This is probably just do to the construction of the repro sum, but I'm a bit confused by the two length array of indexForReproSum. It seems position 1 is always just 1 and position 2 is the total number of entries in the sum. Is that right? What is position 1 of this index array used for? It never appears to be modified and then just get used in the globalSum call.

@vanroekel The reproducible sums in MPAS allow sums over full arrays and over restricted address ranges in each dimension. For full generality, the range must be specified in min/max pairs for each array dimension. In this case, the array is getting packed in advance so the min is always 1 but the max can vary. But both need to be provided for the interface.

Thanks @philipwjones for the explanation. It didn't make sense to me either. Can we add a comment to explain that, if it's cleaner to retain the indexForReproSum with dimensions nSums and indexForReproSum(1) = min = 1 ?

@vanroekel this has always been part of the algorithm (essentially the "if deltaS .ne. 0.0" part) to account for possible cases where we explicitly don't want to apply restoring to some cells (eg, under land ice maybe?). then we don't actually want to include every cell in these sums. does that make sense?

Thanks @philipwjones for the help understanding this. I'd like to include the comment from @alicebarthel in the PR for clarity. If it is too long for a comment, perhaps we can think of a shorter version.

@philipwjones It's a minor detail, but I'm curious. Can you confirm if I understood this correctly: in this case, it's a coincidence that indexForReproSum and reductions have the same dimensions of nSums?
Technically, indexForReproSum should always have 2 (the min, max you mentioned), while nSums could be anything given the needs of the routine? (here, 2 since we need the area sum and the area-weighted salinity sum).
Does it make sense to use nSums to define indexForReproSum then? It seems misleading to me.

@alicebarthel Good catch. The index array should be dimensioned 2*(number of dimensions being summed over) - in this case just 2 since the arrays are just 1-d. So nSums is coincidentally correct but in incorrect in general.

@alicebarthel I wouldn't say it is "a coincidence" that nSums=2; this routine isn't meant to be general which is why I hardwired it to be correct for this case.

@maltrud sure, I understand it's not meant to be general. I don't mind hard-coding the dimensions of indexForReproSum to 2. I mind hard-coding it to nSums if it's not supposed to have nSums as a dimension in general.

ok, maybe I still don't understand the question. we have 2 sums to do: area and areadeltaS, so nSums = 2. so we need the same number of outputs from the 2 global sum calls: global_sum(area) and global_sum(areadeltaS) which are put into reductions(1) and reductions(2), respectively. so reductions should always be dimensioned nSums. I guess I could have just put sumAreaGlobal and sumAreaDeltaSGlobal directly in the global sum calls and not needed reductions(), but I wanted to keep the new version as similar to the current version as possible. does this make sense?

ah, ok, now I understand. you're right, that is misleading. should I just place it with "2"?

and a comment? thanks for clarifying.

I think you should create a variable ThroatWarblerMangrove that's pronounced "two"...

@maltrud Sounds good to me, thanks!

Could I suggest Rhabarberbarbarabarbarbarenbartbarbierbier as a suitable alternative?

@maltrud just curious: is there any reason you went with reductions as a name for these variables? Sums is more intuitive to me, but maybe I'm not familiar with the jargon?

@alicebarthel I wanted to make as few code changes as possible so I retained the same variable names that already existed whenever possible. in the new code, "sums" isn't needed anymore, while "reductions" serves the same purpose in both the current and new versions. probably should have done things differently many years ago, but that's the rationale.

thanks for your careful reviewing.

@maltrud I totally understand the wisdom of making minimal code changes. As a newcomer to these routines, I allow myself to make minor comments as to readability to new users. Take it or leave it :-)