Population Monotonic Allocation Schemes for Vertex Cover Games
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For the class of vertex cover games (introduced by Deng et al., Math. Oper. Res., 24:751-766, 1999), we investigate the population monotonic allocation schemes (introduced by Sprumont, Games Econ. Behav., 2: 378-394, 1990). We present a complete characterization for the class of vertex cover games admitting a population monotonic allocation scheme (PMAS for short), i.e., a vertex cover game has a PMAS if and only if the underlying graph is (K_3,C_4,P_5)-free. Our characterization implies that the existence of a PMAS can be determined efficiently for vertex cover games. We also propose an alternative description for PMAS-es in vertex cover games based on the dual linear program of the vertex cover problem, which reveals the dual-based allocation scheme nature of PMAS-es. Moreover, we give a complete characterization for integral PMAS-es in vertex cover games via stable matchings and show that the celebrated Gale-Shapley algorithm (introduced by Gale and Shapley, Amer. Math. Monthly, 69:9-15, 1962) can be used to produce all integral PMAS-es in vertex cover games.
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