Looking at mean-payoff and total-payoff through windows

摘要

We consider two-player games played on weighted directed graphs with mean-payoff and total-payoff objectives, two classical quantitative objectives. While for single-dimensional games the complexity and memory bounds for both objectives coincide, we show that in contrast to multi-dimensional mean-payoff games that are known to be coNP-complete, multi-dimensional total-payoff games are undecidable. We introduce conservative approximations of these objectives, where the payoff is considered over a local finite window sliding along a play, instead of the whole play. For single dimension, we show that (ⅰ) if the window size is polynomial, deciding the winner takes polynomial time, and (ⅱ) the existence of a bounded window can be decided in NP n coNP, and is at least as hard as solving mean-payoff games. For multiple dimensions, we show that (ⅰ) the problem with fixed window size is EXPTIME-complete, and (ⅱ) there is no primitive-recursive algorithm to decide the existence of a bounded window.