Macro, Money and Finance - PrincetonΒ Β· Price-Taking Plannerβs Theorem: A social planner that...
Transcript of Macro, Money and Finance - PrincetonΒ Β· Price-Taking Plannerβs Theorem: A social planner that...
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Macro, Money and FinanceLecture 06: Money versus Debt
Markus Brunnermeier, Lars Hansen, Yuliy Sannikov
Princeton, Chicago, NYU, UPenn, Northwestern, EPFL, Stanford, Chicago Fed Spring 2019
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Towards the I Theory of Money One sector model with idio risk - βThe I Theory without Iβ
(steady state focus) Store of value Insurance role of money within sector
Money as bubble or not Fiscal Theory of the Price Level Medium of Exchange Role β SDF-Liquidity multiplier β Money bubble
2 sector/type model with money and idio risk Generic Solution procedure (compared to lecture 03) Real debt vs. Money Implicit insurance role of money across sectors
The curse of insurance Reduces insurance premia and net worth gains
I Theory with Intermediary sector Intermediaries as diversifiers
Welfare analysis Optimal Monetary Policy and Macroprudential Policy
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Two Sector Model w/ Outside Equity & Money
Expert sector Household sector
Experts must hold fraction πππ‘π‘ β₯ πΌπΌπππ‘π‘ (skin in the game constraint)
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A L
Capitalπππ‘π‘πππ‘π‘πΎπΎπ‘π‘
Outside equityπππ‘π‘
Real Debt
A L
Capital1 β πππ‘π‘ πππ‘π‘πΎπΎπ‘π‘
Equity
Net worthπππ‘π‘
Real DebtClaims
β₯ πΌπΌ
Expanded on Handbook of Macroeconomics 2017, Chapter 18- Includes now money and idiosyncratic risk
Money Money/Nominal Debt
Households hold portfolio of expertsβ outside equity and diversify idio risk away
Outside money
Diversification
Money/Nominal Debt
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Two Sector Model Setup
Expert sectorOutput: π¦π¦π‘π‘ = πππππ‘π‘ Consumption rate: πππ‘π‘ Investment rate: πππ‘π‘πππππ‘π‘
οΏ½οΏ½π€
πππ‘π‘οΏ½οΏ½π€
= Ξ¦ πππ‘π‘ βπΏπΏ πππ‘π‘+πππππππ‘π‘+οΏ½ππππ οΏ½πππ‘π‘οΏ½οΏ½π€+ππΞπ‘π‘
ππ,οΏ½οΏ½π€
πΈπΈ0[β«0β ππβπππ‘π‘πππ‘π‘
1βπΎπΎ
1βπΎπΎ ππππ]
Friction: Can only issue Risk-free debt Equity, but most hold πππ‘π‘ β₯ πΌπΌ 4
Household sectorOutput: π¦π¦π‘π‘ = πππππ‘π‘ Consumption rate: πππ‘π‘ Investment rate: πππ‘π‘πππππ‘π‘
οΏ½οΏ½π€
πππ‘π‘οΏ½οΏ½π€
= Ξ¦ πππ‘π‘ βπΏπΏ πππ‘π‘+πππππππ‘π‘+οΏ½ππππ οΏ½πππ‘π‘οΏ½οΏ½π€+ππΞπ‘π‘
ππ,οΏ½οΏ½π€
πΈπΈ0[β«0βππβπππ‘π‘πππ‘π‘
1βπΎπΎ
1βπΎπΎ ππππ]
ππ β₯ ππ
ππ β₯ ππ
πΏπΏ β€ πΏπΏοΏ½ππ β€ οΏ½ππ
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Solving MacroModels Step-by-Step0. Postulate aggregates, price processes & obtain return processes1. For given SDF processes static
a. Real investment ππ, (portfolio π½π½, & consumption choice of each agent) Toolbox 1: Martingale Approach
b. Asset/Risk Allocation across types/sectors & asset market clearing Toolbox 2: βprice-taking social planner approachβ β Fisher separation theorem
2. Value functions backward equationa. Value fcn. as fcn. of individual investment opportunities ππ
Special casesb. De-scaled value fcn. as function of state variables ππ
