Two-way nondeterministic pushdown automata (2PDA2PDA) are classical nondeterministic pushdown automata (PDAPDA) enhanced with two-way motion of the input head. In this paper, the subclass of 2PDA2PDA 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.
Descriptional complexity of two-way pushdown automata with restricted head reversals / A. Malcher, C. Mereghetti, B. Palano (LECTURE NOTES IN COMPUTER SCIENCE). - In: Descriptional Complexity of Formal Systems / [a cura di] M. Holzer, M. Kutrib, G. Pighizzini. - Berlin : Springer, 2011. - ISBN 9783642225994. - pp. 248-260 (( Intervento presentato al 13. convegno International Workshop on Descriptional Complexity of Formal Systems tenutosi a Limburg nel 2011 [10.1007/978-3-642-22600-7_20].
Descriptional complexity of two-way pushdown automata with restricted head reversals
C. MereghettiSecondo
;B. PalanoUltimo
2011
Abstract
Two-way nondeterministic pushdown automata (2PDA2PDA) are classical nondeterministic pushdown automata (PDAPDA) enhanced with two-way motion of the input head. In this paper, the subclass of 2PDA2PDA 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.File | Dimensione | Formato | |
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