MPI_ALLGATHERV, MPI_Allgatherv

Purpose

Collects individual messages from each task in comm and distributes
the resulting message to all tasks. Messages can have different sizes
and displacements.

C synopsis

#include <mpi.h>
int MPI_Allgatherv(void* sendbuf,int sendcount,MPI_Datatype sendtype,
    void* recvbuf,int *recvcounts,int *displs,MPI_Datatype recvtype,
    MPI_Comm comm);

C++ synopsis

#include mpi.h
void MPI::Comm::Allgatherv(const void* sendbuf, int sendcount,
                           const MPI::Datatype& sendtype, void* recvbuf,
                           const int recvcounts[], const int displs[],
                           const MPI::Datatype& recvtype) const;

FORTRAN synopsis

include 'mpif.h' or use mpi
MPI_ALLGATHERV(CHOICE SENDBUF,INTEGER SENDCOUNT,INTEGER SENDTYPE,
               CHOICE RECVBUF,INTEGER RECVCOUNTS(*),INTEGER DISPLS(*),
               INTEGER RECVTYPE,INTEGER COMM,INTEGER IERROR)

Parameters

sendbuf
     is the starting address of the send buffer (choice) (IN)

sendcount
     is the number of elements in the send buffer (integer) (IN)

sendtype
     is the datatype of the send buffer elements (handle) (IN)

recvbuf
     is the address of the receive buffer (choice) (OUT)

recvcounts
     integer array (of length groupsize) that contains the number of
     elements received from each task (IN)

displs
     integer array (of length groupsize). Entry i specifies the
     displacement (relative to recvbuf) at which to place the incoming data
     from task i (IN)

recvtype
     is the datatype of the receive buffer elements (handle) (IN)

comm
     is the communictor (handle) (IN)

IERROR
     is the FORTRAN return code. It is always the last argument.

Description

This subroutine collects individual messages from each task in comm and
distributes the resulting message to all tasks. Messages can have different
sizes and displacements.

The block of data sent from task j is recvcounts[j] elements long, and is
received by every task and placed in recvbuf at offset displs[j].

The type signature associated with sendcount, sendtype at task j must be
equal to the type signature of recvcounts[j], recvtype at any other task.

The "in place" option for intracommunicators is specified by passing the
value MPI_IN_PLACE to sendbuf at all tasks. The sendcount and sendtype
arguments are ignored. The input data of each task is assumed to be in the
area where that task would receive its own contribution to the receive
buffer. Specifically, the outcome of a call to MPI_ALLGATHERV in the "in
place" case is as if all tasks executed n calls to:

MPI_GATHERV(MPI_IN_PLACE, 0, MPI_DATATYPE_NULL, recvbuf, recvcount, recvtype,
            root, comm)

for: root = 0, ..., n - 1.

If comm is an intercommunicator, each task in group A contributes a data
item. These items are concatenated and the result is stored at each task in
group B. Conversely, the concatenation of the contributions of the tasks in
group B is stored at each task in group A. The send buffer arguments in
group A must be consistent with the receive buffer arguments in group B,
and vice versa.

MPI_IN_PLACE is not supported for intercommunicators.

When you use this subroutine in a threads application, make sure all
collective operations on a particular communicator occur in the same order
at each task. See IBM Parallel Environment for AIX: MPI Programming Guide
for more information on programming with MPI in a threads environment.

Errors

Fatal errors:

Invalid communicator

Invalid count(s)
     count < 0

Invalid datatype(s)

Type not committed

Unequal message lengths

Invalid use of MPI_IN_PLACE

MPI not initialized

MPI already finalized

Develop mode error if:

None

Related information

     MPE_IALLGATHERV
     MPI_ALLGATHER