It is a long standing open problem whether Yao-Yao graphs YY_{k} are all spanners [Li et al. 2002]. Bauer and Damian [Bauer and Damian, 2012] showed that all YY_{6k} for k >= 6 are spanners. Li and Zhan [Li and Zhan, 2016] generalized their result and proved that all even Yao-Yao graphs YY_{2k} are spanners (for k >= 42). However, their technique cannot be extended to odd Yao-Yao graphs, and whether they are spanners are still elusive. In this paper, we show that, surprisingly, for any integer k >= 1, there exist odd Yao-Yao graph YY_{2k+1} instances, which are not spanners.
@InProceedings{jin_et_al:LIPIcs.SoCG.2018.49, author = {Jin, Yifei and Li, Jian and Zhan, Wei}, title = {{Odd Yao-Yao Graphs are Not Spanners}}, booktitle = {34th International Symposium on Computational Geometry (SoCG 2018)}, pages = {49:1--49:15}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-066-8}, ISSN = {1868-8969}, year = {2018}, volume = {99}, editor = {Speckmann, Bettina and T\'{o}th, Csaba D.}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2018.49}, URN = {urn:nbn:de:0030-drops-87621}, doi = {10.4230/LIPIcs.SoCG.2018.49}, annote = {Keywords: Odd Yao-Yao Graph, Spanner, Counterexample} }
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