A quantitative and constructive proof of Willems' Fundamental Lemma and its implications

1 Aug 2022  ·  Julian Berberich, Andrea Iannelli, Alberto Padoan, Jeremy Coulson, Florian Dörfler, Frank Allgöwer ·

Willems' Fundamental Lemma provides a powerful data-driven parametrization of all trajectories of a controllable linear time-invariant system based on one trajectory with persistently exciting (PE) input. In this paper, we present a novel proof of this result which is inspired by the classical adaptive control literature and differs from existing proofs in multiple aspects. The proof involves a quantitative and directional PE notion, allowing to characterize robust PE properties via singular value bounds, as opposed to binary rank-based PE conditions. Further, the proof is constructive, i.e., we derive an explicit PE lower bound for the generated data. As a contribution of independent interest, we generalize existing PE results from the adaptive control literature and reveal a crucial role of the system's zeros.

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Optimization and Control Systems and Control Systems and Control