Abstract
We study connectivity relations among points, where the precise location of each input point lies in a region of uncertainty. We distinguish two fundamental scenarios under which uncertainty arises. In the favorable Best-Case Uncertainty, each input point can be chosen from a given set to yield the best possible objective value. In the unfavorable Worst-Case Uncertainty, the input set has worst possible objective value among all possible point locations, which are uncertain due, for example, to imprecise data. We consider these notions of uncertainty for the bottleneck spanning tree problem, giving rise to the following Best-Case Connectivity with Uncertainty problem: given a family of geometric regions, choose one point per region, such that the longest edge length of an associated geometric spanning tree is minimized. We show that this problem is NP-hard even for very simple scenarios in which the regions are line segments or squares. On the other hand, we give an exact solution for the case in which there are \(n+k\) regions, where k of the regions are line segments and n of the regions are fixed points. We then give approximation algorithms for cases where the regions are either all line segments or all unit discs. We also provide approximation methods for the corresponding Worst-Case Connectivity with Uncertainty problem: Given a set of uncertainty regions, find the minimal distance r such that for any choice of points, one per region, there is a spanning tree among the points with edge length at most r.
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Notes
We remark that for lists \({\mathcal {L}}\) and \({\mathcal {L}}'\) for two different spanning trees with two different sets of points on the segments, it is possible that \({\mathcal {L}} = {\mathcal {L}}'\), so that optimum solutions that permit minimum solutions trees are in general not unique.
The descriptions are evident from Fig. 13, except perhaps the difference between c.1b and c.2. These are distinguished by the fact that \(f_{p_r}\) lies outside the semi-disc for c.1b, and inside the semi-disc for c.2, where p is \(p_\ell \) or \(p_r\), as appropriate.
Count the number of ordered I-subsets of k segments by \(\sum _{i=1}^k k!/(k-i)!\), and multiply these by the \((n^2+n+1)\) to count ways that \(E_1\) and \(E_m\) might be points.
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Acknowledgments
We are grateful for two Bellairs workshops supporting this research: the 8th and 9th McGill-INRIA-UVictoria Workshop on Computational Geometry in 2009 and 2010. We also thank the anonymous reviewers for many helpful and constructive comments that greatly helped to improve the overall presentation. We also acknowledge financial support by a number of different agencies, as follows. Erin Chambers was supported by NSF Grants CCF 1054779 and IIS 1319573. Alejandro Erickson was supported by the EPSRC, Grant No. EP/K015680/1. Ulrike Stege was supported by an NSERC Discovery Grant. Svetlana Stolpner was supported by the Fonds québécois de la recherche sur la nature et les technologies (FQRNT). Venkatesh Srinivasan was supported by an NSERC Discovery Grant. Sue Whitesides was supported by an NSERC Discovery Grant.
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A preliminary extended abstract summarizing parts of this paper appears in [5].
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Chambers, E., Erickson, A., Fekete, S.P. et al. Connectivity Graphs of Uncertainty Regions. Algorithmica 78, 990–1019 (2017). https://doi.org/10.1007/s00453-016-0191-2
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DOI: https://doi.org/10.1007/s00453-016-0191-2