Approximation rates for finite mixtures of location-scale models and fast least-squares estimators
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866914501227446272 |
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| author | Nguyen, Hien Duy Nguyen, TrungTin Westerhout, Jacob Guo, Xin |
| author_facet | Nguyen, Hien Duy Nguyen, TrungTin Westerhout, Jacob Guo, Xin |
| contents | Finite mixture models provide a flexible framework for approximating and estimating multivariate probability densities. We study mixtures formed from translated and rescaled copies of a fixed density kernel and obtain explicit results for both approximation and least-squares estimation. Our main deterministic result is a quantisation theorem showing that, after smoothing the target density at a fixed resolution, the resulting convolution can be compressed into a finite location mixture with controlled error. Combining this with the smoothing bias yields approximation rates in $\mathcal{L}_{p}$ over Sobolev classes. For estimation, we analyse least-squares $\varepsilon$-minimisers over suitably tuned mixture sieves. Under exponential decay of the Fourier transform of the kernel, a matching moment condition, and bounded Sobolev targets, the estimator attains a squared $\mathcal{L}_{2}$ risk bound whose rate matches the Sobolev minimax benchmark up to a logarithmic factor. If, in addition, the kernel is bandlimited, then the same theorem recovers the Sobolev rate $n^{-2s/\left(2s+d\right)}$. We further report a slower convergence rate under weaker VC-type assumptions. At fixed scale, the Fourier-based approach also gives a nearly parametric risk bound for the associated location-mixture class, and the same bandlimited simplification removes the logarithmic correction. In the Gaussian case, this recovers the known Gaussian location-mixture rate. We also prove matching lower bounds on Gaussian convolution submodels, including strict submodels of the Gaussian location-mixture class, and on the tensor-product odd-degree Student-$t$ location-mixture family. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_10612 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Approximation rates for finite mixtures of location-scale models and fast least-squares estimators Nguyen, Hien Duy Nguyen, TrungTin Westerhout, Jacob Guo, Xin Statistics Theory Finite mixture models provide a flexible framework for approximating and estimating multivariate probability densities. We study mixtures formed from translated and rescaled copies of a fixed density kernel and obtain explicit results for both approximation and least-squares estimation. Our main deterministic result is a quantisation theorem showing that, after smoothing the target density at a fixed resolution, the resulting convolution can be compressed into a finite location mixture with controlled error. Combining this with the smoothing bias yields approximation rates in $\mathcal{L}_{p}$ over Sobolev classes. For estimation, we analyse least-squares $\varepsilon$-minimisers over suitably tuned mixture sieves. Under exponential decay of the Fourier transform of the kernel, a matching moment condition, and bounded Sobolev targets, the estimator attains a squared $\mathcal{L}_{2}$ risk bound whose rate matches the Sobolev minimax benchmark up to a logarithmic factor. If, in addition, the kernel is bandlimited, then the same theorem recovers the Sobolev rate $n^{-2s/\left(2s+d\right)}$. We further report a slower convergence rate under weaker VC-type assumptions. At fixed scale, the Fourier-based approach also gives a nearly parametric risk bound for the associated location-mixture class, and the same bandlimited simplification removes the logarithmic correction. In the Gaussian case, this recovers the known Gaussian location-mixture rate. We also prove matching lower bounds on Gaussian convolution submodels, including strict submodels of the Gaussian location-mixture class, and on the tensor-product odd-degree Student-$t$ location-mixture family. |
| title | Approximation rates for finite mixtures of location-scale models and fast least-squares estimators |
| topic | Statistics Theory |
| url | https://arxiv.org/abs/2508.10612 |