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An excluded minor characterization of Seymour graphs. (English) Zbl 1298.05295
Günlük, Oktay (ed.) et al., Integer programming and combinatoral optimization. 15th international conference, IPCO 2011, New York, NY, USA, June 15–17, 2011. Proceedings. Berlin: Springer (ISBN 978-3-642-20806-5/pbk). Lecture Notes in Computer Science 6655, 1-13 (2011).
Summary: A graph $$G$$ is said to be a Seymour graph if for any edge set $$F$$ there exist $$|F|$$ pairwise disjoint cuts each containing exactly one element of $$F$$, provided for every circuit $$C$$ of $$G$$ the necessary condition $$|C \cap F| \leq |C \setminus F|$$ is satisfied. Seymour graphs behave well with respect to some integer programs including multiflow problems, or more generally odd cut packings, and are closely related to matching theory.
A first coNP characterization of Seymour graphs has been shown by A. A. Ageev et al. [J. Graph Theory 24, No. 4, 357–364 (1997; Zbl 0869.05051)], the recognition problem has been solved in a particular case by A. M. H. Gerards [J. Comb. Theory, Ser. B 55, No. 1, 73–82 (1992; Zbl 0810.05056)], and the related cut packing problem has been solved in the corresponding special cases. In this article we show a new, minor-producing operation that keeps this property, and prove excluded minor characterizations of Seymour graphs: the operation is the contraction of full stars, or of odd circuits. This sharpens the previous results, providing at the same time a simpler and self-contained algorithmic proof of the existing characterizations as well, still using methods of matching theory and its generalizations.
For the entire collection see [Zbl 1216.90002].
##### MSC:
 05C83 Graph minors 05C75 Structural characterization of families of graphs
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##### References:
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