MPI_Dist_graph_create(3) Open MPI MPI_Dist_graph_create(3)
NAME
MPI_Dist_graph_create - Makes a new communicator to which topology in-
formation has been attached.
SYNTAX
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
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_DIST_GRAPH_CREATE(COMM_OLD, N, SOURCES, DEGREES, DESTINATIONS, WEIGHTS,
INFO, REORDER, COMM_DIST_GRAPH, IERROR)
INTEGER COMM_OLD, N, SOURCES(*), DEGRES(*), WEIGHTS(*), INFO
INTEGER COMM_DIST_GRAPH, IERROR
LOGICAL REORDER
Fortran 2008 Syntax
USE mpi_f08
MPI_Dist_Graph_create(comm_old, n, sources, degrees, destinations, weights,
info, reorder, comm_dist_graph, ierror)
TYPE(MPI_Comm), INTENT(IN) :: comm_old
INTEGER, INTENT(IN) :: n, sources(n), degrees(n), destinations(*)
INTEGER, INTENT(IN) :: weights(*)
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).
n Number of source nodes for which this process specifies edges
(non-negative integer).
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 inte-
gers).
destinations
Destination nodes for the source nodes in the source node ar-
ray (array of non-negative integers).
weights Weights for source to destination edges (array of non-nega-
tive 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 creates a new communicator comm_dist_graph with
distrubuted graph topology and returns a handle to the new communica-
tor. 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 desti-
nations 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 outgo-
ing 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 as-
sociated 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
Weights are specied as non-negative integers and can be used to influ-
ence the process remapping strategy and other internal MPI optimiza-
tions. For instance, approximate count arguments of later communication
calls along specic edges could be used as their edge weights. Multi-
plicity of edges can likewise indicate more intense communication be-
tween 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_UN-
WEIGHTED 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.
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_adjacent MPI_Dist_graph_neighbors
MPI_Dist_graph_neighbors_count
4.1.2 Nov 24, 2021 MPI_Dist_graph_create(3)
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