MPI_COMM_SPLIT_TYPE(3)				     Open MPI				    MPI_COMM_SPLIT_TYPE(3)

MPI_Comm_split_type — Creates new communicators based on colors and keys.

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>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#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 <#
       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>/MPI_Comm_spawn_multiple	<#
       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 <#mpi-abort> was called on that communicator. If called
	 on  a window or file, acts as if MPI_Abort <#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	<#mpi-comm-create-errhandler>	  then	   MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	 <#mpi-file-create-errhandler>	   then	    MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       See the Error Handling section of the MPI-3.1 standard for more information.

       See also:

	  • MPI_Comm_create <#mpi-comm-create>

	  • MPI_Intercomm_create <#mpi-intercomm-create>

	  • MPI_Comm_dup <#mpi-comm-dup>

	  • MPI_Comm_free <#mpi-comm-free>

	  • MPI_Comm_split <#mpi-comm-split>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				    MPI_COMM_SPLIT_TYPE(3)
