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arXiv 0905.1045cs.FL
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有界上下文无关语言的描述复杂性

Descriptional complexity of bounded context-free languages

Andreas Malcher, Giovanni Pighizzini

摘要:

研究了多轮下推自动机(PDA)的几何复杂性。已知它们完全接受超线性上下文无关语言类。此外,当将接受超线性语言的任意PDA转换为有限回合PDA时,大小的增加不能由任何递归函数限制。后一种现象被称为非递归权衡。在本文中,有限轮PDA接受有界语言被认为是。首先,研究了字母有界语言。我们证明,在这种情况下,非递归权衡被简化为递归权衡,更准确地说,是指数权衡。给出了一个转换算法,并通过证明紧下界证明了该构造的最优性。此外,减少的问题,一个给定的有限匝PDA的匝数进行了研究。再次,提供了转换算法,其示出了在这种情况下,折衷最多是多项式的。最后,更一般的情况下,词有界的语言进行了研究。我们展示了如何字母有界语言的结果可以扩展到词有界语言。

英文摘要:

Finite-turn pushdown automata (PDA) are investigated concerning their descriptional complexity. It is known that they accept exactly the class of ultralinear context-free languages. Furthermore, the increase in size when converting arbitrary PDAs accepting ultralinear languages to finite-turn PDAs cannot be bounded by any recursive function. The latter phenomenon is known as non-recursive trade-off. In this paper, finite-turn PDAs accepting bounded languages are considered. First, letter-bounded languages are studied. We prove that in this case the non-recursive trade-off is reduced to a recursive trade-off, more precisely, to an exponential trade-off. A conversion algorithm is presented and the optimality of the construction is shown by proving tight lower bounds. Furthermore, the question of reducing the number of turns of a given finite-turn PDA is studied. Again, a conversion algorithm is provided which shows that in this case the trade-off is at most polynomial. Finally, the more general case of word-bounded languages is investigated. We show how the results obtained for letter-bounded languages can be extended to word-bounded languages.

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