MPIGraphneighbors(3OpenMPI) MPIGraphneighbors(3OpenMPI)

NAME
       MMPPIIGGrraapphhnneeiigghhbboorrss   - Returns the neighbors of a node associated with
       a graph topology.


SSYYNNTTAAXX
CC SSyynnttaaxx
       #include 
       int MPIGraphneighbors(MPIComm comm, int rank, int maxneighbors,
            int *neighbors)


FFoorrttrraann SSyynnttaaxx
       INCLUDE 'mpif.h'
       MPIGRAPHNEIGHBORS(COMM, RANK, MAXNEIGHBORS, NEIGHBORS, IERROR)
            INTEGER   COMM, RANK, MAXNEIGHBORS, NEIGHBORS(*), IERROR


CC++++ SSyynnttaaxx
       #include 
       void Graphcomm::Getneighbors(int rank, int maxneighbors,
            int neighbors[]) const


IINNPPUUTT PPAARRAAMMEETTEERRSS
       comm      Communicator with graph topology (handle).

       rank      Rank of process in group of comm (integer).

       maxneighbors
                 Size of array neighbors (integer).


OOUUTTPPUUTT PPAARRAAMMEETTEERRSS
       neighbors Ranks of processes that are neighbors  to  specified  process
                 (array of integers).

       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       EExxaammppllee::   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 MPICOMMRANK(comm, myrank, ierr)
             CALL MPIGRAPHNEIGHBORS(comm, myrank, 3, neighbors, ierr)
       C  perform exchange permutation
             CALL MPISENDRECVREPLACE(A, 1, MPIREAL, neighbors(1), 0,
            +     neighbors(1), 0, comm, status, ierr)
       C  perform shuffle permutation
             CALL MPISENDRECVREPLACE(A, 1, MPIREAL, neighbors(2), 0,
            +     neighbors(3), 0, comm, status, ierr)
       C  perform unshuffle permutation
             CALL MPISENDRECVREPLACE(A, 1, MPIREAL, neighbors(3), 0,
            +     neighbors(2), 0, comm, status, ierr)


EERRRROORRSS
       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::ERRORSTHROWEXCEPTIONS, 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
       MPICommseterrhandler; the predefined error handler MPIERRORSRETURN
       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
       MPIGraphneighborscount




Open MPI 1.2                    September 2006   MPIGraphneighbors(3OpenMPI)