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arXiv 1909.04650math.ACmath.CO
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S_n-不变单项理想的正则性

Regularity of S_n-invariant monomial ideals

Claudiu Raicu

摘要:

对n元多项式环S,通过置换变量,考虑S上对称群Sn的自然作用.对于S中的Sn-不变单项式理想I且j >= 0,我们给出了计算模Ext^j(S/I,S)的显式公式,并用它来描述I的投射维数和正则性.本文对具有线性自由分解的Sn-不变单项理想进行了分类,并刻画了Cohen-Macaulay型的Sn-不变单项理想。然后,我们考虑两个设置来分析正则性的渐近行为:一个是我们看固定理想I的幂,另一个是我们改变周围多项式环的维数,并检查由I诱导的不变单项理想。在第一种情况下,我们通过求解一个整数线性最优化问题,确定了由单个单式的S_n-轨道生成的理想I的渐近正则性。在第二种情况下,我们描述的行为规律性的任何我,恢复最近的结果Murai。

英文摘要:

For a polynomial ring S in n variables, we consider the natural action of the symmetric group S_n on S by permuting the variables. For an S_n-invariant monomial ideal I in S and j >= 0, we give an explicit recipe for computing the modules Ext^j(S/I,S), and use this to describe the projective dimension and regularity of I. We classify the S_n-invariant monomial ideals that have a linear free resolution, and also characterize those which are Cohen-Macaulay. We then consider two settings for analyzing the asymptotic behavior of regularity: one where we look at powers of a fixed ideal I, and another where we vary the dimension of the ambient polynomial ring and examine the invariant monomial ideals induced by I. In the first case we determine the asymptotic regularity for those ideals I that are generated by the S_n-orbit of a single monomial by solving an integer linear optimization problem. In the second case we describe the behavior of regularity for any I, recovering a recent result of Murai.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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