Benign Overfitting in Deep Neural Networks under Lazy Training
Zhenyu Zhu Fanghui Liu Grigorios G Chrysos Francesco Locatello Volkan Cevher
This paper focuses on over-parameterized deep neural networks (DNNs) with
ReLU activation functions and proves that when the data distribution is
well-separated, DNNs can achieve Bayes-optimal test error for classification
while obtaining (nearly) zero-training error under the lazy training regime.
For this purpose, we unify three interrelated concepts of overparameterization,
benign overfitting, and the Lipschitz constant of DNNs. Our results indicate
that interpolating with smoother functions leads to better generalization.
Furthermore, we investigate the special case where interpolating smooth
ground-truth functions is performed by DNNs under the Neural Tangent Kernel
(NTK) regime for generalization. Our result demonstrates that the
generalization error converges to a constant order that only depends on label
noise and initialization noise, which theoretically verifies benign
overfitting. Our analysis provides a tight lower bound on the normalized margin
under non-smooth activation functions, as well as the minimum eigenvalue of NTK
under high-dimensional settings, which has its own interest in learning theory.