17.2.85. MPI_Dist_graph_create_adjacent

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

17.2.85.1. SYNTAX

17.2.85.1.1. 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)

17.2.85.1.2. Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_DIST_GRAPH_CREATE_ADJACENT(COMM_OLD, INDEGREE, SOURCES, SOURCEWEIGHTS, OUTDEGREE,
                DESTINATIONS, DESTWEIGHTS, INFO, REORDER, COMM_DIST_GRAPH, IERROR)
     INTEGER COMM_OLD, INDEGREE, SOURCES(*), SOURCEWEIGHTS(*), OUTDEGREE, DESTINATIONS(*), DESTWEIGHTS(*), INFO
     INTEGER COMM_DIST_GRAPH, IERROR
     LOGICAL REORDER

17.2.85.1.3. Fortran 2008 Syntax

USE mpi_f08
MPI_Dist_Graph_create_adjacent(comm_old, ndegree, sources, sourceweights,
             outdegree, destinations, destweights, info, reorder,
             comm_dist_graph, ierror)
     TYPE(MPI_Comm), INTENT(IN) :: comm_old
     INTEGER, INTENT(IN) :: indegree, sources(indegree), outdegree, destinations(outdegree)
     INTEGER, INTENT(IN) :: sourceweights(*), destweights(*)
     TYPE(MPI_Info), INTENT(IN) :: info
     LOGICAL, INTENT(IN) :: reorder
     TYPE(MPI_Comm), INTENT(OUT) :: comm_dist_graph
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

17.2.85.2. 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).

  • info: Hints on optimization and interpretation of weights (handle).

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

17.2.85.3. OUTPUT PARAMETERS

  • comm_dist_graph: Communicator with distributed graph topology added (handle).

  • IERROR: Fortran only: Error status (integer).

17.2.85.4. DESCRIPTION

MPI_Dist_graph_create_adjacent creates a new communicator comm_dist_graph with distributed 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 specification of the communication graph. Isolated processes (i.e., processes with no outgoing or incoming edges, that is, processes that have specified indegree and outdegree as zero and thus do not occur as source or destination rank in the graph specification) are allowed. The call to MPI_Dist_graph_create_adjacent is collective.

17.2.85.5. WEIGHTS

Weights are specified 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 specific 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 specified 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 section 2.5.4.

17.2.85.6. 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.