arXiv:2412.03393cs.LG2024-12NeurIPS被引 5

证明神经算子无法总被连续离散化,提出新框架确保离散化一致性。

Can neural operators always be continuously discretized?

  • 基于无穷维微分同胚理论,构建离散化不可行的反例。
  • 引入强单调算子结构,实现有限维逼近的连续收敛。
  • 适用于需严格离散不变性的物理建模与科学计算场景。

我们研究希尔伯特空间间神经算子在包含跳跃连接的一般框架下的离散化问题。聚焦于通过无穷维微分同胚表示的双射神经算子,利用范畴论框架给出一个否定性定理:希尔伯特空间或希尔伯特流形间的微分同胚可能无法被任何有限维空间上的微分同胚(即使非线性)连续逼近。自然解法是引入强单调微分同胚及逐层强单调神经算子,其可在有限维空间上实现强单调微分同胚的连续逼近。此类算子可保证离散化不变性,并确保有限维逼近不仅函数序列收敛,其表征也在合适意义下收敛。进一步证明双利普希茨神经算子可表示为强单调神经算子交替组合加简单等距变换。由此建立神经算子离散化的严格平台。同时,此类算子可通过有限秩残差神经算子复合逼近,每个块均为强单调,且可通过迭代局部求逆。最后给出一般双利普希茨神经算子离散化的一个量化逼近结果。

原文摘要 · Abstract (English)

We consider the problem of discretization of neural operators between Hilbert spaces in a general framework including skip connections. We focus on bijective neural operators through the lens of diffeomorphisms in infinite dimensions. Framed using category theory, we give a no-go theorem that shows that diffeomorphisms between Hilbert spaces or Hilbert manifolds may not admit any continuous approximations by diffeomorphisms on finite-dimensional spaces, even if the approximations are nonlinear. The natural way out is the introduction of strongly monotone diffeomorphisms and layerwise strongly monotone neural operators which have continuous approximations by strongly monotone diffeomorphisms on finite-dimensional spaces. For these, one can guarantee discretization invariance, while ensuring that finite-dimensional approximations converge not only as sequences of functions, but that their representations converge in a suitable sense as well. Finally, we show that bilipschitz neural operators may always be written in the form of an alternating composition of strongly monotone neural operators, plus a simple isometry. Thus we realize a rigorous platform for discretization of a generalization of a neural operator. We also show that neural operators of this type may be approximated through the composition of finite-rank residual neural operators, where each block is strongly monotone, and may be inverted locally via iteration. We conclude by providing a quantitative approximation result for the discretization of general bilipschitz neural operators.

神经算子离散化微分同胚强单调

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