A faster and simpler algorithm for learning shallow networks

We revisit the well-studied problem of learning a linear combination of $k$ ReLU activations given labeled examples drawn from the standard $d$-dimensional Gaussian measure. Chen et al. recently gave the first algorithm for this problem to run in $\mathrm{poly}(d,1/\epsilon)$ time when $k = O(1)$, where $\epsilon$ is the target error. More precisely, their algorithm runs in time $(d/\epsilon)^{\mathrm{quasipoly}(k)}$ and learns over multiple stages. Here we show that a much simpler one-stage version of their algorithm suffices, and moreover its runtime is only $(d k/\epsilon)^{O(k^2)}$.