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NAME

       MPI_Op_create -  Creates a user-defined combination function handle

SYNOPSIS

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

INPUT PARAMETERS

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

OUTPUT PARAMETERS

       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 example,
       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

       /tmp/gyCYfBi4J6/mpich-3.1/src/mpi/coll/op_create.c

                                   2/20/2014                  MPI_Op_create(3)



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