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A matrix-analytic approach to the N-player ruin problem

Published online by Cambridge University Press:  14 July 2016

Yvik C. Swan*
Université Libre de Bruxelles
F. Thomas Bruss*
Université Libre de Bruxelles
Postal address: Département de Mathématique et ISRO, Université Libre de Bruxelles, Campus Plaine, CP 210, B-1050 Brussels, Belgium.
Postal address: Département de Mathématique et ISRO, Université Libre de Bruxelles, Campus Plaine, CP 210, B-1050 Brussels, Belgium.
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Consider N players, respectively owning x1, x2, …, xN monetary units, who play a sequence of games, winning from and losing to each other integer amounts according to fixed rules. The sequence stops as soon as (at least) one player is ruined. We are interested in the ruin process of these N players, i.e. in the probability that a given player is ruined first, and also in the expected ruin time. This problem is called the N-player ruin problem. In this paper, the problem is set up as a multivariate absorbing Markov chain with an absorbing state corresponding to the ruin of each player. This is then discussed in the context of phase-type distributions where each phase is represented by a vector of size N and the distribution has as many absorbing points as there are ruin events. We use this modified phase-type distribution to obtain an explicit solution to the N-player problem. We define a partition of the set of transient states into different levels, and on it give an extension of the folding algorithm (see Ye and Li (1994)). This provides an efficient computational procedure for calculating some of the key measures.

Research Article
© Applied Probability Trust 2006 


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