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Fan Chen

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#machine learning Preprint Oct 2026

Sharp dimensional analysis of midpoint methods for Langevin sampling

We study deterministic and randomized midpoint discretizations of Langevin dynamics for a target $\pi \propto e^{-V}$, where $0 \prec \alpha I\preceq\nabla^2V\preceq\beta I$ and $\kappa=\beta/\alpha$. To achieve $\sqrt\alpha\,W_2\leqslant\varepsilon$, we show that deterministic Heun uses at most $\widetilde O(\kappa^{4...

Fan Chen, Sinho Chewi, Jian-Feng Lu et al. · 0 citations
Preprint Sep 2026

High-accuracy simulation of Picard HMC, part I: Gaussian cloud correction

We study the problem of sampling from a continuous density $\pi\propto \exp(-V)$ on $\mathbb R^d$, where $V\in C^2(\mathbb R^d)$ has a $\beta$-Lipschitz gradient and $\pi$ satisfies a logarithmic Sobolev inequality with constant $\alpha^{-1}$, and write $\kappa = \beta/\alpha$. We introduce the Gaussian cloud sampler,...

Fan Chen, Sinho Chewi, Jian-Feng Lu et al. · 0 citations
Preprint Sep 2026

Sharp Gaussian divergence and Bernstein-Markov inequalities

We prove two dimension-free estimates in Gaussian space. The first is an optimal Meyer-type inequality for the Gaussian divergence: for $p\geq2$, \[ \|\delta V\|_{L^p(\gamma_d)} \leq \sqrt p\,|\mathbb E V| +Cp\,\|DV\|_{L^p(\gamma_d;\mathrm{HS}_d)}\, . \] Here $\mathrm{HS}_d$ is the space of $d\times d$ matrices with it...

Fan Chen, Sinho Chewi, Jian-Feng Lu et al. · 0 citations
#machine learning Preprint Sep 2026

On the Two Faces of Adam in Separable Linear Classification

This work gives sufficient conditions under which an Adam-trained classifier nearly maximizes the max-norm margin before the updates become gradient-like, and shows that for polynomially decreasing stepsizes with exponent \(a), the updates become approximately proportional to the negative gradient after $\Theta(1/\epsi...

Fan Chen, Csaba Szepesvari · 0 citations
#machine learning Preprint Sep 2026

Smoothed Picard Hamiltonian Monte Carlo

We develop a new low-accuracy sampler, called smoothed Picard Hamiltonian Monte Carlo, which combines Gaussian smoothing, Picard iteration, and higher-order discretization. For a log-concave target $\pi \propto \exp(-V)$ in dimension $d$ satisfying $0 \prec \alpha I \preceq \nabla^2 V \preceq \beta I$, with condition n...

Fan Chen, Sinho Chewi, Jian-Feng Lu et al. · 1 citation
#machine learning Preprint Sep 2026

Accelerated High-Accuracy Sampling from a Warm Start via the Proximal Bouncy Particle Sampler

The Proximal Bouncy Particle Sampler is a new sampler that combines ideas from the proximal sampler and the bouncy particle sampler that returns a sample whose law is $\varepsilon$-close to $\mu$ in total variation distance using gradient queries in expectation.

Fan Chen, Sinho Chewi, Jian-Feng Lu et al. · 0 citations
Preprint Aug 2026

Exact simulation of diffusions and improved algorithms for log-concave sampling

We study exact simulation of diffusions via rejection sampling on path space using unbiased estimators of the density ratio obtained from Girsanov's theorem. When applied to the underdamped Langevin diffusion, it yields an algorithm for sampling from a strongly log-concave and log-smooth distribution with condition num...

Fan Chen, Sinho Chewi, Alexander Rakhlin et al. · 1 citation

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