Legendre Order Consistency Checks

In deterministic transport simulations, the Legendre expansion order may be independently specified in the following components:

scattering_order_aquad: Angular quadrature - maximum supported Legendre moment (e.g., for spherical harmonics integration).
scattering_order_mgxs: Cross-section library - highest Legendre moment for scattering data.
scattering_order_groupset: Flux solver - number of Legendre flux moments to compute and store.

To ensure consistency and provide helpful feedback, the following logic is applied.

Tip

Valid Configurations

``scattering_order_groupset <= scattering_order_mgxs`` The solver computes fewer or equal scattering moments than the cross-section library provides. Informational message:
```
"Computing the flux with fewer scattering moments than are available in the cross-section library."
```
``scattering_order_groupset <= scattering_order_aquad`` The solver uses fewer angular basis functions than the quadrature supports. Informational message:
```
"Using fewer rows/columns of angular matrices (M, D) than the quadrature supports."
```

``scattering_order_aquad > scattering_order_mgxs`` The quadrature supports more moments than are available in the cross-section library. Informational message:

"The quadrature supports more scattering moments than are present in the cross-section library. These additional moments will not affect the scattering source but may be useful if ``scattering_order_groupset > scattering_order_mgxs``."

Warning

``scattering_order_groupset > scattering_order_mgxs`` The solver computes more flux moments than the scattering data supports. Higher-order moments are unaffected by scattering and are useful only for plotting/postprocessing.

Warning message:

"The solution will be the same as with ``scattering_order_groupset = scattering_order_mgxs``. Higher-order flux moments are unaffected by scattering."

Error

``scattering_order_groupset > scattering_order_aquad`` The solver requests more flux moments than the angular quadrature can represent. This is not allowed.

Error message:

"The solver requires more flux moments than the angular quadrature supports. Increase ``scattering_order_aquad`` or reduce ``scattering_order_groupset``."

Only comparisons involving scattering_order_groupset are enforced. The comparison between scattering_order_aquad and scattering_order_mgxs is informational and may indicate over-resolution of the angular domain relative to the available scattering data.