Digression: HJB-approach (instead of martingale approach & envelop condition)
c. Derive ππ price of risk, πΆπΆ/ππ-ratio from value fcn. envelop condition
3. Evolution of state variable ππ forward equation Toolbox 3: Change in numeraire to total wealth (including SDF) βMoney evaluation equationβ ππππ
4. Value function iteration & goods market clearinga. PDE of de-scaled value fcn.b. Value function iteration by solving PDE 5
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0. Postulate Aggregates Individual capital evolution:
πππππ‘π‘ππ,οΏ½οΏ½π€
πππ‘π‘ππ,οΏ½οΏ½π€ = Ξ¦ ππππ,οΏ½οΏ½π€ β πΏπΏ ππππ + πππππππ‘π‘ + οΏ½ππππππ οΏ½πππ‘π‘
ππ,οΏ½οΏ½π€ + ππΞπ‘π‘ππ,ππ,οΏ½οΏ½π€
Where Ξπ‘π‘ππ,οΏ½οΏ½π€,ππ is the individual cumulative capital purchase process
Capital aggregation: Within sector ππ: πΎπΎπ‘π‘ππ β‘ β« πππ‘π‘
ππ,οΏ½οΏ½π€ππ π€π€ Across sectors: πΎπΎπ‘π‘ β‘ βππ πΎπΎπ‘π‘ππ Capital share: πππ‘π‘ππ β‘ πΎπΎπ‘π‘ππ/πΎπΎπ‘π‘
πππΎπΎπ‘π‘πΎπΎπ‘π‘
= β« Ξ¦ ππππ β πΏπΏ ππππ ππππ + πππππππ‘π‘ Networth aggregation: Within sector ππ: πππ‘π‘ππ β‘ β« πππ‘π‘
ππ,οΏ½οΏ½π€ππ π€π€ Across sectors: πππ‘π‘ β‘ βππ πππ‘π‘ππ Wealth share: πππ‘π‘ππ β‘ πππ‘π‘ππ/πππ‘π‘
Value of capital: πππ‘π‘πΎπΎπ‘π‘ Value of money: πππ‘π‘πΎπΎπ‘π‘
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0. Postulate Processes
Value of capital: πππ‘π‘πΎπΎπ‘π‘ Value of money: πππ‘π‘πΎπΎπ‘π‘ Postulate
πππππ‘π‘/πππ‘π‘ = πππ‘π‘ππππππ + πππ‘π‘
πππππππ‘π‘πππππ‘π‘/πππ‘π‘ = πππ‘π‘
ππππππ + πππ‘π‘πππππππ‘π‘
πππππ‘π‘ππ/πππ‘π‘ππ = οΏ½πππ‘π‘ππ ππππβ‘βπππ‘π‘
+ οΏ½πππ‘π‘ππππ
β‘βπππ‘π‘ππ
πππππ‘π‘ + οΏ½οΏ½ππππππ
β‘βοΏ½πππ‘π‘ππππ οΏ½πππ‘π‘οΏ½οΏ½π€
Derive return processes
πππππ‘π‘πΎπΎ,ππ,οΏ½οΏ½π€ =
ππππ β πππ‘π‘οΏ½οΏ½π€
πππ‘π‘+ Ξ¦ πππ‘π‘οΏ½οΏ½π€ β πΏπΏ + πππ‘π‘
ππ + πππππ‘π‘ππ ππππ + ππ + πππ‘π‘
ππ πππππ‘π‘ + οΏ½ππππππ οΏ½πππ‘π‘οΏ½οΏ½π€
πππππ‘π‘ππ = Ξ¦ πππ‘π‘ β πΏπΏ + πππ‘π‘ππ + πππππ‘π‘
ππ β ππππ ππππ + ππ + πππ‘π‘ππ πππππ‘π‘
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Solving MacroModels Step-by-Step0. Postulate aggregates, price processes & obtain return processes1. For given SDF processes static
a. Real investment ππ, (portfolio π½π½, & consumption choice of each agent) Toolbox 1: Martingale Approach
b. Asset/Risk Allocation across types/sectors & asset market clearing Toolbox 2: βprice-taking social planner approachβ β Fisher separation theorem
2. Value functions backward equationa. Value fcn. as fcn. of individual investment opportunities ππ
Special casesb. De-scaled value fcn. as function of state variables ππ
Digression: HJB-approach (instead of martingale approach & envelop condition)
c. Derive ππ price of risk, πΆπΆ/ππ-ratio from value fcn. envelop condition
3. Evolution of state variable ππ forward equation Toolbox 3: Change in numeraire to total wealth (including SDF) βMoney evaluation equationβ ππππ
4. Value function iteration & goods market clearinga. PDE of de-scaled value fcn.b. Value function iteration by solving PDE 8
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1a. Agent Choice of ππ, ππ, ππ Portfolio Choice: Martingale Approach Let π₯π₯π‘π‘π΄π΄ be the value of a βself-financing trading strategyβ
(reinvest dividends) Theorem: πππ‘π‘π₯π₯π‘π‘π΄π΄ follows a Martingale, i.e. drift = 0.
