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arXiv 1507.06111math.COcs.DM
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定向拟阵的复形

COMs: Complexes of Oriented Matroids

Hans-Juergen Bandelt, Victor Chepoi, Kolja Knauer

摘要:

在他1983年的开创性论文中,Jim Lawrence引入了不平衡集,并将它们作为定向拟阵的非对称对应物,两者都具有强消去的关键属性。此外,面的对称性在这两种结构中以及在所谓的仿射定向拟阵中保持。这两个基本性质(为余向量而制定)共同导致了“条件定向拟阵“(缩写为COM)的自然概念。这些新的结构可以用三个余圈公理来刻画,推广了定向拟阵的熟悉刻画。我们描述了一个二进制的组合方案,每个COM可以连续竖立作为一定的复杂的定向拟阵,在本质上相同的方式作为一个不平衡的集可以粘在一起,从它的最大超立方体的面孔。一个可实现的COM表示的超平面安排限制在一个开放的凸集。其中有有序集的线性扩展形成的例子,推广对应于置换面体的定向拟阵。放松可实现性的局部可实现性,我们捕捉到更广泛的组合对象类:我们表明,非正弯曲Coxeter zonotopal复合物引起局部可实现的COM。

英文摘要:

In his seminal 1983 paper, Jim Lawrence introduced lopsided sets and featured them as asymmetric counterparts of oriented matroids, both sharing the key property of strong elimination. Moreover, symmetry of faces holds in both structures as well as in the so-called affine oriented matroids. These two fundamental properties (formulated for covectors) together lead to the natural notion of "conditional oriented matroid" (abbreviated COM). These novel structures can be characterized in terms of three cocircuits axioms, generalizing the familiar characterization for oriented matroids. We describe a binary composition scheme by which every COM can successively be erected as a certain complex of oriented matroids, in essentially the same way as a lopsided set can be glued together from its maximal hypercube faces. A realizable COM is represented by a hyperplane arrangement restricted to an open convex set. Among these are the examples formed by linear extensions of ordered sets, generalizing the oriented matroids corresponding to the permutohedra. Relaxing realizability to local realizability, we capture a wider class of combinatorial objects: we show that non-positively curved Coxeter zonotopal complexes give rise to locally realizable COMs.

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