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arXiv 2109.01050cs.LGcs.AIcs.NAmath.NAphysics.comp-ph
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物理信息神经网络中可能失效模式的表征

Characterizing possible failure modes in physics-informed neural networks

Lawrence Berkeley National Laboratory(劳伦斯伯克利国家实验室);University of California, Berkeley(加州大学伯克利分校);University of Utah(犹他大学);International Computer Science Institute(国际计算机科学研究所)

Aditi S. Krishnapriyan, Amir Gholami, Shandian Zhe, Robert M. Kirby, Michael W. Mahoney

摘要:

科学机器学习的最新工作开发了所谓的物理信息神经网络(PINN)模型。典型的方法是将物理领域知识作为经验损失函数的软约束,并使用现有的机器学习方法来训练模型。我们证明,虽然现有的PINN方法可以学习相对琐碎的问题的好模型,他们很容易无法学习相关的物理现象,甚至稍微复杂的问题。特别是,我们分析了几种不同的情况下广泛的物理利益,包括学习微分方程与对流,反应和扩散算子。我们提供的证据表明,PINN中的软正则化,其中涉及基于PDE的微分算子,可以引入一些微妙的问题,包括使问题更加病态。重要的是,我们表明,这些可能的故障模式并不是因为NN架构缺乏表达能力,而是PINN的设置使得损失景观很难优化。然后,我们描述了两个有前途的解决方案,以解决这些故障模式。第一种方法是使用课程正则化,其中PINN的损失项从简单的PDE正则化开始,并且随着NN的训练而逐渐变得更加复杂。第二种方法是将问题视为序列到序列的学习任务,而不是学习一次预测整个时空。广泛的测试表明,与常规PINN训练相比,这些方法可以实现高达1-2个数量级的低误差。

英文摘要:

Recent work in scientific machine learning has developed so-called physics-informed neural network (PINN) models. The typical approach is to incorporate physical domain knowledge as soft constraints on an empirical loss function and use existing machine learning methodologies to train the model. We demonstrate that, while existing PINN methodologies can learn good models for relatively trivial problems, they can easily fail to learn relevant physical phenomena for even slightly more complex problems. In particular, we analyze several distinct situations of widespread physical interest, including learning differential equations with convection, reaction, and diffusion operators. We provide evidence that the soft regularization in PINNs, which involves PDE-based differential operators, can introduce a number of subtle problems, including making the problem more ill-conditioned. Importantly, we show that these possible failure modes are not due to the lack of expressivity in the NN architecture, but that the PINN's setup makes the loss landscape very hard to optimize. We then describe two promising solutions to address these failure modes. The first approach is to use curriculum regularization, where the PINN's loss term starts from a simple PDE regularization, and becomes progressively more complex as the NN gets trained. The second approach is to pose the problem as a sequence-to-sequence learning task, rather than learning to predict the entire space-time at once. Extensive testing shows that we can achieve up to 1-2 orders of magnitude lower error with these methods as compared to regular PINN training.

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