用学习模型快速生成高精度积分节点,替代传统大量采样。
Amortized mean-shift interacting particles

- 用可训练映射直接从观测和少量样本生成加权节点
- 在任意节点数量下均优于同等数量的独立采样
- 适合需要高效贝叶斯推断的高维物理模拟场景
贝叶斯反问题中的积分计算(如后验期望、尾概率)通常依赖蒙特卡洛平均,误差随样本数平方根衰减,需大量采样,代价高昂。均值偏移交互粒子方法通过确定性求积节点减少样本需求,但每个观测需优化求解,仍耗时。本文提出“摊销均值偏移交互粒子”,通过一个学习映射,在单次前向传播中从观测和少量后验样本生成加权节点。训练仅需联合参数-观测样本与一个可采样的后验分布(如条件归一化流或经验后验),无需计算密度或得分。训练后模型泛化性强,可在任意节点预算下适应新观测与积分函数。其优势在于重加权(理论不劣于均匀权重)与位置迁移(实证进一步降低误差)。在闭合形式、采样、学习及基于物理的后验(最多含千系数的地下水场)上,始终优于相同数量的独立采样,且经后验白化与维度感知核处理,突破高维瓶颈。该方法实现了对蒙特卡洛的帕累托改进,而非替代更多采样。
原文摘要 · Abstract (English)
Bayesian inference for inverse problems is run to evaluate integrals -- posterior expectations, tail probabilities, and risks -- across a stream of observations. The standard estimate averages the integrand over posterior samples, a Monte-Carlo average whose error decays only as the square root of the sample size, so accuracy demands many samples -- prohibitive when each one calls a partial-differential-equation forward model. Mean-shift interacting particles need far fewer: they return a small set of signed-weight nodes -- a deterministic quadrature whose weighted averages estimate those integrals. Finding the nodes, however, is a per-observation optimization that, in its most accurate form, reads the posterior score at every step -- returning the cost it meant to save. We introduce amortized mean-shift interacting particles, a learned map that emits the weighted nodes from an observation and a few posterior samples in a single forward pass. Training asks only for joint parameter-observation samples and a posterior to draw from -- a conditional normalizing flow, an empirical conditional, or any reference the user can sample -- and the map learns to integrate that posterior from samples alone, evaluating neither its density nor its score. Once trained, it generalizes to unseen observations and integrands at any node budget and improves on independent samples in two ways: by reweighting them, provably no worse than the equal weights of Monte-Carlo; and by moving them, which empirically lowers it further. Across closed-form, sampled, learned, and physics-based posteriors -- up to a thousand-coefficient groundwater field -- it integrates more accurately than the same number of samples at every budget, and a posterior-whitened, dimension-aware kernel removes the high-dimensional wall. The result is a Pareto improvement on Monte-Carlo integration, not a competitor to drawing more samples.
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