192 строки
7.4 KiB
Plaintext
192 строки
7.4 KiB
Plaintext
.\" -*- nroff -*-
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.\" Copyright 2013 Los Alamos National Security, LLC. All rights reserved.
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.\" Copyright 2010 Cisco Systems, Inc. All rights reserved.
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.\" Copyright 2006-2008 Sun Microsystems, Inc.
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.\" Copyright (c) 1996 Thinking Machines Corporation
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.TH MPI_Neighbor_alltoallv 3 "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
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.SH NAME
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\fBMPI_Neighbor_alltoallv, MPI_Ineighbor_alltoallv\fP \- All processes send different amounts of data to, and receive different amounts of data from, all neighbors
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.SH SYNTAX
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.ft R
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.SH C Syntax
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.nf
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#include <mpi.h>
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int MPI_Neighbor_alltoallv(const void *\fIsendbuf\fP, const int \fIsendcounts\fP[],
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const int \fIsdispls\f[]P, MPI_Datatype \fIsendtype\fP,
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void *\fIrecvbuf\fP, const int\fI recvcounts\fP[],
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const int \fIrdispls\fP[], MPI_Datatype \fIrecvtype\fP, MPI_Comm \fIcomm\fP)
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int MPI_Ineighbor_alltoallv(const void *\fIsendbuf\fP, const int \fIsendcounts\fP[],
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const int \fIsdispls\f[]P, MPI_Datatype \fIsendtype\fP,
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void *\fIrecvbuf\fP, const int\fI recvcounts\fP[],
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const int \fIrdispls\fP[], MPI_Datatype \fIrecvtype\fP, MPI_Comm \fIcomm\fP,
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MPI_Request \fI*request\fP)
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.fi
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.SH Fortran Syntax
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.nf
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INCLUDE 'mpif.h'
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MPI_NEIGHBOR_ALLTOALLV(\fISENDBUF, SENDCOUNTS, SDISPLS, SENDTYPE,
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RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPE, COMM, IERROR\fP)
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<type> \fISENDBUF(*), RECVBUF(*)\fP
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INTEGER \fISENDCOUNTS(*), SDISPLS(*), SENDTYPE\fP
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INTEGER \fIRECVCOUNTS(*), RDISPLS(*), RECVTYPE\fP
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INTEGER \fICOMM, IERROR\fP
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MPI_INEIGHBOR_ALLTOALLV(\fISENDBUF, SENDCOUNTS, SDISPLS, SENDTYPE,
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RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPE, COMM, REQUEST, IERROR\fP)
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<type> \fISENDBUF(*), RECVBUF(*)\fP
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INTEGER \fISENDCOUNTS(*), SDISPLS(*), SENDTYPE\fP
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INTEGER \fIRECVCOUNTS(*), RDISPLS(*), RECVTYPE\fP
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INTEGER \fICOMM, REQUEST, IERROR\fP
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.fi
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.SH INPUT PARAMETERS
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.ft R
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.TP 1.2i
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sendbuf
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Starting address of send buffer.
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.TP 1.2i
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sendcounts
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Integer array, where entry i specifies the number of elements to send
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to neighbor i.
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.TP 1.2i
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sdispls
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Integer array, where entry i specifies the displacement (offset from
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\fIsendbuf\fP, in units of \fIsendtype\fP) from which to send data to
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neighbor i.
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.TP 1.2i
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sendtype
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Datatype of send buffer elements.
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.TP 1.2i
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recvcounts
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Integer array, where entry j specifies the number of elements to
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receive from neighbor j.
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.TP 1.2i
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rdispls
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Integer array, where entry j specifies the displacement (offset from
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\fIrecvbuf\fP, in units of \fIrecvtype\fP) to which data from neighbor j
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should be written.
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.TP 1.2i
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recvtype
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Datatype of receive buffer elements.
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.TP 1.2i
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comm
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Communicator over which data is to be exchanged.
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.SH OUTPUT PARAMETERS
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.ft R
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.TP 1.2i
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recvbuf
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Address of receive buffer.
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.TP 1i
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request
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Request (handle, non-blocking only).
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.ft R
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.TP 1.2i
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IERROR
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Fortran only: Error status.
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.SH DESCRIPTION
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.ft R
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MPI_Neighbor_alltoallv is a generalized collective operation in which all
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processes send data to and receive data from all neighbors. It
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adds flexibility to MPI_Neighbor_alltoall by allowing the user to specify data
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to send and receive vector-style (via a displacement and element
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count). The operation of this routine can be thought of as follows,
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where each process performs 2n (n being the number of neighbors in
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to topology of communicator \fIcomm\fP) independent point-to-point communications.
