NAME

MPI_Graph_create - Creates a graph communicator

SYNOPSIS

#include <mpi.h> 
int MPI_Graph_create(MPI_Comm comm , int nnodes , int *index , int *edges , int reorder ,
	 MPI_Comm *out ); 
#include <pmpi.h> 
int PMPI_Graph_create(MPI_Comm comm , int nnodes , int *index , int *edges , int reorder ,
	 MPI_Comm *out ); 

INPUT PARAMETERS

comm - communicator (handle)

nnodes - number of nodes (integer)

index - array of nnodes integers describing graph degrees (array)

edges - array of integers describing graph edges (array)

reorder - reorder ranks for optimal placement (boolean)

OUTPUT PARAMETER

out - the new graph communicator (handle).

DESCRIPTION

The MPI_Graph_create() function is used to create a new graph communicator out using the index and edges arrays to describe the topology of the graph.

The size of the index array is given by nnodes . The index array contains the cumulative number of edges attached to each node. The edges array contains the ranks connected to each node sorted in node order. The index array thus allows one to find which set of edges connnect to a given node. A node n, is connected to the nodes listed from edges [ index [n-1]] to edges [ index [n]-1].

If reorder is true, then the output ranks will be arranged in an optimal order. Otherwise, the same order as in comm is chosen.

If the size of the new communicator is smaller than current communicator, then some of the nodes will receive an output of MPI_COMM_NULL. The new communicator should eventually be freed with MPI_Comm_free.

Note that the input communicator must be valid (not MPI_COMM_NULL). PMPI_Graph_create() is the profiling version of this function.

ERRORS

All MPI routines except for MPI_Wtime and MPI_Wtick return an error value. The the current MPI error handler is invoked if this 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.

MPI_SUCCESS - No error;

MPI_ERR_COMM - Invalid communicator;

MPI_ERR_DIMS - Invalid dimensions;

MPI_ERR_ARG - Invalid output pointer, or graph topology information;

MPI_ERR_INTERN - Out of Memory. This may be fatal.

SEE ALSO

MPI_Cart_create (3) MPI_Graph_create (3) MPI_Graphdims_get (3) MPI_Graph_get (3) MPI_Graph_neighbors_count (3) MPI_Graph_neighbors (3) MPI_Graph_map (3) MPI_Comm_free (3)

• Lockless
• MPI Documentation
• MPI_Graph_create