On the Complexity of Parity Word Automata
Different types of nondeterministic automata on infinite words differ
in their succinctness and in the complexity for their nonemptiness
problem. A simple translation of a parity automaton to an equivalent
\buchi automaton is quadratic: a parity automaton with $n$ states, $m$
transitions, and index $k$ may result in a \buchi automaton of size
$O((n+m)k)$. The best algorithm known for the nonemptiness problem of
parity automata goes through \buchi automata, leading to
a complexity of $O((n+m)k)$.
In this paper we show that while the translation of parity
automata to \buchi automata cannot be improved, the special structure
of the acceptance condition of parity automata can be used in order to
solve the nonemptiness problem directly, with a dynamic graph
algorithm of complexity $O((n+m) \log k)$.