Seminal works on light spanners over the years provide spanners with optimal or near-optimal lightness in various graph classes, such as in general graphs, Euclidean spanners, and minor-free graphs. Two shortcomings of all previous work on light spanners are: (1) The techniques are ad hoc per graph class, and thus can't be applied broadly (e.g., some require large stretch and are thus suitable to general graphs, while others are naturally suitable to stretch $1 + \epsilon$). (2) The runtimes of these constructions are almost always sub-optimal, and usually far from optimal. This work aims at initiating a unified theory of light spanners by presenting a single framework that can be used to construct light spanners in a variety of graph classes. This theory is developed in two papers. The current paper is the first of the two -- it lays the foundations of the theory of light spanners and then applies it to design fast constructions with optimal lightness for several graph classes. Our new constructions are significantly faster than the state-of-the-art for every examined graph class; moreover, our runtimes are near-linear and usually optimal. Specifically, this paper includes the following results: (i) An $O(m \alpha(m,n))$-time construction of $(2k-1)(1+\epsilon)$-spanner with lightness $O(n^{1/k})$ for general graphs; (ii) An $O(n\log n)$-time construction of Euclidean $(1+\epsilon)$-spanners with lightness and degree both bounded by constants in the basic algebraic computation tree (ACT) model. This construction resolves a major problem in the area of geometric spanners, which was open for three decades; (iii) An $O(n\log n)$-time construction of $(1+\epsilon)$-spanners with constant lightness and degree, in the ACT model for unit disk graphs; (iv) a linear-time algorithm for constructing $(1+\epsilon)$-spanners with constant lightness for minor-free graphs.
翻译:这些年来,光光扇上的所有工作都存在两个缺点:(1) 光扇上的所有以往工作都是临时性的,因此无法广泛应用(例如,有些技术需要大伸缩,因此适合一般图表,而另一些则自然适合伸展1美元+美元。(2) 这些构造的运行时间几乎总是次优化的,通常也远离最佳。这项工作的目的是通过展示一个单一的框架来启动光扇常数常数理论,用于在各种图形类中构建光扇。这一理论在两份文件中得到发展。当前文件是第两份文件 -- 它为光谱仪的理论打下基础,然后通过一些图形类设计快速的光度。 我们的光度模型几乎总是次优化的,通常远离最优化的。 美元平流速模型通常比固定的平价水平要快。