We show that the integrality gap of the standard SDP for \vc~on instances of $n$ vertices remains $2-o(1)$ even after the addition of \emph{all} hypermetric inequalities. Our lower bound requires new insights into the structure of SDP solutions behaving like $\ell_1$ metric spaces when one point is removed. We also show that the addition of all $\ell_1$ inequalities eliminates any solutions that are not convex combination of integral solutions. Consequently, we provide the strongest possible separation between hypermetrics and $\ell_1$ inequalities with respect to the tightening of the standard SDP for \vc.
@InProceedings{georgiou_et_al:LIPIcs.FSTTCS.2009.2319, author = {Georgiou, Konstantinos and Magen, Avner and Tourlakis, Iannis}, title = {{On the Tightening of the Standard SDP for Vertex Cover with \$ell\underline1\$ Inequalities}}, booktitle = {IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science}, pages = {203--214}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-13-2}, ISSN = {1868-8969}, year = {2009}, volume = {4}, editor = {Kannan, Ravi and Narayan Kumar, K.}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2009.2319}, URN = {urn:nbn:de:0030-drops-23195}, doi = {10.4230/LIPIcs.FSTTCS.2009.2319}, annote = {Keywords: Semidefinite Programming, Vertex Cover, Integrality Gap, Hypermetric Inequalities} }
Feedback for Dagstuhl Publishing