My favorite theoretical description of multilayer networks comes from the first multilayer network, the 1986 harmonium [1]. It used a free energy minimization m

My favorite theoretical description of multilayer networks comes from the first multilayer network, the 1986 harmonium [1]. It used a free energy minimization model (in the paper it is called harmony maximization), which is both concise, natural and effective. I find the paper very well written and insightful — even today. I haven't fully read the current paper, but it doesn't mention "free energy"— which seems odd given their emphasis on thermodynamics and first principles. [1] https://www.researchgate.net/publication/239571798_Information_processing_in_dynamical_systems_Foundations_of_harmony_theory https://www.researchgate.net/publication/239571798_Informati...