State Aggregations in Markov Chains and Block Models of Networks

Faccin, Mauro [UCL] Schaub, Michael. T [University of Oxford, Oxford OX1 2JD, United Kingdom and RWTH Aachen University, 52074 Aachen, Germany] Delvenne, Jean-Charles [UCL]

We consider state-aggregation schemes for Markov chains from an information-theoretic perspective. Specifically, we consider aggregating the states of a Markov chain such that the mutual information of the aggregated states separated by T time steps is maximized. We show that for T ¼ 1 this recovers the maximum-likelihood estimator of the degree-corrected stochastic block model as a particular case, which enables us to explain certain features of the likelihood landscape of this generative network model from a dynamical lens. We further highlight how we can uncover coherent, long-range dynamical modules for which considering a timescale T ≫ 1 is essential. We demonstrate our results using synthetic flows and real-world ocean currents, where we are able to recover the fundamental features of the surface currents of the oceans.