Universal approximation results for neural networks with non-polynomial activation function over non-compact domains

This paper extends the universal approximation property of single-hidden-layer feedforward neural networks beyond compact domains, which is of particular interest for the approximation within weighted $C^k$-spaces and weighted Sobolev spaces over unbounded domains. More precisely, by assuming that the activation function is non-polynomial, we establish universal approximation results within function spaces defined over non-compact subsets of a Euclidean space, including $L^p$-spaces, weighted $C^k$-spaces, and weighted Sobolev spaces, where the latter two include the approximation of the (weak) derivatives. Moreover, we provide some dimension-independent rates for approximating a function with sufficiently regular and integrable Fourier transform by neural networks with non-polynomial activation function.

@article{neufeld2025_2410.14759,
  title={ Universal approximation results for neural networks with non-polynomial activation function over non-compact domains },
  author={ Ariel Neufeld and Philipp Schmocker },
  journal={arXiv preprint arXiv:2410.14759},
  year={ 2025 }
}