# Generous and greedy strategies

Document type: Journal Articles Original article Yes Bengt Carlsson, Stefan J. Johansson, Magnus Boman Generous and greedy strategies Complexity International 1999 6 1320-0682 Blekinge Institute of Technology School of Engineering - Dept. Mathematics and Science (Sektionen för teknik – avd. för matematik och naturvetenskap)School of Engineering S- 371 79 Karlskrona+46 455 38 50 00http://www.tek.bth.se/ bca@bth.se, sja@bth.se, mab@sics.se English We introduce generous, even-matched, and greedy strategies ÊÊas concepts for analyzing games. A two person prisoner's dilemma Êgame is described by the four outcomes (C,D), (C,C), (D,C), and (D,D). In a generous strategy the proportion of (C,D) is larger than that of (D,C), i.e. the probability of facing a defecting agent is larger than the probability of defecting. An even-matched strategy has the (C,D) proportion approximately equal to that of (D,C). A greedy strategy is an inverted generous strategy. The basis of the partition is that it is a zero-sum game given that the sum of the proportions of strategies (C,D) must equal that of (D,C). In a population simulation, we compare the prisoner's dilemma (PD) game with the chicken game Ê(CG), given complete as well as partial knowledge of the rules for moves in the other strategies. In a traffic intersection example, we expected a co-operating generous strategy to be successful when the cost for collision was high in addition to the presence of uncertainty. The simulation indeed showed that a generous strategy was successful in the CG part, in which agents faced uncertainty about the outcome. If the resulting zero-sum game is changed from a PD game to a CG, or if the noise level is increased, it will favor generous strategies rather than an even-matched or greedy strategies. Computer Science\Artificial IntelligenceComputer Science\Distributed Computing