recvbuf | address of receive buffer (choice, significant only at root) |
| IN recvcount | number of elements for any single receive (non-negative integer, significant only at root) |
| IN recvtype | data type of recv buffer elements (significant only at root) (handle) |
| IN root | rank of receiving process (integer) |
| IN comm | communicator (handle) |
int MPI_Gather(void* sendbuf, int sendcount, MPI_Datatype sendtype, void* recvbuf, int recvcount, MPI_Datatype recvtype, int root, MPI_Comm comm)
MPI_GATHER(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT, RECVTYPE, ROOT, COMM, IERROR)
If comm is an intracommunicator,
each process (root process included) sends the contents of its send
buffer to the root process. The root process receives the messages and
stores them in rank order.
The outcome is as if each of the n processes in the group
(including the root process) had executed a call to
MPI_Send(sendbuf, sendcount, sendtype, root , ...),
and the
root had executed n calls to
MPI_Recv(recvbuf+i· recvcount· extent(recvtype), recvcount, recvtype, i,...),
where extent(recvtype) is the type extent obtained from a call to
MPI_Type_get_extent().
An alternative description is that the n messages sent by the
processes in the group are concatenated in rank order, and the
resulting message is received by the root as if by a call to
MPI_RECV(recvbuf, recvcount·n, recvtype, ...).
The receive buffer is ignored for all non-root processes.
General, derived datatypes are allowed for both sendtype
and recvtype.
The type signature of sendcount, sendtype on
each process
must be equal to the type signature of
recvcount, recvtype at the root.
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 sendbuf, sendcount,
sendtype, 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 written more than
once. Such a call is erroneous.
Note that the recvcount argument at the root indicates
the number of items it receives from each process, not the total number
of items it receives.
The ``in place'' option for intracommunicators is specified by passing
MPI_IN_PLACE as
the value of sendbuf at the root. In such a case,
sendcount and sendtype are ignored, and the
contribution of the root to the gathered vector is assumed to be already
in the correct place in the receive buffer.
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 gathered from all processes in group B to the root.
The send
buffer arguments of the processes in group B must be consistent with
the receive buffer argument of the root.
int MPI_Gatherv(void* sendbuf, int sendcount, MPI_Datatype sendtype, void* recvbuf, int *recvcounts, int *displs, MPI_Datatype recvtype, int root, MPI_Comm comm)
MPI_GATHERV(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNTS, DISPLS, RECVTYPE, ROOT, COMM, IERROR)
MPI_GATHERV extends the functionality of MPI_GATHER
by allowing a varying count of data from each process, since
recvcounts
is now an array. It also allows more flexibility as to where the data
is placed on the root, by providing the new argument, displs.
If comm is an intracommunicator,
the outcome is as if each process, including the root process,
sends a message to the root,
MPI_Send(sendbuf, sendcount, sendtype, root, ...),
and the root executes n receives,
The
data received from process j is placed into recvbuf of the root
process beginning at offset displs[j] elements (in terms of the
recvtype).
The receive buffer is ignored for all non-root processes.
The type signature implied by sendcount, sendtype on process i
must be equal to the type signature implied by recvcounts[i], recvtype
at the root.
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,
as illustrated in Example Examples using MPI_GATHER, MPI_GATHERV
.
All arguments to the function are significant on process root,
while on other processes, only arguments sendbuf, sendcount,
sendtype, 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 written more than
once. Such a call is erroneous.
The ``in place'' option for intracommunicators is specified by passing
MPI_IN_PLACE as
the value of sendbuf at the root. In such a case,
sendcount and sendtype are ignored, and the
contribution of the root to the gathered vector is assumed to be already
in the correct place in the receive buffer
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 gathered from all processes in group B to the root.
The send
buffer arguments of the processes in group B must be consistent with
the receive buffer argument of the root.
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, ROOT, COMM, IERROR
{ void MPI::Comm::Gather(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
) }
MPI_GATHERV( sendbuf, sendcount, sendtype, recvbuf,
recvcounts, displs, recvtype, root, comm) IN sendbuf starting address of send buffer (choice) IN sendcount number of elements in send buffer (non-negative
integer) IN sendtype data type of send buffer elements (handle) OUT recvbuf address of receive buffer (choice,
significant only at root) IN recvcounts non-negative
integer array (of length group size)
containing the number of elements that are received from each process
(significant only at root) IN displs integer array (of length group size). Entry
i specifies the displacement relative to recvbuf at
which to place the incoming data from process i (significant only
at root) IN recvtype data type of recv buffer elements
(significant only at root) (handle) IN root rank of receiving process (integer) IN comm communicator (handle)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNT, SENDTYPE, RECVCOUNTS(*), DISPLS(*), RECVTYPE, ROOT, COMM, IERROR
{ void MPI::Comm::Gatherv(const void* sendbuf, int sendcount, const MPI::Datatype& sendtype, void* recvbuf, const int recvcounts[], const int displs[], const MPI::Datatype& recvtype, int root) const = 0 (binding deprecated, see Section Deprecated since MPI-2.2
) }
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