Learning (Very) Simple Generative Models Is Hard

Motivated by the recent empirical successes of deep generative models, we study the computational complexity of the following unsupervised learning problem. We show under the statistical query (SQ) model that no polynomial-time algorithm can solve this problem even when the output coordinates of F are one-hidden-layer ReLU networks with \log(d) neurons. Previously, the best lower bounds for this problem simply followed from lower bounds for *supervised learning* and required at least two hidden layers and \textrm{poly}(d) neurons [Daniely-Vardi '21, Chen-Gollakota-Klivans-Meka '22]. The key ingredient in our proof is an ODE-based construction of a compactly supported, piecewise-linear function f with polynomially-bounded slopes such that the pushforward of \mathcal{N}(0,1) under f matches all low-degree moments of \mathcal{N}(0,1) .