pub fn bartlett_se(acf: &[f64], n: usize) -> Vec<f64>Expand description
Bartlett large-sample standard error of acf[k] under the hypothesis that
the process is MA(k−1) (i.e. true autocorrelations vanish from lag k on):
sqrt((1 + 2 Σ_{j<k} ρ_j²) / n). Used to studentize the ACF so that the
Fine–Hwang threshold is scale-free for MA order selection.