Include wavelength component in Q resolution calculation

[welbournR]

Description of work:

Q-resolution calculation updated to include both lambda and theta components. Includes prior functions that weren't integrated into the workflow.

DRAFT - this needs tests to be updated. Request other eyes on the code to check the changes.

Check all that apply:

• updated documentation
• Source added/refactored
• Added unit tests
• Added integration tests
• Verified that tests requiring the /SNS and /HFIR filesystems pass without fail

References:

• Links to IBM EWM items:
• Links to related issues or pull requests:

⚠️ Manual test for the reviewer

(Instructions for testing here)

Check list for the reviewer

• best software practices
  • clearly named variables (better to be verbose in variable names)
  • code comments explaining the intent of code blocks
• All the tests are passing
• The documentation is up to date
• code comments added when explaining intent

[codecov-commenter]

Codecov Report

❌ Patch coverage is 88.34356% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.25%. Comparing base (d4c6005) to head (df24037).

Files with missing lines	Patch %	Lines
src/lr_reduction/time_resolved.py	66.66%	13 Missing ⚠️
src/lr_reduction/event_reduction.py	88.09%	5 Missing ⚠️
src/lr_reduction/output.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next     #112      +/-   ##
==========================================
+ Coverage   85.16%   85.25%   +0.09%     
==========================================
  Files          23       24       +1     
  Lines        2925     3032     +107     
==========================================
+ Hits         2491     2585      +94     
- Misses        434      447      +13     

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[Copilot]

Pull request overview

Updates LR’s Q-resolution calculation to include both wavelength (λ) and angular (θ) components, and wires the resulting per-bin resolution through the reduction/template/workflow outputs.

Changes:

• Add new θ- and λ-based resolution helpers and return dq_over_q alongside reduced R(Q) results.
• Introduce a SymPy-based UserDefinedFunction to evaluate the wavelength-resolution function string.
• Update workflow/output plumbing and adjust unit/integration tests for the new return signatures and new resolution behavior.

Reviewed changes

Copilot reviewed 16 out of 17 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/lr_reduction/event_reduction.py	Implements new θ/λ resolution computation and returns dq_over_q_bins from specular.
src/lr_reduction/template.py	Propagates dq_over_q through process_from_template_ws and switches θ selection to CoordinateSystem.
src/lr_reduction/workflow.py	Stores dq (absolute) in outputs and updates explorer return to include dq.
src/lr_reduction/user_defined_function.py	Adds SymPy-based parser/evaluator for user-provided resolution functions.
src/lr_reduction/data_info.py	Adds CoordinateSystem enum and refactors DataType.from_workspace to use it.
src/lr_reduction/gravity_correction.py	Uses CoordinateSystem.from_workspace for θ-in selection.
src/lr_reduction/time_resolved.py	Keeps legacy resolution for backwards compatibility; updates slice reductions/plotting to use dq.
src/lr_reduction/output.py	Adds fwhm flag to ASCII header labeling for dq column.
tests/unit/lr_reduction/test_user_defined_function.py	New unit tests for parsing/evaluating user-defined functions.
tests/unit/lr_reduction/test_event_reduction.py	Adds tests for θ- and λ-resolution helpers; adjusts mock log exception type.
tests/unit/lr_reduction/test_data_info.py	Rewrites tests to use real Mantid workspaces; adds CoordinateSystem tests.
tests/test_reduction.py	Updates test expectations/unpacking for new dq_over_q return; removes obsolete wavelength test.
tests/test_dead_time.py	Updates unpacking for new return shape.
pyproject.toml	Adds sympy (runtime + env) and jupyter (env) dependencies.
pixi.lock	Lockfile updates for new dependencies and pixi options.
docs/api/lr_reduction.rst	Fixes API docs module reference from typing to types.
.gitattributes	Marks pixi.lock as generated and binary-merged.

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[Copilot]

In the fallback branch when BL4B:Mot:xi.RBV is missing, compute_theta_resolution returns (theta_deg, default_dq), but default_dq is documented as a fractional dθ/θ (and historically was used as a dimensionless dQ/Q). Returning it as degrees makes the later (delta_th_deg / theta_deg) term scale as default_dq/theta_deg, which is incorrect. Convert the default fractional value into degrees (e.g., dtheta_deg = default_dq * theta_deg) or rename/retune the parameter so units are consistent across all return paths.

Suggested change

	return theta_deg, default_dq
	dtheta_deg = default_dq * theta_deg
	return theta_deg, dtheta_deg

[backmari]

@welbournR This is a good catch by copilot! Previously, when there was only a theta component, the fallback value if theta could not be computed would be dQ/Q = 0.027, but now this value is returned as the fallback dtheta, which is combined with the wavelength resolution.
What would be a reasonable default dtheta?

[Copilot]

compute_wavelength_resolution’s docstring still describes the old Mantid-EvaluateFunction behavior ("fitted wavelength values" and "difference between wavelength and the fit"). The new implementation simply evaluates the provided resolution function on wl_list and returns (wl_list, d_lambda), so the return-value description should be updated to match what the function actually returns (and clarify expected units/meaning of d_lambda).

[Copilot]

These assertions currently hard-code nearly-constant dq_over_q arrays with very loose/placeholder expectations (and TODOs to revisit). This weakens the regression protection for the new Q-resolution calculation. Prefer asserting against values computed from the underlying resolution model (theta+lambda terms) or against a known-good reference dataset so the test fails meaningfully if the resolution implementation changes.