fix: remove cutoff_fraction from Hou-Li filter, use correct h/h_max f…#258
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fix: remove cutoff_fraction from Hou-Li filter, use correct h/h_max f…#258
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…ormula The previous implementation applied σ = exp(-strength*(h/h_cutoff)^order) only above a cutoff threshold, where h_cutoff = cutoff_fraction * h_max. This had two bugs: 1. With cutoff_fraction=1.0 (a natural "no cutoff" choice), h never exceeded h_cutoff so the filter was silently disabled entirely. 2. The formula should use h/h_max, not h/h_cutoff, to match the standard Hou-Li (2007) filter: σ(h) = exp(-strength * (h/h_max)^order). Fix: remove cutoff_fraction entirely, always apply the filter to all modes using h/h_max. The filter naturally acts on all modes with σ→0 at h=h_max and σ=1 at h=0, requiring no explicit cutoff threshold. Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
The filter was previously applied only to dCk/dt from the nonlinear term, leaving the linear free-streaming cascade (Lawson-RK4 exponential operators) completely unfiltered. High Hermite modes filled up unchecked. Now the filter is passed to SplitStepDampingSolver and applied as a multiplicative split step to the full state after each timestep, in the same pattern as sponge boundary damping. Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
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…ormula
The previous implementation applied σ = exp(-strength*(h/h_cutoff)^order) only above a cutoff threshold, where h_cutoff = cutoff_fraction * h_max. This had two bugs:
Fix: remove cutoff_fraction entirely, always apply the filter to all modes using h/h_max. The filter naturally acts on all modes with σ→0 at h=h_max and σ=1 at h=0, requiring no explicit cutoff threshold.