论文标题

通过ParallelLévyWalks搜索$ \ Mathbb {Z}^2 $

Search via Parallel Lévy Walks on $\mathbb{Z}^2$

论文作者

Clementi, Andrea, d'Amore, Francesco, Giakkoupis, George, Natale, Emanuele

论文摘要

以莱维觅食假设的启发 - 各种动物物种都适应了lévy步行以优化其搜索效率的前提 - 我们研究了在无限的二维网格上莱维步行的平行打击时间。我们认为$ k $独立离散时间lévywalks具有相同的指数$α\ in(1,\ infty)$,从同一节点开始,并分析步骤数量,直到第一次步行以距离$ \ ell $访问给定目标。 We show that for any choice of $k$ and $\ell$ from a large range, there is a unique optimal exponent $α_{k,\ell} \in (2,3)$, for which the hitting time is $\tilde O(\ell^2/k)$ w.h.p., while modifying the exponent by an $ε$ term increases the hitting time by a polynomial factor, or the walks fail to hit目标几乎肯定。基于此,我们提出了一个令人惊讶的简单和有效的并行搜索策略,对于$ k $和$ \ ell $的设置未知:每个LévyWalk的指数只是从间隔$(2,3)$中随机地独立和均匀地选择。该策略在所有可能的算法(甚至是知道$ k $的集中式算法)中实现了最佳的搜索时间(Modulo Polygarithmic因素)。我们的结果应与以前的一系列工作形成对比,表明指数$α= 2 $对于各种搜索问题是最佳的。在我们的$ k $并行步行中,我们表明最佳指数取决于$ k $和$ \ ell $,并且将指数的选择随机化,同时适用于所有$ k $和$ \ ell $。

Motivated by the Lévy foraging hypothesis -- the premise that various animal species have adapted to follow Lévy walks to optimize their search efficiency -- we study the parallel hitting time of Lévy walks on the infinite two-dimensional grid. We consider $k$ independent discrete-time Lévy walks, with the same exponent $α\in(1,\infty)$, that start from the same node, and analyze the number of steps until the first walk visits a given target at distance $\ell$. We show that for any choice of $k$ and $\ell$ from a large range, there is a unique optimal exponent $α_{k,\ell} \in (2,3)$, for which the hitting time is $\tilde O(\ell^2/k)$ w.h.p., while modifying the exponent by an $ε$ term increases the hitting time by a polynomial factor, or the walks fail to hit the target almost surely. Based on that, we propose a surprisingly simple and effective parallel search strategy, for the setting where $k$ and $\ell$ are unknown: the exponent of each Lévy walk is just chosen independently and uniformly at random from the interval $(2,3)$. This strategy achieves optimal search time (modulo polylogarithmic factors) among all possible algorithms (even centralized ones that know $k$). Our results should be contrasted with a line of previous work showing that the exponent $α= 2$ is optimal for various search problems. In our setting of $k$ parallel walks, we show that the optimal exponent depends on $k$ and $\ell$, and that randomizing the choice of the exponents works simultaneously for all $k$ and $\ell$.

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