Structure-preserving Lift & Learn: Scientific machine learning for nonlinear conservative partial differential equations
This work addresses the challenge of efficient and physics-respecting model reduction for nonlinear PDEs in scientific computing, representing an incremental improvement over existing structure-preserving data-driven methods.
The paper tackles the problem of learning reduced-order models for nonlinear conservative PDEs by proposing a structure-preserving Lift & Learn method that uses energy quadratization to derive quadratic lifted systems, resulting in computationally efficient models that respect underlying physics. Numerical examples demonstrate competitive accuracy and computational efficiency with state-of-the-art methods.
This work presents structure-preserving Lift & Learn, a scientific machine learning method that employs lifting variable transformations to learn structure-preserving reduced-order models for nonlinear partial differential equations (PDEs) with conservation laws. We propose a hybrid learning approach based on a recently developed energy-quadratization strategy that uses knowledge of the nonlinearity at the PDE level to derive an equivalent quadratic lifted system with quadratic system energy. The lifted dynamics obtained via energy quadratization are linear in the old variables, making model learning very effective in the lifted setting. Based on the lifted quadratic PDE model form, the proposed method derives quadratic reduced terms analytically and then uses those derived terms to formulate a constrained optimization problem to learn the remaining linear reduced operators in a structure-preserving way. The proposed hybrid learning approach yields computationally efficient quadratic reduced-order models that respect the underlying physics of the high-dimensional problem. We demonstrate the generalizability of quadratic models learned via the proposed structure-preserving Lift & Learn method through three numerical examples: the one-dimensional wave equation with exponential nonlinearity, the two-dimensional sine-Gordon equation, and the two-dimensional Klein-Gordon-Zakharov equations. The numerical results show that the proposed learning approach is competitive with the state-of-the-art structure-preserving data-driven model reduction method in terms of both accuracy and computational efficiency.