Journal of Combinatorial Theory Series B ( IF 1.2 ) Pub Date : 2021-06-23 , DOI: 10.1016/j.jctb.2021.06.002 Michał Pilipczuk , Sebastian Siebertz
For , a coloring λ of the vertices of a graph G is p-centered if for every connected subgraph H of G, either H receives more than p colors under λ or there is a color that appears exactly once in H. Centered colorings play an important role in the theory of sparse graph classes introduced by Nešetřil and Ossona de Mendez [31], [32], as they structurally characterize classes of bounded expansion — one of the key sparsity notions in this theory. More precisely, a class of graphs has bounded expansion if and only if there is a function such that every graph for every admits a p-centered coloring with at most colors. Unfortunately, known proofs for the existence of such colorings yield large upper bounds on the function f governing the number of colors needed, even for as simple classes as planar graphs. In this paper, we prove that every -minor-free graph admits a p-centered coloring with colors for some function g. In the special case that the graph is embeddable in a fixed surface Σ we show that it admits a p-centered coloring with colors, with the degree of the polynomial independent of the genus of Σ. This provides the first polynomial upper bounds on the number of colors needed in p-centered colorings of graphs drawn from proper minor-closed classes, which answers an open problem posed by Dvořák [1]. As an algorithmic application, we use our main result to prove that if is a fixed proper minor-closed class of graphs, then given graphs H and G, on p and n vertices, respectively, where , it can be decided whether H is a subgraph of G in time and space .
中文翻译:
适当次要闭合图类上居中着色的多项式边界
为了 ,着色λ的曲线图的顶点的ģ是对中心,如果为每一个连通子ħ的ģ,无论是ħ接收到多于p下的色彩,λ或存在,在恰好出现一次的彩色ħ。中心着色在 Nešetřil 和 Ossona de Mendez [31]、[32] 引入的稀疏图类理论中发挥着重要作用,因为它们在结构上表征了有界扩展的类- 该理论中的关键稀疏性概念之一。更准确地说,一类图 有界展开当且仅当存在函数 使得每个图 对于每个 承认p中心着色最多颜色。不幸的是,这种着色存在的已知证据在控制所需颜色数量的函数f上产生了很大的上限,即使对于像平面图这样简单的类也是如此。在本文中,我们证明了每-minor-free 图承认p中心着色某些函数g 的颜色。在图可嵌入固定表面 Σ 的特殊情况下,我们证明它允许p中心着色颜色,多项式的次数与 Σ 的属无关。这提供了从适当的次闭类绘制的图的p中心着色所需颜色数量的第一个多项式上限,这回答了 Dvořák [1] 提出的一个开放问题。作为一个算法应用,我们使用我们的主要结果来证明如果是固定的适当次闭类图,然后分别在p和n顶点上给定图H和G,其中中,可以决定是否ħ是的一个子图ģ在时间 和空间 .