Let πππππ‘π‘π΄π΄
πππ‘π‘π΄π΄= πππ‘π‘π΄π΄ππππ + πππ‘π‘π΄π΄πππππ‘π‘ + οΏ½πππ‘π‘π΄π΄πποΏ½πππ‘π‘,
Recall πππππ‘π‘ππ
πππ‘π‘ππ = βπππ‘π‘ππππ β πππ‘π‘πππππππ‘π‘ β οΏ½πππ‘π‘πππποΏ½πππ‘π‘ππ
By Ito product ruleππ πππ‘π‘
πππππ‘π‘π΄π΄
πππ‘π‘πππππ‘π‘π΄π΄
= βπππ‘π‘ + πππ‘π‘π΄π΄ β πππ‘π‘πππππ‘π‘π΄π΄ β οΏ½πππ‘π‘ππ οΏ½πππ‘π‘π΄π΄ ππππ=0
+volatility terms
Expected return: πππ‘π‘π΄π΄ = πππ‘π‘ + πππ‘π‘πππππ‘π‘π΄π΄ + οΏ½πππ‘π‘ππ οΏ½πππ‘π‘π΄π΄
For risk-free asset, i.e. πππ‘π‘π΄π΄ = οΏ½πππ‘π‘π΄π΄ = 0:πππ‘π‘ππ = πππ‘π‘
Excess expected return to risky asset B: πππ‘π‘π΄π΄ β πππ‘π‘π΅π΅ = πππ‘π‘ππ(πππ‘π‘π΄π΄ β πππ‘π‘π΅π΅) + οΏ½πππ‘π‘ππ (οΏ½πππ‘π‘π΄π΄ β οΏ½πππ‘π‘π΅π΅)
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Solving MacroModels Step-by-Step0. Postulate aggregates, price processes & obtain return processes1. For given SDF processes static
a. Real investment ππ, (portfolio π½π½, & consumption choice of each agent) Toolbox 1: Martingale Approach
b. Asset/Risk Allocation across types/sectors & asset market clearing Toolbox 2: βprice-taking social planner approachβ β Fisher separation theorem
2. Value functions backward equationa. Value fcn. as fcn. of individual investment opportunities ππ
Special casesb. De-scaled value fcn. as function of state variables ππ
Digression: HJB-approach (instead of martingale approach & envelop condition)
c. Derive ππ price of risk, πΆπΆ/ππ-ratio from value fcn. envelop condition
3. Evolution of state variable ππ forward equation Toolbox 3: Change in numeraire to total wealth (including SDF) βMoney evaluation equationβ ππππ
4. Value function iteration & goods market clearinga. PDE of de-scaled value fcn.b. Value function iteration by solving PDE 10
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1b. Asset/Risk Allocation across Types Price-Taking Plannerβs Theorem:
A social planner that takes prices as given chooses an physical asset and money allocation, πππ‘π‘, and risk allocation πππ‘π‘,οΏ½πππ‘π‘, that coincides with the choices implied by all individualsβ portfolio choices.
Plannerβs problemmax
{πππ‘π‘,πππ‘π‘,οΏ½πππ‘π‘}πΈπΈπ‘π‘[πππππ‘π‘
οΏ½ππ πππ‘π‘ ] β πππ‘π‘ππ πππ‘π‘,πππ‘π‘ β οΏ½πππ‘π‘ οΏ½ππ(ππππ, οΏ½πππ‘π‘)
subject to friction: πΉπΉ πππ‘π‘,πππ‘π‘, οΏ½πππ‘π‘ β€ 0 Example:
1. πππ‘π‘ = πππ‘π‘ (if one holds capital, one has to hold risk)2. πππ‘π‘ β₯ πΌπΌπππ‘π‘ (skin in the game constraint, outside equity up to a limit)
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= πππππΉπΉ in equilibrium
πππ‘π‘ = πππ‘π‘1, β¦ , πππ‘π‘πΌπΌππππ = πππ‘π‘1, β¦ ,πππ‘π‘πΌπΌ
ππ πππ‘π‘,πππ‘π‘ = πππ‘π‘1πποΏ½ππ(πππ‘π‘), β¦ ,πππ‘π‘πΌπΌππ
οΏ½ππ(πππ‘π‘)οΏ½ππ πππ‘π‘,πππ‘π‘ = οΏ½ππππ1(πππ‘π‘, οΏ½πππ‘π‘), β¦ , οΏ½πππππΌπΌ(ππππ, οΏ½πππ‘π‘)
Note: By holding a portfolio of various expertsβ outside equity HH can diversify idio risk away
Return on total wealth (including money)
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1b. Allocation of Capital, ππ, and Risk, ππ
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Cases πππ‘π‘ β₯ πΌπΌπππ‘π‘ πππ‘π‘ β€ 1 ππ β πππππ‘π‘
β₯ πΌπΌ πππ‘π‘ β πππ‘π‘ ππ + πππ‘π‘ππ
