LNSE assembly

Owner: linstabpy.operators.assembly.

Public names: build_lnse_system, build_lnse_operator, build_lnse_system_result. State \(q = [\rho, u, v, w, T]\).

LNSESystem

The assembly handoff. It carries the assembled operator, index map, boundary-condition indices, and recipe analysis. Runtime callers ask for this object. They do not rebuild pieces of the sequence.

Construction order

1. Prepare coefficients (operators.coefficients, physical-order packing).
2. Build the raw block operator from SBP derivatives.
3. Apply the inverse mass/metric block (_apply_inv_B).
4. Apply sponge and operator dissipation.
5. Apply boundary conditions last.

Backends: SciPy CSC, or PETSc Mat. Direct PETSc assembly cannot apply dissipation_epsilon; auto/petsc may SciPy-assemble then convert.

Other files

File	Role
coefficients.py	Block tensors A0, Ax, Ay, Axx, Ayy, Axy, B
energy_norm.py	Chu compressible energy inner product
metrics.py	Curvilinear metric terms
spatial.py	Spatial-EVP left/right operators

Floquet shift of streamwise derivatives is applied inside assembly when configured. Do not apply it a second time in the driver.