用机器学习设计高效且可证明收敛的分裂方法,兼顾大步长计算效率与小步长物理守恒。
Learning efficient and provably convergent splitting methods
- 结合机器学习与数学分析,构建可证明收敛的新型分裂方法框架。
- 在有限计算预算下,对薛定谔方程的求解效率显著优于传统高阶方法。
- 既保证小步长下二阶收敛和物理守恒性,又适用于大步长实际应用。
分裂方法因其能将复杂演化分解为更易处理的子问题,被广泛用于求解初值问题(IVPs)。传统方法基于数值分析中的解析与代数技巧,如截断泰勒展开及其李代数形式的Baker--Campbell--Hausdorff公式,可构造高阶精度方法,实现小时间步下的高精度,并通常近似保持质量、幺正性和能量等重要物理守恒量。然而,在许多实际场景中计算资源受限,需在固定预算内实现最佳精度,此时传统高阶方法因仅在小步长下渐近最优,常因采用较大时间步而产生显著误差。机器学习可提供替代方案,但通常纯数据驱动,缺乏小步长下的收敛保证,且不保证守恒性。本文提出一种框架,用于发现具有计算效率的机器学习分裂方法,同时在小步长极限下具备可证明的收敛性与守恒性。数值实验表明,所学方法在构造上对时间步长呈二阶收敛,当计算预算受限时,其对薛定谔方程的求解效率显著优于现有方法。
原文摘要 · Abstract (English)
Splitting methods are widely used for solving initial value problems (IVPs) due to their ability to simplify complicated evolutions into more manageable subproblems which can be solved efficiently and accurately. Traditionally, these methods are derived using analytic and algebraic techniques from numerical analysis, including truncated Taylor series and their Lie algebraic analogue, the Baker--Campbell--Hausdorff formula. These tools enable the development of high-order numerical methods that provide exceptional accuracy for small timesteps. Moreover, these methods often (nearly) conserve important physical invariants, such as mass, unitarity, and energy. However, in many practical applications the computational resources are limited. Thus, it is crucial to identify methods that achieve the best accuracy within a fixed computational budget, which might require taking relatively large timesteps. In this regime, high-order methods derived with traditional methods often exhibit large errors since they are only designed to be asymptotically optimal. Machine Learning techniques offer a potential solution since they can be trained to efficiently solve a given IVP with less computational resources. However, they are often purely data-driven, come with limited convergence guarantees in the small-timestep regime and do not necessarily conserve physical invariants. In this work, we propose a framework for finding machine learned splitting methods that are computationally efficient for large timesteps and have provable convergence and conservation guarantees in the small-timestep limit. We demonstrate numerically that the learned methods, which by construction converge quadratically in the timestep size, can be significantly more efficient than established methods for the Schrödinger equation if the computational budget is limited.
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