在{ \em distributed all-pairs shortest paths}问题(APSP)中,加权无向分布式网络(CONGEST模型)中的每个节点都需要使用最少的通信轮数(通常称为{ \em时间复杂度})来知道与其他节点的距离。该问题允许$(1+o(1))$ -近似$\tildeΘ(n)$ -时间算法和接近紧的$\tilde Ω(n)$下界[Nanongkai,STOC'14; Lenzen和Patt-Shamir PODC'15] \footnote{$\tilde Θ$, $\tilde O$ and $\tilde Ω$ hide polylogarithmic factors. Note that the lower bounds also hold even in the unweighted case and in the weighted case with polynomial approximation ratios~\cite{LenzenP_podc13,HolzerW12,PelegRT12,Nanongkai-STOC14}.}。对于确切的情况,Elkin [STOC'17]提出了一个$O(n^{5/3} \log^{2/3} n)$时间界限,后来改进为$\tilde O(n^{5/4})$ [Huang,Nanongkai,Saranurak FOCS'17]。研究表明,任何超线性下限(在$n$中)都需要一种新的技术[Censor-Hillel、Khoury、Paz、DISC'17],但除此之外,是否存在用于精确情况的$\tilde O(n)$时间算法(该算法将匹配最佳可能的近似算法)仍然是一个广泛的开放问题。本文解决了这个问题积极:我们提出了一个随机(拉斯维加斯)的$\tilde O(n)$时间算法,匹配的下限多对数因子。与前面的$\tilde O(n^{5/4})$界一样,我们的结果适用于边权重为零(甚至为负)的有向图。除了改进的运行时间之外,我们的算法在比先前的$\tilde O(n^{5/4})$界限所要求的更一般的设置中工作;在我们的设置中(i)通信仅沿着边缘方向(与双向相反),以及(ii)边缘权重是任意的(与{1,2,. poly(n)})。...
英文摘要:
In the {\em distributed all-pairs shortest paths} problem (APSP), every node in the weighted undirected distributed network (the CONGEST model) needs to know the distance from every other node using least number of communication rounds (typically called {\em time complexity}). The problem admits $(1+o(1))$-approximation $\tildeΘ(n)$-time algorithm and a nearly-tight $\tilde Ω(n)$ lower bound [Nanongkai, STOC'14; Lenzen and Patt-Shamir PODC'15]\footnote{$\tilde Θ$, $\tilde O$ and $\tilde Ω$ hide polylogarithmic factors. Note that the lower bounds also hold even in the unweighted case and in the weighted case with polynomial approximation ratios~\cite{LenzenP_podc13,HolzerW12,PelegRT12,Nanongkai-STOC14}.}. For the exact case, Elkin [STOC'17] presented an $O(n^{5/3} \log^{2/3} n)$ time bound, which was later improved to $\tilde O(n^{5/4})$ [Huang, Nanongkai, Saranurak FOCS'17]. It was shown that any super-linear lower bound (in $n$) requires a new technique [Censor-Hillel, Khoury, Paz, DISC'17], but otherwise it remained widely open whether there exists a $\tilde O(n)$-time algorithm for the exact case, which would match the best possible approximation algorithm.
This paper resolves this question positively: we present a randomized (Las Vegas) $\tilde O(n)$-time algorithm, matching the lower bound up to polylogarithmic factors. Like the previous $\tilde O(n^{5/4})$ bound, our result works for directed graphs with zero (and even negative) edge weights. In addition to the improved running time, our algorithm works in a more general setting than that required by the previous $\tilde O(n^{5/4})$ bound; in our setting (i) the communication is only along edge directions (as opposed to bidirectional), and (ii) edge weights are arbitrary (as opposed to integers in {1, 2, ... poly(n)}). ...
A Deterministic Distributed Algorithm for Weighted All Pairs Shortest Paths Through Pipelining
本文提出了一种新的流水线方法来计算分布式环境下CONGEST模型中具有非负整数边权值(包括零权值)的有向图中的所有对最短路径(APSP)。我们的确定性分布式算法计算最多$2 n \sqrtΔ + 2n$轮中所有顶点对的最多$Δ$距离的最短路径,更一般地,它计算$2\sqrt{nkh} + n + k$轮中k个源的h跳最短路径。该算法简单,具有一些新颖的特性和非平凡的分析,只利用图中的有向边进行通信。该算法可以作为一个基础内的渐近更快的算法,匹配或改善当前的最佳确定性界的$\tilde{O}(n^{3/2})$轮为这个问题时,边的权重是$O(n)$或最短路径距离是$\tilde{O}(n^{3/2})$。
Distributed Exact Weighted All-Pairs Shortest Paths in $\tilde O(n^{5/4})$ Rounds
我们研究计算{ \em所有对最短路径}(APSP)的分布式网络(CONGEST模型)。目标是让(加权)网络中的每个节点都知道使用通信的每个其他节点的距离。该问题允许$(1+o(1))$ -近似$\tilde O(n)$ -时间算法~ \cite{LenzenP-podc15,Nanongkai-STOC14},它与$\tilde Ω(n)$ -时间下界~ \cite{Nanongkai-STOC14,LenzenP_stoc13,FrischknechtHW12} \footnote{$\tilde Θ$, $\tilde O$ and $\tilde Ω$ hide polylogarithmic factors. Note that the lower bounds also hold even in the unweighted case and in the weighted case with polynomial approximation ratios.}相匹配.没有$ω(n)$下限或$o(m)$上限已知的精确计算。在本文中,我们提出了一个$\tilde O(n^{5/4})$ -时间随机(拉斯维加斯)算法精确加权APSP,这提供了第一个改进的天真$O(m)$ -时间算法时,网络不是那么稀疏。我们的结果也适用于边权重是{PDMATHAMM不对称}(a.k.a.通信是双…