MPI_Op_create(3)							MPI							  MPI_Op_create(3)

NAME

       MPI_Op_create -	Creates a user-defined combination function handle

SYNOPSIS

       int MPI_Op_create(MPI_User_function *function, int commute, MPI_Op *op)

INPUT PARAMETERS

       function
	      - user defined function (function)
       commute
	      - true if commutative;  false otherwise. (logical)

OUTPUT PARAMETER

       op     - operation (handle)

NOTES ON THE USER FUNCTION

       The calling list for the user function type is
       typedef void (MPI_User_function) ( void * a,
       void * b, int * len, MPI_Datatype * );

       where the operation is b[i] = a[i] op b[i] , for i=0,...,len-1 .  A pointer to the datatype given to the MPI collective computation routine
       (i.e., MPI_Reduce , MPI_Allreduce , MPI_Scan , or MPI_Reduce_scatter ) is also passed to the user-specified routine.

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.

NOTES ON COLLECTIVE OPERATIONS

       The reduction functions ( MPI_Op ) do not return an error value.  As a result, if the functions detect an error, all they can do is  either
       call  MPI_Abort or silently skip the problem.  Thus, if you change the error handler from MPI_ERRORS_ARE_FATAL to something else, for exam-
       ple, MPI_ERRORS_RETURN , then no error may be indicated.

       The reason for this is the performance problems in ensuring that all collective routines return the same error value.

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.

SEE ALSO

       MPI_Op_free

LOCATION

       op_create.c

								     3/5/2011							  MPI_Op_create(3)