On Hilbert bases of cuts

نویسندگان

  • Luis A. Goddyn
  • Tony Huynh
  • Tanmay Deshpande
چکیده

A Hilbert basis is a set of vectors X ⊆ R such that the integer cone (semigroup) generated by X is the intersection of the lattice generated by X with the cone generated by X. Let H be the class of graphs whose set of cuts is a Hilbert basis in R (regarded as {0, 1}-characteristic vectors indexed by edges). We show that H is not closed under edge deletions, subdivisions, nor 2-sums. Furthermore, no graph having K6 \ e as a minor belongs to H . This corrects an error in [M. Laurent. Hilbert bases of cuts. Discrete Math., 150(1-3):257-279 (1996)]. For positive results, we give conditions under which the 2-sum of two graphs produces a member of H . Using these conditions we show that all K⊥ 5 -minor-free graphs are in H , where K⊥ 5 is the unique 3-connected graph obtained by uncontracting an edge of K5. We also establish a relationship between edge deletion and subdivision. Namely, if G′ is obtained from G ∈H by subdividing e two or more times, then G \ e ∈H if and only if G′ ∈H .

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عنوان ژورنال:
  • Discrete Mathematics

دوره 339  شماره 

صفحات  -

تاریخ انتشار 2016