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NAME

MPI_Graph_get - Returns the graph topology information from a graph communicator

SYNOPSIS

#include <mpi.h> int MPI_Graph_get(MPI_Comm comm , int maxindex , int maxedges , int *index , int *edges );

#include <pmpi.h> int PMPI_Graph_get(MPI_Comm comm , int maxindex , int maxedges , int *index , int *edges );

#include <mpi.h> void MPI::Graphcomm::Get_topo(int maxindex , int maxedges , int *index , int *edges ) const;

INCLUDE 'mpif.h' MPI_GRAPH_GET(comm , maxindex , maxedges , index , edges , ierr ) INTEGER comm , maxindex , maxedges , index (*), edges (*), ierr

INPUT PARAMETERS

comm - graph communicator (handle)

maxindex - size of the index array (integer)

maxedges - size of the edges array (integer)

OUTPUT PARAMETERS

index - index topology information from the graph (array)

edges - edge topology information from the graph (array).

DESCRIPTION

The MPI_Graph_get() function is used to obtain the topology information from a graph communicator comm . Arrays of size maxindex and maxedges are filled. If these are too small, then the error MPI_ERR_DIMS is returned. Use the MPI_Graphdims_get() function to make sure there is enough room.

The topology information stored in the index and edges arrays is that given to the graph communicator when it was created by the MPI_Graph_create() function.

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

ERRORS

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_DIMS - Invalid output pointers, or arrays too small.

SEE ALSO

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

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