Dear MPI Forum,
In chapter 5.9.5 (User-Defined Reduction Operations), page 185 of MPI
3.1 and page 187 of MPI 2019 Draft,
it reads :
Advice to implementors. We outline below a naive and inefficient
implementation of
MPI_REDUCE not supporting the "in place" option.
Strictly speaking, the outlined implementation is only valid for
intra-communicators (and does not support the "in place" option),
so you might consider amending this line before MPI 2019 is out.
Best regards,
Gilles
