MPI_Op_create - Creates a user-defined combination function handle
int MPI_Op_create(MPI_User_function func, int commute,
func - user defined function (function)
- true if commutative; false otherwise.
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.
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
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.
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.
- No error; MPI routine completed successfully.
- 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.
- 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.
- This error is returned when some part of the LAM/MPI
implementation is unable to acquire memory.
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).
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.