[us-commits] [ehb54/ultrascan3] 3760c5: SAXS extrap-to-c0: Zimm fit-broadening (smooth con...

[emre brookes]

  Branch: refs/heads/ehb54-issue-920
  Home:   https://github.com/ehb54/ultrascan3
  Commit: 3760c59a96e15cedb87b5313e37db081afd4094f
      https://github.com/ehb54/ultrascan3/commit/3760c59a96e15cedb87b5313e37db081afd4094f
  Author: ehb54 <brookes at uthscsa.edu>
  Date:   2026-07-12 (Sun, 12 Jul 2026)

  Changed paths:
    M us_somo/develop/include/us_hydrodyn_saxs_iqq_extrap_c0_conc.h
    M us_somo/develop/include/us_hydrodyn_saxs_iqq_extrap_c0_regplot.h
    M us_somo/develop/src/us_hydrodyn_saxs_iqq_extrap_c0.cpp
    M us_somo/develop/src/us_hydrodyn_saxs_iqq_extrap_c0_conc.cpp
    M us_somo/develop/src/us_hydrodyn_saxs_iqq_extrap_c0_regplot.cpp
    M us_somo/somo/doc/manual/somo/somo_saxs_extrap_c0.html

  Log Message:
  -----------
  SAXS extrap-to-c0: Zimm fit-broadening (smooth concentration slope across q)

Adds an optional "Zimm fit broadening (q-window)" control to the
concentration dialog. The interparticle/interaction term (the per-q fit's
slope vs concentration) varies smoothly with q and dies off at high q, so
smoothing it across an N-point q-window and recomputing the intercept
(a = <I/c> - b_smoothed*<c>) removes extrapolation noise WITHOUT smearing
the form-factor detail carried by the intercept. Smoothing the output
curve directly (which would smear real features) is deliberately not done.

- 0 (default) = independent per-q fits, unchanged behavior.
- N > 1 = average the slope over an N-point window, then recompute each
  c=0 intercept. Validated against a known dilute-limit ground truth:
  N=5 improved accuracy (RMS 0.0089 vs 0.0139) and halved point-to-point
  noise on a simulated strong-interaction series.
- Zimm only; the field is disabled while Primus mode is checked.

The optional regression pop-up reflects it: reg_a/reg_b are updated so the
fit line uses the smoothed slope and its c=0 intercept, with a note above
the plot when broadening is active. Main plot uses the broadened curve.
Manual updated (Zimm section + regression-plot section).

Co-Authored-By: Claude Fable 5 <noreply at anthropic.com>



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