미시경제학 게임이론 문제 질문

미시경제학 게임이론 문제 질문

작성일 2023.10.23댓글 2건
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①  Consider an industry in which two firms compete by simultaneously and independently selecting prices for their goods. Firm 1's product and firm 2's product are imperfect substitutes, so that an increase in one firm's price will lead to an increase in the quantity demanded of the other firm's product. In particular, each firm i faces the following demand curve: 

qi = max{0, 24 − 2pi + pj}, 

where qi is the quantity that firm i sells, pi is firm i's price, and pj is the other firm's price. (The maximum operator is needed to ensure that quantity demanded is never negative.) 
Suppose that the maximum possible price is 20 and the minimum price is zero, so the strategy space for each firm i is Si = [0, 20]. Both firms produce with no costs. 

(a) What is rm i's prot as a function of the strategy profile (p1, p2)? Let each firm's pay off be defined as its profit. 

(b) Show that for each firm i, prices less than 6 and prices greater than 11 are dominated strategies, whereas prices from 6 to 11 are not dominated. 

(c) Consider a reduced game in which firms select prices between x and y, where x < y. 
What strategies are undominated in such a game? Use your answer to compute the set of strategies profiles in their survives iterated dominance in the original game.


② Two players are involved in a dispute over an object. The value of the object to player i is vi > 0. Time is modeled as a continuous variable that starts at 0 and runs indefinitely. Each player chooses when to concede the object to the other player; if the first player to concede does so at time t, the other player obtains the object at that time. If both players concede simultaneously, the object is split equally between them, player i receiving a pay off of vi/2. Time is valuable: until the first concession each player loses one unit of pay off per unit of time. 

(a) Formulate this situation as a normal-form game. 
(b) Show that in all Nash equilibria one of the players concedes immediately

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where qi is the quantity sold by firm i, pi is the price set by firm i, and pj is the price set by the other firm.

a. Find the best response function for each firm.

To find the best response function for each firm, we need to determine the price that maximizes each firm's profit given the price set by the other firm.

For Firm 1, the profit function is given by π1 = (p1 - c) * q1, where c is the cost per unit.

Substituting the demand curve into the profit function, we have:

π1 = (p1 - c) * max{0, 24 - 2p1 + p2}

To find the price that maximizes Firm 1's profit, we take the derivative of the profit function with respect to p1 and set it equal to zero:

dπ1/dp1 = -2 * (p1 - c) + max{0, 24 - 2p1 + p2} = 0

To simplify the expression, we consider two cases:

1. When 24 - 2p1 + p2 > 0:

In this case, the best response function for Firm 1 is:

p1 = (24 + p2) / 2

2. When 24 - 2p1 + p2 ≤ 0:

In this case, Firm 1 will not produce any quantity, so the best response function is:

p1 = undefined (no price is set)

Similarly, we can find the best response function for Firm 2. The profit function for Firm 2 is given by π2 = (p2 - c) * q2, where q2 = max{0, 24 - 2p2 + p1}.

Taking the derivative of the profit function with respect to p2 and setting it equal to zero, we have:

dπ2/dp2 = -2 * (p2 - c) + max{0, 24 - 2p2 + p1} = 0

Again, considering two cases:

1. When 24 - 2p2 + p1 > 0:

The best response function for Firm 2 is:

p2 = (24 + p1) / 2

2. When 24 - 2p2 + p1 ≤ 0:

Firm 2 will not produce any quantity, so the best response function is:

p2 = undefined (no price is set)

b. Find the Nash equilibrium of this game.

The Nash equilibrium is a combination of strategies where no firm has an incentive to unilaterally deviate. In this case, it is a combination of prices (p1, p2) where both firms choose their best response strategies simultaneously.

From the best response functions derived above, we can observe that the only possible Nash equilibrium is when both firms choose the same price, resulting in p1 = p2 = (24 + p1) / 2.

Simplifying the equation, we have:

2p1 = 24 + p1

p1 = 24

Therefore, the Nash equilibrium is p1 = p2 = 24.

c. Calculate the quantity sold by each firm at the Nash equilibrium.

To calculate the quantity sold by each firm at the Nash equilibrium, we substitute p1 = p2 = 24 into the demand curve for each firm.

