Only track non-scalar attributes in UNVECTORIZED_NUM_ATTR_DIMS

[cr-xu]

Description

• Remove default zeros in Beam.UNVECTORIZED_NUM_ATTR_DIMS and only track attributes with non-zero dimension in ParticleBeam and ParameterBeam;
• Introduce a defining_features property in the same fashion as for Elements.
• Simplify some unit tests by using the defining_features property in beam classes to verify dtypes and devices are tracked properly. All the tested attributes are generateed from these definiing_features and the test was bit redundant.

Motivation and Context

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)

Checklist

• I have updated the changelog accordingly (required).
• My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.
• I have reformatted the code and checked that formatting passes (required).
• I have have fixed all issues found by flake8 (required).
• I have ensured that all pytest tests pass (required).
• I have run pytest on a machine with a CUDA GPU and made sure all tests pass (required).
• I have checked that the documentation builds (required).

Note: We are using a maximum length of 88 characters per line.

[cr-xu]

This one is actually ready for review since a while.

[Copilot]

Pull request overview

This PR refactors how beam attributes are enumerated by (1) clearing the scalar-heavy default Beam.UNVECTORIZED_NUM_ATTR_DIMS, (2) introducing a defining_features property for ParticleBeam/ParameterBeam (mirroring Element), and (3) updating tests and segment metric collection to use these new patterns.

Changes:

• Empties Beam.UNVECTORIZED_NUM_ATTR_DIMS and relies on subclasses to list only non-scalar attributes.
• Adds defining_features to ParticleBeam and ParameterBeam, and updates multiple tests to use it (excluding species).
• Updates Segment.get_beam_attrs_along_segment to default missing UNVECTORIZED_NUM_ATTR_DIMS entries to 0.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/test_particle_beam.py	Switch dtype/device assertions to iterate over defining_features (excluding species).
tests/test_elements.py	Use outgoing_beam.defining_features to validate dtype/device propagation.
tests/test_drift.py	Use defining_features for equality checks between tracked beams (but introduces >88-char lines).
tests/test_clone.py	Validate cloned beam buffers via defining_features rather than attr-dims dict keys.
tests/test_beam.py	Use defining_features for dtype conversion assertions.
cheetah/particles/particle_beam.py	Adds ParticleBeam.defining_features.
cheetah/particles/parameter_beam.py	Adds ParameterBeam.defining_features.
cheetah/particles/beam.py	Clears default UNVECTORIZED_NUM_ATTR_DIMS and introduces abstract defining_features.
cheetah/accelerator/segment.py	Defaults missing attr-dims to 0 when stacking metrics along a segment.
CHANGELOG.md	Adds an entry describing the attr-dims refactor and segment stacking default.

Comments suppressed due to low confidence (1)

tests/test_drift.py:109

• This line exceeds the repo’s Flake8 max-line-length = 88 (see .flake8). Please wrap the list comprehension across multiple lines (as done in other updated tests) to avoid CI lint failures.

    beam_attributes = [attr for attr in outgoing.defining_features if attr != "species"]

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.