MPI_Dist_graph_create_adjacent(3)

NAME
MPI_Dist_graph_create_adjacent - Makes a new communicator to which topology information has been attached.

SYNTAX

C Syntax
#include <mpi.h>
int MPI_Dist_graph_create_adjacent(MPI_Comm comm_old, int indegree, const int sources[],
	const int sourceweights[], int outdegree, const int destinations[], const int destweights[],
        MPI_Info info, int reorder, MPI_Comm *comm_dist_graph)

INPUT PARAMETERS

comm_old
    Input communicator without topology (handle).

indegree
    Size of sources and sourceweights arrays (non-negative integer).

sources
    Ranks of processes for which the calling process is a destination (array of non-negative integers).

sourceweights
    Weights of the edges into the calling process (array of non-negative integers).

outdegree
    Size of destinations and destweights arrays (non-negative integer).

destinations
    Ranks of processes for which the calling process is a source (array of non-negative integers).

destweights
    Weights of the edges out of the calling process (array of non-negative integers).

Hints on optimization and interpretation of weights (handle).

reorder
    Ranking may be reordered (true) or not (false) (logical).

OUTPUT PARAMETERS

comm_dist_graph
    Communicator with distibuted graph topology added (handle).

IERROR
    Fortran only: Error status (integer).

DESCRIPTION
MPI_Dist_graph_create_adjacent creats a new communicator comm_dist_graph with distrubuted graph topology and returns a handle to the new communicator. The number of processes in comm_dist_graph is identical to the number of processes in comm_old. Each process passes all information about its incoming and outgoing edges in the virtual distributed graph topology. The calling processes must ensure that each edge of the graph is described in the source and in the destination process with the same weights. If there are multiple edges for a given (source,dest) pair, then the sequence of the weights of these edges does not matter. The complete communication topology is the combination of all edges shown in the sources arrays of all processes in comm_old, which must be identical to the combination of all edges shown in the destinations arrays. Source and destination ranks must be process ranks of comm_old. This allows a fully distributed specication of the communication graph. Isolated processes (i.e., processes with no outgoing or incoming edges, that is, processes that have specied indegree and outdegree as zero and thus do not occur as source or destination rank in the graph specication) are allowed. The call to MPI_Dist_graph_create_adjacent is collective.

WEIGHTS
Weights are specied as non-negative integers and can be used to influence the process remapping strategy and other internal MPI optimizations. For instance, approximate count arguments of later communication calls along specic edges could be used as their edge weights. Multiplicity of edges can likewise indicate more intense communication between pairs of processes. However, the exact meaning of edge weights is not specied by the MPI standard and is left to the implementation. An application can supply the special value MPI_UNWEIGHTED for the weight array to indicate that all edges have the same (effectively no) weight. It is erroneous to supply MPI_UNWEIGHTED for some but not all processes of comm_old. If the graph is weighted but indegree or outdegree is zero, then MPI_WEIGHTS_EMPTY or any arbitrary array may be passed to sourceweights or destweights respectively. Note that MPI_UNWEIGHTED and MPI_WEIGHTS_EMPTY are not special weight values; rather they are special values for the total array argument. In Fortran, MPI_UNWEIGHTED and MPI_WEIGHTS_EMPTY are objects like MPI_BOTTOM (not usable for initialization or assignment). See MPI-3 § 2.5.4.

ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument.

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.

SEE ALSO

MPI_Dist_graph_create MPI_Dist_graph_neighbors MPI_Dist_graph_neighbors_count