Topic
Pushdown automaton
About: Pushdown automaton is a research topic. Over the lifetime, 1868 publications have been published within this topic receiving 35399 citations.
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01 Jan 2000
TL;DR: It is shown that for each context-free grammar a new grammar can be constructed that generates a regular language that differs from existing methods of approximation in that use of a pushdown automaton is avoided.
Abstract: We show that for each context-free grammar a new grammar can be constructed that generates a regular language. This construction differs from some existing methods of approximation in that use of a pushdown automaton is avoided. This allows better insight into how the generated language is affected.
53 citations
05 Nov 2013
TL;DR: A new technique is illustrated that uses parameterized arrays as the main data structure to model strings, and converts string constraints into quantified expressions that are solved through quantifier elimination, and can achieve much better accuracy and efficiency.
Abstract: The problem of solving string constraints together with numeric constraints has received increasing interest recently. Existing methods use either bit-vectors or automata (or their combination) to model strings, and reduce string constraints to bit-vector constraints or automaton operations, which are then solved in the respective domain. Unfortunately, they often fail to achieve a good balance between efficiency, accuracy, and comprehensiveness. In this paper we illustrate a new technique that uses parameterized arrays as the main data structure to model strings, and converts string constraints into quantified expressions that are solved through quantifier elimination. We present an efficient and sound quantifier elimination algorithm. In addition, we use an automaton model to handle regular expressions and reason about string values faster. Our method does not need to enumerate string lengths (as bit-vector based methods do), or concrete string values (as automaton based methods do). Hence, it can achieve much better accuracy and efficiency. In particular, it can identify unsatisfiable cases quickly. Our solver (named PASS) supports most of the popular string operations, including string comparisons, string-numeric conversions, and regular expressions. Experimental results demonstrate the advantages of our method.
53 citations
TL;DR: It is shown that the minimum number of agents required to solve the ANTS problem crucially depends on the computational capabilities of the agents as well as the timing parameters of the execution environment.
53 citations
09 Sep 1991
TL;DR: It is demonstrated that closure under complement of unambiguous classes implies equivalence of unambiguity and “unambiguous fewness” in the cases of reach and strong unambIGuity for log space.
Abstract: We consider various types of unambiguity and fewness for log space bounded Turing machines and polynomial time bounded log space auxiliary pushdown automata. In particular, we introduce the notions of (general), reach, and strong unambiguity and fewness. We demonstrate that closure under complement of unambiguous classes implies equivalence of unambiguity and “unambiguous fewness”. This, as we will show, applies in the cases of reach and strong unambiguity for log space. Among the many relations we exhibit, we show that the unambiguous linear contextfree languages, which are not known to be contained in deterministic log space, nevertheless are contained in strongly unambiguous log space, and, consequently, are log space reducible to deterministic contextfree languages.
52 citations
09 Jul 2012
TL;DR: A natural extension of collapsible pushdown systems called annotated push down systems that replaces collapse links with stack annotations is introduced and a saturation method for global backwards reachability analysis of these models is presented.
Abstract: We introduce a natural extension of collapsible pushdown systems called annotated pushdown systems that replaces collapse links with stack annotations. We believe this new model has many advantages. We present a saturation method for global backwards reachability analysis of these models that can also be used to analyse collapsible pushdown systems. Beginning with an automaton representing a set of configurations, we build an automaton accepting all configurations that can reach this set. We also improve upon previous saturation techniques for higher-order pushdown systems by significantly reducing the size of the automaton constructed and simplifying the algorithm and proofs.
52 citations