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.TH "MPI_ALLGATHERV_INIT" "3" "May 30, 2025" "" "Open MPI"
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.INDENT 3.5
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.sp
\fI\%MPI_Allgatherv\fP, \fI\%MPI_Iallgatherv\fP, \fI\%MPI_Allgatherv_init\fP \- Gathers data
from all processes and delivers it to all. Each process may contribute a
different amount of data.
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#include <mpi.h>

int MPI_Allgatherv(const void *sendbuf, int sendcount,
     MPI_Datatype sendtype, void *recvbuf, const int recvcounts[],
     const int displs[], MPI_Datatype recvtype, MPI_Comm comm)

int MPI_Iallgatherv(const void *sendbuf, int sendcount,
     MPI_Datatype sendtype, void *recvbuf, const int recvcounts[],
     const int displs[], MPI_Datatype recvtype, MPI_Comm comm,
        MPI_Request *request)

int MPI_Allgatherv_init(const void *sendbuf, int sendcount,
     MPI_Datatype sendtype, void *recvbuf, const int recvcounts[],
     const int displs[], MPI_Datatype recvtype, MPI_Comm comm,
        MPI_Info info, MPI_Request *request)
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq
MPI_ALLGATHERV(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF,
             RECVCOUNT, DISPLS, RECVTYPE, COMM, IERROR)
     <type>  SENDBUF(*), RECVBUF(*)
     INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT(*)
     INTEGER DISPLS(*), RECVTYPE, COMM, IERROR

MPI_IALLGATHERV(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF,
             RECVCOUNT, DISPLS, RECVTYPE, COMM,  REQUEST,  IERROR)
     <type>  SENDBUF(*), RECVBUF(*)
     INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT(*),
     INTEGER DISPLS(*), RECVTYPE, COMM, REQUEST, IERROR

MPI_ALLGATHERV_INIT(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF,
             RECVCOUNT, DISPLS, RECVTYPE, COMM,  INFO,  REQUEST,  IERROR)
     <type>  SENDBUF(*), RECVBUF(*)
     INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT(*),
     INTEGER DISPLS(*), RECVTYPE, COMM, INFO, REQUEST, IERROR
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran 2008 Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE mpi_f08
MPI_Allgatherv(sendbuf, sendcount, sendtype, recvbuf, recvcounts, displs,
             recvtype, comm, ierror)
     TYPE(*), DIMENSION(..), INTENT(IN) :: sendbuf
     TYPE(*), DIMENSION(..) :: recvbuf
     INTEGER, INTENT(IN) :: sendcount, recvcounts(*), displs(*)
     TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
     TYPE(MPI_Comm), INTENT(IN) :: comm
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

MPI_Iallgatherv(sendbuf, sendcount, sendtype, recvbuf, recvcounts, displs,
             recvtype, comm, request, ierror)
     TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
     TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
     INTEGER, INTENT(IN) :: sendcount
     INTEGER, INTENT(IN), ASYNCHRONOUS :: recvcounts(*), displs(*)
     TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
     TYPE(MPI_Comm), INTENT(IN) :: comm
     TYPE(MPI_Request), INTENT(OUT) :: request
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

MPI_Allgatherv_init(sendbuf, sendcount, sendtype, recvbuf, recvcounts, displs,
                     recvtype, comm, info, request, ierror)
     TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: sendbuf
     TYPE(*), DIMENSION(..), ASYNCHRONOUS :: recvbuf
     INTEGER, INTENT(IN) :: sendcount
     INTEGER, INTENT(IN), ASYNCHRONOUS :: recvcounts(*), displs(*)
     TYPE(MPI_Datatype), INTENT(IN) :: sendtype, recvtype
     TYPE(MPI_Comm), INTENT(IN) :: comm
     TYPE(MPI_Info), INTENT(IN) :: info
     TYPE(MPI_Request), INTENT(OUT) :: request
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
.ft P
.fi
.UNINDENT
.UNINDENT
.SH INPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBsendbuf\fP: Starting address of send buffer (choice).
.IP \(bu 2
\fBsendcount\fP: Number of elements in send buffer (integer).
.IP \(bu 2
\fBsendtype\fP: Datatype of send buffer elements (handle).
.IP \(bu 2
\fBrecvcount\fP: Integer array (of length group size) containing the number of elements that are received from each process.
.IP \(bu 2
\fBdispls\fP: Integer array (of length group size). Entry i specifies the displacement (relative to recvbuf) at which to place the incoming data from process i.
.IP \(bu 2
\fBrecvtype\fP: Datatype of receive buffer elements (handle).
.IP \(bu 2
\fBcomm\fP: Communicator (handle).
.IP \(bu 2
\fBinfo\fP: Info (handle, persistent only).
.UNINDENT
.SH OUTPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBrecvbuf\fP: Address of receive buffer (choice).
.IP \(bu 2
\fBrequest\fP: Request (handle, non\-blocking only).
.IP \(bu 2
\fBierror\fP: Fortran only: Error status (integer).
.UNINDENT
.SH DESCRIPTION
.sp
\fI\%MPI_Allgatherv\fP is similar to \fI\%MPI_Allgather\fP in that all processes gather
data from all other processes, except that each process can send a
different amount of data. The block of data sent from the jth process is
received by every process and placed in the jth block of the buffer
\fIrecvbuf.\fP
.sp
The type signature associated with sendcount, sendtype, at process j
must be equal to the type signature associated with recvcounts[j],
recvtype at any other process.
.sp
The outcome is as if all processes executed calls to
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.INDENT 3.5
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.nf
.ft C
MPI_Allgatherv(sendbuf, sendcount, sendtype, recvbuf, recvcount,
              displs,recvtype,root,comm);

