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GSOE9210 Engineering Decisions
Problem Set 09
1. Consider the following game tree for a zero-sum game (payoffs shown are
for player X):
X
Y
1B
X
4d
3c
A
b
2a
(a) What are the possible strategies for players X and Y?
(b) Draw the corresponding normal (matrix) form from the perspective
of player X
(c) Simplify the game by eliminating strategies which aren’t best re-
sponses
(d) Does this game have a saddle point?
2. Find all saddle points for the zero-sum game with the following matrix:
b1 b2 b3 b4
a1 6 −1 1 0
a2 5 1 7 −2
a3 3 2 4 3
a4 −1 0 0 6-1.0
3. Find all saddle points for the following zero-sum game:
b1 b2 b3 b4
a1 4 2 5 2
a2 2 1 −1 −2
a3 3 2 4 2
a4 −1 0 6 1-1.0
4. Show that for any zero-sum game in normal (strategic) form the column
miniMax value is no less than the row Maximin.
Consequently, verify that the column maxima are all greater than the row
minima.
1
5. Consider the game matrix below for a non zero-sum game in which the
row player is R and the column player is C.
b1 b2 b3
a1 0, 0 1, 2 0, 2
a2 1, 3 1, 4 0, 0
00
13
(a) Identify the equilibrium plays.
(b) Which plays survive simplification?
(c) Which plays are Pareto optimal?
(d) Summarise your findings about non-zero-sum games and the rela-
tionship between:
i. plays obtained by dominance elimination and equilibria
ii. equilibria and Pareto optimal plays
6. Show that in a zero-sum game every outcome is Pareto optimal.
7. The game ‘Matching Pennies’ is a two-player zero-sum game in which each
player places a covered coin on a table. Each player chooses the face on
the coin but keeps it covered so that the other player doesn’t know which
face is up. The players uncover their coins simultaneously. The ‘matching’
player (M) wins if the faces on the coin match, and the ‘opposites’ player
(O) wins if the faces are opposite. The winner takes both coins.
(a) Represent this game in normal form, showing M’s payoffs.
(b) Reduce the game using dominance.
(c) Find the equilibria of this game.
(d) If M believes that O is twice as likely to play heads than tails, what
would be his best response?
(e) What should be M’s best response if he believes O will play heads
and tails with equal likelihood?
(f) Repeat question 7e above for O.
(g) If the game is repeated many times, what strategy should the players
play?
8. The following game tree represent the example in lectures for the case in
which Alice the gorilla moves first and Bob the monkey moves second.
A
B
0, 0w
9, 1c
W
B
4, 4w
5, 3c
C
(a) What is Bob’s best response to Alice if she waits? If Alice climbs?
(b) Are there any equilibrium points? If so, which are they?
2
(c) Rationalise the game using dominance.
9. If Alice and Bob move simultaneously we have the game tree below.
A
B
0, 0w
9, 1c
W
B
4, 4w
5, 3c
C
(a) Draw the game matrix.
(b) Are there any equilibrium plays/points? If so, which are they?
(c) If Bob had an injured arm, indicating that he would be less likely to
climb than to wait, which would be the rational solution?
10. Show that if a zero-sum game has a dominant row and column, then the
two determine an equilibrium play.