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We consider a network design problem called the generalized terminal backup problem. Whereas earlier work investigated the edge-connectivity constraints only, we consider both edge- and node-connectivity constraints for this problem. A major contribution of this paper is the development of a strongly polynomial-time 4/3-approximation algorithm for the problem. Specifically, we show that a linear programming relaxation of the problem is half-integral, and that the half-integral optimal solution can be rounded to a 4/3-approximate solution. We also prove that the linear programming relaxation of the problem with the edge-connectivity constraints is equivalent to minimizing the cost of half-integral multiflows that satisfy flow demands given from terminals. This observation implies a strongly polynomial-time algorithm for computing a minimum cost half-integral multiflow under flow demand constraints.
@InProceedings{fukunaga:LIPIcs.STACS.2015.316,
author = {Fukunaga, Takuro},
title = {{Approximating the Generalized Terminal Backup Problem via Half-integral Multiflow Relaxation}},
booktitle = {32nd International Symposium on Theoretical Aspects of Computer Science (STACS 2015)},
pages = {316--328},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-939897-78-1},
ISSN = {1868-8969},
year = {2015},
volume = {30},
editor = {Mayr, Ernst W. and Ollinger, Nicolas},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2015.316},
URN = {urn:nbn:de:0030-drops-49236},
doi = {10.4230/LIPIcs.STACS.2015.316},
annote = {Keywords: survivable network design, multiflow, LP rounding}
}