arXiv Machine Learning

Beyond the $d^{2.5}$-mixing bound for Dikin walks on polytopes

arXiv:2607. 13943v1 Announce Type: cross Abstract: Inspired by interior-point methods (IPM) for structured convex optimization, Kannan and Narayanan introduced the Dikin walk for sampling uniformly from polytopes in 2009.

arXiv Machine Learning
Aug 31

On two proofs of $d^2$ mixing of weighted Dikin walks

The paper investigates the mixing time of weighted Dikin walks used for sampling from exponential distributions on polytopes and truncated positive-semidefinite cones. It presents a general total-variation mixing bound under conditions of strong self-concordance, ν-symmetry, and mixed-trace regularity, achieving an “~O(d^2)" bound for polytopes and “~O(d^4)" for truncated PSD cones. A second result introduces a fourth-order bootstrap condition that yields stronger χ^2-divergence guarantees and an improved “~O(d^2)" mixing bound for a scaled Lee–Sidford metric.

By Yuansi Chen, Yunbum Kook
arXiv Machine Learning
Sep 14

Poisson-Corrector Complexity Bounds for Moreau--Yosida Unadjusted Langevin Sampling

arXiv:2609. 12594v1 Announce Type: new Abstract: We study the classical Moreau--Yosida unadjusted Langevin algorithm (MYULA) for $\pi(\,\mathrm{d} x)\propto e^{-f(x)-g(x)}\,\mathrm{d} x$, where $f\in C^2(\mathbb{R}^d)$ is $m$-strongly convex with $L_f$-Lipschitz gradient and $g:\mathbb{R}^d\to\mathbb{R}$ is convex and globally $G$-Lipschitz.

By Yuchen Xin, Zhihua Zhang
arXiv Machine Learning
Aug 27

Adaptivity via a Parallel Architecture for Stochastic Gradient Methods

The paper introduces a parallel architecture for stochastic gradient methods that adaptively selects the number of iterations. An algorithm A(x₀, y) takes an initial point and a step limit y, and p processors search for an appropriate iteration count T using a prescribed function h. The framework guarantees a (p, αₚ)-approximation, meaning for any T ≥ T₀ there exists a processor and stage where the cumulative iterations lie within a factor αₚ of T, and the authors prove tight lower bounds for αₚ while presenting simple arithmetic stochastic gradient methods that use only divisions by powers of two.

By Bin Fu