Equivariance and partial observations in Koopman operator theory for partial differential equations

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Main Authors: Peitz, Sebastian, Harder, Hans, Nüske, Feliks, Philipp, Friedrich, Schaller, Manuel, Worthmann, Karl
Format: Preprint
Published: 2023
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_version_ 1866917828343365632
author Peitz, Sebastian
Harder, Hans
Nüske, Feliks
Philipp, Friedrich
Schaller, Manuel
Worthmann, Karl
author_facet Peitz, Sebastian
Harder, Hans
Nüske, Feliks
Philipp, Friedrich
Schaller, Manuel
Worthmann, Karl
contents The Koopman operator has become an essential tool for data-driven analysis, prediction and control of complex systems. The main reason is the enormous potential of identifying linear function space representations of nonlinear dynamics from measurements. This equally applies to ordinary, stochastic, and partial differential equations (PDEs). Until now, with a few exceptions only, the PDE case is mostly treated rather superficially, and the specific structure of the underlying dynamics is largely ignored. In this paper, we show that symmetries in the system dynamics can be carried over to the Koopman operator, which allows us to significantly increase the model efficacy. Moreover, the situation where we only have access to partial observations (i.e., measurements, as is very common for experimental data) has not been treated to its full extent, either. Moreover, we address the highly-relevant case where we cannot measure the full state, where alternative approaches (e.g., delay coordinates) have to be considered. We derive rigorous statements on the required number of observables in this situation, based on embedding theory. We present numerical evidence using various numerical examples including the wave equation and the Kuramoto-Sivashinsky equation.
format Preprint
id arxiv_https___arxiv_org_abs_2307_15325
institution arXiv
publishDate 2023
record_format arxiv
spellingShingle Equivariance and partial observations in Koopman operator theory for partial differential equations
Peitz, Sebastian
Harder, Hans
Nüske, Feliks
Philipp, Friedrich
Schaller, Manuel
Worthmann, Karl
Dynamical Systems
Machine Learning
The Koopman operator has become an essential tool for data-driven analysis, prediction and control of complex systems. The main reason is the enormous potential of identifying linear function space representations of nonlinear dynamics from measurements. This equally applies to ordinary, stochastic, and partial differential equations (PDEs). Until now, with a few exceptions only, the PDE case is mostly treated rather superficially, and the specific structure of the underlying dynamics is largely ignored. In this paper, we show that symmetries in the system dynamics can be carried over to the Koopman operator, which allows us to significantly increase the model efficacy. Moreover, the situation where we only have access to partial observations (i.e., measurements, as is very common for experimental data) has not been treated to its full extent, either. Moreover, we address the highly-relevant case where we cannot measure the full state, where alternative approaches (e.g., delay coordinates) have to be considered. We derive rigorous statements on the required number of observables in this situation, based on embedding theory. We present numerical evidence using various numerical examples including the wave equation and the Kuramoto-Sivashinsky equation.
title Equivariance and partial observations in Koopman operator theory for partial differential equations
topic Dynamical Systems
Machine Learning
url https://arxiv.org/abs/2307.15325