二人用ゲームの戦略とチャンス

タイトル: Percolation games on rooted, edge-weighted random trees

概要: Consider a rooted Galton-Watson tree $T$, to each of whose edges we assign, independently, a weight that equals $+1$ with probability $p_{1}$, $0$ with probability $p_{0}$ and $-1$ with probability $p_{-1}=1-p_{1}-p_{0}$. We play a game on this rooted, edge-weighted Galton-Watson tree, involving two players and a token. The token is allowed to be moved from where it is currently located, say a vertex $u$ of $T$, to any child $v$ of $u$. The players begin with initial capitals that amount to $i$ and $j$ units respectively, and a player wins if either she is the first to amass a capital worth $\kappa$ units, where $\kappa$ is a pre-specified positive integer, or her opponent is the first to have her capital dwindle to $0$, or she is able to move the token to a leaf vertex, from where her opponent cannot move it any farther. This paper is concerned with studying the probabilities of the three possible outcomes (i.e. win for the first player, loss for the first player, and draw for both players) of this game, as well as finding conditions under which the expected duration of this game is finite. The theory we develop in this paper for the analysis of this game is further supported by observations obtained via computer simulations, and these observations provide a deeper insight into how the above-mentioned probabilities behave as the underlying parameters and / or offspring distributions are allowed to vary. We conclude the paper with a couple of conjectures, one of which suggests the occurrence of a phase transition phenomenon whereby the probability of draw in this game goes from being $0$ to being strictly positive as the parameter-pair $(p_{0},p_{1})$ is varied suitably while keeping the underlying offspring distribution of $T$ fixed.