David Pierre Ruelle is a Belgian mathematical physicist, naturalized French. He has worked on statistical physics and dynamical systems. With Floris Takens, Ruelle coined the term strange attractor, and developed a new theory of turbulence.
Inspired by a NeurIPs 2020 paper on non-stochastic control systems from Princeton University, I am intrigued by this topic of "differentiable dynamics."
Differentiable dynamics has the following implications/characteristics: 1) Example formulation: x_{t+1} = A x_t + B u_t + w_t, where u_t is the action, and w_t is noise, together with a reward/regret function to evaluate x_{t+1} versus x*_{t+1}. 2) It is prevalent in control systems, reinforcement learning, Markov chain, etc. 3) It belongs more to mathematical research, than to physics or applied science.
Basic concepts: 1) Manifold: the environment that provides feedbacks on how x changes after the action u, e.g., Banach spaces. 2) Differential dynamics: the time evolution of a natural system by a differential equation: dx / dt = X(x), where X is an operator. 3) Common assumptions: e.g., the manifold is differentiable. 4) Fixed points & Attracting sets.
Content of the book: Part 1) Concepts and notations, incl. manifolds, fixed points, periodic orbits, etc. Part 2) Bifurcations, incl., attracting sets Part 3) A collection of appendices.