I was wondering if the Nash Equilibrium example shown in the movie A Beautiful Mind is accurate? and if not, what's wrong with it?
Thanks
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3 Answers
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It's not quite right (unless you assume Nash was intentionally misleading his friends via a plausible, but incorrect, argument in order to maximize his chances with the blonde). This has been analyzed here.
answered Jul 2, 2014 at 6:15
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No it is not.
Loosely speaking, a Nash equilibrium is a strategy profile (specifying a strategy for each agent involved) with the property that no agent could unilaterally change his/her strategy and be better off.
The example in the movie suggests as a Nash equilibrium the strategy profile in which all bachelors ignore the prettiest girl, and instead go for her friends. This is not a Nash equilibrium because, assuming that everyone prefers the best looking gal (as is implicitly assumed in the movie), any one of the bachelors could unilaterally deviate by going for her. Presumably, since no one else is paying her any attention, she would accept him and he would be better off that according to the proposed strategies. Hence, the proposed strategies are not a Nash equilibrium.
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The movie doesn't actually claim that the strategy Nash proposes is a Nash Equilibrium. And it isn't. Any one of the agents could go for the blonde and be better off.
Nor is it ideal for all parties, as 1 of them picked as random being with the blonde is more ideal.
So no, it is not a Nash Equilibrium. It is however a practical solution to the problem.
