保测度动力系统数据驱动计算的mpEDMD算法
The mpEDMD Algorithm for Data-Driven Computations of Measure-Preserving Dynamical Systems
摘要：
Koopman算子使非线性动力系统全局线性化，其谱信息是分析和分解非线性动力系统的有力工具。然而，Koopman算子是无限维的，计算它们的谱信息是一个相当大的挑战。本文介绍了保测扩展动态模式分解（$\texttt{mpEDMD}$），它是第一种截断方法，其特征分解收敛于一般保测动力系统的Koopman算子的谱量。$\texttt{mpEDMD}$是一种基于正交Procrustes问题的数据驱动算法，该算法使用可观测量的通用字典强制执行Koopman算子的测量保持截断。它灵活且易于与任何预先存在的DMD类型方法以及不同类型的数据一起使用。我们证明了收敛的$\texttt{mpEDMD}$的投影值和标量值的谱测度，频谱和Koopman模式分解。对于延迟嵌入（Krylov子空间）的情况下，我们的结果包括第一收敛速度的近似谱测度的字典的大小增加。我们证明了$\texttt{mpEDMD}$在一系列具有挑战性的例子，其增加的鲁棒性噪声相比，其他DMD型的方法，它能够捕捉能量守恒和级联的实验测量的湍流边界层流动的雷诺数$> 6\times 10^4$和状态空间维度$>10^5$。
英文摘要：
Koopman operators globally linearize nonlinear dynamical systems and their spectral information is a powerful tool for the analysis and decomposition of nonlinear dynamical systems. However, Koopman operators are infinite-dimensional, and computing their spectral information is a considerable challenge. We introduce measure-preserving extended dynamic mode decomposition ($\texttt{mpEDMD}$), the first truncation method whose eigendecomposition converges to the spectral quantities of Koopman operators for general measure-preserving dynamical systems. $\texttt{mpEDMD}$ is a data-driven algorithm based on an orthogonal Procrustes problem that enforces measure-preserving truncations of Koopman operators using a general dictionary of observables. It is flexible and easy to use with any pre-existing DMD-type method, and with different types of data. We prove convergence of $\texttt{mpEDMD}$ for projection-valued and scalar-valued spectral measures, spectra, and Koopman mode decompositions. For the case of delay embedding (Krylov subspaces), our results include the first convergence rates of the approximation of spectral measures as the size of the dictionary increases. We demonstrate $\texttt{mpEDMD}$ on a range of challenging examples, its increased robustness to noise compared with other DMD-type methods, and its ability to capture the energy conservation and cascade of experimental measurements of a turbulent boundary layer flow with Reynolds number $> 6\times 10^4$ and state-space dimension $>10^5$.
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