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Moving Hermite basis 5/5: expose the hypercollision spectrum and order >= 2 - #60
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hypercollision_spectrum(Nn, Nm, Np, order) returns the per-mode damping of -nu * col * C (top mode of each axis damped at nu; zero for n <= 2*order-2), so every moment of total degree <= 2 is untouched in any basis. order=2 is the existing default, bitwise; order=1 is rejected. A user collision_matrix overrides the default.
This was referenced Oct 4, 2026
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Exposes the hypercollision closure, which is diagonal and commutes with the remap.
hypercollision_spectrum(Nn, Nm, Np, order=2)returns the per-mode damping of-nu * col * C. Each axis's top mode is damped at nu.order=2is the existing default and is bitwise checked on 4 layouts.order=1(Lenard-Bernstein-like) is rejected: in a moving basis it damps momentum and energy.collision_matrixparameter overrides the default.Not included: a Hou-Li filter.
Tested SHA d3379cc. Command:
python -m pytest -q -n 2 tests. Result: 184 passed.New tests:
-nu col Cexactly, and n, M_i, M_ii have exactly zero rate in shifted, anisotropic bases.DG note for the whole stack:
u, aare per species and uniform in x, so the moving-basis terms, remap and closure carry over to the DG branch unchanged.Stack: base
adaptive/base=integration/dark-baseline9d0982d (main ab87385 + #48, #46, #13, #12, #9, #55, #50, #44, #18, #51). This lands on main after those foundation PRs and the earlier PRs of this stack (#56 first). Local results only (macOS, Python 3.12, JAX 0.11.2, x64); GitHub CI on this branch has not been checked yet.