Optimal network online change point localisation
This work addresses the challenge of quickly detecting changes in network data for applications like monitoring or anomaly detection, offering incremental improvements with new algorithms for specific error controls.
The paper tackles the problem of online network change point detection in Bernoulli networks, establishing minimax lower bounds and proposing novel polynomial-time algorithms that achieve detection delays with theoretical guarantees and outperform state-of-the-art methods in experiments.
We study the problem of online network change point detection. In this setting, a collection of independent Bernoulli networks is collected sequentially, and the underlying distributions change when a change point occurs. The goal is to detect the change point as quickly as possible, if it exists, subject to a constraint on the number or probability of false alarms. In this paper, on the detection delay, we establish a minimax lower bound and two upper bounds based on NP-hard algorithms and polynomial-time algorithms, i.e., \[ \mbox{detection delay} \begin{cases} \gtrsim \log(1/α) \frac{\max\{r^2/n, \, 1\}}{κ_0^2 n ρ},\\ \lesssim \log(Δ/α) \frac{\max\{r^2/n, \, \log(r)\}}{κ_0^2 n ρ}, & \mbox{with NP-hard algorithms},\\ \lesssim \log(Δ/α) \frac{r}{κ_0^2 n ρ}, & \mbox{with polynomial-time algorithms}, \end{cases} \] where $κ_0, n, ρ, r$ and $α$ are the normalised jump size, network size, entrywise sparsity, rank sparsity and the overall Type-I error upper bound. All the model parameters are allowed to vary as $Δ$, the location of the change point, diverges. The polynomial-time algorithms are novel procedures that we propose in this paper, designed for quick detection under two different forms of Type-I error control. The first is based on controlling the overall probability of a false alarm when there are no change points, and the second is based on specifying a lower bound on the expected time of the first false alarm. Extensive experiments show that, under different scenarios and the aforementioned forms of Type-I error control, our proposed approaches outperform state-of-the-art methods.