Kuperberg, Denis and Majumdar, Anirban - Computing the Width of Non-deterministic Automata

lmcs:4953 - Logical Methods in Computer Science, November 29, 2019, Volume 15, Issue 4 - https://doi.org/10.23638/LMCS-15(4:10)2019
Computing the Width of Non-deterministic Automata

Authors: Kuperberg, Denis and Majumdar, Anirban

We introduce a measure called width, quantifying the amount of nondeterminism in automata. Width generalises the notion of good-for-games (GFG) automata, that correspond to NFAs of width 1, and where an accepting run can be built on-the-fly on any accepted input. We describe an incremental determinisation construction on NFAs, which can be more efficient than the full powerset determinisation, depending on the width of the input NFA. This construction can be generalised to infinite words, and is particularly well-suited to coBüchi automata. For coBüchi automata, this procedure can be used to compute either a deterministic automaton or a GFG one, and it is algorithmically more efficient in the last case. We show this fact by proving that checking whether a coBüchi automaton is determinisable by pruning is NP-complete. On finite or infinite words, we show that computing the width of an automaton is EXPTIME-complete. This implies EXPTIME-completeness for multipebble simulation games on NFAs.

Volume: Volume 15, Issue 4
Published on: November 29, 2019
Submitted on: November 2, 2018
Keywords: Computer Science - Formal Languages and Automata Theory


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