The widely observed 'benign overfitting phenomenon' in the neural network literature raises the challenge to the 'bias-variance trade-off' doctrine in the statistical learning theory. Since the generalization ability of the 'lazy trained' over-parametrized neural network can be well approximated by that of the neural tangent kernel regression, the curve of the excess risk (namely, the learning curve) of kernel ridge regression attracts increasing attention recently. However, most recent arguments on the learning curve are heuristic and are based on the 'Gaussian design' assumption. In this paper, under mild and more realistic assumptions, we rigorously provide a full characterization of the learning curve: elaborating the effect and the interplay of the choice of the regularization parameter, the source condition and the noise. In particular, our results suggest that the 'benign overfitting phenomenon' exists in very wide neural networks only when the noise level is small.

在这篇论文中，我们在温和且更现实的假设下，对学习曲线进行了全面的描述，详细阐述了正则化参数、源条件和噪声的选择对学习曲线的影响和相互作用。特别地，我们的结果表明，在噪声水平较小时，'良性过拟合现象'只存在于非常宽的神经网络中。

核岭回归在幂律衰减下的渐近学习曲线