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Universal lex ideal approximations of extended Hilbert functions and Hamilton numbers
Journal of Algebra ( IF 0.8 ) Pub Date : 2020-10-01 , DOI: 10.1016/j.jalgebra.2020.06.009
Tigran Ananyan , Melvin Hochster

Let $R^h$ denote the polynomial ring in variables $x_1,\,\ldots,\, x_h$ over a specified field $K$. We consider all of these rings simultaneously, and in each use lexicographic (lex) monomial order with $x_1 > \cdots > x_h$. Given a fixed homogeneous ideal $I$ in $R^h$, for each $d$ there is unique lex ideal generated in degree at most $d$ whose Hilbert function agrees with the Hilbert function of $I$ up to degree $d$. When we consider $IR^N$ for $N \geq h$, the set $\mathfrak{B}_d(I,N)$ of minimal generators for this lex ideal in degree at most $d$ may change, but $\mathfrak{B}_d(I,N)$ is constant for all $N \gg 0$. We let $\mathfrak{B}_d(I)$ denote the set of generators one obtains for all $N \gg 0$, and we let $b_d = b_d(I)$ be its cardinality. The sequences $b_1, \, \ldots, \, b_d, \, \ldots$ obtained in this way may grow very fast. Remarkably, even when $I = (x_1^2, x_2^2)$, one obtains a very interesting sequence, 0, 2, 3, 4, 6, 12, 924, 409620,$\,\ldots$. This sequence is the same as $H_{d-1} + 1$ for $d \geq 2$, where $H_d$ is the $d\,$th Hamilton number. The Hamilton numbers were studied by Hamilton and by Hammond and Sylvester because of their occurrence in a counting problem connected with the use of Tschirnhaus transformations in manipulating polynomial equations.

中文翻译:

扩展 Hilbert 函数和 Hamilton 数的通用 lex 理想近似

让 $R^h$ 表示变量 $x_1,\,\ldots,\, x_h$ 中指定字段 $K$ 上的多项式环。我们同时考虑所有这些环,并且在每个环中使用 $x_1 > \cdots > x_h$ 的字典序 (lex) 单项式顺序。给定 $R^h$ 中的一个固定齐次理想 $I$,对于每个 $d$,在至多 $d$ 的度数中生成唯一的 lex 理想,其希尔伯特函数与 $I$ 的希尔伯特函数一致,直到度数 $d $. 当我们为 $N\geq h$ 考虑 $IR^N$ 时,这个 lex 理想度数最多 $d$ 的最小生成器的集合 $\mathfrak{B}_d(I,N)$ 可能会改变,但是 $ \mathfrak{B}_d(I,N)$ 对于所有 $N \gg 0$ 都是常数。我们让 $\mathfrak{B}_d(I)$ 表示对所有 $N \gg 0$ 获得的一组生成器,我们让 $b_d = b_d(I)$ 为其基数。这样得到的序列$b_1、\、\ldots、\、b_d、\、\ldots$可能会增长得非常快。值得注意的是,即使当 $I = (x_1^2, x_2^2)$ 时,也会得到一个非常有趣的序列,0, 2, 3, 4, 6, 12, 924, 409620,$\,\ldots$。此序列与 $d\geq 2$ 的 $H_{d-1} + 1$ 相同,其中 $H_d$ 是 $d\,$th 汉密尔顿数。Hamilton 以及 Hammond 和 Sylvester 研究了 Hamilton 数,因为它们出现在与使用 Tschirnhaus 变换处理多项式方程相关的计数问题中。
更新日期:2020-10-01
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