+ πΌπΌ πππ‘π‘ β πππ‘π‘ οΏ½ππ
πππ‘π‘ ππ + πππ‘π‘ππ + πππ‘π‘ οΏ½ππ
> πππ‘π‘ ππ + πππ‘π‘ππ
1a = < = >
1b = = > >
2a > = > =
Impossible
Note that HH, which hold a portfolio of different expertsβ outside equitycan diversify idiosyncratic risk away
If you shift one capital unit from HH to experts- Dividend yield rises by LHS, - Change the aggregate required
risk premium (alpha fraction dueto skin of the game constraint)
- HH reduce their risk by one unit, sell back 1 β πΌπΌ and diversified away
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1b. Allocation of Capital, ππ, and Risk, ππ
)
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Cases πππ‘π‘ β₯ πΌπΌπππ‘π‘ πππ‘π‘ β€ 1 ππ β πππππ‘π‘
β₯ πΌπΌ πππ‘π‘ β πππ‘π‘ ππ + πππ‘π‘ππ
+ πΌπΌ πππ‘π‘ β πππ‘π‘ οΏ½ππ
πππ‘π‘ ππ + πππ‘π‘ππ + πππ‘π‘ οΏ½ππ
> πππ‘π‘ ππ + πππ‘π‘ππ
1a = < = >
1b = = > >
2a > = > =
Impossible
Case 1a Case 1b Case 2aππ
Expertsβ skin in the game constraint binds, πππ‘π‘ = πΌπΌπππ‘π‘
HHsβ short-sale constraint of capital binds, πππ‘π‘ = 1
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Solving MacroModels Step-by-Step0. Postulate aggregates, price processes & obtain return processes1. For given SDF processes static
a. Real investment ππ, (portfolio π½π½, & consumption choice of each agent) Toolbox 1: Martingale Approach
b. Asset/Risk Allocation across types/sectors & asset market clearing Toolbox 2: βprice-taking social planner approachβ β Fisher separation theorem
2. Value functions backward equationa. Value fcn. as fcn. of individual investment opportunities ππ
Special casesb. De-scaled value fcn. as function of state variables ππ
Digression: HJB-approach (instead of martingale approach & envelop condition)
c. Derive ππ price of risk, πΆπΆ/ππ-ratio from value fcn. envelop condition
3. Evolution of state variable ππ forward equation Toolbox 3: Change in numeraire to total wealth (including SDF) βMoney evaluation equationβ ππππ
4. Value function iteration & goods market clearinga. PDE of de-scaled value fcn.b. Value function iteration by solving PDE 14
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2b. CRRA Value Fcn: Isolating Idio. Risk
Rephrase the conjecture value function as
πππ‘π‘ =1πππππ‘π‘πππ‘π‘ 1βπΎπΎ
1 β πΎπΎ=
1ππ(1 β πΎπΎ)
πππ‘π‘πππ‘π‘πΎπΎπ‘π‘
1βπΎπΎ
=:π£π£π‘π‘
πππ‘π‘πππ‘π‘
1βπΎπΎ
=: οΏ½πππ‘π‘οΏ½οΏ½π€ 1βπΎπΎ
πΎπΎπ‘π‘1βπΎπΎ
π£π£π‘π‘ depends only on aggregate state πππ‘π‘ Itoβs quotation ruleππ οΏ½πππ‘π‘οΏ½οΏ½π€
οΏ½πππ‘π‘οΏ½οΏ½π€=ππ πππ‘π‘/πππ‘π‘πππ‘π‘/πππ‘π‘
= πππ‘π‘ππ β πππ‘π‘ππ + πππ‘π‘ππ 2 β ππππππππ ππππ + πππ‘π‘ππ β πππ‘π‘ππ πππππ‘π‘ + οΏ½ππππππ οΏ½πππ‘π‘οΏ½οΏ½π€ = οΏ½ππππππ οΏ½πππ‘π‘οΏ½οΏ½π€
Itoβs Lemmaππ οΏ½πππ‘π‘οΏ½οΏ½π€
1βπΎπΎ
οΏ½πππ‘π‘οΏ½οΏ½π€1βπΎπΎ = β
12πΎπΎ 1 β πΎπΎ οΏ½ππππ 2ππππ + 1 β πΎπΎ οΏ½ππππππ οΏ½πππ‘π‘οΏ½οΏ½π€
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2b. CRRA Value Function
πππππ‘π‘πππ‘π‘
=ππ π£π£π‘π‘ οΏ½πππ‘π‘οΏ½οΏ½π€
1βπΎπΎπΎπΎπ‘π‘1βπΎπΎ
π£π£π‘π‘ οΏ½πππ‘π‘οΏ½οΏ½π€1βπΎπΎπΎπΎπ‘π‘
1βπΎπΎ
By Itoβs product rule
= πππ‘π‘π£π£ + 1 β πΎπΎ Ξ¦ ππ β πΏπΏ β12πΎπΎ 1 β πΎπΎ ππ2 + οΏ½ππππ 2 + 1 β πΎπΎ πππππ‘π‘π£π£ ππππ
