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arXiv · 2504.15251

On Learning Parallel Pancakes with Mostly Uniform Weights

Ilias Diakonikolas·Daniel M. Kane·Sushrut Karmalkar·Jasper C. H. Lee·Thanasis Pittas
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Abstract

We study the complexity of learning $k$-mixtures of Gaussians ($k$-GMMs) on $\mathbb{R}^d$. This task is known to have complexity $d^{Ω(k)}$ in full generality. To circumvent this exponential lower bound on the number of components, research has focused on learning families of GMMs satisfying additional structural properties. A natural assumption posits that the component weights are not exponentially small and that the components have the same unknown covariance. Recent work gave a $d^{O(\log(1/w_{\min}))}$-time algorithm for this class of GMMs, where $w_{\min}$ is the minimum weight. Our first main result is a Statistical Query (SQ) lower bound showing that this quasi-polynomial upper bound is essentially best possible, even for the special case of uniform weights. Specifically, we show that it is SQ-hard to distinguish between such a mixture and the standard Gaussian. We further explore how the distribution of weights affects the complexity of this task. Our second main result is a quasi-polynomial upper bound for the aforementioned testing task when most of the weights are uniform while a small fraction of the weights are potentially arbitrary.

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Ilias Diakonikolas, Daniel M. Kane, Sushrut Karmalkar, Jasper C. H. Lee, Thanasis Pittas. 2025-04-21. On Learning Parallel Pancakes with Mostly Uniform Weights. https://arxiv.org/abs/2504.15251

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