Adds corrected intensities to Corfunc output

[jellybean2004]

Description

The Export Extrapolation button in Corfunc would save a CSV file with q and I. As suggested by @smk78, I have updated this button to save two files: uncorrected with q and I (same as before) and corrected with q and I minus background.

Fixes #2138

How Has This Been Tested?

Added and ran a unit test and manually tested in the build.

Review Checklist:

Documentation

• There is nothing that needs documenting
• Documentation changes are in this PR
• There is an issue open for the documentation (link?)

Installers

• There is a chance this will affect the installers, if so
  • Windows installer (GH artifact) has been tested (installed and worked)
  • MacOSX installer (GH artifact) has been tested (installed and worked)
  • Wheels installer (GH artifact) has been tested (installed and worked)

Licensing

• The introduced changes comply with SasView license (BSD 3-Clause)

[Copilot]

Pull request overview

Updates Corfunc’s “Export Extrapolated” workflow to export both raw extrapolated intensities and background-corrected intensities for downstream use.

Changes:

• Export now writes two CSVs: *_uncorrected.csv and *_corrected.csv (background-subtracted).
• CorfuncPerspective passes the calculator background into the export dialog.
• Adds a unit test for the two-file export behavior and updates Corfunc documentation.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/sas/qtgui/Perspectives/Corfunc/media/corfunc-how-to.rst	Documents the updated extrapolated export behavior (two CSV outputs).
src/sas/qtgui/Perspectives/Corfunc/UnitTesting/SaveExtrapolatedPopupTest.py	Adds a unit test asserting both uncorrected and corrected files are created with expected contents.
src/sas/qtgui/Perspectives/Corfunc/SaveExtrapolatedPopup.py	Implements two-file export and background subtraction in the corrected output.
src/sas/qtgui/Perspectives/Corfunc/CorfuncPerspective.py	Wires the calculator background through to the export popup.

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[jellybean2004]

Hi @smk78! If you have some time, would you mind reviewing this PR, please?

[smk78]

Installed and tested CI Build #5766 on W11/x64.
Performed Corfunc analysis on example data ISIS_98929.txt using automatic settings and Guinier End: 0.01469087, Porod Start: 0.1658318 and Porod End: 0.2364554. Then used Export Extrapolated setting Lowest Q: 0.001 and Highest Q: 0.3 (input data ranged 0.007 - 0.285).
SasView computed a Background=0.30151 and generated two extrapolation files (_uncorrected and _corrected) which were read back into SasView and then compared with the input data:

Further comparing the data values in all three files showed that the extrapolations were performed and integrated as expected (ie, 0.001 - Guinier End and Porod Start - 0.3) and that the intensities in the _corrected file are those in the _uncorrected file minus the computed Background to 4 decimal places. This is probably sufficient for most use cases, but if anyone performs their own subtractions manually using the Background value quoted (to 5 d.p.) in the GUI they will get very slightly different output.
Otherwise this improved functionality seems to perform exactly as described.
The corfunc-how-to Help file has also been updated to mention that Export Extrapolated now generates two files.
I also reviewed the correlation_function_analysis_in_sasview_v6 Tutorial. Whilst this mentions the Export Extrapolated functionality, it is written in such a way that I do not see a need to make any changes to the Tutorial.
I am happy to approve this.

[smk78]

NB: I did not perform a code review!

[DrPaulSharp]

NB: I did not perform a code review!

Sounds like that might be a job for me then!

[DrPaulSharp]

This looks good, but I came to the same conclusion as copilot - you need to check for the existence of [filename]_corrected.csv and [filename]_uncorrected.csv. Currently, you warn about overwriting [filename].csv despite the fact that you do not do this.

I recommend passing the QFileDialog.Option.DontConfirmOverwrite to the save dialog, and launching dialogs immediately after obtaining the filename that check for whether the files exist and acting accordingly.

[jellybean2004]

Hey @DrPaulSharp! I have pushed new commits adding the following functionality:

• Added file dialog option DontConfirmOverwrite to suppress Qt’s base-path overwrite prompt.
• If either output file already exists, show a custom overwrite confirmation dialog.
• If the user says no, create files with numeric suffixes.

[DrPaulSharp]

A couple more things to consider.

[DrPaulSharp]

The iteration for suffix_index = 0 requires an additional if statement for every iteration of this loop (suffix = "" if suffix_index == 0 else f"_{suffix_index}") and it's already been established prior to calling this routine that either of base_path.parent / f"{base_path.name}_uncorrected.csv or base_path.parent / f"{base_path.name}_corrected.csv exists. Could you simplify this routine by starting from suffix_index = 1 instead?

[DrPaulSharp]

What happens if there are an extremely large number of numerical files here? Should there be an escape after a certain number of attempts?

[jellybean2004]

Hey @DrPaulSharp! Just pushed some commits implementing the suggested changes.

I have also added a cap for the suffix, set to 1000. Let me know what you think.

[DrPaulSharp]

I think a default of 1000, as stated in your text, would be a better value here.

[DrPaulSharp]

All looks good! Merge when ready.