MPI_ALLTOALLV, MPI_Alltoallv

Purpose

Sends a distinct message from each task to every task. Messages can have
different sizes and displacements.

C synopsis

#include <mpi.h>
int MPI_Alltoallv(void* sendbuf,int *sendcounts,int *sdispls,
    MPI_Datatype sendtype,void* recvbuf,int *recvcounts,int *rdispls,
    MPI_Datatype recvtype,MPI_Comm comm);

C++ synopsis

#include mpi.h
void MPI::Comm::Alltoallv(const void* sendbuf, const int sendcounts[],
                          const int sdispls[], const MPI::Datatype& sendtype,
                          void* recvbuf, const int recvcounts[],
                          const int rdispls[], const MPI::Datatype& recvtype)
                          const;

FORTRAN synopsis

include 'mpif.h' or use mpi
MPI_ALLTOALLV(CHOICE SENDBUF,INTEGER SENDCOUNTS(*),
              INTEGER SDISPLS(*),INTEGER SENDTYPE,CHOICE RECVBUF,
              INTEGER RECVCOUNTS(*),INTEGER RDISPLS(*),INTEGER RECVTYPE,
              INTEGER COMM,INTEGER IERROR)

Parameters

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

sendcounts
     integer array (of length groupsize) specifying the number of elements
     to send to each task (IN)

sdispls
     integer array (of length groupsize). Entry j specifies the
     displacement relative to sendbuf from which to take the outgoing data
     destined for task j. (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) specifying the number of elements
     to be received from each task (IN)

rdispls
     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 communicator (handle) (IN)

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

Description

MPI_ALLTOALLV sends a distinct message from each task to every task.
Messages can have different sizes and displacements.

This subroutine is similar to MPI_ALLTOALL with the following differences.
MPI_ALLTOALLV allows you the flexibility to specify the location of the
data for the send with sdispls and the location of where the data will be
placed on the receive with rdispls.

The block of data sent from task i is sendcounts[j] elements long, and is
received by task j and placed in recvbuf at offset rdispls[i]. These blocks
do not have to be the same size.

The type signature associated with sendcount[j], sendtype at task i must be
equal to the type signature associated with recvcounts[i], recvtype at task
j. This means the amount of data sent must be equal to the amount of data
received, pair wise between every pair of tasks. Distinct type maps between
sender and receiver are allowed.

All arguments on all tasks are significant.

MPI_ALLTOALLV does not support MPI_IN_PLACE on either type of communicator.

If comm is an intercommunicator, the outcome is as if each task in group A
sends a message to each task in group B, and vice versa. The jth send
buffer of task i in group A should be consistent with the ith receive
buffer of task j in group B, and vice versa.

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 count(s)
     count < 0

Invalid datatype(s)

Type not committed

Invalid communicator

A send and receive have unequal message lengths

Invalid use of MPI_IN_PLACE

MPI not initialized

MPI already finalized

Related information

     MPE_IALLTOALLV
     MPI_ALLTOALL