Undiscounted Games Research Articles

On Completely Mixed Stochastic Games

In this paper, we consider a two-person finite state stochastic games with finite number of pure actions for both players in all the states. In particular, for a large number of results we also consider one-player controlled transition probability and show that if all the optimal strategies of the undiscounted stochastic game are completely mixed then for beta sufficiently close to 1; all the optimal strategies of beta-discounted stochastic games are also completely mixed. A counterexample is provided to show that the converse is not true. Further, for single-player controlled completely mixed stochastic games if the individual payoff matrices are symmetric in each state, then we show that the individual matrix games are also completely mixed. For the non-zerosum single-player controlled stochastic game under some non-singularity conditions, we show that if the undiscounted game is completely mixed, then the Nash equilibrium is unique. For non-zerosum beta-discounted stochastic games when Nash equilibrium exists, we provide equalizer rules for corresponding value of the game.

Stochastic games with information lag

Two-player zero-sum stochastic games with finite state and action spaces are known to have undiscounted values. We study such games under the assumption that one or both players observe the actions of their opponent after some time-dependent delay. We develop criteria for the rate of growth of the delay such that a player subject to such an information lag can still guarantee himself in the undiscounted game as much as he could have with perfect monitoring. We also demonstrate that the player in the Big Match with the absorbing action subject to information lags that grows too rapidly will not be able to guarantee as much as he could have in the game with perfect monitoring.

Orderfield property of mixtures of stochastic games

We consider certain mixtures, Γ, of classes of stochastic games and provide sufficient conditions for these mixtures to possess the orderfield property. For 2-player zero-sum and non-zero sum stochastic games, we prove that if we mix a set of states S1 where the transitions are controlled by one player with a set of states S2 constituting a sub-game having the orderfield property (where S1 ∩ S2 = ∅), the resulting mixture Γ with states S = S1 ∪ S2 has the orderfield property if there are no transitions from S2 to S1. This is true for discounted as well as undiscounted games. This condition on the transitions is sufficient when S1 is perfect information or SC (Switching Control) or ARAT (Additive Reward Additive Transition). In the zero-sum case, S1 can be a mixture of SC and ARAT as well. On the other hand,when S1 is SER-SIT (Separable Reward — State Independent Transition), we provide a counter example to show that this condition is not sufficient for the mixture Γ to possess the orderfield property. In addition to the condition that there are no transitions from S2 to S1, if the sum of all transition probabilities from S1 to S2 is independent of the actions of the players, then Γ has the orderfield property even when S1 is SER-SIT. When S1 and S2 are both SERSIT, their mixture Γ has the orderfield property even if we allow transitions from S2 to S1. We also extend these results to some multi-player games namely, mixtures with one player control Polystochastic games. In all the above cases, we can inductively mix many such games and continue to retain the orderfield property.