src/offline/cable_output.F90: Update order of operations for CASA unit conversions

[SeanBryan51]

This change updates the order of operations for applying unit conversions CASA output variables such that the unit conversion factor is computed before applying the conversion to the array being written.

This change is required to demonstrate bitwise equivalence with the new parallel I/O output module (#655).

Type of change

• Enhancement

Testing

• Are the changes bitwise-compatible with the main branch? If working on an optional feature, are the results bitwise-compatible when this feature is off? If yes, copy benchcab output showing successful completion of the bitwise compatibility tests or equivalent results below this line.

Benchcab currently does not test CASA, so benchcab results are bitwise identical:

2026-03-13 14:27:58,185 - INFO - benchcab.benchcab.py:380 - Running comparison tasks...
2026-03-13 14:27:58,211 - INFO - benchcab.benchcab.py:381 - tasks: 168 (models: 2, sites: 42, science configurations: 4)
2026-03-13 14:30:40,431 - INFO - benchcab.benchcab.py:391 - 0 failed, 168 passed

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📚 Documentation preview 📚: https://cable--710.org.readthedocs.build/en/710/

[SeanBryan51]

Running CASA manually using these scripts shows precision level differences:

nccmp -df -c 1 archive_main/output000/outputs/cable_out.nc archive_cable-output-update-CASA-unit-conversions/output000/outputs/cable_out.nc
DIFFER : VARIABLE : RootResp : POSITION : [0,20,166] : VALUES : 0.205504 <> 0.205504
DIFFER : VARIABLE : StemResp : POSITION : [0,21,170] : VALUES : 0.0347765 <> 0.0347765
DIFFER : VARIABLE : NBP : POSITION : [0,22,167] : VALUES : -0.743505 <> -0.743505
DIFFER : VARIABLE : dCdt : POSITION : [0,22,167] : VALUES : -0.743505 <> -0.743505
DIFFER : VARIABLE : PlantTurnover : POSITION : [0,21,166] : VALUES : 0.167951 <> 0.167951
DIFFER : VARIABLE : PlantTurnoverLeaf : POSITION : [0,22,168] : VALUES : 0.0308066 <> 0.0308066
DIFFER : VARIABLE : PlantTurnoverFineRoot : POSITION : [0,22,167] : VALUES : 0.148981 <> 0.148981
DIFFER : VARIABLE : PlantTurnoverWood : POSITION : [0,22,169] : VALUES : 2.95271e-08 <> 2.95271e-08

The values are equivalent when allowing for an absolute tolerance of 1e-6:

nccmp -d -t 1e-6 archive_main/output000/outputs/cable_out.nc archive_cable-output-update-CASA-unit-conversions/output000/outputs/cable_out.nc
echo $?
0

[Whyborn]

I'm guessing this is because conversion factors will be applied as a multiplication before writing? It's a good idea anyway, since divisions are slower than multiplications.

[SeanBryan51]

I'm guessing this is because conversion factors will be applied as a multiplication before writing?

Yup