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arXiv 1109.5804cs.LOcs.DS
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MSO1模型检验复杂度的下界

Lower Bounds on the Complexity of MSO1 Model-Checking

Robert Ganian, Petr Hliněný, Alexander Langer, Jan Obdržálek, Peter Rossmanith, Somnath Sikdar

摘要:

最重要的算法元定理之一是Courcelle的一个著名结果,该结果指出,任何可在一元二阶逻辑中定义的具有边集量化的图问题(即,MSO 2(模型检验)在任意一类有界树宽的图上都是线性时间可判定的。最近,Kreutzer和Tazari证明了一个相应的复杂性下限-MSO 2模型检验甚至不在XP中。公式大小作为子图封闭的图类的参数,并且其树宽度是多边形无界的。当然,这不是一个无条件的结果,而是对某个复杂性理论假设取模,即指数时间假设(ETH)。在本文中,我们提出了一个密切相关的结果。我们表明,即使MSO 1模型检验与一组固定的顶点标签,但没有边集量化,是不是在XP的书面。公式大小作为子图闭合的图类的参数,并且除非非均匀ETH失败,否则其树宽度是多项式无界的。与Kreutzer和Tazari相比,$(1)$使用了更强的前提条件,即非均匀而不是均匀ETH,以避免有效性假设和证明中使用的某些障碍; $(2)$假设一组不同的问题是有效可判定的,即在顶点标记图上的MSO 1-可定义属性,而不是在未标记图上的MSO 2-可定义属性。我们的结果有一个有趣的后果领域的有向图宽度措施:加强最近的结果,我们表明,没有subdigraph单调措施可以是“算法上有用的”,除非它是在一个多对数因子的无向树宽度。

英文摘要:

One of the most important algorithmic meta-theorems is a famous result by Courcelle, which states that any graph problem definable in monadic second-order logic with edge-set quantifications (i.e., MSO2 model-checking) is decidable in linear time on any class of graphs of bounded tree-width. Recently, Kreutzer and Tazari proved a corresponding complexity lower-bound - that MSO2 model-checking is not even in XP wrt. the formula size as parameter for graph classes that are subgraph-closed and whose tree-width is poly-logarithmically unbounded. Of course, this is not an unconditional result but holds modulo a certain complexity-theoretic assumption, namely, the Exponential Time Hypothesis (ETH). In this paper we present a closely related result. We show that even MSO1 model-checking with a fixed set of vertex labels, but without edge-set quantifications, is not in XP wrt. the formula size as parameter for graph classes which are subgraph-closed and whose tree-width is poly-logarithmically unbounded unless the non-uniform ETH fails. In comparison to Kreutzer and Tazari; $(1)$ we use a stronger prerequisite, namely non-uniform instead of uniform ETH, to avoid the effectiveness assumption and the construction of certain obstructions used in their proofs; and $(2)$ we assume a different set of problems to be efficiently decidable, namely MSO1-definable properties on vertex labeled graphs instead of MSO2-definable properties on unlabeled graphs. Our result has an interesting consequence in the realm of digraph width measures: Strengthening the recent result, we show that no subdigraph-monotone measure can be "algorithmically useful", unless it is within a poly-logarithmic factor of undirected tree-width.

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