GSP
Quick Navigator

Search Site

Unix VPS
A - Starter
B - Basic
C - Preferred
D - Commercial
MPS - Dedicated
Previous VPSs
* Sign Up! *

Support
Contact Us
Online Help
Handbooks
Domain Status
Man Pages

FAQ
Virtual Servers
Pricing
Billing
Technical

Network
Facilities
Connectivity
Topology Map

Miscellaneous
Server Agreement
Year 2038
Credits
 

USA Flag

 

 

Man Pages


Manual Reference Pages  -  MPI_INEIGHBOR_ALLTOALLV (3)

NAME

MPI_Neighbor_alltoallv, MPI_Ineighbor_alltoallv - All processes send different amounts of data to, and receive different amounts of data from, all neighbors

CONTENTS

Syntax
C Syntax
Fortran Syntax
Input Parameters
Output Parameters
Description
Neighbor Ordering
Notes
Errors
See Also

SYNTAX

C Syntax

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

int MPI_Ineighbor_alltoallv(const void *sendbuf, const int sendcounts[],         const int sdispls[], MPI_Datatype sendtype,         void *recvbuf, const int recvcounts[],         const int rdispls[], MPI_Datatype recvtype, MPI_Comm comm,         MPI_Request *request)

Fortran Syntax

INCLUDE ’mpif.h’

MPI_NEIGHBOR_ALLTOALLV(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPE,         RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPE, COMM, IERROR)

        <type>  SENDBUF(*), RECVBUF(*)         INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPE         INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPE         INTEGER COMM, IERROR

MPI_INEIGHBOR_ALLTOALLV(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPE,         RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPE, COMM, REQUEST, IERROR)

        <type>  SENDBUF(*), RECVBUF(*)         INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPE         INTEGER RECVCOUNTS(*), RDISPLS(*), RECVTYPE         INTEGER COMM, REQUEST, IERROR

INPUT PARAMETERS

sendbuf Starting address of send buffer.
sendcounts Integer array, where entry i specifies the number of elements to send to neighbor i.
sdispls Integer array, where entry i specifies the displacement (offset from sendbuf, in units of sendtype) from which to send data to neighbor i.
sendtype Datatype of send buffer elements.
recvcounts Integer array, where entry j specifies the number of elements to receive from neighbor j.
rdispls Integer array, where entry j specifies the displacement (offset from recvbuf, in units of recvtype) to which data from neighbor j should be written.
recvtype Datatype of receive buffer elements.
comm Communicator over which data is to be exchanged.

OUTPUT PARAMETERS

recvbuf Address of receive buffer.
request Request (handle, non-blocking only).
IERROR Fortran only: Error status.

DESCRIPTION

MPI_Neighbor_alltoallv is a generalized collective operation in which all processes send data to and receive data from all neighbors. It adds flexibility to MPI_Neighbor_alltoall by allowing the user to specify data to send and receive vector-style (via a displacement and element count). The operation of this routine can be thought of as follows, where each process performs 2n (n being the number of neighbors in to topology of communicator comm) independent point-to-point communications. The neighbors and buffer layout are determined by the topology of comm.

        MPI_Cart_get(comm, maxdims, dims, periods, coords);
        for (dim = 0, i = 0 ; dim < dims ; ++dim) {
            MPI_Cart_shift(comm, dim, 1, &r0, &r1);
            MPI_Isend(sendbuf + sdispls[i]  * extent(sendtype),
                      sendcount, sendtype, r0, ..., comm, ...);
            MPI_Irecv(recvbuf + rdispls[i] * extent(recvtype),
                      recvcount, recvtype, r0, ..., comm, ...);
            ++i;
            MPI_Isend(sendbuf + sdispls[i] * extent(sendtype),
                      sendcount, sendtype, r1, ..., comm, &req[i]);
            MPI_Irecv(recvbuf + rdispls[i] * extent(recvtype),
                      recvcount, recvtype, r1, ..., comm, ...);
            ++i;
        }

Process j sends the k-th block of its local sendbuf to neighbor k, which places the data in the j-th block of its local recvbuf.

When a pair of processes exchanges data, each may pass different element count and datatype arguments so long as the sender specifies the same amount of data to send (in bytes) as the receiver expects to receive.

Note that process i may send a different amount of data to process j than it receives from process j. Also, a process may send entirely different amounts of data to different processes in the communicator.

NEIGHBOR ORDERING

For a distributed graph topology, created with MPI_Dist_graph_create, the sequence of neighbors in the send and receive buffers at each process is defined as the sequence returned by MPI_Dist_graph_neighbors for destinations and sources, respectively. For a general graph topology, created with MPI_Graph_create, the order of neighbors in the send and receive buffers is defined as the sequence of neighbors as returned by MPI_Graph_neighbors. Note that general graph topologies should generally be replaced by the distributed graph topologies.

For a Cartesian topology, created with MPI_Cart_create, the sequence of neighbors in the send and receive buffers at each process is defined by order of the dimensions, first the neighbor in the negative direction and then in the positive direction with displacement 1. The numbers of sources and destinations in the communication routines are 2*ndims with ndims defined in MPI_Cart_create. If a neighbor does not exist, i.e., at the border of a Cartesian topology in the case of a non-periodic virtual grid dimension (i.e., periods[...]==false), then this neighbor is defined to be MPI_PROC_NULL.

If a neighbor in any of the functions is MPI_PROC_NULL, then the neighborhood collective communication behaves like a point-to-point communication with MPI_PROC_NULL in this direction. That is, the buffer is still part of the sequence of neighbors but it is neither communicated nor updated.

NOTES

The MPI_IN_PLACE option for sendbuf is not meaningful for this operation.

The specification of counts and displacements should not cause any location to be written more than once.

All arguments on all processes are significant. The comm argument, in particular, must describe the same communicator on all processes.

The offsets of sdispls and rdispls are measured in units of sendtype and recvtype, respectively. Compare this to MPI_Neighbor_alltoallw, where these offsets are measured in bytes.

ERRORS

Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument.

Before the error value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

SEE ALSO

MPI_Neighbor_alltoall
MPI_Neighbor_alltoallw
MPI_Cart_create
MPI_Graph_create
MPI_Dist_graph_create

Search for    or go to Top of page |  Section 3 |  Main Index


1.10.2 MPI_NEIGHBOR_ALLTOALLV (3) Jan 21, 2016

Powered by GSP Visit the GSP FreeBSD Man Page Interface.
Output converted with manServer 1.07.