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MPI_Graph_neighbors_count - Returns the number of edges connected to a given node in a graph communicator


#include <mpi.h> int MPI_Graph_neighbors_count(MPI_Comm comm , int rank , int *nneighbors );

#include <pmpi.h> int PMPI_Graph_neighbors_count(MPI_Comm comm , int rank , int *nneighbors );

#include <mpi.h> int MPI::Graphcomm::Get_neighbors_count(int rank ) const;

INCLUDE 'mpif.h' MPI_GRAPH_NEIGHBORS_COUNT(comm , rank , nneighbors , ierr ) INTEGER comm , rank , nneighbors , ierr


comm - graph communicator (handle)

rank - rank of the node to count edges of (integer)


nneighbors - total number of edges connected to that rank (integer).


The MPI_Graph_neighbors_count() function is used to obtain the total number of edges connected to the node at rank , within the graph communicator comm . This is returned via the nneighbors pointer.

The C++ version of this function passes the number of neighbors as the return value.

The communicator must be a valid one (not MPI_COMM_NULL). PMPI_Graph_neighbors_count() is the profiling version of this function.


All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.

In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.

MPI_SUCCESS - No error;

MPI_ERR_PENDING - Pending exception;

MPI_ERR_COMM - Invalid communicator;

MPI_ERR_TOPOLOGY - Not a graph communicator;

MPI_ERR_RANK - Invalid rank;

MPI_ERR_DIMS - Invalid output pointer.


MPI_Cart_get (3) MPI_Cartdim_get (3) MPI_Graph_create (3) MPI_Graphdims_get (3) MPI_Graph_get (3) MPI_Graph_neighbors (3)

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