MPI_Comm_split

MPI_Comm_split(3)                     MPI                    MPI_Comm_split(3)



NAME
       MPI_Comm_split -  Creates new communicators based on colors and keys

SYNOPSIS
       int MPI_Comm_split(MPI_Comm comm, int color, int key, MPI_Comm *newcomm)

INPUT PARAMETERS
       comm   - communicator (handle)
       color  - control of subset assignment (nonnegative integer).  Processes
              with the same color are in the same new communicator
       key    - control of rank assignment (integer)


OUTPUT PARAMETERS
       newcomm
              - new communicator (handle)


NOTES
       The color must be non-negative or MPI_UNDEFINED .



THREAD AND INTERRUPT SAFETY
       This routine is thread-safe.  This means that this routine may be
       safely used by multiple threads without the need for any user-provided
       thread locks.  However, the routine is not interrupt safe.  Typically,
       this is due to the use of memory allocation routines such as malloc or
       other non-MPICH runtime routines that are themselves not interrupt-
       safe.


NOTES FOR FORTRAN
       All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have
       an additional argument ierr at the end of the argument list.  ierr is
       an integer and has the same meaning as the return value of the routine
       in C.  In Fortran, MPI routines are subroutines, and are invoked with
       the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in
       Fortran.


ALGORITHM
       1. Use MPI_Allgather to get the color and key from each process
       2. Count the number of processes with the same color; create a
       communicator with that many processes.  If this process has
       MPI_UNDEFINED
       as the color, create a process with a single member.
       3. Use key to order the ranks
       4. Set the VCRs using the ordered key values



ERRORS
       All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error
       value; C routines as the value of the function and Fortran routines in
       the last argument.  Before the value is returned, the current MPI error
       handler is called.  By default, this error handler aborts the MPI job.
       The error handler may be changed with MPI_Comm_set_errhandler (for
       communicators), MPI_File_set_errhandler (for files), and
       MPI_Win_set_errhandler (for RMA windows).  The MPI-1 routine
       MPI_Errhandler_set may be used but its use is deprecated.  The
       predefined error handler MPI_ERRORS_RETURN may be used to cause error
       values to be returned.  Note that MPI does not guarentee that an MPI
       program can continue past an error; however, MPI implementations will
       attempt to continue whenever possible.

       MPI_SUCCESS
              - No error; MPI routine completed successfully.
       MPI_ERR_COMM
              - Invalid communicator.  A common error is to use a null
              communicator in a call (not even allowed in MPI_Comm_rank ).
       MPI_ERR_INTERN
              - This error is returned when some part of the MPICH
              implementation is unable to acquire memory.


SEE ALSO
       MPI_Comm_free

LOCATION
       src/mpi/comm/comm_split.c



                                   8/22/2013                 MPI_Comm_split(3)