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NAME

MPI_Alltoallw - Send differently sized and typed buffers from all processes to all other processes in a communicator

SYNOPSIS

#include <mpi.h> int MPI_Alltoallw(void *sendbuf , int *sendcount , int *sdisp , MPI_Datatype *sendtype , void *recvbuf , int *recvcount , int *rdisp , MPI_Datatype *recvtype , MPI_Comm comm );

#include <pmpi.h> int PMPI_Alltoallw(void *sendbuf , int *sendcount , int *sdisp , MPI_Datatype *sendtype , void *recvbuf , int *recvcount , int *rdisp , MPI_Datatype *recvtype , MPI_Comm comm );

#include <mpi.h> void MPI::Comm::Alltoallw(const void *sendbuf , const int *sendcount , const int *sdisp , const MPI::Datatype *sendtype , void *recvbuf , const int *recvcount , const int *rdisp , const MPI::Datatype *recvtype ) const;

INCLUDE 'mpif.h' MPI_ALLTOALLW(sendbuf , sendcount , sdisp , sendtype , recvbuf , recvcount , rdisp , recvtype , comm , ierr ) <type> sendbuf (*), recvbuf (*) INTEGER sendcount (*), sdisp (*), sendtype (*), recvcount (*), rdisp (*), recvtype (*), comm , ierr

INPUT PARAMETERS

sendbuf - send buffer (array)

sendcount - array of counts of elements to send per rank (array of integers)

sdisp - array of byte offsets for send buffer to each rank (array of integers)

sendtype - array of types of elements in send buffer to each rank (array of handles)

recvcount - array of counts of elements to receive per rank (array of integers)

rdisp - array of byte offsets for receive buffer from each rank (array of integers)

recvtype - array of types of elements in receive buffer from each rank (array of handles)

comm - communicator for messages (handle)

OUTPUT PARAMETER

recvbuf - receive buffer (array)

DESCRIPTION

The MPI_Alltoallw() function is used to send messages from all processes to all other processes in the communicator comm . The type of the messages are given by the elements of sendtype , their size by sendcount , and they are sent from the send buffer, sendbuf in using the sdisp array to locate them. Similarly, they are stored into the receive buffer recvbuf , using the types in the recvtype array, sizes in the recvcount array, and the offsets in rdisp . The displacements are in units of bytes. This differs from the MPI_Alltoallv() function which uses an element size as granularity for the offsets, and has all messages of the same type.

Specifying MPI_IN_PLACE for a buffer is not supported in this function.

Note that each process should send the amount of data expected to be received. If that is not the case, then the messages will be silently truncated. Note that for performance reasons this MPI library does not check that the sent and received datatypes match.

The communicator must be a valid one (not MPI_COMM_NULL). PMPI_Alltoallw() is the profiling version of this function.

ERRORS

All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.

In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.

MPI_SUCCESS - No error;

MPI_ERR_PENDING - Pending exception;

MPI_ERR_COMM - Invalid communicator;

MPI_ERR_COUNT - Invalid element count;

MPI_ERR_BUFFER - Invalid buffer;

MPI_ERR_TYPE - Invalid data type;

MPI_ERR_ARG - Invalid pointer;

MPI_ERR_INTERN - Out of Memory. This may be fatal.

SEE ALSO

MPI_Send (3) MPI_Recv (3) MPI_Bcast (3) MPI_Allgather (3) MPI_Alltoall (3) MPI_Alltoallv (3)

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