MPI_Dist_graph_create_adjacent(3) | Open MPI | 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_Commcomm_old, intindegree, const intsources[], const intsourceweights[], intoutdegree, const intdestinations[], const intdestweights[],

MPI_Info info, intreorder, 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) INTEGERCOMM_OLD, INDEGREE, SOURCES(*), SOURCEWEIGHTS(*), OUTDEGREE, DESTINATIONS(*), DESTWEIGHTS(*), INFOINTEGERCOMM_DIST_GRAPH, IERRORLOGICALREORDER

# 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_oldINTEGER, INTENT(IN) ::indegree,sources(indegree),outdegree,destinations(outdegree)INTEGER, INTENT(IN) ::sourceweights(*),destweights(*)TYPE(MPI_Info), INTENT(IN) ::infoLOGICAL, INTENT(IN) :: reorder TYPE(MPI_Comm), INTENT(OUT) ::comm_dist_graphINTEGER, 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).
- 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

November 24, 2021 | 4.1.2 |