Teams: clarify behavior of split ops with strides <= 0

[davidozog]

Summary of changes

This addresses #491 by clarifying the behavior of team split operations when stride is zero or negative.

Proposal Checklist

• Link to issue(s)
• Changelog entry
• Reviewed for changes to front matter
• Reviewed for changes to back matter

[jdinan]

@davidozog Start description needs to be changed in order to allow negative strides:

\apiargument{IN}{start}{The lowest \ac{PE} number of the subset of \acp{PE} from
the parent team that will form the new team.}

With a negative stride, start is no longer the lowest PE index of the members in the parent team.

[davidozog]

@davidozog Start description needs to be changed in order to allow negative strides...

Agreed!

How about "the first" PE number...? Any suggestions on how to handle this fix?

[jdinan]

I can't see a small edit that will make this clear. I'd suggest another sentence or two to explain it clearly.

[jdinan]

Adding a note that "lowest" is doing some work here by forbidding "wrap-arounds". The updated text should specify "lowest/highest".