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



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



                                   11/12/2019                  MPI_Comm_split(3)