144 research outputs found
Fragility and Robustness in Mean-Payoff Adversarial Stackelberg Games
Two-player mean-payoff Stackelberg games are nonzero-sum infinite duration games played on a bi-weighted graph by Leader (Player 0) and Follower (Player 1). Such games are played sequentially: first, Leader announces her strategy, second, Follower chooses his best-response. If we cannot impose which best-response is chosen by Follower, we say that Follower, though strategic, is adversarial towards Leader. The maximal value that Leader can get in this nonzero-sum game is called the adversarial Stackelberg value (ASV) of the game.
We study the robustness of strategies for Leader in these games against two types of deviations: (i) Modeling imprecision - the weights on the edges of the game arena may not be exactly correct, they may be delta-away from the right one. (ii) Sub-optimal response - Follower may play epsilon-optimal best-responses instead of perfect best-responses. First, we show that if the game is zero-sum then robustness is guaranteed while in the nonzero-sum case, optimal strategies for ASV are fragile. Second, we provide a solution concept to obtain strategies for Leader that are robust to both modeling imprecision, and as well as to the epsilon-optimal responses of Follower, and study several properties and algorithmic problems related to this solution concept
Fragility and Robustness in Mean-payoff Adversarial Stackelberg Games
Two-player mean-payoff Stackelberg games are nonzero-sum infinite duration
games played on a bi-weighted graph by a leader (Player~0) and a follower
(Player~1). Such games are played sequentially: first, the leader announces her
strategy, second, the follower chooses his strategy. This pair of strategies
defines a unique infinite path in the graph and both players receive their
respective payoff computed as the mean of the rewards that they receive when
traversing edges along the infinite path.
As a consequence, if we assume that the follower is rational then we can
deduce that the follower's response to the leader strategy is a strategy that
maximizes his payoff against the strategy proposed by the leader; it is thus a
best-response to this strategy. Knowing that, the leader should choose a
strategy that maximizes the payoff that she receives when the follower chooses
a best-response to her strategy. If we cannot impose which best-response is
chosen by the follower, we say that the follower, though strategic, is
\emph{adversarial} towards the leader. The maximal value that the leader can
get in this nonzero-sum game is called the {\em adversarial Stackelberg value}
of the game.
First, we show that the nonzero-sum nature of the mean-payoff Stackelberg
game makes it fragile against modelling imprecisions. This is in contrast with
mean-payoff games in the zero-sum setting which are robust. Second, we show how
robustness is recovered when considering -best responses of the
follower instead of best-responses only. This lead to the notion of
-adversarial Stackelberg value. Third, we provide algorithms to
decide the threshold problem for this robust value as well as ways to compute
it effectively. Finally, we characterize the memory needed by the strategies of
the leader and the follower in these games.Comment: Added discussion on fragility and robustness of mean-payoff games for
both non-zero sum and zero-sum cases, and new results on NP-completeness of
games restricted to memoryless strategies of the leade
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