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Following groundbreaking work by Haussler and Welzl (1987), the use of small epsilon-nets has become a standard technique for solving algorithmic and extremal problems in geometry and learning theory. Two significant recent developments are: (i) an upper bound on the size of the smallest epsilon-nets for set systems, as a function of their so-called shallow-cell complexity (Chan, Grant, Konemann, and Sharpe); and (ii) the construction of a set system whose members can be obtained by intersecting a point set in R^4 by a family of half-spaces such that the size of any epsilon-net for them is at least (1/(9*epsilon)) log (1/epsilon) (Pach and Tardos). The present paper completes both of these avenues of research. We (i) give a lower bound, matching the result of Chan et al., and (ii) generalize the construction of Pach and Tardos to half-spaces in R^d, for any d >= 4, to show that the general upper bound of Haussler and Welzl for the size of the smallest epsilon-nets is tight.
@InProceedings{kupavskii_et_al:LIPIcs.SoCG.2016.54,
author = {Kupavskii, Andrey and Mustafa, Nabil and Pach, J\'{a}nos},
title = {{New Lower Bounds for epsilon-Nets}},
booktitle = {32nd International Symposium on Computational Geometry (SoCG 2016)},
pages = {54:1--54:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-009-5},
ISSN = {1868-8969},
year = {2016},
volume = {51},
editor = {Fekete, S\'{a}ndor and Lubiw, Anna},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2016.54},
URN = {urn:nbn:de:0030-drops-59467},
doi = {10.4230/LIPIcs.SoCG.2016.54},
annote = {Keywords: epsilon-nets; lower bounds; geometric set systems; shallow-cell complexity; half-spaces}
}