Empirically, large-scale deep learning models often satisfy a neural scaling law: the test error of the trained model improves polynomially as the model size and data size grow. However, conventional wisdom suggests the test error consists of approximation, bias, and variance errors, where the variance error increases with model size. This disagrees with the general form of neural scaling laws, which predict that increasing model size monotonically improves performance. We study the theory of scaling laws in an infinite dimensional linear regression setup. Specifically, we consider a model with $M$ parameters as a linear function of sketched covariates. The model is trained by one-pass stochastic gradient descent (SGD) using $N$ data. Assuming the optimal parameter satisfies a Gaussian prior and the data covariance matrix has a power-law spectrum of degree $a>1$, we show that the reducible part of the test error is $\Theta(M^{-(a-1)} + N^{-(a-1)/a})$. The variance error, which increases with $M$, is dominated by the other errors due to the implicit regularization of SGD, thus disappearing from the bound. Our theory is consistent with the empirical neural scaling laws and verified by numerical simulation.

大规模深度学习模型的实证研究表明，随着模型大小和数据规模的增加，训练模型的测试误差呈多项式改进；然而，神经缩放定律的一般形式预测增加模型大小会单调改善性能，这与传统的认知不同，即测试误差包含逼近、偏差和方差误差，并且方差错误随模型大小增加而增加。本研究在无限维线性回归设置下研究了缩放规律的理论；假设最优参数符合高斯先验，数据协方差矩阵具有幂律谱指数为a>1，我们证明了测试误差的可还原部分为Θ(M^{-(a-1)} + N^{-(a-1)/a})；方差错误随M的增加而增加，但由于随机梯度下降的隐式正则化作用，被其他误差所主导从而在界限中消失。我们的理论与实证神经缩放定律一致，并经过数值模拟验证。

线性回归中的缩放定律：计算、参数和数据