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Macroeconomics IV/Advanced

Macroeconomics B

Problem set 1

Summer 2022


Question 1


Consider the following utility maximization problem:


 

 

{ct ,kt+1>0}0 s.t.


E0  ,  pt (ln ct + y ln kt+1)

kt+1 + ct  = A t(1) -a kt(a)


where a e (0, 1), p e (0, 1), y | 0, ct  denotes consumption in period t , kt+1  is the amount of capital stock held at the   end of period t (and thus at the beginning of period t + 1), and At  is the productivity of capital stock in period t .

Assume that

ln At+1 = p ln At + et+1

for all t, where p e (0, 1) and et+1  is an independent white noise.

 

You can guess and verify that the value function in the       Bellman equation for this problem takes the following form:

V (At , kt) = F + G ln At + H ln kt

where F , G , and H are constants.

Suppose that a = 0.6, p = 0.9, y = 0.2, and p = 0.5. Given these parameter values, derive the values of F , G , and H with 2 decimal places (i.e., if the value of F is 1.6875, only answer 1.68). (Note: you do not need to de-trend the model, because there is no trend in At .)


Question 2                             

Consider the following utility maximization problem for a household:

{ct ,at+1 ,bt1a,dt(x)+1>0}0    pt  /  + y \

s.t. at+1 + bt+1 + dt+1 + ct  = (1 + i)at + (1 + ib)bt + (1 + id)dt

where f | 0, p e (0, 1), y | 0, ct  denotes consumption in    period t, and at+1 , bt+1 , dt+1  is the amounts of capital stock, government bonds, and bank deposits held at the end of         period t (and thus at the beginning of period t + 1). i , ib, and id  denote the constant gross rates of return on at , bt, and dt , respectively, at period t . Thus, the household faces no            uncertainty.


In the utility maximization problem, qt+1  measures the         “liquidity aggregate” that consists of government bonds and bank deposits. The value of this variable represents the         amount of convenience provided by the two types of financial assets, which are easily convertible into cash when the           household needs to make payments. The utility of this          convenience is assumed to be determined by the following     function form:

qt   [(1 - )bt(p) + dt(p)]

where  e (0, 1) and p ) 1.            

In the following questions, you can assume ct  | 0, at+1  | 0, bt+1  | 0, and dt+1  | 0 for all t at the optimum.

a.  Derive the rst order condition for at+1 . Suppose f = 2, p = 0.9, y = 0.2, and i = 0.05. Also, assume ct+1 = 5. What is the value of ct  implied by the first order             condition for at  in this case? Derive the answer with 2    decimal places.

b.  In addition, derive the rst order conditions for bt+1  and dt+1 . Suppose  = 0.5, p = 0.5, i = 0.05, ib  = 0.02,    id  = 0. What is the ratio of bt+1 to dt+1  implied by the

first order conditions in this case? Derive the answer with 2 decimal places.