arXiv:2606.22652cs.LGstat.ML2026-06

用马尔可夫链直接建模人类偏好,实现生成模型对齐。

A Markov Chain Approach to Preference Alignment

论文配图:A Markov Chain Approach to Preference Alignment
图 1 · 摘自论文原文
  • 基于人类偏好构建马尔可夫转移核,直接利用成对判断。
  • 收敛速度由非传递性度量 $\|U\|_\oplus$ 控制,几何级收敛。
  • 统一了强化学习、博弈论与马尔可夫方法的对齐视角。

我们提出马尔可夫链人类反馈(MCHF),一种从成对人类偏好中对齐生成模型的简单方法。不同于基于标量奖励的强化学习人类反馈(RLHF),也不同于通过KL正则极小极大优化保留成对效用的纳什学习人类反馈(NLHF),MCHF直接利用成对偏好定义模型输出间的转移机制。给定成对效用 $U(x,y)$(表示人类更偏好 $y$ 而非 $x$)和参考分布 $μ_{\mathsf{ref}}$,我们定义马尔可夫核 $\mathsf{P}(x, dy)\propto \exp(U(x,y))μ_{\mathsf{ref}}(dy)$,并将从 $μ_{\mathsf{ref}}$ 开始的马尔可夫链作为迭代对齐过程。我们证明 MCHF 几何快速收敛至平稳分布,收敛速率由半范数 $\|U\|_\oplus=\inf_{g,f\in L^\infty(μ_{\mathsf{ref}})}\|U-g\oplus f\|_\infty$ 决定,该值量化了成对效用的非传递结构。我们进一步证明 NLHF 的镜面下降算法具有类似结构自适应的收敛保证。通过扰动分析,我们证明当 $\|U\|_\oplus$ 较小时,MCHF 与 NLHF 在 RLHF 解附近一阶一致,从而统一了基于奖励、博弈论和马尔可夫的方法。特别地,对于两个收敛于 MCHF/NLHF 平衡点的自然算法,其第一步恢复了基于列和奖励 $\hat{f}(y)=\int μ_{\mathsf{ref}}(dx) U(x, y)$ 的 RLHF 解;从第二步起,两者均引入残差 $U-(-\hat f)\oplus \hat f$ 的线性泛函,刻画了 $U$ 的非传递结构。

原文摘要 · Abstract (English)

We propose Markov Chain from Human Feedback (MCHF), an elementary approach for aligning generative models from pairwise human preferences. Unlike Reinforcement Learning from Human Feedback (RLHF), which reduces comparisons to a scalar reward, and Nash Learning from Human Feedback (NLHF), which preserves pairwise utilities through a KL-regularized minimax optimization, MCHF uses pairwise preferences directly to define a transition mechanism over model outputs. Given a pairwise utility $U(x,y)$, which quantifies human preference for $y$ over $x$, and a reference probability distribution $μ_{\mathsf{ref}}$, we define a Markov kernel $\mathsf{P}(x, dy)\propto \exp(U(x,y))μ_{\mathsf{ref}}(dy)$, and take the Markov chain starting from $μ_{\mathsf{ref}}$ as an iterative alignment procedure. We show that MCHF converges geometrically fast to the stationary distribution, with a convergence rate governed by the seminorm $\|U\|_\oplus=\inf_{g,f\in L^\infty(μ_{\mathsf{ref}})}\|U-g\oplus f\|_\infty$, which quantifies the non-transitive structure of the pairwise utility. We further show that a mirror-descent algorithm for NLHF satisfies an analogous structure-adaptive convergence guarantee. Finally, through a perturbation analysis, we prove that when $\|U\|_\oplus$ is small, MCHF and NLHF agree up to first order around an RLHF solution, which yields a unified view of reward-based, game-theoretic, and Markovian approaches to alignment. In particular, for two natural algorithms that converge to the MCHF/NLHF equilibria, we show that the first step of MCHF and NLHF recovers the RLHF solution based on the column-sum reward $\hat{f}(y)=\int μ_{\mathsf{ref}}(dx) U(x, y)$, and starting from the second iteration, both algorithms incorporate the same linear functional of the residual $U-(-\hat f)\oplus \hat f$, which captures the non-transitive structure of the pairwise utility $U$.

偏好对齐马尔可夫链人类反馈生成模型

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