On Learning Parallel Pancakes with Mostly Uniform Weights

• URL: http://arxiv.org/abs/2504.15251v1
• Date: Mon, 21 Apr 2025 17:31:55 GMT
• Title: On Learning Parallel Pancakes with Mostly Uniform Weights
• Authors: Ilias Diakonikolas, Daniel M. Kane, Sushrut Karmalkar, Jasper C. H. Lee, Thanasis Pittas,
• Abstract summary: We study the complexity of learning $k$-mixtures of Gaussians ($k$-GMMs) on $mathbbRd$.<n>We show that it is SQ-hard to distinguish between such a mixture and the standard Gaussian.
• Score: 42.63152235265314
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: We study the complexity of learning $k$-mixtures of Gaussians ($k$-GMMs) on $\mathbb{R}^d$. This task is known to have complexity $d^{\Omega(k)}$ 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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