Decompose across panels

[thomasmelvin]

PR Summary

Sci/Tech Reviewer: @tommbendall
Code Reviewer: @christophermaynard

This is a port of the previous SRS ticket (https://code.metoffice.gov.uk/trac/lfric_apps/ticket/1070) & its linked ticket https://code.metoffice.gov.uk/trac/lfric/ticket/4699 Both these tickets have already been science and code reviewed on the SRS and will go to the same reviewers here to check for any further issues.

In detail, the aim of this ticket is to modify the existing partitioning strategy so that it can partition multiple panels (either 3 sets of 2 or 2 sets of 3) into uniform rectangular domains. This will mean that the number of mpi ranks needs to only have a factor of 2 or 3 instead of 6 as a base requirement.

Using this option means that code that assumes all owned cells are on the same panel (we think only the extended mesh in the transport code) will not give the correct results here.

As part of this change I have also fixed the plotting script for the baroclinic wave on azspice where the figures were not coming out correct

• linked Decompose across panels lfric_core#220

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 Core rose-stem suite
• If required (e.g. API changes) I have also run the LFRic Apps test suite using this branch
• 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)

This change has been well tested & used in the Dec2025 KPI report for the global lfric model and is required to run the model on the target ~100 nodes at C896 resolution

trac.log

Test Suite Results - lfric_apps - decompose_across_panels/run11

Suite Information

Item	Value
Suite Name	decompose_across_panels/run11
Suite User	thomas.melvin
Workflow Start	2026-01-19T15:59:16
Groups Run	developer

Dependency	Reference	Main Like
casim	MetOffice/casim@2025.12.1	True
jules	MetOffice/jules@2025.12.1	True
lfric_apps	thomasmelvin/lfric_apps@decompose_across_panels	False
lfric_core	thomasmelvin/lfric_core@decompose_across_panels	True
moci	MetOffice/moci@2025.12.1	True
SimSys_Scripts	MetOffice/SimSys_Scripts@2025.12.1	True
socrates	MetOffice/socrates@2025.12.1	True
socrates-spectral	MetOffice/socrates-spectral@2025.12.1	True
ukca	MetOffice/ukca@2025.12.1	True

Task Information

✅ succeeded tasks - 1115

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

[tommbendall]

The Apps part of this ticket is very straightforward, and I already science reviewed it on trac. As we noted elsewhere, the changes to the plotting script will conflict with #74.

However I think this branch is picking up on some changes to the local_build.py script, presumably to get around local compilation issues with the vn3.0 release. I suggest you revert these as this is already fixed on main.

Otherwise I'll be happy for this to proceed.

[thomasmelvin]

The Apps part of this ticket is very straightforward, and I already science reviewed it on trac. As we noted elsewhere, the changes to the plotting script will conflict with #74.

However I think this branch is picking up on some changes to the local_build.py script, presumably to get around local compilation issues with the vn3.0 release. I suggest you revert these as this is already fixed on main.

Otherwise I'll be happy for this to proceed.

I've removed the changes to local_build

[tommbendall]

I'm happy with these updates from a science review point-of-view, so this is ready for code review @christophermaynard

[thomasmelvin]

@christophermaynard Science review is all filled in, this is ready for code review