334 lines
11 KiB
Groff
334 lines
11 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH "MPI_SCATTER_INIT" "3" "Feb 14, 2025" "" "Open MPI"
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.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
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.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
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..
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.INDENT 0.0
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.INDENT 3.5
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.UNINDENT
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.UNINDENT
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.sp
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\fI\%MPI_Scatter\fP, \fI\%MPI_Iscatter\fP, \fI\%MPI_Scatter_init\fP \- Sends data from one
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task to all tasks in a group.
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.SH SYNTAX
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.SS C Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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#include <mpi.h>
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int MPI_Scatter(const void *sendbuf, int sendcount, MPI_Datatype sendtype,
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void *recvbuf, int recvcount, MPI_Datatype recvtype, int root,
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MPI_Comm comm)
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int MPI_Iscatter(const void *sendbuf, int sendcount, MPI_Datatype sendtype,
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void *recvbuf, int recvcount, MPI_Datatype recvtype, int root,
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MPI_Comm comm, MPI_Request *request)
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int MPI_Scatter_init(const void *sendbuf, int sendcount, MPI_Datatype sendtype,
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void *recvbuf, int recvcount, MPI_Datatype recvtype, int root,
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MPI_Comm comm, MPI_Info info, MPI_Request *request)
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SS Fortran Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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USE MPI
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! or the older form: INCLUDE \(aqmpif.h\(aq
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MPI_SCATTER(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
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RECVTYPE, ROOT, COMM, IERROR)
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<type> SENDBUF(*), RECVBUF(*)
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INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, ROOT
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INTEGER COMM, IERROR
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MPI_ISCATTER(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
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RECVTYPE, ROOT, COMM, REQUEST, IERROR)
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<type> SENDBUF(*), RECVBUF(*)
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INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, ROOT
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INTEGER COMM, REQUEST, IERROR
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MPI_SCATTER_INIT(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
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RECVTYPE, ROOT, COMM, INFO, REQUEST, IERROR)
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<type> SENDBUF(*), RECVBUF(*)
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INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, ROOT
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INTEGER COMM, INFO, REQUEST, IERROR
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SS Fortran 2008 Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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USE mpi_f08
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MPI_Scatter(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype,
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root, comm, ierror)
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TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
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TYPE(*), DIMENSION(..) :: recvbuf
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INTEGER, INTENT(IN) :: sendcount, recvcount, root
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TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
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TYPE(MPI_Comm), INTENT(IN) :: comm
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INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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MPI_Iscatter(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype,
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root, comm, request, ierror)
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TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
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TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
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INTEGER, INTENT(IN) :: sendcount, recvcount, root
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TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
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TYPE(MPI_Comm), INTENT(IN) :: comm
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TYPE(MPI_Request), INTENT(OUT) :: request
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INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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MPI_Scatter_init(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype,
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root, comm, info, request, ierror)
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TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
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TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
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INTEGER, INTENT(IN) :: sendcount, recvcount, root
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TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
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TYPE(MPI_Comm), INTENT(IN) :: comm
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TYPE(MPI_Info), INTENT(IN) :: info
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TYPE(MPI_Request), INTENT(OUT) :: request
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INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SH INPUT PARAMETERS
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.INDENT 0.0
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.IP \(bu 2
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\fBsendbuf\fP: Address of send buffer (choice, significant only at root).
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.IP \(bu 2
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\fBsendcount\fP: Number of elements sent to each process (integer, significant only at root).
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.IP \(bu 2
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\fBsendtype\fP: Datatype of send buffer elements (handle, significant only at root).
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.IP \(bu 2
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\fBrecvcount\fP: Number of elements in receive buffer (integer).
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.IP \(bu 2
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\fBrecvtype\fP: Datatype of receive buffer elements (handle).
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.IP \(bu 2
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\fBroot\fP: Rank of sending process (integer).
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.IP \(bu 2
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\fBcomm\fP: Communicator (handle).
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.IP \(bu 2
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\fBinfo\fP: Info (handle, persistent).
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.UNINDENT
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.SH OUTPUT PARAMETERS
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.INDENT 0.0
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.IP \(bu 2
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\fBrecvbuf\fP: Address of receive buffer (choice).
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.IP \(bu 2
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\fBrequest\fP: Request (handle, non\-blocking only).
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.IP \(bu 2
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\fBierror\fP: Fortran only: Error status (integer).
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.UNINDENT
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.SH DESCRIPTION
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.sp
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\fI\%MPI_Scatter\fP is the inverse operation to \fI\%MPI_Gather\fP\&.
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.sp
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The outcome is as if the root executed n send operations,
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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MPI_Send(sendbuf + i * sendcount * extent(sendtype), sendcount,
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sendtype, i, ...);
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.sp
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and each process executed a receive,
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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MPI_Recv(recvbuf, recvcount, recvtype, i, ...).;
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.sp
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An alternative description is that the root sends a message with
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\fBMPI_Send(sendbuf, sendcount * n, sendtype, ...)\fP\&. This message
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is split into \fIn\fP equal segments, the ith segment is sent to the ith
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process in the group, and each process receives this message as above.
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.sp
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The send buffer is ignored for all nonroot processes.
