MPI_Graph_neighbors(3) | Open MPI | MPI_Graph_neighbors(3) |
MPI_Graph_neighbors - Returns the neighbors of a node associated with a graph topology.
#include <mpi.h> int MPI_Graph_neighbors(MPI_Comm comm, int rank, int maxneighbors, int neighbors[])
USE MPI ! or the older form: INCLUDE 'mpif.h' MPI_GRAPH_NEIGHBORS(COMM, RANK, MAXNEIGHBORS, NEIGHBORS, IERROR) INTEGER COMM, RANK, MAXNEIGHBORS, NEIGHBORS(*), IERROR
USE mpi_f08 MPI_Graph_neighbors(comm, rank, maxneighbors, neighbors, ierror) TYPE(MPI_Comm), INTENT(IN) :: comm INTEGER, INTENT(IN) :: rank, maxneighbors INTEGER, INTENT(OUT) :: neighbors(maxneighbors) INTEGER, OPTIONAL, INTENT(OUT) :: ierror
#include <mpi.h> void Graphcomm::Get_neighbors(int rank, int maxneighbors, int neighbors[]) const
Example: Suppose that comm is a communicator with a shuffle-exchange topology. The group has 2n members. Each process is labeled by a(1), ..., a(n) with a(i) E{0,1}, and has three neighbors: exchange (a(1), ..., a(n) = a(1), ..., a(n-1), a(n) (a = 1 - a), shuffle (a(1), ..., a(n)) = a(2), ..., a(n), a(1), and unshuffle (a(1), ..., a(n)) = a(n), a(1), ..., a(n-1). The graph adjacency list is illustrated below for n=3.
exchange shuffle unshuffle
node neighbors(1) neighbors(2) neighbors(3)
0(000) 1 0 0
1(001) 0 2 4
2(010) 3 4 1
3(011) 2 6 5
4(100) 5 1 2
5(101) 4 3 6
6(110) 7 5 3
7(111) 6 7 7
Suppose that the communicator comm has this topology associated with it. The following code fragment cycles through the three types of neighbors and performs an appropriate permutation for each.
C assume: each process has stored a real number A. C extract neighborhood information
CALL MPI_COMM_RANK(comm, myrank, ierr)
CALL MPI_GRAPH_NEIGHBORS(comm, myrank, 3, neighbors, ierr) C perform exchange permutation
CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, neighbors(1), 0,
+ neighbors(1), 0, comm, status, ierr) C perform shuffle permutation
CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, neighbors(2), 0,
+ neighbors(3), 0, comm, status, ierr) C perform unshuffle permutation
CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, neighbors(3), 0,
+ neighbors(2), 0, comm, status, ierr)
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.
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.
MPI_Graph_neighbors_count
October 29, 2018 | 3.1.3 |