Alltoallw rationale mentions an MPI_SCATTERW function

[jaegerj]

Problem

Rationale in alltoallw description mentions "... this achieves an MPI_SCATTERW function. (End of rationale.)".
However, this function doesn't exist in the standard.

Proposal

Change the text to say that this achieves what would exepcted of an MPI_SCATTERW function if such existed, and quickly described what the example does.

Changes to the Text

"..., this achieves an MPI_SCATTERW function. (End of rationale.)"

becomes

"..., this achieves what on could expect from an "MPI_SCATTERW" if such function existed, which is equivalent to an MPI_SCATTERV but with the blocks needing not all have the same datatypes. (End of rationale.)"

Impact on Implementations

None

Impact on Users

Better understanding of the example

References and Pull Requests

[jeffhammond]

We should deprecate ALLTOALLW. It's worthless. A loop over send-recv is better.

IALLTOALLW has the tiniest utility but it wasn't the reason ALLTOALLW was added so I don't think it's worth keeping.