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.sp
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The type signature associated with \fIsendcount\fP, \fIsendtype\fP at the root
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must be equal to the type signature associated with \fIrecvcount\fP,
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\fIrecvtype\fP at all processes (however, the type maps may be different).
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This implies that the amount of data sent must be equal to the amount of
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data received, pairwise between each process and the root. Distinct type
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maps between sender and receiver are still allowed.
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.sp
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All arguments to the function are significant on process \fIroot\fP, while
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on other processes, only arguments \fIrecvbuf\fP, \fIrecvcount\fP, \fIrecvtype\fP,
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\fIroot\fP, \fIcomm\fP are significant. The arguments \fIroot\fP and \fIcomm\fP must
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have identical values on all processes.
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.sp
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The specification of counts and types should not cause any location on
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the root to be read more than once.
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.sp
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\fBRationale:\fP Though not needed, the last restriction is imposed so as
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to achieve symmetry with \fI\%MPI_Gather\fP, where the corresponding restriction
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(a multiple\-write restriction) is necessary.
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.sp
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\fBExample:\fP The reverse of Example 1 in the \fI\%MPI_Gather\fP manpage. Scatter
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sets of 100 ints from the root to each process in the group.
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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MPI_Comm comm;
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int gsize,*sendbuf;
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int root, rbuf[100];
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\&...
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MPI_Comm_size(comm, &gsize);
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sendbuf = (int *)malloc(gsize*100*sizeof(int));
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\&...
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MPI_Scatter(sendbuf, 100, MPI_INT, rbuf, 100,
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MPI_INT, root, comm);
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SH USE OF IN-PLACE OPTION
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.sp
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When the communicator is an intracommunicator, you can perform a scatter
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operation in\-place (the output buffer is used as the input buffer). Use
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the variable MPI_IN_PLACE as the value of the root process \fIrecvbuf\fP\&. In
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this case, \fIrecvcount\fP and \fIrecvtype\fP are ignored, and the root process
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sends no data to itself.
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.sp
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Note that MPI_IN_PLACE is a special kind of value; it has the same
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restrictions on its use as MPI_BOTTOM.
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.sp
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Because the in\-place option converts the receive buffer into a
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send\-and\-receive buffer, a Fortran binding that includes INTENT must
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mark these as INOUT, not OUT.
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.SH WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR
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.sp
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When the communicator is an inter\-communicator, the root process in the
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first group sends data to all processes in the second group. The first
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group defines the root process. That process uses MPI_ROOT as the value
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of its \fIroot\fP argument. The remaining processes use \fBMPI_PROC_NULL\fP as the
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value of their \fIroot\fP argument. All processes in the second group use
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the rank of that root process in the first group as the value of their
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\fIroot\fP argument. The receive buffer argument of the root process in the
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first group must be consistent with the receive buffer argument of the
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processes in the second group.
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.SH ERRORS
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.sp
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Almost all MPI routines return an error value; C routines as the return result
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of the function and Fortran routines in the last argument.
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.sp
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Before the error value is returned, the current MPI error handler associated
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with the communication object (e.g., communicator, window, file) is called.
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If no communication object is associated with the MPI call, then the call is
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considered attached to MPI_COMM_SELF and will call the associated MPI error
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handler. When MPI_COMM_SELF is not initialized (i.e., before
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\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
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Model exclusively) the error raises the initial error handler. The initial
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error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
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MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
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argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
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If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
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error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
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handler is called for all other MPI functions.
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.sp
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Open MPI includes three predefined error handlers that can be used:
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.INDENT 0.0
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.IP \(bu 2
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\fBMPI_ERRORS_ARE_FATAL\fP
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Causes the program to abort all connected MPI processes.
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.IP \(bu 2
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\fBMPI_ERRORS_ABORT\fP
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An error handler that can be invoked on a communicator,
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window, file, or session. When called on a communicator, it
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acts as if \fI\%MPI_Abort\fP was called on that communicator. If
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called on a window or file, acts as if \fI\%MPI_Abort\fP was called
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on a communicator containing the group of processes in the
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corresponding window or file. If called on a session,
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aborts only the local process.
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.IP \(bu 2
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\fBMPI_ERRORS_RETURN\fP
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Returns an error code to the application.
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.UNINDENT
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.sp
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MPI applications can also implement their own error handlers by calling:
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.INDENT 0.0
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.IP \(bu 2
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\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
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.IP \(bu 2
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\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
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.UNINDENT
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.sp
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Note that MPI does not guarantee that an MPI program can continue past
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an error.
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.sp
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See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
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.sp
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See the Error Handling section of the MPI\-3.1 standard for
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more information.
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.sp
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\fBSEE ALSO:\fP
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.INDENT 0.0
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.INDENT 3.5
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.INDENT 0.0
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.IP \(bu 2
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\fI\%MPI_Scatterv\fP
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.IP \(bu 2
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\fI\%MPI_Gather\fP
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.IP \(bu 2
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\fI\%MPI_Gatherv\fP
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.UNINDENT
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.UNINDENT
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.UNINDENT
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.SH COPYRIGHT
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2003-2025, The Open MPI Community
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.\" Generated by docutils manpage writer.
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.
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