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arXiv 1409.2233math.CO
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拟阵的多个2层多面体

Many 2-level polytopes from matroids

Francesco Grande, Juanjo Rué

摘要:

2-水平拟阵族,即基多面体为2-水平拟阵,是近年来研究的一类拟阵,并利用组合性质对其进行了刻画。2-水平拟阵推广了串并行图,这已经成功地从枚举的角度进行了分析。我们揭示了2级拟阵的一些结构性质,并利用它们进行枚举。此外,计数结果还表明,组合非等价的(n-1)维2-层多面体的个数由$c \cdot n^{-5/2} \cdot ρ^{-n}$从下有界,其中$c\approx 0.03791727 $和$ρ^{-1} \approx 4.88052854$ .

英文摘要:

The family of 2-level matroids, that is, matroids whose base polytope is 2-level, has been recently studied and characterized by means of combinatorial properties. 2-level matroids generalize series-parallel graphs, which have been already successfully analyzed from the enumerative perspective. We bring to light some structural properties of 2-level matroids and exploit them for enumerative purposes. Moreover, the counting results are used to show that the number of combinatorially non-equivalent (n-1)-dimensional 2-level polytopes is bounded from below by $c \cdot n^{-5/2} \cdot ρ^{-n}$, where $c\approx 0.03791727 $ and $ρ^{-1} \approx 4.88052854$.

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