For Firm 1:

q1 = max{0, 24 - 2(24) + 24} = max{0, 24 - 48 + 24} = max{0, 0} = 0

For Firm 2:

q2 = max{0, 24 - 2(24) + 24} = max{0, 24 - 48 + 24} = max{0, 0} = 0

Therefore, at the Nash equilibrium, both firms will not sell any quantity.

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where qi is the quantity demanded by firm i, pi is the price chosen by firm i, and pj is the price chosen by the other firm.

a) Find the reaction function for each firm, i.e. the price that each firm will choose as a function of the other firm's price.

To find the reaction function for each firm, we need to determine the price that maximizes its profit given the price chosen by the other firm.

For firm 1:

The profit function for firm 1 is given by π1 = (p1 - c) * q1, where c is the cost per unit for firm 1.

Substituting the demand function into the profit function, we have:

π1 = (p1 - c) * max{0, 24 - 2p1 + p2}

To maximize profit, we set the derivative of the profit function with respect to p1 equal to zero:

∂π1/∂p1 = 0

Differentiating the profit function with respect to p1, we have:

-2 * (p1 - c) + max{0, 24 - 2p1 + p2} = 0

Simplifying the equation, we get:

p1 = (24 + p2 - c) / 3

Therefore, the reaction function for firm 1 is:

p1 = (24 + p2 - c) / 3

For firm 2:

Using a similar approach, the profit function for firm 2 is given by π2 = (p2 - c) * q2.

Substituting the demand function into the profit function, we have:

π2 = (p2 - c) * max{0, 24 - 2p2 + p1}

To maximize profit, we set the derivative of the profit function with respect to p2 equal to zero:

∂π2/∂p2 = 0

Differentiating the profit function with respect to p2, we have:

-2 * (p2 - c) + max{0, 24 - 2p2 + p1} = 0

Simplifying the equation, we get:

p2 = (24 + p1 - c) / 3

Therefore, the reaction function for firm 2 is:

p2 = (24 + p1 - c) / 3

b) Find the Nash equilibrium, i.e. the combination of prices that both firms will choose.

The Nash equilibrium occurs when each firm chooses a price that is a best response to the price chosen by the other firm. In other words, the Nash equilibrium is the combination of prices (p1, p2) such that p1 is the best response to p2, and p2 is the best response to p1.

Substituting the reaction function for firm 2 into the reaction function for firm 1, we have:

p1 = (24 + [(24 + p1 - c) / 3] - c) / 3

Simplifying the equation, we get:

p1 = (72 + 2p1 - 2c - 3c) / 9

9p1 = 72 + 2p1 - 2c - 3c

7p1 = 72 - 5c

Similarly, substituting the reaction function for firm 1 into the reaction function for firm 2, we have:

p2 = (24 + [(24 + p2 - c) / 3] - c) / 3

Simplifying the equation, we get:

p2 = (72 + 2p2 - 2c - 3c) / 9

9p2 = 72 + 2p2 - 2c - 3c

7p2 = 72 - 5c

Solving these two equations simultaneously, we can find the Nash equilibrium prices (p1, p2).

c) Discuss the implications of this game for the firms' pricing strategies and profits.

In this game, both firms have an incentive to undercut each other's prices in order to gain a larger market share. However, since an increase in one firm's price leads to an increase in the quantity demanded of the other firm's product, the firms need to carefully consider the trade-off between price and quantity.

The reaction functions derived in part (a) show that each firm's price depends on the other firm's price. This indicates that the firms are strategic in their pricing decisions, taking into account the potential actions of their competitor.

The Nash equilibrium prices obtained in part (b) represent the combination of prices that both firms will choose. These prices will depend on the cost parameter, c, and can vary depending on the specific values of c.

The implications for the firms' pricing strategies are that they need to consider not only their own costs and demand, but also the potential actions of their competitor. They need to strategically set their prices to maximize their profits, taking into account the interdependence between their pricing decisions.

The profits of the firms will depend on the prices chosen and the resulting quantity demanded. Higher prices may lead to higher profit margins per unit sold, but lower demand. Lower prices may lead to higher demand, but lower profit margins. The firms need to find a balance between price and quantity that maximizes their overall profit.

Overall, this game highlights the strategic nature of pricing decisions in a competitive market where firms' products are imperfect substitutes. The firms need to carefully consider their pricing strategies and the potential actions of their competitor in order to achieve their profit objectives.

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