MPI_Graph_neighborsReturns the neighbors of a node associated with a graph topology
int MPI_Graph_neighbors( MPI_Comm comm, int rank, int maxneighbors, int *neighbors );
- [in] communicator with graph topology (handle)
- [in] rank of process in group of comm (integer)
- [in] size of array neighbors (integer)
- [out] ranks of processes that are neighbors to specified process (array of integer)
MPI_GRAPH_NEIGHBORS provides adjacency information for a general, graph topology.
Suppose that comm is a communicator with a shuffle-exchange
topology. The group has 2n members. Each process is
labeled by with , and has
three neighbors: exchange( (
), shuffle( , and unshuffle(
. The graph adjacency list is illustrated below for n=3.
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)
Thread and Interrupt Safety
This routine is both thread- and interrupt-safe. This means that this routine may safely be used by multiple threads and from within a signal handler.
Notes for FortranAll MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.
All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.
All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.
- No error; MPI routine completed successfully.
- Invalid topology. Either there is no topology associated with this communicator, or it is not the correct type (e.g., MPI_CART when expecting MPI_GRAPH).
- Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).
- Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).
- Invalid source or destination rank. Ranks must be between zero and the size of the communicator minus one; ranks in a receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_SOURCE.
The following sample code illustrates MPI_Graph_neighbors.
Insert code here.