MPI_Comm_split_type(3) Open MPI MPI_Comm_split_type(3)NAMEMPI_Comm_split_type - Creates new communicators based on colors and
keys.
SYNTAXC Syntax
#include <mpi.h>
int MPI_Comm_split_type(MPI_Comm comm, int split_type, int key,
MPI_Info info, MPI_Comm *newcomm)
Fortran Syntax
INCLUDE 'mpif.h'
MPI_COMM_SPLIT_TYPE(COMM, SPLIT_TYPE, KEY, INFO, NEWCOMM, IERROR)
INTEGER COMM, SPLIT_TYPE, KEY, INFO, NEWCOMM, IERROR
INPUT PARAMETERS
comm Communicator (handle).
split_type
Type of processes to be grouped together (integer).
key Control of rank assignment (integer).
info Info argument (handle).
OUTPUT PARAMETERS
newcomm New communicator (handle).
IERROR Fortran only: Error status (integer).
DESCRIPTION
This function partitions the group associated with comm into disjoint
subgroups, based on the type specied by split_type. Each subgroup con‐
tains all processes of the same type. Within each subgroup, the pro‐
cesses are ranked in the order defined by the value of the argument
key, with ties broken according to their rank in the old group. A new
communicator is created for each subgroup and returned in newcomm. This
is a collective call; all processes must provide the same split_type,
but each process is permitted to provide different values for key. An
exception to this rule is that a process may supply the type value
MPI_UNDEFINED, in which case newcomm returns MPI_COMM_NULL.
SPLIT TYPES
MPI_COMM_TYPE_SHARED
This type splits the communicator into subcommunicators, each
of which can create a shared memory region.
NOTES
This is an extremely powerful mechanism for dividing a single communi‐
cating group of processes into k subgroups, with k chosen implicitly by
the user (by the number of colors asserted over all the processes).
Each resulting communicator will be nonoverlapping. Such a division
could be useful for defining a hierarchy of computations, such as for
multigrid or linear algebra.
Multiple calls to MPI_Comm_split_type can be used to overcome the
requirement that any call have no overlap of the resulting communica‐
tors (each process is of only one color per call). In this way, multi‐
ple overlapping communication structures can be created. Creative use
of the color and key in such splitting operations is encouraged.
Note that keys need not be unique. It is MPI_Comm_split_type's respon‐
sibility to sort processes in ascending order according to this key,
and to break ties in a consistent way. If all the keys are specified in
the same way, then all the processes in a given color will have the
relative rank order as they did in their parent group. (In general,
they will have different ranks.)
Essentially, making the key value zero for all processes of a given
split_type means that one needn't really pay attention to the rank-
order of the processes in the new communicator.
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_Comm_create
MPI_Intercomm_create
MPI_Comm_dup
MPI_Comm_free
MPI_Comm_split
1.7.4 Feb 04, 2014 MPI_Comm_split_type(3)
