Learning Hierarchical Polynomials with Three-Layer Neural Networks
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Abstract (arXiv)
We study the problem of learning hierarchical polynomials over the standard Gaussian distribution with three-layer neural networks. We specifically consider target functions of the form h = g circ p where p : ℝd rightarrow ℝ is a degree k polynomial and g: ℝ rightarrow ℝ is a degree q polynomial. This function class generalizes the single-index model, which corresponds to k=1, and is a natural class of functions possessing an underlying hierarchical structure. Our main result shows that for a large subclass of degree k polynomials p, a three-layer neural network trained via layerwise gradient descent on the square loss learns the target h up to vanishing test error in widetildeO(dk) samples and polynomial time. This is a strict improvement over kernel methods, which require widetilde Theta(dkq) samples, as well as existing guarantees for two-layer networks, which require the target function to be low-rank. Our result also generalizes prior works on three-layer neural networks, which were restricted to the case of p being a quadratic. When p is indeed a quadratic, we achieve the information-theoretically optimal sample complexity widetildeO(d2), which is an improvement over prior work~citepnichani2023provable requiring a sample size of widetildeTheta(d4). Our proof proceeds by showing that during the initial stage of training the network performs feature learning to recover the feature p with widetildeO(dk) samples. This work demonstrates the ability of three-layer neural networks to learn complex features and as a result, learn a broad class of hierarchical functions.
Key facts. Cited by 9 papers in the map (data through 14 Oct 2026). Builds on 26 of its 38 references that are in the map. First posted on arXiv 23 Nov 2023.
Builds on
26 of 38 references.
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14 more
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Citing papers per year: 2024: 5; 2025: 0; 2026: 4.
9 papers.
- 2024Learning sum of diverse features: computational hardness and efficient gradient-based training for ridge combinationscited by 13
- 2024How Transformers Get Rich: Approximation and Dynamics Analysiscited by 8
- 2026Provable Learning of Random Hierarchy Models and Hierarchical Shallow-to-Deep Chainingcited by 6
- 2024Robust Feature Learning for Multi-Index Models in High Dimensionscited by 5
- 2026Deep Learning of Compositional Targets with Hierarchical Spectral Methodscited by 5
- 2024Bilinear Sequence Regression: A Model for Learning from Long Sequences of High-dimensional Tokenscited by 3
- 2024Generalization for Least Squares Regression With Simple Spiked Covariancescited by 2
- 2026Scaling Laws from Sequential Feature Recovery: A Solvable Hierarchical Modelcited by 0
- 2026Feature Learning in Linear-Width Two-Layer Networks: Two vs. One Step of Gradient Descentcited by 0
- 2026Feature Learning in Linear-Width Two-Layer Networks: Two vs. One Step of Gradient Descent18 May 2026
- 2026Scaling Laws from Sequential Feature Recovery: A Solvable Hierarchical Model14 May 2026
- 2026Deep Learning of Compositional Targets with Hierarchical Spectral Methods11 Feb 2026
- 2026Provable Learning of Random Hierarchy Models and Hierarchical Shallow-to-Deep Chaining27 Jan 2026
- 2024Bilinear Sequence Regression: A Model for Learning from Long Sequences of High-dimensional Tokens24 Oct 2024
- 2024Robust Feature Learning for Multi-Index Models in High Dimensions21 Oct 2024
- 2024Generalization for Least Squares Regression With Simple Spiked Covariances17 Oct 2024
- 2024How Transformers Get Rich: Approximation and Dynamics Analysis15 Oct 2024
- 2024Learning sum of diverse features: computational hardness and efficient gradient-based training for ridge combinations17 Jun 2024