+ π£π£π£π£π£π£πππππππ£π£πππππ¦π¦ πππππππ‘π‘π‘π‘
Recall by consumption optimality πππππ‘π‘πππ‘π‘β ππππππ + πππ‘π‘
πππ‘π‘ππππ follows a martingale
Hence, drift above = ππ β πππ‘π‘πππ‘π‘
16Still have to solve for πππ‘π‘π£π£, πππ‘π‘π£π£
Poll 16: Why martingale?a) Because we can βpriceβ
networth with SDFb) because ππ and πππ‘π‘/πππ‘π‘
cancel out
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2b. CRRA Value Fcn BSDE Only conceptual interim solution
We will transform it into a PDE in Step 4 below From last slideπππ‘π‘π£π£ + 1 β πΎπΎ Ξ¦ ππ β πΏπΏ β
12πΎπΎ 1 β πΎπΎ ππ2 + οΏ½ππππ 2 + 1 β πΎπΎ πππππ‘π‘π£π£
=:πππ‘π‘ππ
= ππ βπππ‘π‘πππ‘π‘
Can solve for πππ‘π‘π£π£, then π£π£π‘π‘ must followπππ£π£π‘π‘π£π£π‘π‘
= ππ πππ‘π‘ , π£π£π‘π‘,πππ‘π‘π£π£ ππππ + πππ‘π‘π£π£πππππ‘π‘with
ππ πππ‘π‘ , π£π£π‘π‘,πππ‘π‘π£π£ = ππ βπππ‘π‘πππ‘π‘β 1 β πΎπΎ Ξ¦ ππ β πΏπΏ +
12πΎπΎ 1 β πΎπΎ ππ2 + οΏ½ππππ 2 β 1 β πΎπΎ πππππ‘π‘π£π£
Together with terminal condition π£π£ππ (possibly a constant for 1000 periods ahead), this is a backward stochastic differential equation (BSDE)
A solution consists of processes π£π£ and πππ£π£
Can use numerical BSDE solution methods (as random objects, so only get simulated paths)
To solve this via a PDE we also need to get state evolution
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Solving MacroModels Step-by-Step0. Postulate aggregates, price processes & obtain return processes1. For given SDF processes static
a. Real investment ππ, (portfolio π½π½, & consumption choice of each agent) Toolbox 1: Martingale Approach
b. Asset/Risk Allocation across types/sectors & asset market clearing Toolbox 2: βprice-taking social planner approachβ β Fisher separation theorem
2. Value functions backward equationa. Value fcn. as fcn. of individual investment opportunities ππ
Special casesb. De-scaled value fcn. as function of state variables ππ
Digression: HJB-approach (instead of martingale approach & envelop condition)
c. Derive ππ, ππ price of risk, πΆπΆ/ππ-ratio from value fcn. envelop condition
3. Evolution of state variable ππ forward equation Toolbox 3: Change in numeraire to total wealth (including SDF) βMoney evaluation equationβ ππππ
4. Value function iteration & goods market clearinga. PDE of de-scaled value fcn.b. Value function iteration by solving PDE 18
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2c. Get ππs from Value Function Envelop Experts value function HHβs value function
π£π£π‘π‘πΎπΎπ‘π‘1βπΎπΎ
1βπΎπΎοΏ½πππ‘π‘οΏ½οΏ½π€
1βπΎπΎ π£π£π‘π‘πΎπΎπ‘π‘1βπΎπΎ
1βπΎπΎοΏ½πππ‘π‘οΏ½οΏ½π€
1βπΎπΎ
To obtain πππππ‘π‘ πππππππ‘π‘
use πΎπΎπ‘π‘ = πππ‘π‘πππ‘π‘ πππ‘π‘+πππ‘π‘
= 1οΏ½πππ‘π‘οΏ½οΏ½π€
πππ‘π‘πππ‘π‘ πππ‘π‘+πππ‘π‘
πππ‘π‘ ππ = π£π£π‘π‘πππ‘π‘1βπΎπΎ/(πππ‘π‘ πππ‘π‘+πππ‘π‘ )1βπΎπΎ
1βπΎπΎβ¦
Envelop condition πππππ‘π‘ πππππππ‘π‘
= ππππ πππ‘π‘πππππ‘π‘
π£π£π‘π‘πππ‘π‘βπΎπΎ
(πππ‘π‘ πππ‘π‘+πππ‘π‘ )1βπΎπΎ= πππ‘π‘
βπΎπΎ β¦
Using πΎπΎπ‘π‘ = 1οΏ½πππ‘π‘οΏ½οΏ½π€
πππ‘π‘πππ‘π‘ πππ‘π‘+πππ‘π‘
, πΆπΆπ‘π‘ = 1οΏ½πππ‘π‘οΏ½οΏ½π€ πππ‘π‘
π£π£π‘π‘πππ‘π‘ πππ‘π‘+πππ‘π‘
