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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	assigment (integer)

OUTPUT PARAMETER
       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 com-
       municators),  MPI_File_set_errhandler  (for files), and MPI_Win_set_er-
       rhandler	(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	 when-
       ever possible.

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

SEE ALSO
       MPI_Comm_free

LOCATION
       src/mpi/comm/comm_split.c

				   9/25/2012		     MPI_Comm_split(3)

NAME | SYNOPSIS | INPUT PARAMETERS | OUTPUT PARAMETER | NOTES | THREAD AND INTERRUPT SAFETY | NOTES FOR FORTRAN | ALGORITHM | ERRORS | SEE ALSO | LOCATION

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