[Mpi-comments] User-Defined Reduction Operations: possible enhancement

[Gilles Gouaillardet]

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