NAME

       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 specied 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 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