Replace copy_field_alg_mod with real_to_real_x builtin

[Alistair Pirrie (mo-alistairp)]

PR Summary

Sci/Tech Reviewer: Benjamin Went (@MetBenjaminWent)
Code Reviewer: Andrew Coughtrie (@andrewcoughtrie)

PSyclone has introduced the builtin real_to_real_x. This allows us to remove copy_field_alg_mod. Replacing this helps reduce technical debt and allow for more potential optimisation. Note that the arguments have swapped order to match the standard where outputs occur first.

The PSyKAl-lite code originates in LFRic core. Hence, this ticket blocks the LFRic core PR, as the PSyKAl-lite cannot be removed before we remove references to it in LFRic apps.

towards MetOffice/lfric_core/316 (MetOffice/lfric_core#316)
blocks MetOffice/lfric_core/317 (MetOffice/lfric_core#317)

Code Quality Checklist

• I have performed a self-review of my own code
• My code follows the project's style guidelines
• Comments have been included that aid understanding and enhance the readability of the code
• My changes generate no new warnings
• All automated checks in the CI pipeline have completed successfully

Testing

• I have tested this change locally, using the LFRic Apps rose-stem suite
• If any tests fail (rose-stem or CI) the reason is understood and acceptable (e.g. kgo changes)
• I have added tests to cover new functionality as appropriate (e.g. system tests, unit tests, etc.)
• Any new tests have been assigned an appropriate amount of compute resource and have been allocated to an appropriate testing group (i.e. the developer tests are for jobs which use a small amount of compute resource and complete in a matter of minutes)

trac.log

Test Suite Results - lfric_apps - replace_copy_field_alg_mod_lfric_apps/run1

Suite Information

Item	Value
Suite Name	replace_copy_field_alg_mod_lfric_apps/run1
Suite User	alistair.pirrie
Workflow Start	2026-03-27T10:08:36
Groups Run	all

Dependency	Reference	Main Like
casim	MetOffice/casim@2026.03.2	True
jules	MetOffice/jules@2026.03.2	True
lfric_apps	mo-alistairp/lfric_apps@replace_copy_field_alg_mod	False
lfric_core	MetOffice/lfric_core@018e40c	True
moci	MetOffice/moci@2026.03.2	True
SimSys_Scripts	MetOffice/SimSys_Scripts@4387949	True
socrates	MetOffice/socrates@2026.03.2	True
socrates-spectral	MetOffice/socrates-spectral@2026.03.2	True
ukca	MetOffice/ukca@2026.03.2	True

Task Information

✅ succeeded tasks - 1512

Security Considerations

• I have reviewed my changes for potential security issues
• Sensitive data is properly handled (if applicable)
• Authentication and authorisation are properly implemented (if applicable)

Performance Impact

• Performance of the code has been considered and, if applicable, suitable performance measurements have been conducted

AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance of Generative AI tool name (e.g., Met Office Github Copilot Enterprise, Github Copilot Personal, ChatGPT GPT-4, etc) and I have followed the Simulation Systems AI policy (including attribution labels)

Documentation

• Where appropriate I have updated documentation related to this change and confirmed that it builds correctly

PSyclone Approval

• If you have edited any PSyclone-related code (e.g. PSyKAl-lite, Kernel interface, optimisation scripts, LFRic data structure code) then please contact the TCD Team

Sci/Tech Review

• I understand this area of code and the changes being added
• The proposed changes correspond to the pull request description
• Documentation is sufficient (do documentation papers need updating)
• Sufficient testing has been completed

(Please alert the code reviewer via a tag when you have approved the SR)

Code Review

• All dependencies have been resolved
• Related Issues have been properly linked and addressed
• CLA compliance has been confirmed
• Code quality standards have been met
• Tests are adequate and have passed
• Documentation is complete and accurate
• Security considerations have been addressed
• Performance impact is acceptable

[DrTVockerodtMO]

Code owner review passed!

[Thomas Bendall (tommbendall)]

Just some very minor style suggestions involving spacings in invokes to have these calls be consistent with the style in the rest of the file. Otherwise looks good!

[Alistair Pirrie (mo-alistairp)]

Just some very minor style suggestions involving spacings in invokes to have these calls be consistent with the style in the rest of the file. Otherwise looks good!

Good spot, I've applied all the changes

[Thomas Bendall (tommbendall)]

Thanks for making those changes!

[Benjamin Went (MetBenjaminWent)]

I've commented a few lines which might follow a CO suggestion made earlier?

However otherwise changes look good, I've checked the reversal of the ordering of the two fields in the change from call to invoke and they are correct, see the docs here:
https://psyclone.readthedocs.io/en/latest/user_guide/lfric.html#real-to-real-x

SR Approved - Noting that developer may include comments, but are not a blocker for the ticket

[Alistair Pirrie (mo-alistairp)]

Thanks Benjamin Went (@MetBenjaminWent), I've made those style fixes