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MPI_Intercomm_merge(3)		      MPI		MPI_Intercomm_merge(3)

NAME
       MPI_Intercomm_merge  -  Creates an intracommuncator from	an intercommu-
       nicator

SYNOPSIS
       int MPI_Intercomm_merge(MPI_Comm	intercomm, int high, MPI_Comm *newintracomm)

INPUT PARAMETERS
       comm   -	Intercommunicator (handle)
       high   -	Used to	order the groups within	comm (logical)	when  creating
	      the  new	communicator.  This is a boolean value;	the group that
	      sets high	true has its processes ordered after  the  group  that
	      sets this	value to false.	 If all	processes in the intercommuni-
	      cator provide the	same value, the	choice of which	group  is  or-
	      dered first is arbitrary.

OUTPUT PARAMETER
       comm_out
	      -	Created	intracommunicator (handle)

NOTES
       While  all processes may	provide	the same value for the high parameter,
       this requires the MPI implementation to determine which group  of  pro-
       cesses should be	ranked first.

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
       \neAllocate contexts \neLocal and remote	group leaders swap high	values
       \neDetermine the	high value.  \neMerge the two groups and make the  in-
       tra-communicator

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_Intercomm_create, MPI_Comm_free

LOCATION
       src/mpi/comm/intercomm_merge.c

				   9/20/2012		MPI_Intercomm_merge(3)

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

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