Suggested modifications for age-selectivity type 11

[kellijohnson-NOAA]

when working with age-specific selectivity of 1.0 for a range of ages.

Sorry if I made this pull request to the wrong base branch, i.e., it should not go into main. Feel free to suggest a different branch and I can rebase and submit a different/modified pull request.

The change in wording will be helpful to users that are new to selectivity type = 11. Even though I have used the type before I had to go to the Report.sso to make sure that it was doing what I thought it was. I was not sure if the parameters corresponded to the bins for ages or to the actual age numbers themselves. I also included an example in the suggested text.

[iantaylor-NOAA]

This is a helpful clarification.

I would make two additional changes if you have time.

First, I would move the description of the age-selectivity approach to the top, because I think it is more commonly used and is simpler to describe. Then the average reader doesn't have to sift through the stuff about population length bins to get what they want.

Second, I would change the last sentence from "The maximum age allowed is equal to the maximum age in the modelled population, not the maximum age in the data bins." to "The maximum p2 value allowed is the maximum age, not the maximum age bin." The terms "maximum age" and "age bin" are commonly used throughout the User Manual and I think are clear enough.

[iantaylor-NOAA]

Clarification: I edited the second suggestion to read "from...to..." instead of "to...to...".

[Rick-Methot-NOAA]

Also: selectivity operates on real ages, not data age bins.

[kellijohnson-NOAA]

@iantaylor-NOAA thank you for the helpful suggestions. If you have time, can you go ahead and just make the needed changes directly to this branch?

[iantaylor-NOAA]

I just attempted to implement my suggested changes--slightly differently than what I originally thought.

@Rick-Methot-NOAA, I added you as a review hoping you can look at this one more time.

[kellijohnson-NOAA]

Thanks @iantaylor-NOAA, there is one typo though The these .

[e-perl-NOAA]

Just fixed that Kelli!

[iantaylor-NOAA]

@Rick-Methot-NOAA,
Looking at the mirror_mask and mirror_mask_a vectors at
https://github.com/nmfs-ost/ss3-source-code/blob/main/SS_readcontrol_330.tpl#L4241
and
https://github.com/nmfs-ost/ss3-source-code/blob/main/SS_readcontrol_330.tpl#L4319
I see that the 1e-10 constant seems to only be added to the length-based formulation, not the age-based version. If you recall some good reason for that difference, we could document it for posterity. If it's just happenstance, I don't see a need to spend more time on this.

[Rick-Methot-NOAA]

No good reason for the difference. Just happenstance by not doing both at same time and not having today's coding tools at the time.

[Rick-Methot-NOAA]

Looks good. Definitely more informative. The rationale for the small constant with length selectivity is lost in antiquity but I suspect it was because of crashes that were happening due to no fish being selected.

[kellijohnson-NOAA]

Thank you everyone for your help on this pull request. @e-perl-NOAA I will leave it to you to merge it in to whatever branch you want when you think the time is appropriate.