FineGrained Analysis of Optimization and Generalization for Overparameterized TwoLayer Neural Networks
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Proceedings of the 36th International Conference on Machine Learning, PMLR 97:322332, 2019.
Abstract
Recent works have cast some light on the mystery of why deep nets fit any data and generalize despite being very overparametrized. This paper analyzes training and generalization for a simple 2layer ReLU net with random initialization, and provides the following improvements over recent works: (i) Using a tighter characterization of training speed than recent papers, an explanation for why training a neural net with random labels leads to slower training, as originally observed in [Zhang et al. ICLR’17]. (ii) Generalization bound independent of network size, using a datadependent complexity measure. Our measure distinguishes clearly between random labels and true labels on MNIST and CIFAR, as shown by experiments. Moreover, recent papers require sample complexity to increase (slowly) with the size, while our sample complexity is completely independent of the network size. (iii) Learnability of a broad class of smooth functions by 2layer ReLU nets trained via gradient descent. The key idea is to track dynamics of training and generalization via properties of a related kernel.
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