pub fn filter_kernel(pulses: &[i64], g: &NoiseGrid) -> Vec<i64>Expand description
The filter kernel of a DD sequence on the grid: kern[i] = (1/π)·|ỹ(ω_i)|²·dω,
so the coherence overlap against a PSD is simply χ = Σ_i psd[i]·kern[i].
ỹ(ω) = ∫₀ᵀ y(t) e^{iωt} dt with the toggling-frame switching function
y(t) = (−1)^k between pulses; |ỹ|² = |Σ_k (−1)^k (e^{iωt_{k+1}} − e^{iωt_k})|² / ω².