A Little Game Theory1 A LITTLE GAME THEORY Mike Bailey MSIM 852
A Little Game Theory2 BASICS Two or more competitors Each chooses a strategy Pay-off determined when all strategies known John Von Newmann and Oskar Morganstern, Theory of Games and Economic Behavior (1944) seen by many as the first publication of Operations Research Linear Programming is introduced in a chapter
A Little Game Theory3 TWO-PERSON ZERO-SUM GAME Most common form Two competitors, each will be rewarded Fixed reward total What one wins, the other loses
A Little Game Theory4 PAY-OFF MATRIX Presented as reward for player A xyz B’s strategy A’s strategy
A Little Game Theory5 MAXIMIN (MINIMAX) A chooses the strategy where he gets the best payoff if B acts optimally Maximizes the minimum xyz
A Little Game Theory6 MAXIMIN (MINIMAX) A chooses the strategy where he gets the best payoff if B acts optimally Maximizes the minimum xyz Does not always occur “Saddlepoint” Value of the Game
A Little Game Theory7 DOMINANCE y dominates x for player B xyz
A Little Game Theory8 DOMINANCE y dominates x for player B...then 1 dominates 2 for player A xyz
A Little Game Theory9 DOMINANCE y dominates x for player B...then 1 dominates 2 for player A......then y dominates z for player B xyz
A Little Game Theory10 DOMINANCE y dominates x for player B...then 1 dominates 2 for player A......then y dominates z for player B done xyz Doesn’t always happen Useful for big tables
A Little Game Theory11 MIXED STRATEGIES wxyz
A Little Game Theory12 MIXED STRATEGIES wxyz
A Little Game Theory13 MIXED STRATEGIES wxyz
A Little Game Theory14 MIXED STRATEGY A will choose strategy 1 with probability p V(y) = 65p + 50(1-p) V(z) = 45p + 55(1-p) What value of p makes A indifferent to B’s choice? yz
A Little Game Theory15 MIXED STRATEGY A will choose strategy 1 with probability p 65p + 50(1-p) = 45p + 55(1-p) p = 0.8 V = 53 B will choose y with probability q 65q + 45(1-q) = 50q + 55(1-q) q = 0.6 V = 53 yz
A Little Game Theory16 PRISONER’S DILEMMA Payoffs are jail sentences (for A, for B) in years silentbetray silent1/2, 1/210, free betrayfree, 102,2
A Little Game Theory17 PRISONER’S DILEMMA Pareto Optimum No move can make a player better off without harming another Nash Equilibrium No player can improve payoff unilaterally silentbetray silent1/2, 1/210, free betrayfree, 102,2
A Little Game Theory18 APPLICATIONS ASW (Hide and Seek) Arms Control Advertising Strategy Smuggling Making the All-Star Team Multiethnic Insurgency and Revolt Drug Testing (Wired, August 2006)
A Little Game Theory19 ITERATED PD Set a strategy involving a sequence of choices and memory of the (choice, outcome) Random termination of the game Noise in the game Specified payoff matrix The Iterated Prisoner's Dilemma Competition: Celebrating the 20 th Anniversary