Add generic vol avg profile function

[chris-ashe]

This pull request introduces a new utility function for calculating the volume-averaged value of a radially normalized profile and adds detailed documentation explaining the mathematical derivation behind this calculation. These changes improve both code reusability and the clarity of the underlying physics for future developers and users.

New functionality

• Added calculate_vol_avg_of_profile() to process/models/physics/profiles.py, which computes the volume-averaged value of a normalized radial profile, including comprehensive input validation.

Documentation improvements

• Added a new section to plasma_profiles.md that explains the derivation and usage of the volume-averaging calculation, including all relevant equations and context.

Checklist

I confirm that I have completed the following checks:

• My changes follow the PROCESS style guide
• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made.
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly.
• I have added documentation for my change, if appropriate.

[je-cook]

Am I mistaken here or is all of the changes hiding the main change which is just this?:

    return 2.0 * sp.integrate.simpson(
        profile_y * profile_x,
        x=profile_x,
        dx=profile_x[1] - profile_x[0],
    )

[chris-ashe]

Am I mistaken here or is all of the changes hiding the main change which is just this?:

    return 2.0 * sp.integrate.simpson(
        profile_y * profile_x,
        x=profile_x,
        dx=profile_x[1] - profile_x[0],
    )

Yes, still WIP and needs cherry-picked

[codecov-commenter]

Codecov Report

❌ Patch coverage is 8.33333% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.85%. Comparing base (bd5e644) to head (d1d1210).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
process/models/physics/fusion_reactions.py	7.69%	24 Missing ⚠️
process/models/physics/profiles.py	10.00%	9 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4568   +/-   ##
=======================================
  Coverage   49.85%   49.85%           
=======================================
  Files         151      151           
  Lines       29875    29893   +18     
=======================================
+ Hits        14894    14903    +9     
- Misses      14981    14990    +9     

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[timothy-nunn]

If you implement my suggestions below, then it should be possible to use this new function to replace at least some uses of integrate.simpson within the PROCESS repository.

[timothy-nunn]

Suggested change

	def calculate_vol_avg_of_profile(profile_x: np.ndarray, profile_y: np.ndarray) -> float:
	def calculate_vol_avg_of_profile(profile_x: np.ndarray, profile_y: np.ndarray, dx: float | None = None) -> float:

I would add an ability for the user to specify dx themselves. If a dx is not provided (is None), then calculate dx as it currently is.

[timothy-nunn]

Happy with code, requesting modeller to check docs etc

[timothy-nunn]

Just noticed pre-commit is failing