Approximation Theory for Neural Networks: Old and New

Fuente: arXiv
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Autores principales: Mukherjee, Soumendu Sundar, Talukdar, Himasish
Formato: Preprint
Publicado: 2026
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author Mukherjee, Soumendu Sundar
Talukdar, Himasish
author_facet Mukherjee, Soumendu Sundar
Talukdar, Himasish
contents Universal approximation theorems provide a mathematical explanation for the expressive power of neural networks. They assert that, under mild conditions on the activation function, feedforward neural networks are dense in broad function classes, such as continuous functions on compact subsets of $\mathbb{R}^d$, $L^p$ spaces, or Sobolev spaces. Over the past four decades, these qualitative universality results have evolved into a rich quantitative theory addressing approximation rates, parameter efficiency, and the role of architectural features such as depth and width. This survey presents several glimpses into this theory. We review classical density results for single-hidden-layer networks, as well as quantitative bounds that relate approximation error to network size and smoothness assumptions on target functions. Particular emphasis is placed on depth--width trade-offs and on results demonstrating that deeper architectures can achieve superior parameter efficiency for structured function classes. In addition to standard feedforward neural networks, we also review recent developments on Kolmogorov--Arnold Networks (KANs), which offer an alternative architectural paradigm and whose approximation-theoretic properties have begun to attract significant theoretical attention.
format Preprint
id arxiv_https___arxiv_org_abs_2605_21451
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Approximation Theory for Neural Networks: Old and New
Mukherjee, Soumendu Sundar
Talukdar, Himasish
Machine Learning
Disordered Systems and Neural Networks
Artificial Intelligence
Neural and Evolutionary Computing
Universal approximation theorems provide a mathematical explanation for the expressive power of neural networks. They assert that, under mild conditions on the activation function, feedforward neural networks are dense in broad function classes, such as continuous functions on compact subsets of $\mathbb{R}^d$, $L^p$ spaces, or Sobolev spaces. Over the past four decades, these qualitative universality results have evolved into a rich quantitative theory addressing approximation rates, parameter efficiency, and the role of architectural features such as depth and width. This survey presents several glimpses into this theory. We review classical density results for single-hidden-layer networks, as well as quantitative bounds that relate approximation error to network size and smoothness assumptions on target functions. Particular emphasis is placed on depth--width trade-offs and on results demonstrating that deeper architectures can achieve superior parameter efficiency for structured function classes. In addition to standard feedforward neural networks, we also review recent developments on Kolmogorov--Arnold Networks (KANs), which offer an alternative architectural paradigm and whose approximation-theoretic properties have begun to attract significant theoretical attention.
title Approximation Theory for Neural Networks: Old and New
topic Machine Learning
Disordered Systems and Neural Networks
Artificial Intelligence
Neural and Evolutionary Computing
url https://arxiv.org/abs/2605.21451