Universal set of Observables for the Koopman Operator through Causal Embedding

Obtaining repeated measurements from physical and natural systems for building a more informative dynamical model of such systems is engraved in modern science. Results in reconstructing equivalent chaotic dynamical systems through delay coordinate mappings, Koopman operator based data-driven approach and reservoir computing methods have shown the possibility of finding model equations on a new phase space that is relatable to the dynamical system generating the data. Recently, rigorous results that point to reducing the functional complexity of the map that describes the dynamics in the new phase have made the Koopman operator based approach very attractive for data-driven modeling. However, choosing a set of nonlinear observable functions that can work for different data sets is an open challenge. We use driven dynamical systems comparable to that in reservoir computing with the \emph{causal embedding property} to obtain the right set of observables through which the dynamics in the new space is made equivalent or topologically conjugate to the original system. Deep learning methods are used to learn a map that emerges as a consequence of the topological conjugacy. Besides stability, amenability for hardware implementations, causal embedding based models provide long-term consistency even for maps that have failed under previously reported data-driven or machine learning methods.