[mpich-discuss] Why do predefined MPI_Ops function elementwise in MPI_Accumulate, but not in MPI-1 routines?

[Jed Brown]

On Tue, Apr 24, 2012 at 12:57, Dave Goodell <goodell at mcs.anl.gov> wrote:

> (a) is potentially doable, but you'll need additional functionality to
> register operations that doesn't currently exist in MPI.  Also, it would be
> difficult to pass in the MPI Forum.
>
> (b) is much more feasible, assuming you apply the same restrictions about
> having only a single basic datatype.
>
> (c) has the advantage of making MPI_PROD work correctly as well even if
> (a) is not permitted.
>
> Out of curiosity, how do you feel about just cheating a bit and using
> MPI_C_DOUBLE_COMPLEX for this particular use case?  Do you believe the risk
> of some sort of mismatch between C's _Complex and std::complex to be too
> great?
>

We tried to do this, but learned that MPI_C_DOUBLE_COMPLEX was floating
around in mpi.h just to trick our configure tests (since it fails at
run-time on Windows) and the bug report was closed by you as INVALID.

http://trac.mcs.anl.gov/projects/mpich2/ticket/1525

I'm not concerned about C99 complex being binary-incompatible with
std::complex.
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