Worst Case Branching and Other Measures of Nondeterminism

Abstract

Many nondeterminism measures for finite automata have been studied in the literature. The tree width of an NFA (nondeterministic finite automaton) counts the number of leaves of computation trees as a function of input length. The trace of an NFA is defined in terms of the largest product of the degrees of nondeterministic choices in computations on inputs of given length. Branching is the corresponding best case measure based on the product of nondeterministic choices in the computation that minimizes this value. We establish upper and lower bounds for the trace of an NFA in terms of its tree width. We give a tight bound for the size blow-up of determinizing an NFA with finite trace. Also we show that the trace of any NFA either is bounded by a constant or grows exponentially.