Abstract
Two-way nondeterministic pushdown automata (\(\textrm{2PDA}\)) are classical nondeterministic pushdown automata (\(\textrm{PDA}\)) enhanced with two-way motion of the input head. In this paper, the subclass of \(\textrm{2PDA}\) accepting bounded languages and making at most a constant number of input head turns is studied with respect to descriptional complexity aspects. In particular, the effect of reducing the number of pushdown reversals to a constant number is of interest. It turns out that this reduction leads to an exponential blow-up in case of nondeterministic devices, and to a doubly-exponential blow-up in case of deterministic devices. If the restriction on boundedness of the languages considered and on the finiteness of the number of head turns is dropped, the resulting trade-offs are no longer bounded by recursive functions, and so-called non-recursive trade-offs are shown.
Keywords
Partially supported by CRUI/DAAD under the project “Programma Vigoni: Descriptional Complexity of Non-Classical Computational Models”.
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Malcher, A., Mereghetti, C., Palano, B. (2011). Descriptional Complexity of Two-Way Pushdown Automata with Restricted Head Reversals. In: Holzer, M., Kutrib, M., Pighizzini, G. (eds) Descriptional Complexity of Formal Systems. DCFS 2011. Lecture Notes in Computer Science, vol 6808. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-22600-7_20
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DOI: https://doi.org/10.1007/978-3-642-22600-7_20
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