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arXiv 0904.0679math.CO
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Ehrhart多项式的有限微积分方法

A finite calculus approach to Ehrhart polynomials

Steven V Sam, Kevin M. Woods

摘要:

有理多面体是$\R^d$中具有有理坐标的有限点集的凸包。给定一个有理多面体$P \subseteq \R^d$,埃赫哈特证明,对于$t\in\Z_{\ge 0}$,功能$#(tP \cap \Z^d)$同意与准多项式$L_P(t)$,所谓的埃赫哈特准多项式。Ehrhart拟多项式可以看作是一个多面体体积的离散形式。我们用这个类比来推导埃赫哈特定理的一个新证明。这个证明也使我们能够快速证明其他两个事实埃赫哈特准多项式:麦克马伦定理的周期性的个别系数的准多项式和埃赫哈特-麦克唐纳定理的互易性。

英文摘要:

A rational polytope is the convex hull of a finite set of points in $\R^d$ with rational coordinates. Given a rational polytope $P \subseteq \R^d$, Ehrhart proved that, for $t\in\Z_{\ge 0}$, the function $#(tP \cap \Z^d)$ agrees with a quasi-polynomial $L_P(t)$, called the Ehrhart quasi-polynomial. The Ehrhart quasi-polynomial can be regarded as a discrete version of the volume of a polytope. We use that analogy to derive a new proof of Ehrhart's theorem. This proof also allows us to quickly prove two other facts about Ehrhart quasi-polynomials: McMullen's theorem about the periodicity of the individual coefficients of the quasi-polynomial and the Ehrhart-Macdonald theorem on reciprocity.

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