πΎπΎπ‘π‘βπΎπΎ = πΆπΆπ‘π‘
βπΎπΎ β¦
πππ‘π‘π£π£ β πππ‘π‘ππ β πππ‘π‘
ππ+ππ β πΎπΎππ = βπΎπΎπππ‘π‘ππ , πππ‘π‘π£π£ β πππ‘π‘
ππβ πππ‘π‘
ππ+ππ β πΎπΎππ = βπΎπΎπππ‘π‘ππ
= βπππ‘π‘ = βπππ‘π‘ 19
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2c. Get ππs from Value Function Envelop Experts value function HHβs value function
π£π£π‘π‘πΎπΎπ‘π‘1βπΎπΎ
1βπΎπΎοΏ½πππ‘π‘οΏ½οΏ½π€
1βπΎπΎ π£π£π‘π‘πΎπΎπ‘π‘1βπΎπΎ
1βπΎπΎοΏ½πππ‘π‘οΏ½οΏ½π€
1βπΎπΎ
To obtain πππππ‘π‘ πππππππ‘π‘
use πΎπΎπ‘π‘ = πππ‘π‘πππ‘π‘ πππ‘π‘+πππ‘π‘
= 1οΏ½πππ‘π‘οΏ½οΏ½π€
πππ‘π‘πππ‘π‘ πππ‘π‘+πππ‘π‘
πππ‘π‘ ππ = π£π£π‘π‘πππ‘π‘1βπΎπΎ/(πππ‘π‘ πππ‘π‘+πππ‘π‘ )1βπΎπΎ
1βπΎπΎβ¦
Envelop condition πππππ‘π‘ πππππππ‘π‘
= ππππ πππ‘π‘πππππ‘π‘
π£π£π‘π‘πππ‘π‘βπΎπΎ
(πππ‘π‘ πππ‘π‘+πππ‘π‘ )1βπΎπΎ= πππ‘π‘
βπΎπΎ β¦
Using πΎπΎπ‘π‘ = 1οΏ½πππ‘π‘οΏ½οΏ½π€
πππ‘π‘πππ‘π‘ πππ‘π‘+πππ‘π‘
, πΆπΆπ‘π‘ = 1οΏ½πππ‘π‘οΏ½οΏ½π€ πππ‘π‘
π£π£π‘π‘πππ‘π‘ πππ‘π‘+πππ‘π‘
πΎπΎπ‘π‘βπΎπΎ = πΆπΆπ‘π‘
βπΎπΎ β¦
πππ‘π‘π£π£ β πππ‘π‘ππ β πππ‘π‘
ππ+ππ β πΎπΎππ = βπΎπΎπππ‘π‘ππ , πππ‘π‘π£π£ β πππ‘π‘
ππβ πππ‘π‘
ππ+ππ β πΎπΎππ = βπΎπΎπππ‘π‘ππ
= βπππ‘π‘ = βπππ‘π‘ 20
By Itoβs Lemmaπππ‘π‘ + πππ‘π‘ πππ‘π‘
ππ+ππ = πππ‘π‘πππ‘π‘ππ + πππ‘π‘πππ‘π‘
ππ
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2c. Get ππs from Value Function Envelop Experts risk-premia HHβs risk premia
π£π£π‘π‘πΎπΎπ‘π‘1βπΎπΎ
1βπΎπΎοΏ½πππ‘π‘οΏ½οΏ½π€
1βπΎπΎ π£π£π‘π‘πΎπΎπ‘π‘1βπΎπΎ
1βπΎπΎοΏ½πππ‘π‘οΏ½οΏ½π€
1βπΎπΎ
πππ‘π‘ = πΎπΎπππ‘π‘ππ = πππ‘π‘ = πΎπΎπππ‘π‘ππ =
βπππ‘π‘π£π£ + πππ‘π‘ππ + πππ‘π‘
ππ+ππ + πΎπΎππ βπππ‘π‘π£π£ β πππ‘π‘πππ‘π‘
ππ
1βπππ‘π‘+ πππ‘π‘
ππ+ππ + πΎπΎππ
For πππ‘π‘note that from
π£π£π‘π‘πππ‘π‘βπΎπΎ
(πππ‘π‘ πππ‘π‘+πππ‘π‘ )1βπΎπΎ= πππ‘π‘
βπΎπΎ follows οΏ½πππ‘π‘ππ = οΏ½πππ‘π‘ππ
Hence, πππ‘π‘ = πΎπΎ οΏ½πππ‘π‘ππ πππ‘π‘ = πΎπΎ οΏ½πππ‘π‘ππ
Recall Martingale approach asset pricing21
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2c. Get πΆπΆπ‘π‘πππ‘π‘
, πΆπΆπ‘π‘πππ‘π‘
from Value Function Envelop
Experts Households
Recall π£π£π‘π‘πππ‘π‘βπΎπΎ
(πππ‘π‘ πππ‘π‘+πππ‘π‘ )1βπΎπΎ= πππ‘π‘
βπΎπΎ
πππ‘π‘πππ‘π‘
= (πππ‘π‘(πππ‘π‘+πππ‘π‘))1/πΎπΎβ1
π£π£π‘π‘1/πΎπΎ
πΆπΆπ‘π‘πππ‘π‘
= (πππ‘π‘ πππ‘π‘+πππ‘π‘ )1/πΎπΎβ1
π£π£π‘π‘1/πΎπΎ
πΆπΆπ‘π‘πππ‘π‘
= ((1βπππ‘π‘) πππ‘π‘+πππ‘π‘ )1/πΎπΎβ1
π£π£π‘π‘1/πΎπΎ
πΆπΆπ‘π‘ + πΆπΆπ‘π‘πππ‘π‘ + πππ‘π‘
= πππ‘π‘πΆπΆπ‘π‘πππ‘π‘
+ (1 β πππ‘π‘)πΆπΆπ‘π‘πππ‘π‘
Plug in from above
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Solving MacroModels Step-by-Step0. Postulate aggregates, price processes & obtain return processes1. For given SDF processes static
a. Real investment ππ, (portfolio π½π½, & consumption choice of each agent) Toolbox 1: Martingale Approach
b. Asset/Risk Allocation across types/sectors & asset market clearing Toolbox 2: βprice-taking social planner approachβ β Fisher separation theorem
2. Value functions backward equationa. Value fcn. as fcn. of individual investment opportunities ππ
Special casesb. De-scaled value fcn. as function of state variables ππ
Digression: HJB-approach (instead of martingale approach & envelop condition)
c. Derive ππ price of risk, πΆπΆ/ππ-ratio from value fcn. envelop condition
