,
Marco Ricci
,
Jonathan Rollin
,
André Schulz
Creative Commons Attribution 4.0 International license
A graph is 2-degenerate if every subgraph contains a vertex of degree at most 2. We show that every 2-degenerate graph can be drawn with straight lines such that the drawing decomposes into 4 plane forests. Therefore, the geometric arboricity, and hence the geometric thickness, of 2-degenerate graphs is at most 4. On the other hand, we show that there are 2-degenerate graphs that do not admit any straight-line drawing with a decomposition of the edge set into 2 plane graphs. That is, there are 2-degenerate graphs with geometric thickness, and hence geometric arboricity, at least 3. This answers two questions posed by Eppstein [Separating thickness from geometric thickness. In Towards a Theory of Geometric Graphs, vol. 342 of Contemp. Math., AMS, 2004].
@InProceedings{jain_et_al:LIPIcs.SoCG.2023.44,
author = {Jain, Rahul and Ricci, Marco and Rollin, Jonathan and Schulz, Andr\'{e}},
title = {{On the Geometric Thickness of 2-Degenerate Graphs}},
booktitle = {39th International Symposium on Computational Geometry (SoCG 2023)},
pages = {44:1--44:15},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-273-0},
ISSN = {1868-8969},
year = {2023},
volume = {258},
editor = {Chambers, Erin W. and Gudmundsson, Joachim},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2023.44},
URN = {urn:nbn:de:0030-drops-178946},
doi = {10.4230/LIPIcs.SoCG.2023.44},
annote = {Keywords: Degeneracy, geometric thickness, geometric arboricity}
}