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Split mol with transport_efficiency #149

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@cjohnson-pi cjohnson-pi commented Jan 16, 2026 •
edited by jameskent-metoffice
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PR Summary

Sci/Tech Reviewer: James Kent @jameskent-metoffice
Code Reviewer: @mo-marqh

  • Adds split transport to the linear and adjoint code (to give e.g. VHV vertical horizontal vertical rather than 3d)
  • Adds a transport_efficiency switch to the split transport and the mol (method of lines) transport code
  • Tests in the linear_model app and adjoint_tests

Associated with #108 and #113

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)
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trac.log

Test Suite Results - lfric_apps - test_split_mol/run15

Suite Information

Item Value
Suite Name test_split_mol/run15
Suite User christine.johnson
Workflow Start 2026-01-16T12:23:18
Groups Run suite_default
Dependency Reference Main Like
casim MetOffice/casim@2025.12.1 True
jules MetOffice/jules@2025.12.1 True
lfric_apps cjohnson-pi/lfric_apps@split_mol False
lfric_core MetOffice/lfric_core@5d4d72f 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 - 1106

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

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@github-actions github-actions bot added the cla-required The CLA has not yet been signed by the author of this PR - added by GA label Jan 16, 2026
@github-actions github-actions bot added cla-signed This contributor has signed the CLA. and removed cla-required The CLA has not yet been signed by the author of this PR - added by GA labels Jan 16, 2026
@cjohnson-pi cjohnson-pi self-assigned this Jan 16, 2026
jameskent-metoffice
jameskent-metoffice reviewed Jan 16, 2026
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science/linear/source/algorithm/transport/control/tl_split_transport_mod.x90 Outdated
if ( .not. transport_efficiency ) then

! When we have multiple split steps, we need an intermediate field for the
! field at the start of each substeps
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"substep" instead of "substeps" in comment "field at the start of each substep"

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@cjohnson-pi cjohnson-pi Jan 16, 2026

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Corrected

jameskent-metoffice
jameskent-metoffice reviewed Jan 16, 2026
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science/linear/source/algorithm/transport/control/tl_split_transport_mod.x90
num_split_steps = get_num_split_steps(transport_metadata%get_splitting())

! When we have multiple split steps, we need an intermediate field for the
! field at the start of each substeps
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"substep" instead of "substeps" in comment "field at the start of each substep"

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Corrected

jameskent-metoffice
jameskent-metoffice reviewed Jan 16, 2026
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...ications/adjoint_tests/source/algorithm/transport/common/adjt_end_transport_step_alg_mod.x90

call sum_flux%initialise( vector_space = vector_space_w2_ptr )
call flux_last_step%initialise( vector_space = vector_space_w2_ptr )
call flux_last_step%initialise( vector_space = vector_space_w2v_ptr )
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Are you hardwiring the flux_last_step to always be W2V? Is it possible to put in a check based on the splitting used? If not is it worth commenting that this is only suitable for testing VHV splitting?

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Comment added

jameskent-metoffice
jameskent-metoffice approved these changes Jan 16, 2026
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This work sets up the split transport option for the linear model. This is vital as it will speed up the MoL linear transport, but is also necessary for FFSL linear transport (when we come to implement it).

I "pre-reviewed" this work when we were on trac, and I can see that the developer has addressed any issues I had. I have left 3 small comments in the code and I will leave it up to the developer to decide whether they warrant any changes.

It is good that the split MoL transport is tested in the linear suite, and it is the default config. It is also good that the old 3D MoL is still tested. I have looked at the plots for the kgo change tests and everything is looking good.

I am happy to approve.

@cjohnson-pi cjohnson-pi requested a review from mo-marqh January 16, 2026 16:36
@cjohnson-pi cjohnson-pi added KGO This PR contains changes to KGO macro This PR contains a metadata upgrade macro labels Jan 16, 2026
This was referenced Jan 19, 2026
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@cjohnson-pi cjohnson-pi added this to the Spring 2026 milestone Jan 19, 2026
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@jameskent-metoffice jameskent-metoffice jameskent-metoffice approved these changes

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