2026-08-10T19:43:05Z https://drops.dagstuhl.de/oai

oai:drops-oai.dagstuhl.de:16957 2024-03-06T10:58:49Z ddc:004 open_access

Sparse Temporal Spanners with Low Stretch Bilò, Davide D'Angelo, Gianlorenzo Gualà, Luciano Leucci, Stefano Rossi, Mirko temporal spanners temporal graphs graph sparsification approximate distances A temporal graph is an undirected graph G = (V,E) along with a function λ : E → ℕ^+ that assigns a time-label to each edge in E. A path in G such that the traversed time-labels are non-decreasing is called a temporal path. Accordingly, the distance from u to v is the minimum length (i.e., the number of edges) of a temporal path from u to v. A temporal α-spanner of G is a (temporal) subgraph H that preserves the distances between any pair of vertices in V, up to a multiplicative stretch factor of α. The size of H is measured as the number of its edges. In this work, we study the size-stretch trade-offs of temporal spanners. In particular we show that temporal cliques always admit a temporal (2k-1)-spanner with Õ(kn^{1+1/k}) edges, where k > 1 is an integer parameter of choice. Choosing k = ⌊log n⌋, we obtain a temporal O(log n)-spanner with Õ(n) edges that has almost the same size (up to logarithmic factors) as the temporal spanner given in [Casteigts et al., JCSS 2021] which only preserves temporal connectivity. We then turn our attention to general temporal graphs. Since Ω(n²) edges might be needed by any connectivity-preserving temporal subgraph [Axiotis et al., ICALP'16], we focus on approximating distances from a single source. We show that Õ(n/log(1+ε)) edges suffice to obtain a stretch of (1+ε), for any small ε > 0. This result is essentially tight in the following sense: there are temporal graphs G for which any temporal subgraph preserving exact distances from a single-source must use Ω(n²) edges. Interestingly enough, our analysis can be extended to the case of additive stretch for which we prove an upper bound of Õ(n² / β) on the size of any temporal β-additive spanner, which we show to be tight up to polylogarithmic factors. Finally, we investigate how the lifetime of G, i.e., the number of its distinct time-labels, affects the trade-off between the size and the stretch of a temporal spanner. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Davide Bilò and Gianlorenzo D'Angelo and Luciano Gualà and Stefano Leucci and Mirko Rossi 2022 Is Part Of LIPIcs, Volume 244, 30th Annual European Symposium on Algorithms (ESA 2022) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.ESA.2022.19 urn:nbn:de:0030-drops-169575 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2022.19 eng https://creativecommons.org/licenses/by/4.0/legalcode