Semi-Blind Inference of Topologies and Dynamical Processes over Graphs

TL;DR

This paper introduces algorithms for jointly inferring network topology and dynamics from partial observations, leveraging structural models like SEMs and SVARMs, with applications to time-evolving and sparse networks.

Contribution

It develops novel algorithms for joint topology and process inference from partial data, including online methods for dynamic networks, using structural equation models and Kalman smoothing.

Findings

Algorithms effectively infer directed topologies from partial observations.

Sparse networks require fewer observations for unique identification.

Numerical tests validate the approach on synthetic and real data.

Abstract

Network science provides valuable insights across numerous disciplines including sociology, biology, neuroscience and engineering. A task of major practical importance in these application domains is inferring the network structure from noisy observations at a subset of nodes. Available methods for topology inference typically assume that the process over the network is observed at all nodes. However, application-specific constraints may prevent acquiring network-wide observations. Alleviating the limited flexibility of existing approaches, this work advocates structural models for graph processes and develops novel algorithms for joint inference of the network topology and processes from partial nodal observations. Structural equation models (SEMs) and structural vector autoregressive models (SVARMs) have well-documented merits in identifying even directed topologies of complex graphs; while SEMs capture contemporaneous causal dependencies among nodes, SVARMs further account for time-lagged influences. This paper develops algorithms that iterate between inferring directed graphs that "best" fit the data, and estimating the network processes at reduced computational complexity by leveraging tools related to Kalman smoothing. To further accommodate delay-sensitive applications, an online joint inference approach is put forth that even tracks time-evolving topologies. Furthermore, conditions for identifying the network topology given partial observations are specified. It is proved that the required number of observations for unique identification reduces significantly when the network structure is sparse. Numerical tests with synthetic as well as real datasets corroborate the effectiveness of the novel approach.