提出神经ODE驱动的稀疏网格积分法,可高效计算高维期望值。
Consistency of Learned Sparse Grid Quadrature Rules using NeuralODEs
- 用神经ODE学习传输映射,结合克伦肖-柯蒂斯稀疏网格求积
- 在任意目标下实现m^{-k/d}(log m)^{(d-1)(k/d+1)}收敛率
- 适用于高维积分,尤其对乘积型目标有最优收敛性能
我们证明了一种新方法的一致性:通过将学习到的传输映射与可处理的乘积源上的克伦肖-柯蒂斯稀疏网格求积组合,来评估期望值。分析基于一个结构性事实:若一个具有混合C^k正则性的函数(具有快速收敛率m^{-k}(log m)^{(d-1)(k+1)})与一个C^1微分同胚复合,则仅当该同胚为坐标置换意义下的对角形式时,复合函数仍保持C^k_{ ext{mix}}正则性。因此,快速收敛率仅适用于乘积型目标。分析分为两种情形:在一般情形下,通过最大似然训练带有ReLU^{k+1}激活的神经ODE,学习时间一阶流,其位于各向同性空间C^k,获得收敛率m^{-k/d}(log m)^{(d-1)(k/d+1)};提升密度光滑度k和匹配激活阶数k+1可缓解维度灾难,但优化难度增加。在对角情形(乘积目标)下,采用点态经验分位数传输估计科诺特-罗森布拉特映射,无需学习即可恢复全混合正则性速率。两种情形下,所得LtI估计器均为PAC一致,在样本量n和求积预算m趋于无穷时,以高概率逼近真实值至任意精度。
原文摘要 · Abstract (English)
We prove consistency of a recently proposed scheme that evaluates expected values by composing a learned transport map with Clenshaw--Curtis sparse-grid quadrature on a tractable product source. Our analysis hinges on the structural fact that composition of a $C^k_{\mathrm{mix}}$-regular function -- which carries the fast quadrature rate $m^{-k}(\log m)^{(d-1)(k+1)}$ -- with a $C^1$-diffeomorphism can only be guaranteed to be $C^k_{\mathrm{mix}}$ itself, if the diffeomorphism is diagonal up to a permutation of coordinates. The fast rate is therefore available exclusively for product targets, and the analysis splits into two regimes. In the general regime of arbitrary targets, we learn the transport as the time-one flow of a $\mathrm{ReLU}^{k+1}$-neural ODE trained by maximum likelihood. The resulting flow lies in the isotropic space $C^k$ and yields the rate $m^{-k/d}(\log m)^{(d-1)(k/d+1)}$, with raising the density smoothness $k$ and the matched activation order $k+1$ mitigating the curse of dimensionality at the cost of harder optimization. In the diagonal regime of product targets, the Knothe--Rosenblatt map is itself diagonal and we estimate it pointwise via empirical quantile transport, a lightweight alternative that recovers the full mixed-regularity rate. In both regimes, the resulting LtI estimator is PAC (probably approximately correct) consistent. With high probability the numerical integral approximates the true value to arbitrary accuracy as both the sample size $n$ and the quadrature budget $m$ tend to infinity.
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