Dimension-independent rates for structured neural density estimation
This provides a theoretical justification for deep learning's ability to avoid the curse of dimensionality in high-dimensional applications such as image and text processing, though it is incremental in extending existing theory to structured densities.
The paper tackles the problem of nonparametric density estimation for structured data like images and text, showing that deep neural networks achieve dimension-independent convergence rates of n^{-1/(4+r)} in L^2 and n^{-1/(2+r)} in L^1, where r is the maximum clique size in a Markov random field, often constant in practice.
We show that deep neural networks achieve dimension-independent rates of convergence for learning structured densities such as those arising in image, audio, video, and text applications. More precisely, we demonstrate that neural networks with a simple $L^2$-minimizing loss achieve a rate of $n^{-1/(4+r)}$ in nonparametric density estimation when the underlying density is Markov to a graph whose maximum clique size is at most $r$, and we provide evidence that in the aforementioned applications, this size is typically constant, i.e., $r=O(1)$. We then establish that the optimal rate in $L^1$ is $n^{-1/(2+r)}$ which, compared to the standard nonparametric rate of $n^{-1/(2+d)}$, reveals that the effective dimension of such problems is the size of the largest clique in the Markov random field. These rates are independent of the data's ambient dimension, making them applicable to realistic models of image, sound, video, and text data. Our results provide a novel justification for deep learning's ability to circumvent the curse of dimensionality, demonstrating dimension-independent convergence rates in these contexts.