1. CHAPTER 30 EXCHANGE

2. Partial equilibrium analysis: The equilibrium conditions of ONE particular market, leaving other markets untreated.
General equilibrium analysis: The equilibrium conditions of ALL markets, allowing interactions between different markets.

3. 30.1 The Edgeworth Box Two consumers: A and B. Two goods: 1 and 2.
Initial endowment:
Allocation:
Feasible allocation: total consumption does not exceed total endowment for both goods.

4. 30.1 The Edgeworth Box

5. 30.1 The Edgeworth Box
Each point in the Edgeworth box represents a feasible allocation.
From W to M:
Person A trades units of good 1 for units of good 2;
Person B trades units of good 2 for units of good 1.

6. 30.2 Trade

7. 30.2 Trade Trade happens whenever both consumers are better off.
Starting from W, M is a possible outcome of the exchange economy because:
Person A is strictly better off with than with ;
Person B is strictly better off with than with

8. 30.3 Pareto Efficient Allocations
An allocation is Pareto efficient whenever:
There is no way to make everyone strictly better off;
There is no way to make some strictly better off without making someone else worse off;
All of the gains from trade have been exhausted;
There are no (further) mutually advantageous trades to be made.

9. 30.3 Pareto Efficient Allocations

10. 30.3 Pareto Efficient Allocations
Pareto efficiency is given by the tangency of the indifference curves.
Contract curve: the locus of all Pareto efficient allocations.
Any allocation off the contract curve is Pareto inefficient.

11. 30.4 Market Trade
Gross demand: Quantity demanded for a good by a particular consumer at the market price.
Excess demand: The difference between the gross demand and the initial endowment of a good by a particular consumer.
Disequilibrium: Excess demands by both consumers do not sum up to zero.

12. 30.4 Market Trade

13. 30.4 Market Trade
Competitive equilibrium: A relative price and an allocation , such that:
The allocation matches the gross demands by both consumers, given the relative price and initial endowments;
The allocation is feasible.

14. 30.4 Market Trade

15. 30.5 The Algebra of Equilibrium
Consumer A’s demands:
Consumer B’s demands:
The equilibrium condition:
Re-arrangement:

16. 30.5 The Algebra of Equilibrium
Net demand:
Aggregate excess demand:
Another expression:

17. 30.6 Walras’ Law
Budget constraints:
Re-arrange the terms:
Adding up:

18. 30.6 Walras’ Law
Walras’ Law: The value of aggregate excess demand is always zero.
Applications of the Walras’ law:
implies ;
Market clearing for one good implies that of the other good;
With k goods, we only need to find a set of prices where k-1 of the markets are cleared.

19. 30.7 Relative Prices
Walras’ law implies k-1 independent equations for k unknown prices.
Only k-1 independent prices.
Numeraire prices: the price which can be used to measure all other prices.
If we choose p1 as the numeraire price, then it is just like multiplying all prices by the constant t=1/p1.

20. EXAMPLE: An Algebraic Example of Equilibrium
The Cobb-Douglas utility function:
The demand functions:

21. EXAMPLE: An Algebraic Example of Equilibrium
Income from endowments:
Aggregate excess demand for good 1:

22. EXAMPLE: An Algebraic Example of Equilibrium
Equilibrium condition:
Equilibrium price:

23. 30.8 The Existence of Equilibrium
The existence of a competitive equilibrium can be proved rigorously.
A formal proof is quite complicated and far beyond the scope of this course.

24. 30.9 Equilibrium and Efficiency
Both indifference curves are tangent to the budget line at the equilibrium allocation.
The equilibrium allocation lies upon the contract curve.
The First Theorem of Welfare Economics: Any competitive equilibrium is Pareto efficient.

25. EXAMPLE: Monopoly in the Edgeworth Box
A regular monopolist

26. EXAMPLE: Monopoly in the Edgeworth Box
First degree price discrimination

27. 30.11 Efficiency and Equilibrium
Reverse engineering:
Starting from any Pareto efficient allocation;
Use the common tangent line as the budget line;
Use any allocation on the budget line as the initial endowment.
The Second Theorem of Welfare Economics: For convex preferences, any Pareto efficient allocation is a competitive equilibrium for some set of prices and some initial endowments.

28. 30.11 Efficiency and Equilibrium
The Second Theorem of Welfare Economics

29. 30.11 Efficiency and Equilibrium
A Pareto efficient allocation that is not a competitive equilibrium.