For a set $Q$ of points in the plane and a real number $\delta \ge 0$, let $\mathbb{G}_\delta(Q)$ be the graph defined on $Q$ by connecting each pair of points at distance at most $\delta$. We consider the connectivity of $\mathbb{G}_\delta(Q)$ in the best scenario when the location of a few of the points is uncertain, but we know for each uncertain point a line segment that contains it. More precisely, we consider the following optimization problem: given a set $P$ of $n-k$ points in the plane and a set $S$ of $k$ line segments in the plane, find the minimum $\delta\ge 0$ with the property that we can select one point $p_s\in s$ for each segment $s\in S$ and the corresponding graph $\mathbb{G}_\delta ( P\cup \{ p_s\mid s\in S\})$ is connected. It is known that the problem is NP-hard. We provide an algorithm to compute exactly an optimal solution in $O(f(k) n \log n)$ time, for a computable function $f(\cdot)$. This implies that the problem is FPT when parameterized by $k$. The best previous algorithm is using $O((k!)^k k^{k+1}\cdot n^{2k})$ time and computes the solution up to fixed precision.
翻译:给定平面上的点集$Q$和实数$\delta \geq 0$,设$\mathbb{G}_\delta(Q)$为由距离不超过$\delta$的每对点构成的图。本文考虑了当少数点的位置是不确定的时的最优连通性情况,但我们知道每个不确定点所对应的包含它的线段。更具体地,我们考虑以下优化问题:给定平面上的$n-k$个点的集合$P$和$k$条线段的集合$S$,找到最小的$\delta \geq 0$,使得我们可以为每条线段$s \in S$选择一个点$p_s \in s$,使得相应的图$\mathbb{G}_{\delta}(P \cup \{ p_s \mid s \in S \})$是连通的。已知该问题是NP难的。我们提供了一个算法,以$O(f(k)n \log n)$的时间精确计算最优解,其中$f(\cdot)$是可计算函数。这意味着该问题在以$k$为参数化时是FPT的。最好的先前算法使用了$O((k!)^k k^{k+1}\cdot n^{2k})$的时间,并计算固定精度的解。