3. Evolution of state variable ππ forward equation Toolbox 3: Change in numeraire to total wealth (including SDF) βMoney evaluation equationβ ππππ
4. Value function iteration & goods market clearinga. PDE of de-scaled value fcn.b. Value function iteration by solving PDE 23
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3. ππππDrift of Wealth Share: Two Types Asset pricing formula (relative to benchmark asset)
πππ‘π‘ππ +
πΆπΆπ‘π‘πππ‘π‘
β πππ‘π‘ππππ β πππ‘π‘ππ = ππ β ππππ ππππ β ππππ + ππ οΏ½πππ‘π‘ππ
Add up across types (weighted), (capital letters without superscripts are aggregates for total economy)
(πππ‘π‘πππ‘π‘ππ + 1 β πππ‘π‘ πππ‘π‘
ππ)
=0
+πΆπΆπ‘π‘οΏ½πππ‘π‘β πππ‘π‘ππππ β πππ‘π‘ππ =
πππ‘π‘ πππ‘π‘ β πππ‘π‘οΏ½ππ πππ‘π‘
ππ β πππ‘π‘ππ + 1 β πππ‘π‘ πππ‘π‘ β πππ‘π‘οΏ½ππ πππ‘π‘
ππβ πππ‘π‘ππ + πππ‘π‘ ππ οΏ½πππ‘π‘ππ + 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘
ππ
Subtract from each other yields wealth share driftπππ‘π‘ππ = 1 β πππ‘π‘ πππ‘π‘ β πππ‘π‘
οΏ½ππ πππ‘π‘ππ β πππ‘π‘ππ β (1 β πππ‘π‘) πππ‘π‘ β πππ‘π‘
οΏ½ππ πππ‘π‘ππβ πππ‘π‘ππ
+ 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘ππ β 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘ππ β πΆπΆπ‘π‘
πππ‘π‘β πΆπΆπ‘π‘+πΆπΆπ‘π‘
πππ‘π‘+πππ‘π‘ πΎπΎπ‘π‘ 24
Seignorage due to money supply growth leads to transfers
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3. ππππ Volatility of Wealth Share Since πππ‘π‘ππ = πππ‘π‘ππ/οΏ½πππ‘π‘,
πππ‘π‘ππππ = πππ‘π‘ππ
ππ β πππ‘π‘οΏ½ππ = πππ‘π‘ππ
ππ βοΏ½ππβ²πππ‘π‘ππ
β²πππ‘π‘ππππβ²
= 1 β πππ‘π‘ππ πππ‘π‘ππππ β οΏ½
ππββ ππ
πππ‘π‘ππβπππ‘π‘ππ
ππβ
Note for 2 types exampleπππ‘π‘ππ = 1 β πππ‘π‘ πππ‘π‘ππ β πππ‘π‘
ππ
πππ‘π‘ππ = ππ + πππ‘π‘ππ + πππ‘π‘
πππ‘π‘(1 β ππ)
=ππππ+ππππππ
(πππ‘π‘ππ β πππ‘π‘
ππ), πππ‘π‘ππ = ππ + πππ‘π‘
ππ + 1βπππ‘π‘1βπππ‘π‘
(1 β ππ)(πππ‘π‘ππ β πππ‘π‘
ππ)
Hence, πππ‘π‘ππ = πππ‘π‘βπππ‘π‘
πππ‘π‘(1 β ππ)(πππ‘π‘
ππ β πππ‘π‘ππ)
=βπππ‘π‘ππ
Note also, πππ‘π‘πππ‘π‘ππ + 1 β πππ‘π‘ πππ‘π‘
ππ= 0 β πππ‘π‘
ππ= β πππ‘π‘
1βπππ‘π‘πππ‘π‘ππ
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Change in notation in 2 type settingType-networth is ππ = ππππ
Apply Itoβs Lemma on ππ
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Solving MacroModels Step-by-Step0. Postulate aggregates, price processes & obtain return processes1. For given SDF processes static
a. Real investment ππ, (portfolio π½π½, & consumption choice of each agent) Toolbox 1: Martingale Approach
b. Asset/Risk Allocation across types/sectors & asset market clearing Toolbox 2: βprice-taking social planner approachβ β Fisher separation theorem
2. Value functions backward equationa. Value fcn. as fcn. of individual investment opportunities ππ
Special casesb. De-scaled value fcn. as function of state variables ππ
Digression: HJB-approach (instead of martingale approach & envelop condition)
c. Derive ππ price of risk, πΆπΆ/ππ-ratio from value fcn. envelop condition
3. Evolution of state variable ππ forward equation Toolbox 3: Change in numeraire to total wealth (including SDF) βMoney evaluation equationβ ππππ
