pub fn walsh_hadamard_energy(cover: &Cover) -> Vec<f64>Expand description
Analysis — the Walsh–Hadamard (Fourier) spectrum. Expand the cover’s vertex-energy function over
the cube’s characters χ_S(x) = (-1)^{⟨S,x⟩}: f̂(S) = 2⁻ⁿ Σ_x energy(x) χ_S(x). Harmonic analysis on
the hypercube — the coefficients are the analytic invariant. (n ≤ ~16.)