// for root = 0 , ..., n\-1.
.ft P
.fi
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.sp
The rules for correct usage of \fI\%MPI_Allgatherv\fP
are easily found from the corresponding rules for \fI\%MPI_Gatherv\fP\&.
.SH USE OF IN-PLACE OPTION
.sp
When the communicator is an intracommunicator, you can perform an
all\-gather operation in\-place (the output buffer is used as the input
buffer). Use the variable MPI_IN_PLACE as the value of \fIsendbuf\fP\&. In
this case, \fIsendcount\fP and \fIsendtype\fP are ignored. The input data of
each process is assumed to be in the area where that process would
receive its own contribution to the receive buffer. Specifically, the
outcome of a call to \fI\%MPI_Allgatherv\fP that used the in\-place option is
identical to the case in which all processes executed \fIn\fP calls to
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.INDENT 3.5
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.nf
.ft C
MPI_Allgatherv ( MPI_IN_PLACE, 0, MPI_DATATYPE_NULL, recvbuf,
                 recvcounts, displs, recvtype, root, comm );

// for root =0, ... , n\-1.
.ft P
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.sp
Note that MPI_IN_PLACE is a special kind of value; it has the same
restrictions on its use as MPI_BOTTOM.
.sp
Because the in\-place option converts the receive buffer into a
send\-and\-receive buffer, a Fortran binding that includes INTENT must
mark these as INOUT, not OUT.
.SH WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR
.sp
When the communicator is an inter\-communicator, the gather operation
occurs in two phases. The data is gathered from all the members of the
first group, concatenated, and received by all the members of the second
group. Then the data is gathered from all the members of the second
group, concatenated, and received by all the members of the first. The
send buffer arguments in the one group must be consistent with the
receive buffer arguments in the other group, and vice versa. The
operation must exhibit symmetric, full\-duplex behavior.
.SH ERRORS
.sp
Almost all MPI routines return an error value; C routines as the return result
of the function and Fortran routines in the last argument.
.sp
Before the error value is returned, the current MPI error handler associated
with the communication object (e.g., communicator, window, file) is called.
If no communication object is associated with the MPI call, then the call is
considered attached to MPI_COMM_SELF and will call the associated MPI error
handler. When MPI_COMM_SELF is not initialized (i.e., before
\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
Model exclusively) the error raises the initial error handler. The initial
error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
handler is called for all other MPI functions.
.sp
Open MPI includes three predefined error handlers that can be used:
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\fBMPI_ERRORS_ARE_FATAL\fP
Causes the program to abort all connected MPI processes.
.IP \(bu 2
\fBMPI_ERRORS_ABORT\fP
An error handler that can be invoked on a communicator,
window, file, or session. When called on a communicator, it
acts as if \fI\%MPI_Abort\fP was called on that communicator. If
called on a window or file, acts as if \fI\%MPI_Abort\fP was called
on a communicator containing the group of processes in the
corresponding window or file. If called on a session,
aborts only the local process.
.IP \(bu 2
\fBMPI_ERRORS_RETURN\fP
Returns an error code to the application.
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MPI applications can also implement their own error handlers by calling:
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.IP \(bu 2
\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
.IP \(bu 2
\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
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.sp
Note that MPI does not guarantee that an MPI program can continue past
an error.
.sp
See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
.sp
See the Error Handling section of the MPI\-3.1 standard for
more information.
.sp
\fBSEE ALSO:\fP
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.IP \(bu 2
\fI\%MPI_Gatherv\fP
.IP \(bu 2
\fI\%MPI_Allgather\fP
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.SH COPYRIGHT
2003-2025, The Open MPI Community
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