论文标题

部分可观测时空混沌系统的无模型预测

Closing the Gap Between Directed Hopsets and Shortcut Sets

论文作者

Bernstein, Aaron, Wein, Nicole

论文摘要

储层计算是预测湍流的有力工具,其简单的架构具有处理大型系统的计算效率。然而,其实现通常需要完整的状态向量测量和系统非线性知识。我们使用非线性投影函数将系统测量扩展到高维空间,然后将其输入到储层中以获得预测。我们展示了这种储层计算网络在时空混沌系统上的应用,该系统模拟了湍流的若干特征。我们表明,使用径向基函数作为非线性投影器,即使只有部分观测并且不知道控制方程,也能稳健地捕捉复杂的系统非线性。最后,我们表明,当测量稀疏、不完整且带有噪声,甚至控制方程变得不准确时,我们的网络仍然可以产生相当准确的预测,从而为实际湍流系统的无模型预测铺平了道路。

For an n-vertex directed graph $G = (V,E)$, a $β$-\emph{shortcut set} $H$ is a set of additional edges $H \subseteq V \times V$ such that $G \cup H$ has the same transitive closure as $G$, and for every pair $u,v \in V$, there is a $uv$-path in $G \cup H$ with at most $β$ edges. A natural generalization of shortcut sets to distances is a $(β,ε)$-\emph{hopset} $H \subseteq V \times V$, where the requirement is that $H$ and $G \cup H$ have the same shortest-path distances, and for every $u,v \in V$, there is a $(1+ε)$-approximate shortest path in $G \cup H$ with at most $β$ edges. There is a large literature on the tradeoff between the size of a shortcut set / hopset and the value of $β$. We highlight the most natural point on this tradeoff: what is the minimum value of $β$, such that for any graph $G$, there exists a $β$-shortcut set (or a $(β,ε)$-hopset) with $O(n)$ edges? Not only is this a natural structural question in its own right, but shortcuts sets / hopsets form the core of many distributed, parallel, and dynamic algorithms for reachability / shortest paths. Until very recently the best known upper bound was a folklore construction showing $β= O(n^{1/2})$, but in a breakthrough result Kogan and Parter [SODA 2022] improve this to $β= \tilde{O}(n^{1/3})$ for shortcut sets and $\tilde{O}(n^{2/5})$ for hopsets. Our result is to close the gap between shortcut sets and hopsets. That is, we show that for any graph $G$ and any fixed $ε$ there is a $(\tilde{O}(n^{1/3}),ε)$ hopset with $O(n)$ edges. More generally, we achieve a smooth tradeoff between hopset size and $β$ which exactly matches the tradeoff of Kogan and Parter for shortcut sets (up to polylog factors). Using a very recent black-box reduction of Kogan and Parter, our new hopset implies improved bounds for approximate distance preservers.

扫码加入交流群

加入微信交流群

微信交流群二维码

扫码加入学术交流群,获取更多资源