NAME

       MPI_Op_create -  Creates a user-defined combination function handle

SYNOPSIS

       #include <mpi.h>
       int MPI_Op_create(MPI_User_function func, int commute,
                        MPI_Op *pop)

INPUT PARAMETERS

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

OUTPUT PARAMETER

       pop    - 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.

NOTES

       When  the MPI_Op created by this function is no longer being used, it should be freed with
       MPI_Op_free .

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 (e.g., MPI_ERRORS_RETURN ), then no error may be indicated.

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

ERRORS

       If  an  error occurs in an MPI function, the current MPI error handler is called to handle
       it.  By default, this error handler aborts the MPI job.  The error handler may be  changed
       with  MPI_Errhandler_set  ;  the predefined error handler MPI_ERRORS_RETURN may be used to
       cause error values to be returned (in C and Fortran; this error handler is less useful  in
       with  the  C++  MPI  bindings.   The predefined error handler MPI::ERRORS_THROW_EXCEPTIONS
       should be used in C++ if the error value needs to be recovered).  Note that MPI  does  not
       guarantee that an MPI program can continue past an error.

       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.  The C++ bindings for
       MPI  do  not  return  error  values;  instead,  error  values are communicated by throwing
       exceptions of type MPI::Exception (but not by default).  Exceptions are only thrown if the
       error value is not MPI::SUCCESS .

       Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return
       upon an error, there will be no way to recover what the actual error value was.
       MPI_SUCCESS
              - No error; MPI routine completed successfully.
       MPI_ERR_OP
              - Invalid operation.  MPI operations (objects of type MPI_Op ) must either  be  one
              of  the  predefined  operations  (e.g.,  MPI_SUM  ) or created with MPI_Op_create .
              Additionally, only certain datatypes are alloed with given  predefined  operations.
              See MPI-1, section 4.9.2.
       MPI_ERR_ARG
              -  Invalid  argument.  Some argument is invalid and is not identified by a specific
              error class.  This is typically a NULL pointer or other such error.
       MPI_ERR_OTHER
              - This error is returned when some part of the LAM/MPI implementation is unable  to
              acquire memory.

SEE ALSO

       MPI_Op_free

MORE INFORMATION

       For  more information, please see the official MPI Forum web site, which contains the text
       of both the MPI-1 and MPI-2 standards.  These documents contain detailed information about
       each MPI function (most of which is not duplicated in these man pages).

       http://www.mpi-forum.org/

ACKNOWLEDGEMENTS

       The  LAM  Team  would  like the thank the MPICH Team for the handy program to generate man
       pages  ("doctext"  from  ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz  ),  the   initial
       formatting, and some initial text for most of the MPI-1 man pages.

LOCATION

       opcreate.c