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arxiv: 1804.01046 · v3 · pith:MKW4OJUInew · submitted 2018-04-03 · 🧮 math.AC

Fiber cones, analytic spreads of the canonical and anticanonical ideals and limit Frobenius complexity of Hibi rings

classification 🧮 math.AC
keywords omegamathbbringsbigoplusmathfrakanalyticcanonicalcomplexity
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Let ${\cal R}_{\mathbb{K}}[H]$ be the Hibi ring over a field $\mathbb{K}$ on a finite distributive lattice $H$, $P$ the set of join-irreducible elements of $H$ and $\omega$ the canonical ideal of ${\cal R}_{\mathbb{K}}[H]$. We show the powers $\omega^{(n)}$ of $\omega$ in the group of divisors $\mathrm{Div}({\cal R}_{\mathbb{K}}[H])$ is identical with the ordinal powers of $\omega$, describe the $\mathbb{K}$-vector space basis of $\omega^{(n)}$ for $n\in\mathbb{Z}$. Further, we show that the fiber cones $\bigoplus_{n\geq 0}\omega^n/\mathfrak{m}\omega^n$ and $\bigoplus_{n\geq0}(\omega^{(-1)})^n/\mathfrak{m}(\omega^{(-1)})^n$ of $\omega$ and $\omega^{(-1)}$ are sum of the Ehrhart rings, defined by sequences of elements of $P$ with a certain condition, which are polytopal complex version of Stanley-Reisner rings. Moreover, we show that the analytic spread of $\omega$ and $\omega^{(-1)}$ are maximum of the dimensions of these Ehrhart rings. Using these facts, we show that the question of Page about Frobenius complexity is affirmative: $\lim_{p\to\infty}\mathrm{cx}_F({\cal R}_{\mathbb{K}}[H])= \dim(\bigoplus_{n\geq0}\omega^{(-n)}/\mathfrak{m}\omega^{(-n)})-1$, where $p$ is the characteristic of the field $\mathbb{K}$.

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