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arXiv 1208.1640cs.GTcs.CC
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奇偶对策的图运算与多项式时间算法

Graph Operations on Parity Games and Polynomial-Time Algorithms

Christoph Dittmann, Stephan Kreutzer, Alexandru I. Tomescu

摘要:

奇偶游戏是在有向图上进行的游戏,其顶点由自然数标记,称为优先级。玩家沿着有向图的边缘推一个记号。获胜者是由在这个无限博弈中无限频繁出现的最大优先权的对等决定的。研究奇偶博弈的一个动机来自于通过模型检验对系统进行形式化验证的领域。在奇偶博弈中决定赢家是多项式时间等价于模态μ演算的模型检验问题。另一个强大的动机在于,解决奇偶博弈的精确复杂性是一个长期存在的开放问题,目前最知名的算法是次指数。已知问题是在复杂性类UP和coUP中。在本文中,我们确定了限制类的有向图的问题是可解的多项式时间,从结构图理论的方法。我们考虑三个标准的图形操作:两个图的连接,沿着顶点重复粘贴,以及添加一个顶点。给定一类C的有向图,我们可以解决奇偶游戏在多项式时间,我们表明,同样适用于从C获得的类,通过应用一次这三个操作的任何一个元素。这些结果提供,特别是,多项式时间算法的奇偶校验游戏的基础图是一个方向的完全图,完全二分图,块图,或块仙人掌图。这些类的问题是不知道是有效的解决。关于限制类的奇偶对策是在多项式时间可解的先前的结果包括类的有界树宽度,有界DAG宽度,和有界树宽度。我们还证明,承认一个平价游戏的获胜区域并不比从头开始计算它们更容易。

英文摘要:

Parity games are games that are played on directed graphs whose vertices are labeled by natural numbers, called priorities. The players push a token along the edges of the digraph. The winner is determined by the parity of the greatest priority occurring infinitely often in this infinite play. A motivation for studying parity games comes from the area of formal verification of systems by model checking. Deciding the winner in a parity game is polynomial time equivalent to the model checking problem of the modal mu-calculus. Another strong motivation lies in the fact that the exact complexity of solving parity games is a long-standing open problem, the currently best known algorithm being subexponential. It is known that the problem is in the complexity classes UP and coUP. In this paper we identify restricted classes of digraphs where the problem is solvable in polynomial time, following an approach from structural graph theory. We consider three standard graph operations: the join of two graphs, repeated pasting along vertices, and the addition of a vertex. Given a class C of digraphs on which we can solve parity games in polynomial time, we show that the same holds for the class obtained from C by applying once any of these three operations to its elements. These results provide, in particular, polynomial time algorithms for parity games whose underlying graph is an orientation of a complete graph, a complete bipartite graph, a block graph, or a block-cactus graph. These are classes where the problem was not known to be efficiently solvable. Previous results concerning restricted classes of parity games which are solvable in polynomial time include classes of bounded tree-width, bounded DAG-width, and bounded clique-width. We also prove that recognising the winning regions of a parity game is not easier than computing them from scratch.

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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