325 lines
10 KiB
Groff
325 lines
10 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH "MPI_IALLGATHER" "3" "Feb 14, 2025" "" "Open MPI"
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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_Allgather\fP, \fI\%MPI_Iallgather\fP, \fI\%MPI_Allgather_init\fP \- Gathers data
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from all processes and distributes it to all processes
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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_Allgather(const void *sendbuf, int sendcount,
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MPI_Datatype sendtype, void *recvbuf, int recvcount,
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MPI_Datatype recvtype, MPI_Comm comm)
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int MPI_Iallgather(const void *sendbuf, int sendcount,
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MPI_Datatype sendtype, void *recvbuf, int recvcount,
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MPI_Datatype recvtype, MPI_Comm comm, MPI_Request *request)
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int MPI_Allgather_init(const void *sendbuf, int sendcount,
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MPI_Datatype sendtype, void *recvbuf, int recvcount,
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MPI_Datatype recvtype, 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_ALLGATHER(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
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RECVTYPE, COMM, IERROR)
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<type> SENDBUF (*), RECVBUF (*)
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INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, COMM,
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INTEGER IERROR
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MPI_IALLGATHER(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
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RECVTYPE, COMM, REQUEST, IERROR)
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<type> SENDBUF(*), RECVBUF (*)
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INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, COMM
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INTEGER REQUEST, IERROR
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MPI_ALLGATHER_INIT(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT,
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RECVTYPE, COMM, INFO, REQUEST, IERROR)
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<type> SENDBUF(*), RECVBUF (*)
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INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, COMM
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INTEGER 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_Allgather(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype,
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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
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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_Iallgather(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype,
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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
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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_Allgather_init(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype,
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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
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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: Starting address of send buffer (choice).
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.IP \(bu 2
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\fBsendcount\fP: Number of elements in send buffer (integer).
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.IP \(bu 2
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\fBsendtype\fP: Datatype of send buffer elements (handle).
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.IP \(bu 2
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\fBrecvbuf\fP: Starting address of recv buffer (choice).
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.IP \(bu 2
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\fBrecvcount\fP: Number of elements received from any process (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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\fBcomm\fP: Communicator (handle).
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.IP \(bu 2
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\fBinfo\fP: Info (handle, persistent only).
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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_Allgather\fP is similar to \fI\%MPI_Gather\fP, except that all processes
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receive the result, instead of just the root. In other words, all
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processes contribute to the result, and all processes receive the
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result.
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.sp
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The type signature associated with sendcount, sendtype at a process must
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be equal to the type signature associated with recvcount, recvtype at
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any other process.
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.sp
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The outcome of a call to \fI\%MPI_Allgather\fP is as if all processes
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executed n calls to
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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_Gather(sendbuf, sendcount, sendtype, recvbuf, recvcount,
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recvtype, root, comm);
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// for root = 0 , ..., n\-1.
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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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The rules for correct usage of \fI\%MPI_Allgather\fP
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are easily found from the corresponding rules for \fI\%MPI_Gather\fP\&.
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.sp
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\fBExample:\fP The all\-gather version of Example 1 in \fI\%MPI_Gather\fP\&. Using
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\fI\%MPI_Allgather\fP, we will gather 100 ints from every process in the group
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to every process.
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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,sendarray[100];
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int *rbuf;
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\&...
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MPI_Comm_size( comm, &gsize);
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rbuf = (int *)malloc(gsize*100*sizeof(int));
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MPI_Allgather( sendarray, 100, MPI_INT, rbuf, 100, MPI_INT, 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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.sp
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After the call, every process has the group\-wide concatenation of the
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sets of data.
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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 an
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all\-gather operation in\-place (the output buffer is used as the input
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buffer). Use the variable MPI_IN_PLACE as the value of \fIsendbuf\fP\&. In
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this case, \fIsendcount\fP and \fIsendtype\fP are ignored. The input data of
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each process is assumed to be in the area where that process would
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receive its own contribution to the receive buffer. Specifically, the
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outcome of a call to \fI\%MPI_Allgather\fP that used the in\-place option is
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identical to the case in which all processes executed \fIn\fP calls to
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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_Allgather( MPI_IN_PLACE, 0, MPI_DATATYPE_NULL, recvbuf,
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recvcount, recvtype, root, comm )
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// for root =0, ... , n\-1.
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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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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 gather operation
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occurs in two phases. The data is gathered from all the members of the
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first group and received by all the members of the second group. Then
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the data is gathered from all the members of the second group and
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received by all the members of the first. The operation, however, need
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not be symmetric. The number of items sent by the processes in first
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group need not be equal to the number of items sent by the the processes
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in the second group. You can move data in only one direction by giving
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\fIsendcount\fP a value of 0 for communication in the reverse direction.
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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_Allgatherv\fP
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.IP \(bu 2
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\fI\%MPI_Gather\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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