Minimum Width for Universal Approximation
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Abstract (arXiv)
The universal approximation property of width-bounded networks has been studied as a dual of classical universal approximation results on depth-bounded networks. However, the critical width enabling the universal approximation has not been exactly characterized in terms of the input dimension dx and the output dimension dy. In this work, we provide the first definitive result in this direction for networks using the ReLU activation functions: The minimum width required for the universal approximation of the Lp functions is exactly maxdx+1,dy. We also prove that the same conclusion does not hold for the uniform approximation with ReLU, but does hold with an additional threshold activation function. Our proof technique can be also used to derive a tighter upper bound on the minimum width required for the universal approximation using networks with general activation functions.
Key facts. Cited by 92 papers in the map (data through 7 Oct 2026). First posted on arXiv 16 Jun 2020.
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Citing papers per year: 2021: 7; 2022: 18; 2023: 17; 2024: 24; 2025: 15; 2026: 11.
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