Simulation of Two-Way Pushdown Automata Revisited
Abstract
The linear-time simulation of 2-way deterministic pushdown automata (2DPDA) by the Cook and Jones constructions is revisited. Following the semantics-based approach by Jones, an interpreter is given which, when extended with random-access memory, performs a linear-time simulation of 2DPDA. The recursive interpreter works without the dump list of the original constructions, which makes Cook's insight into linear-time simulation of exponential-time automata more intuitive and the complexity argument clearer. The simulation is then extended to 2-way nondeterministic pushdown automata (2NPDA) to provide for a cubic-time recognition of context-free languages. The time required to run the final construction depends on the degree of nondeterminism. The key mechanism that enables the polynomial-time simulations is the sharing of computations by memoization.
Cite
@article{arxiv.1309.5142,
title = {Simulation of Two-Way Pushdown Automata Revisited},
author = {Robert Glück},
journal= {arXiv preprint arXiv:1309.5142},
year = {2013}
}
Comments
In Proceedings Festschrift for Dave Schmidt, arXiv:1309.4557