MA3662: Game Theory Mock Paper A 2022
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MA3662: Game Theory
Stage 3 Examination
Mock Paper A 2022
1. Consider a two-player zero-sum game with p x q payoff matrix A for player
(a) Define what it means for one strategy to strictly dominate another. [3]
(b) Consider the game given by
╱ 、
A = .( 1 4 3.. .
i. Calculate the gain floor and loss ceiling for A. [2]
ii. Use strict dominance with a suitable linear combination of strategies to eliminate row 2 from A to form a new matrix B . [6]
iii. Use the Equality of Payoffs Theorem to determine whether it is pos- sible to have a mixed Nash equilibrium for B where player one’s strategy is of the form (a, b, c) with a, b, c > 0. [9]
[Total marks: 20]
2. Consider a two-player non-zero-sum game with payoff matrix given by ← .
(a) Determine the safety values and a maxmin strategy for each player. [6]
(b) Determine the rational reaction sets for the given game, and hence clas- sify the Nash equilibria. [7]
(c) Consider the game where player 1 first picks A or B . If A is picked then player 2 picks either X with payoff vector (5/2, 2) or Y with payoff vector (3, 1). If B is picked then the two players play the non-zero-sum game given above where the first pure strategy for each player is called M and the second is called N . Determine all of the subgame perfect Nash equilibria of this game. [7]
[Total marks: 20]
3. Consider the infinite repeated two-player game where at each stage the play- ers play the non-zero-sum game given by
B
A (4, 4) (-2, 6)
B (6, -2) (2, 2)
(a) Consider the following strategies:
• sa : always play A.
• sB : always play B .
• sT : play A in the first stage, and then at each stage copy what the other player did at the previous stage.
• sC : play B in the first stage, and then at each stage copy what the other player did at the previous stage.
Suppose that the total payoff involves a discount factor 6 and that both players are restricted to the strategies sa , sB , sT , and sC . Determine the
range of values of 6 such that (sT , sT ) is a Nash equilibrium. [7]
(b) State what it means for a pair of strategies to satisfy the one stage devi- ation condition, and state the one stage deviation principle. [3]
(c) Let sP be the strategy where the player starts by playing A and then at each stage plays A if both players played the same strategy at the previous stage and plays B otherwise.
Use the one stage deviation principle to determine whether the pair (sP , sP ) is a subgame perfect Nash equilibrium for some range of val-
ues of 6 . [10]
[Total marks: 20]
4. Consider a two-player game with p x p payoff matrix A for each player.
(a) Give the definition of an Evolutionarily Stable Strategy (ESS). [2]
(b) Consider the game with payoff matrix
A = 、0(3) 2(0) ← .
Determine directly from the definition of an ESS whether the strategy
x = (1, 0) is an ESS. [5]
(c) Give an alternative characterisation of ESSs in terms of the equlibrium and stability conditions. [2]
(d) For the game given in part (b) determine whether the strategy x = (2/5, 3/5)
is an ESS. [4]
(e) Define the support and the pure equilibrium set for a mixed strategy, and state the Bishop-Cannings theorem. [4]
(f) Suppose that A is a 5 x 5 matrix with an ESS of the form x = (0, a, 1 - a, 0, 0) for some 0 < a < 1. Which (if any) of the following could possibly be an ESS? Give reasons for your answer
i. v = (0, 1/2, 1/3, 1/6, 0).
ii. v = (0, 0, 1, 0, 0).
[3] [Total marks: 20]
2022-08-25