void Graphcomm::Get_neighbors(int \fIrank\fP, int \fImaxneighbors\fP,
int \fIneighbors\fP[]) const
.SHINPUTPARAMETERS
.ftR
.TP1i
comm
Communicator with graph topology (handle).
.TP1i
rank
Rank of process in group of comm (integer).
.TP1i
maxneighbors
Size of array neighbors (integer).
.SHOUTPUTPARAMETERS
.ftR
.TP1i
neighbors
Ranks of processes that are neighbors to specified process (array of integers).
.ftR
.TP1i
IERROR
Fortran only: Error status (integer).
.SHDESCRIPTION
.ftR
\fBExample:\fP 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.
.sp
.nf
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
.fi
.sp
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.
.sp
.nf
C assume: each process has stored a real number A.
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.
.sp
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.