JP-4318: Updating Ramp Fitting Tests for New STCAL Slope Computation.

[kmacdonald-stsci]

Resolves JP-4318

This PR addresses using the median rate of a pixel, which is computed across all integrations of a pixel, for the computation of the rate and rateint slopes, using the Poisson variance as part of the weights. This should not happen, since this has the effect of later integrations affecting the slope of earlier integrations. To prevent this the weighting during the computation of rate and rateint slopes use only the read noise variance, rather than a combination of both Poisson and read noise variances.

Tasks

• update or add relevant tests
• update relevant docstrings and / or docs/ page
• Does this PR change any API used downstream? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see changelog readme for instructions)
  • if your change breaks existing functionality, also add a changes/<PR#>.breaking.rst news fragment
• run regression tests with this branch installed ("git+https://github.com/<fork>/stcal@<branch>")
  • jwst regression test
  • romancal regression test

[kmacdonald-stsci]

Regression tests run here:

https://github.com/spacetelescope/RegressionTests/actions/runs/26763461997

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.78%. Comparing base (a04ec58) to head (54156c9).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #550      +/-   ##
==========================================
- Coverage   91.80%   91.78%   -0.03%     
==========================================
  Files          63       63              
  Lines        8855     8857       +2     
==========================================
  Hits         8129     8129              
- Misses        726      728       +2     

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[drlaw1558]

In order to properly reflect the weights being used in the optional output data products I think we also need to change:

Lines 3191-3192 from:

tmp = 1. / seg->var_e;
seg->weight = tmp * tmp;

to

tmp = 1. / seg->var_r;
seg->weight = tmp

Lines 3284-3287 from:

tmp = (seg->var_p + seg->var_r);
wt = 1. / tmp;
wt *= wt;
seg->weight = wt;

to

tmp = seg->var_r;
wt = 1. / tmp;
seg->weight = wt;

Lines 3442-3443 from:

seg->weight = 1. / seg->var_e;
seg->weight *= seg->weight;

to

seg->weight = 1. / seg->var_r;

[drlaw1558]

Looks good to me in local testing now; thanks @kmacdonald-stsci !

[melanieclarke]

Looks like there are a number of unit tests that need updating still.

[kmacdonald-stsci]

Looks like there are a number of unit tests that need updating still.

All the "cases", which tests optional results, were failing due to the change in the weighting computation. They have all been updated and passing now.

[tapastro]

I think this PR is good to go, but the paired JWST PR still has some questions. I'll hold off on merging until that one is squared away.