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SIAM Journal on Control and Optimization, Vol.58, No.3, 1257-1288, 2020
NONZERO-SUM SUBMODULAR MONOTONE-FOLLOWER GAMES: EXISTENCE AND APPROXIMATION OF NASH EQUILIBRIA
We consider a class of N-player stochastic games of multidimensional singular control, in which each player faces a minimization problem of monotone-follower type with submodular costs. We call these games monotone-follower games. In a not necessarily Markovian setting, we establish the existence of Nash equilibria. Moreover, we introduce a sequence of approximating games by restricting, for each n is an element of N, the players' admissible strategies to the set of Lipschitz processes with Lipschitz constant bounded by n. We prove that, for each n is an element of N, there exists a Nash equilibrium of the approximating game and that the sequence of Nash equilibria converges, in the Meyer-Zheng sense, to a weak (distributional) Nash equilibrium of the original game of singular control. As a byproduct, such a convergence also provides approximation results of the equilibrium values across the two classes of games. We finally show how our results can be employed to prove existence of open-loop Nash equilibria in an N-player stochastic differential game with singular controls, and we propose an algorithm to determine a Nash equilibrium for the monotone-follower game.
Keywords:nonzero-sum games;singular control;submodular games;Meyer-Zheng topology;Pontryagin maximum principle;Nash equilibrium;stochastic differential games;monotone-follower problem