Legendre Order Consistency Checks
In deterministic transport simulations, the number of Legendre / spherical- harmonic scattering moments is set in two places:
the angular quadrature’s
scattering_order, a constructor argument common to all angular quadrature classes (e.g.GLCProductQuadrature3DXYZ(..., scattering_order=N)). This determines the number of flux moments the solver computes and stores.the cross-section library’s scattering order: the highest Legendre moment present in the loaded multigroup cross-section data for a given material block.
All groupsets in a DiscreteOrdinatesProblem must use quadratures with the
same scattering_order; otherwise construction fails with:
"Number of scattering moments differs between groupsets"
When the problem is constructed, the solver’s scattering order is taken from
the quadrature (the first groupset’s quadrature.GetScatteringOrder()) and
is compared, per material block, against that block’s cross-section
scattering order. Only these two quantities are compared; there is no
separate, independently specifiable groupset-level scattering order.
Tip
Quadrature and cross-section scattering orders match
No message is produced. The computed flux moments and the cross-section moments line up exactly.
Warning
Quadrature scattering order exceeds the cross-section scattering order
Warning message (per block):
"Computing the flux with more scattering moments than are present in the
cross-section data for block <ID>"
The additional moments are still computed and stored (e.g., for plotting or post-processing), but they are unaffected by scattering.
Warning
Quadrature scattering order is lower than the cross-section scattering order
Warning message (per block):
"Computing the flux with fewer scattering moments than are present in the
cross-section data for block <ID>.
A truncated cross-section expansion will be used."
The cross-section expansion is truncated to the quadrature’s scattering order.
Both cases above are warnings only and do not prevent the run; there is no dedicated error condition tied to comparing the quadrature and cross-section scattering orders.