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SYNTAX
C 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
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_COMM_SPLIT_TYPE(COMM, SPLIT_TYPE, KEY, INFO, NEWCOMM, IERROR)
INTEGER COMM, SPLIT_TYPE, KEY, INFO, NEWCOMM, IERROR
Fortran 2008 Syntax
USE mpi_f08
MPI_Comm_split_type(comm, split_type, key, info, newcomm, ierror)
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, INTENT(IN) :: split_type, key
TYPE(MPI_Info), INTENT(IN) :: info
TYPE(MPI_Comm), INTENT(OUT) :: newcomm
INTEGER, OPTIONAL, INTENT(OUT) :: 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
specified by split_type. Each subgroup contains all processes of the same type. Within each subgroup, the
processes 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.
OMPI_COMM_TYPE_NODE
Synonym for MPI_COMM_TYPE_SHARED.
OMPI_COMM_TYPE_HWTHREAD
This type splits the communicator into subcommunicators, each of which belongs to the same
hardware thread.
OMPI_COMM_TYPE_CORE
This type splits the communicator into subcommunicators, each of which belongs to the same
core/processing unit.
OMPI_COMM_TYPE_L1CACHE
This type splits the communicator into subcommunicators, each of which belongs to the same L1
cache.
OMPI_COMM_TYPE_L2CACHE
This type splits the communicator into subcommunicators, each of which belongs to the same L2
cache.
OMPI_COMM_TYPE_L3CACHE
This type splits the communicator into subcommunicators, each of which belongs to the same L3
cache.
OMPI_COMM_TYPE_SOCKET
This type splits the communicator into subcommunicators, each of which belongs to the same socket.
OMPI_COMM_TYPE_NUMA
This type splits the communicator into subcommunicators, each of which belongs to the same
NUMA-node.
OMPI_COMM_TYPE_BOARD
This type splits the communicator into subcommunicators, each of which belongs to the same board.
OMPI_COMM_TYPE_HOST
This type splits the communicator into subcommunicators, each of which belongs to the same host.
OMPI_COMM_TYPE_CU
This type splits the communicator into subcommunicators, each of which belongs to the same
computational unit.
OMPI_COMM_TYPE_CLUSTER
This type splits the communicator into subcommunicators, each of which belongs to the same
cluster.
NOTES
The communicator keys denoted with an OMPI_ prefix instead of an MPI_ prefix are specific to Open MPI,
and are not part of the MPI standard. Their use should be protected by the OPEN_MPI C preprocessor macro.
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_Comm_create
• MPI_Intercomm_create
• MPI_Comm_dup
• MPI_Comm_free
• MPI_Comm_split
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Sep 06, 2025 MPI_COMM_SPLIT_TYPE(3)