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The neighbors and buffer layout are determined by the topology of \fIcomm\fP.
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.sp
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.nf
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MPI_Cart_get(\fIcomm\fP, maxdims, dims, periods, coords);
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for (dim = 0, i = 0 ; dim < dims ; ++dim) {
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MPI_Cart_shift(\fIcomm\fP, dim, 1, &r0, &r1);
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MPI_Isend(\fIsendbuf\fP + \fIsdispls\fP[i] * extent(\fIsendtype\fP),
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\fIsendcount\fP, \fIsendtype\fP, r0, ..., \fIcomm\fP, ...);
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MPI_Irecv(\fIrecvbuf\fP + \fIrdispls\fP[i] * extent(\fIrecvtype\fP),
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\fIrecvcount\fP, \fIrecvtype\fP, r0, ..., \fIcomm\fP, ...);
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++i;
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MPI_Isend(\fIsendbuf\fP + \fIsdispls\fP[i] * extent(\fIsendtype\fP),
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\fIsendcount\fP, \fIsendtype\fP, r1, ..., \fIcomm\fP, &req[i]);
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MPI_Irecv(\fIrecvbuf\fP + \fIrdispls\fP[i] * extent(\fIrecvtype\fP),
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\fIrecvcount\fP, \fIrecvtype\fP, r1, ..., \fIcomm\fP, ...);
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++i;
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}
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.fi
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.sp
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Process j sends the k-th block of its local \fIsendbuf\fP to neighbor
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k, which places the data in the j-th block of its local
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\fIrecvbuf\fP.
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.sp
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When a pair of processes exchanges data, each may pass different
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element count and datatype arguments so long as the sender specifies
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the same amount of data to send (in bytes) as the receiver expects
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to receive.
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.sp
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Note that process i may send a different amount of data to process j
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than it receives from process j. Also, a process may send entirely
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different amounts of data to different processes in the communicator.
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.sp
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.SH NEIGHBOR ORDERING
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For a distributed graph topology, created with MPI_Dist_graph_create, the sequence of neighbors
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in the send and receive buffers at each process is defined as the sequence returned by MPI_Dist_graph_neighbors
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for destinations and sources, respectively. For a general graph topology, created with MPI_Graph_create, the order of
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neighbors in the send and receive buffers is defined as the sequence of neighbors as returned by MPI_Graph_neighbors.
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Note that general graph topologies should generally be replaced by the distributed graph topologies.
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For a Cartesian topology, created with MPI_Cart_create, the sequence of neighbors in the send and receive
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buffers at each process is defined by order of the dimensions, first the neighbor in the negative direction
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and then in the positive direction with displacement 1. The numbers of sources and destinations in the
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communication routines are 2*ndims with ndims defined in MPI_Cart_create. If a neighbor does not exist, i.e., at
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the border of a Cartesian topology in the case of a non-periodic virtual grid dimension (i.e.,
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periods[...]==false), then this neighbor is defined to be MPI_PROC_NULL.
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If a neighbor in any of the functions is MPI_PROC_NULL, then the neighborhood collective communication behaves
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like a point-to-point communication with MPI_PROC_NULL in this direction. That is, the buffer is still part of
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the sequence of neighbors but it is neither communicated nor updated.
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.sp
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.SH NOTES
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.ft R
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The MPI_IN_PLACE option for \fIsendbuf\fP is not meaningful for this operation.
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.sp
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The specification of counts and displacements should not cause
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any location to be written more than once.
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.sp
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All arguments on all processes are significant. The \fIcomm\fP argument,
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in particular, must describe the same communicator on all processes.
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.sp
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The offsets of \fIsdispls\fP and \fIrdispls\fP are measured in units
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of \fIsendtype\fP and \fIrecvtype\fP, respectively. Compare this to
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MPI_Neighbor_alltoallw, where these offsets are measured in bytes.
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.SH ERRORS
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.ft R
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Almost all MPI routines return an error value; C routines as
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the value of the function and Fortran routines in the last argument.
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.sp
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Before the error value is returned, the current MPI error handler is
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called. By default, this error handler aborts the MPI job, except for
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I/O function errors. The error handler may be changed with
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MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN
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may be used to cause error values to be returned. Note that MPI does not
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guarantee that an MPI program can continue past an error.
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.SH SEE ALSO
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.ft R
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.nf
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MPI_Neighbor_alltoall
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MPI_Neighbor_alltoallw
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MPI_Cart_create
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MPI_Graph_create
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MPI_Dist_graph_create
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