Spanner constructions focus on the initial design of the network. However, networks tend to improve over time. In this paper, we focus on the improvement step. Given a graph and a budget k, which k edges do we add to the graph to minimise its dilation? Gudmundsson and Wong [TALG'22] provided the first positive result for this problem, but their approximation factor is linear in k. Our main result is a (2 √[r]{2} k^{1/r},2r)-bicriteria approximation that runs in O(n³ log n) time, for all r ≥ 1. In other words, if t^* is the minimum dilation after adding any k edges to a graph, then our algorithm adds O(k^{1+1/r}) edges to the graph to obtain a dilation of 2rt^*. Moreover, our analysis of the algorithm is tight under the Erdős girth conjecture.
@InProceedings{buchin_et_al:LIPIcs.ESA.2024.36, author = {Buchin, Kevin and Buchin, Maike and Gudmundsson, Joachim and Wong, Sampson}, title = {{Bicriteria Approximation for Minimum Dilation Graph Augmentation}}, booktitle = {32nd Annual European Symposium on Algorithms (ESA 2024)}, pages = {36:1--36:15}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-338-6}, ISSN = {1868-8969}, year = {2024}, volume = {308}, editor = {Chan, Timothy and Fischer, Johannes and Iacono, John and Herman, Grzegorz}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2024.36}, URN = {urn:nbn:de:0030-drops-211079}, doi = {10.4230/LIPIcs.ESA.2024.36}, annote = {Keywords: Greedy spanner, Graph augmentation} }
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