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arXiv 0810.4120math.COmath.AC
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组合拓扑下边理想的代数性质

Algebraic properties of edge ideals via combinatorial topology

Anton Dochtermann, Alexander Engstrom

摘要:

我们应用组合拓扑学中的一些基本概念来建立图和更一般的Stanley Reisner环的边理想的各种代数性质。通过这种方式,我们提供了新的短证明的一些定理,从文献中关于线性,贝蒂数,(顺序)科恩-麦考利性能的边缘理想弦,补充弦,费勒斯图,以及树木和森林。我们的方法统一(并在许多情况下加强)这些结果,并提供组合/枚举的解释某些代数性质。我们应用我们的设置,以获得新的结果,在局部变化的背景下,一个图形(添加胡须和耳朵),以及有界顶点度的边缘理想的代数性质。这些方法还导致递归关系的某些生成函数的贝蒂数,我们使用建立新的公式的投射维数的边缘理想。我们只使用众所周知的工具,从组合拓扑学沿线的独立复杂的图,(不一定是纯)顶点可分解性,壳,等。

英文摘要:

We apply some basic notions from combinatorial topology to establish various algebraic properties of edge ideals of graphs and more general Stanley-Reisner rings. In this way we provide new short proofs of some theorems from the literature regarding linearity, Betti numbers, and (sequentially) Cohen-Macaulay properties of edges ideals associated to chordal, complements of chordal, and Ferrers graphs, as well as trees and forests. Our approach unifies (and in many cases strengthens) these results and also provides combinatorial/enumerative interpretations of certain algebraic properties. We apply our setup to obtain new results regarding algebraic properties of edge ideals in the context of local changes to a graph (adding whiskers and ears) as well as bounded vertex degree. These methods also lead to recursive relations among certain generating functions of Betti numbers which we use to establish new formulas for the projective dimension of edge ideals. We use only well-known tools from combinatorial topology along the lines of independence complexes of graphs, (not necessarily pure) vertex decomposability, shellability, etc.

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