A competitive search game with a moving target

Benoit Duvocelle*, Janos Flesch, Mathias Staudigl, Dries Vermeulen

*Corresponding author for this work

Research output: Working paper / PreprintPreprint


We introduce a discrete-time search game, in which two players compete to find an object first. The object moves according to a time-varying Markov chain on finitely many states. The players know the Markov chain and the initial probability distribution of the object, but do not observe the current state of the object. The players are active in turns. The active player chooses a state, and this choice is observed by the other player. If the object is in the chosen state, this player wins and the game ends. Otherwise, the object moves according to the Markov chain and the game continues at the next period. We show that this game admits a value, and for any error-term ε > 0, each player has a pure (subgame-perfect) ε-optimal strategy. Interestingly, a 0-optimal strategy does not always exist. The ε-optimal strategies are robust in the sense that they are 2ε-optimal on all finite but sufficiently long horizons, and also 2ε-optimal in the discounted version of the game provided that the discount factor is close to 1. We derive results on the analytic and structural properties of the value and the ε-optimal strategies. Moreover, we examine the performance of the finite truncation strategies, which are easy to calculate and to implement. We devote special attention to the important time-homogeneous case, where additional results hold.
Original languageEnglish
Number of pages34
Publication statusPublished - 2020


  • search game
  • sequential game
  • two-player zero-sum game
  • subgame perfect ε-equilibrium
  • discrete time-varying Markov process


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