[us-commits] [ehb54/ultrascan3] a0bd90: SAXS extrap-to-c0: add Zimm/Primus mode toggle

[emre brookes]

  Branch: refs/heads/ehb54-issue-920
  Home:   https://github.com/ehb54/ultrascan3
  Commit: a0bd9077dbd128970d0b0235a106fc8cb14c33c4
      https://github.com/ehb54/ultrascan3/commit/a0bd9077dbd128970d0b0235a106fc8cb14c33c4
  Author: ehb54 <brookes at uthscsa.edu>
  Date:   2026-07-11 (Sat, 11 Jul 2026)

  Changed paths:
    M us_somo/develop/include/us_hydrodyn_saxs_iqq_extrap_c0_conc.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

  Log Message:
  -----------
  SAXS extrap-to-c0: add Zimm/Primus mode toggle

The zero-concentration extrapolation previously always produced the
concentration-normalized I(q)/c intercept (Zimm-style, tagged Conc:1).
Comparing against ATSAS Primus/almerge output on real alpha-synuclein
data showed almerge instead reports absolute intensity on the
highest-concentration curve's scale.

Add a "Primus mode" checkbox to the concentration-assignment dialog.
When checked, do_extrap_c0:
  1. scales each curve onto the highest-concentration (reference) curve
     by a least-squares factor over the common q-grid,
  2. linearly extrapolates the scaled ABSOLUTE intensity vs c to c=0
     (not I/c), keeping the output on the reference's absolute scale,
  3. carries the reference curve's error bars into the output and tags
     it with the reference concentration instead of Conc:1.

Unchecked (default) preserves the existing Zimm behavior exactly.

Verified against ATSAS zc_001.dat: reproduces the result to ~1.5%
median at low q, with internal scale factors matching almerge's
printed factors.

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



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