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       MPI_Dist_graph_create   -  Makes a new communicator to which topology information has been


C Syntax

       #include <mpi.h>
       int MPI_Dist_graph_create(MPI_Comm comm_old, int n, const int sources[],
            const int degrees[], const int destinations[], const int weights[],
               MPI_Info info, int reorder, MPI_Comm *comm_dist_graph)

Fortran Syntax

       INCLUDE 'mpif.h'
                       INFO, REORDER, COMM_DIST_GRAPH, IERROR)
            LOGICAL   REORDER


       comm_old  Input communicator without topology (handle).

       n         Number of source nodes for which  this  process  specifies  edges  (non-negative

       sources   Array  containing the n source nodes for which this process species edges (array
                 of non-negative integers).

       degrees   Array specifying the number of destinations for each source node in  the  source
                 node array (array of non-negative integers).

                 Destination  nodes  for the source nodes in the source node array (array of non-
                 negative integers).

       weights   Weights for source to destination edges (array of non-negative integers).

       Hints on optimization and interpretation of weights (handle).

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


                 Communicator with distibuted graph topology added (handle).

       IERROR    Fortran only: Error status (integer).


       MPI_Dist_graph_create creates 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.  Concretely,  each
       process  calls  the  constructor with a set of directed (source,destination) communication
       edges as described below.  Every process passes an array of n source nodes in the  sources
       array.  For each source node, a non-negative number of destination nodes is specied in the
       degrees array. The destination nodes are stored in the corresponding  consecutive  segment
       of  the destinations array. More precisely, if the i-th node in sources is s, this species
       degrees[i]   edges   (s,d)   with   d    of    the    j-th    such    edge    stored    in
       destinations[degrees[0]+...+degrees[i-1]+j].   The  weight  of  this  edge  is  stored  in
       weights[degrees[0]+...+degrees[i-1]+j]. Both the sources and the destinations  arrays  may
       contain  the  same  node  more  than  once,  and  the  order  in which nodes are listed as
       destinations or sources is not signicant. Similarly, different processes may specify edges
       with  the  same source and destination nodes. Source and destination nodes must be process
       ranks of comm_old. Different  processes  may  specify  different  numbers  of  source  and
       destination  nodes,  as well as different source to destination edges. 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 do not occur as source or
       destination node in the graph specication) are allowed. The call to  MPI_Dist_graph_create
       is collective.

       If  reorder  =  false,  all  processes  will  have  the same rank in comm_dist_graph as in
       comm_old. If reorder = true then the MPI library is free to remap to other  processes  (of
       comm_old)  in order to improve communication on the edges of the communication graph.  The
       weight associated with each edge is a  hint  to  the  MPI  library  about  the  amount  or
       intensity of communication on that edge, and may be used to compute a


       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 n = 0, then MPI_WEIGHTS_EMPTY or any arbitrary
       array may be passed to weights. 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 ยง 2.5.4.


       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.


       MPI_Dist_graph_create_adjacent MPI_Dist_graph_neighbors MPI_Dist_graph_neighbors_count