.. _mpi_dist_graph_neighbors:


MPI_Dist_graph_neighbors
========================

.. include_body

:ref:`MPI_Dist_graph_neighbors` - Returns the neighbors of the calling
process in a distributed graph topology.


SYNTAX
------


C Syntax
^^^^^^^^

.. code-block:: c

   #include <mpi.h>

   int MPI_Dist_graph_neighbors(MPI_Comm comm, int maxindegree, int sources[], int sourceweights[],
                                int maxoutdegree, int destinations[], int destweights[])


Fortran Syntax
^^^^^^^^^^^^^^

.. code-block:: fortran

   USE MPI
   ! or the older form: INCLUDE 'mpif.h'
   MPI_DIST_GRAPH_NEIGHBORS(COMM, MAXINDEGREE, SOURCES, SOURCEWEIGHTS,
           MAXOUTDEGREE, DESTINATIONS, DESTWEIGHTS, IERROR)
           INTEGER COMM, MAXINDEGREE, SOURCES(*), SOURCEWEIGHTS(*), MAXOUTDEGREE,
                   DESTINATIONS(*), DESTWEIGHTS(*), IERROR


Fortran 2008 Syntax
^^^^^^^^^^^^^^^^^^^

.. code-block:: fortran

   USE mpi_f08
   MPI_Dist_Graph_neighbors(comm, maxindegree, sources, sourceweights,
   		maxoutdegree, destinations, destweights, ierror)
   	TYPE(MPI_Comm), INTENT(IN) :: comm
   	INTEGER, INTENT(IN) :: maxindegree, maxoutdegree
   	INTEGER, INTENT(OUT) :: sources(maxindegree), destinations(maxoutdegree)
   	INTEGER :: sourceweights(*), destweights(*)
   	INTEGER, OPTIONAL, INTENT(OUT) :: ierror


INPUT PARAMETERS
----------------
* ``comm``: Communicator with distributed graph topology (handle).
* ``maxindegree``: Size of *sources* and *sourceweights* arrays (non-negative integer).
* ``maxoutdegree``: Size of *destinations* and *destweights* arrays (non-negative integer).

OUTPUT PARAMETERS
-----------------
* ``sources``: 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).
* ``destinations``: 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).
* ``IERROR``: Fortran only: Error status (integer).

DESCRIPTION
-----------

:ref:`MPI_Dist_graph_neighbors` returns the source and destination ranks in a
distributed graph topology for the calling process. This call will
return up to *maxindegree* source ranks in the *sources* array and up to
*maxoutdegree* destination ranks in the *destinations* array. If weights
were specified at the time of the communicator's creation then the
associated weights are returned in the *sourceweights* and *destweights*
arrays. If the communicator was created with
:ref:`MPI_Dist_graph_create_adjacent` then the order of the values in *sources*
and *destinations* is identical to the input that was used by the
process with the same rank in comm_old in the creation call.


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
:ref:`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.


.. seealso::
   :ref:`MPI_Dist_graph_neighbors_count`
