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)

   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

   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

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).

OUTPUT PARAMETERS

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

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

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.

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.

ERRORS

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

       Before the error value is returned, the current MPI  error  handler  associated  with  the  communication
       object  (e.g.,  communicator, window, file) is called.  If no communication object is associated with the
       MPI call, then the call is considered attached to MPI_COMM_SELF and will call the  associated  MPI  error
       handler.   When   MPI_COMM_SELF   is   not  initialized  (i.e.,  before  MPI_Init/MPI_Init_thread,  after
       MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial  error  handler.
       The  initial  error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
       the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info  key  to  MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.   If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
       error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is  called  for  all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called  on  a  communicator,  it  acts  as if MPI_Abort was called on that communicator. If called on a
         window or file, acts as if MPI_Abort was called on a communicator containing the group of processes  in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

       See the Error Handling section of the MPI-3.1 standard for more information.

       SEE ALSO:

          • MPI_Dist_graph_create

          • MPI_Dist_graph_neighbors

          • MPI_Dist_graph_neighbors_count

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       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                 MPI_DIST_GRAPH_CREATE_ADJACENT(3)