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Ethan X. Fang

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Preprint Oct 2026

PerSPL: Personalized Semi-supervised Preference Learning

Personalized reward models require user-specific preference comparisons, but collecting such feedback is costly and provides only limited supervision for each user. At the same time, large pools of responses can be generated without user identities or preference labels, yet existing personalized reward models leave thi...

Xiao-An Xu, Ting-Han Wei, Jun-Cheng Dong et al. · 0 citations
Preprint Sep 2026

An Improved Lower Bound for the Complex Grothendieck Constant

We prove $K_G^{\mathbb{C}}>1.35584631827168$ for the classical complex Grothendieck constant, closing more than one quarter of the gap between Davie's lower bound and Haagerup's upper bound. The numerical part of the proof is rigorously verified by interval arithmetic. The lower bound and the proof were discovered by t...

Sheng Guo, Ethan X. Fang, Jun-Wei Lu · 1 citation
Preprint Sep 2026

Vector Balancing in Polynomial Time

The Koml\'os problem asks for signs $\varepsilon\in\{-1,1\}^n$ with $\|A\varepsilon\|_\infty$ bounded by an absolute constant whenever the columns of $A\in\mathbb R^{m\times n}$ have Euclidean norm at most $1$. We give the first polynomial-time algorithm for this problem in the unit-cost real-RAM model. Our determinist...

Sheng Guo, Ethan X. Fang, Jun-Wei Lu · 4 citations · ⚡2
Preprint Aug 2026

Weak-Type Bounds for Convolution on the Boolean Hypercube

Let $G$ be the Boolean hypercube which carries uniform measure $\lambda$, and let $T_\mu$ denote convolution by a finite positive measure $\mu$ on $G$. For $\psi_\mu(u)=\sup\{u\lambda(\{T_\mu f\geq u\}):f\geq 0,\|f\|_1=1\},$ we prove Talagrand's convolution conjecture (Talagrand, 1989): if $\mu_a=((1+a)\delta_1/2+(1-a)...

Jun-Wei Lu, Sheng Guo, Ethan X. Fang · 1 citation
Preprint Sep 2026

Vector Balancing via Directional Total Variation

Every finite family of real vectors of Euclidean norm at most one admits a signed sum of $\ell_\infty$-norm less than this constant, independently of the dimension and the family size.

Sheng Guo, Ethan X. Fang, Jun-Wei Lu · 10 citations · ⚡2
Preprint Aug 2026

On Unavoidable Faces of High-Dimensional Polytopes

Kalai's cube--simplex conjecture asserts that for all positive integers $\ell,k$, there is an integer $f(\ell,k)$ such that every polytope of dimension at least $f(\ell,k)$ has either a simplex $\ell$-face or a cube $k$-face; let $f_s(\ell,k)$ denote the threshold restricted to simple polytopes. Finiteness of $f(\ell,k...

J. De Loera, Ethan X. Fang, Sheng Guo et al. · 0 citations
Preprint Aug 2026

A Metric with Positive Sectional Curvature on $S^2\times S^3$

We prove that $S^2\times S^3$ admits a Riemannian metric with positive sectional curvature. We view it as a principal circle bundle over $S^2\times S^2$. A diagonal Cheeger deformation of the base and a connection whose curvature form vanishes on the remaining flat tori yield a nonnegatively curved connection metric wh...

Sheng Guo, Ethan X. Fang, Jun-Wei Lu · 0 citations
Preprint Aug 2026

Diffusion-Based Data-Driven Assortment Optimization

A model-agnostic framework for assortment optimization based on guided discrete diffusion that represents assortments as binary vectors and performs stochastic search via a learned reverse diffusion process, avoiding explicit combinatorial enumeration.

Jun-Yi Liao, Xiaohui Jiang, Zhengwei Tong et al. · 0 citations

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