# mpi_graph_neighbors(3openmpi) [osx man page]

MPI_Graph_neighbors(3OpenMPI) MPI_Graph_neighbors(3OpenMPI)NAME

MPI_Graph_neighbors - Returns the neighbors of a node associated with a graph topology.SYNTAX

C Syntax#include <mpi.h> int MPI_Graph_neighbors(MPI_Comm comm, int rank, int maxneighbors, int *neighbors)Fortran SyntaxINCLUDE 'mpif.h' MPI_GRAPH_NEIGHBORS(COMM, RANK, MAXNEIGHBORS, NEIGHBORS, IERROR) INTEGER COMM, RANK, MAXNEIGHBORS, NEIGHBORS(*), IERRORC++ Syntax#include <mpi.h> void Graphcomm::Get_neighbors(int rank, int maxneighbors, int neighbors[]) constINPUT PARAMETERS

comm Communicator with graph topology (handle). rank Rank of process in group of comm (integer). maxneighbors Size of array neighbors (integer).OUTPUT PARAMETERS

neighbors Ranks of processes that are neighbors to specified process (array of integers). IERROR Fortran only: Error status (integer).DESCRIPTION

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 illus- trated 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)ERRORS

Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ func- tions 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.SEE ALSO

MPI_Graph_neighbors_countOpen MPI 1.2September 2006 MPI_Graph_neighbors(3OpenMPI)

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MPI_Errhandler_get(3OpenMPI) MPI_Errhandler_get(3OpenMPI)NAME

MPI_Errhandler_get - Gets the error handler for a communicatoruse of this routine is deprecated.--SYNTAX

C Syntax#include <mpi.h> int MPI_Errhandler_get(MPI_Comm comm, MPI_Errhandler *errhandler)Fortran SyntaxINCLUDE 'mpif.h' MPI_ERRHANDLER_GET(COMM, ERRHANDLER, IERROR) INTEGER COMM, ERRHANDLER, IERRORINPUT PARAMETER

comm Communicator to get the error handler from (handle).OUTPUT PARAMETERS

errhandler MPI error handler currently associated with communicator (handle). IERROR Fortran only: Error status (integer).DESCRIPTION

Note that use of this routine is deprecated as of MPI-2. Please use MPI_Comm_get_errhandler instead. This deprecated routine is not available in C++. Returns in errhandler (a handle to) the error handler that is currently associated with communicator comm. Example: A library function may register at its entry point the current error handler for a communicator, set its own private error handler for this communicator, and restore before exiting the previous error handler.ERRORS

Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ func- tions 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.SEE ALSO

MPI_Comm_create_errhandler MPI_Comm_get_errhandler MPI_Comm_set_errhandlerOpen MPI 1.2September 2006 MPI_Errhandler_get(3OpenMPI)