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arXiv 2002.05680math.COcs.CG
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两个简单多边形边界交点数目的一个几乎最优上界

An almost optimal bound on the number of intersections of two simple polygons

Eyal Ackerman, Balázs Keszegh, Günter Rote

AI总结:

针对两个简单多边形边界交点数目的最大值问题,当边数均为奇数时,证明了新的上界 mn-(m+n)+C,该结果除常数外最优。

摘要:

在一般位置假设下,一个简单 $m$ 边形与一个简单 $n$ 边形的边界最多能有多少个交点?这是组合几何中的一个基本问题,当 $m$ 和 $n$ 中至少有一个为偶数时,答案很简单:如果 $m$ 和 $n$ 均为偶数,则每对边都可能相交,因此答案为 $mn$。如果恰好一个多边形(设为 $n$ 边形)有奇数条边,则它最多与 $m$ 边形的每条边相交 $n-1$ 次;因此最多有 $mn-m$ 个交点。不难构造达到这些界限的实例。如果 $m$ 和 $n$ 均为奇数,目前已知的最佳构造具有 $mn-(m+n)+3$ 个交点,并且猜想这是最大值。然而,目前已知的最佳上界仅为 $mn-(m + \lceil \frac{n}{6} \rceil)$(当 $m \ge n$ 时)。我们证明了新的上界 $mn-(m+n)+C$,其中 $C$ 为某个常数,该上界除常数 $C$ 的值外是最优的。

英文摘要:

What is the maximum number of intersections of the boundaries of a simple $m$-gon and a simple $n$-gon, assuming general position? This is a basic question in combinatorial geometry, and the answer is easy if at least one of $m$ and $n$ is even: If both $m$ and $n$ are even, then every pair of sides may cross and so the answer is $mn$. If exactly one polygon, say the $n$-gon, has an odd number of sides, it can intersect each side of the $m$-gon at most $n-1$ times; hence there are at most $mn-m$ intersections. It is not hard to construct examples that meet these bounds. If both $m$ and $n$ are odd, the best known construction has $mn-(m+n)+3$ intersections, and it is conjectured that this is the maximum. However, the best known upper bound is only $mn-(m + \lceil \frac{n}{6} \rceil)$, for $m \ge n$. We prove a new upper bound of $mn-(m+n)+C$ for some constant $C$, which is optimal apart from the value of $C$.

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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