Navigating in Trees with Permanently Noisy Advice - Archive ouverte HAL
Article Dans Une Revue ACM Transactions on Algorithms Année : 2021

Navigating in Trees with Permanently Noisy Advice

Résumé

We consider a search problem on trees in which an agent starts at the root of a tree and aims to locate an adversarially placed treasure, by moving along the edges, while relying on local, partial information. Specifically, each node in the tree holds a pointer to one of its neighbors, termed advice. A node is faulty with probability $q$. The advice at a non-faulty node points to the neighbor that is closer to the treasure, and the advice at a faulty node points to a uniformly random neighbor. Crucially, the advice is permanent, in the sense that querying the same node again would yield the same answer. Let $\Delta$ denote the maximum degree. For the expected number of moves (edge traversals), we show that a phase transition occurs when the {\em noise parameter} $q$ is roughly $1/\sqrt{\Delta}$. Below the threshold, there exists an algorithm with expected number of moves $\bigO(D\sqrt{\Delta})$, where $D$ is the depth of the treasure, whereas above the threshold, every search algorithm has expected number of moves which is both exponential in $D$ and polynomial in the number of nodes~$n$. In contrast, if we require to find the treasure with probability at least $1-\delta$, then for every fixed $\epsilon > 0$, if $q<1/\Delta^{\epsilon}$ then there exists a search strategy that with probability $1-\delta$ finds the treasure using $(\delta^{-1}D)^{O(\frac 1 \epsilon)}$ moves. Moreover, we show that $(\delta^{-1}D)^{\Omega(\frac 1 \epsilon)}$ moves are necessary.
Fichier principal
Vignette du fichier
walk_journal_2020 (2).pdf (469.33 Ko) Télécharger le fichier
Origine Fichiers produits par l'(les) auteur(s)

Dates et versions

hal-01958133 , version 1 (17-12-2018)
hal-01958133 , version 2 (20-07-2021)

Identifiants

Citer

Lucas Boczkowski, Uriel Feige, Amos Korman, Yoav Rodeh. Navigating in Trees with Permanently Noisy Advice. ACM Transactions on Algorithms, 2021, Leibniz International Proceedings in Informatics (LIPIcs), pp.1-32. ⟨10.1145/3448305⟩. ⟨hal-01958133v2⟩
70 Consultations
116 Téléchargements

Altmetric

Partager

More