4. Value function iteration & goods market clearinga. PDE of de-scaled value fcn.b. Value function iteration by solving PDE 26
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3. βMoney evaluation equationβ ππππ
Recall πΆπΆπ‘π‘οΏ½πππ‘π‘β πππ‘π‘ππ β πππ‘π‘ππππ =
πππ‘π‘ πππ‘π‘ β πππ‘π‘οΏ½ππ πππ‘π‘
ππ β πππ‘π‘ππ+ 1 β πππ‘π‘ πππ‘π‘ β πππ‘π‘
οΏ½ππ πππ‘π‘ππβ πππ‘π‘ππ + πππ‘π‘ ππ οΏ½πππ‘π‘ππ
+ 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘ππ
If benchmark asset is money Replace πππ‘π‘ππ = πππ‘π‘ππ β ππππ and πππ‘π‘ππ = πππ‘π‘ππ (in the total wealth numeraire)
βπππ‘π‘ππ= β(1 β ππ)ππππ βπΆπΆπ‘π‘οΏ½πππ‘π‘
+ πππ‘π‘ πππ‘π‘ β πππ‘π‘οΏ½ππ πππ‘π‘
ππ β πππ‘π‘ππ
+ 1 β πππ‘π‘ πππ‘π‘ β πππ‘π‘οΏ½ππ πππ‘π‘
ππβ πππ‘π‘ππ + πππ‘π‘ ππ οΏ½πππ‘π‘ππ + 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘
ππ
Why is return on money in new numeriare πππππ‘π‘πππ‘π‘β ππππ?
πππ‘π‘ = πππ‘π‘πΎπΎπ‘π‘/πππ‘π‘ is the value of money stock in total networth units27
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Solving MacroModels Step-by-Step0. Postulate aggregates, price processes & obtain return processes1. For given SDF processes static
a. Real investment ππ, (portfolio π½π½, & consumption choice of each agent) Toolbox 1: Martingale Approach
b. Asset/Risk Allocation across types/sectors & asset market clearing Toolbox 2: βprice-taking social planner approachβ β Fisher separation theorem
2. Value functions backward equationa. Value fcn. as fcn. of individual investment opportunities ππ
Special casesb. De-scaled value fcn. as function of state variables ππ
Digression: HJB-approach (instead of martingale approach & envelop condition)
c. Derive ππ price of risk, πΆπΆ/ππ-ratio from value fcn. envelop condition
3. Evolution of state variable ππ forward equation Toolbox 3: Change in numeraire to total wealth (including SDF) βMoney evaluation equationβ ππππ
4. Value function iteration & goods market clearinga. PDE of de-scaled value fcn.b. Value function iteration by solving PDE 28
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4. PDE Value Function Iteration
Postulate π£π£π‘π‘ = π£π£(πππ‘π‘, ππ) By Itoβs Lemma
πππ£π£π‘π‘π£π£π‘π‘
=πππ‘π‘π£π£π‘π‘+πππππ£π£π‘π‘πππππ‘π‘
ππ+12πππππππ£π£π‘π‘ πππ‘π‘πππ‘π‘ππ 2
π£π£π‘π‘ππππ + πππππ£π£π‘π‘πππππ‘π‘
ππ
π£π£π‘π‘πππππ‘π‘
That is,
πππ‘π‘π£π£π£π£π‘π‘ = πππ‘π‘π£π£π‘π‘ + πππππ£π£π‘π‘πππππ‘π‘ππ + 1
2πππππππ£π£π‘π‘ πππ‘π‘πππ‘π‘
ππ 2
πππ‘π‘π£π£π£π£π‘π‘ = πππππ£π£π‘π‘πππππ‘π‘ππ
Plugging in previous slides drift equation ββgrowth equationβ
πππ‘π‘π£π£π‘π‘ + πππππ‘π‘ππ + 1 β πΎπΎ πππππ‘π‘πππ‘π‘
πππ£π£π‘π‘ πππππ£π£π‘π‘ +12πππππππ£π£π‘π‘ πππ‘π‘πππ‘π‘
ππ 2 =
= ππ β 1 β πΎπΎ Ξ¦ ππ β πΏπΏ +12πΎπΎ(1 β πΎπΎ)(ππ2 + οΏ½ππππ 2) π£π£π‘π‘ β
πππ‘π‘πππ‘π‘π£π£π‘π‘
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πππ‘π‘π£π£ πππ‘π‘π£π£
Short-hand notation:ππππππ for ππππ/πππ₯π₯
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4a. Algorithm
Dynamic steps involves now iterating π£π£(ππ), π£π£ ππ , and ππ(ππ)
Static step only involve plannerβs conditions (which implicitly includes asset market clearing), Solve everything in terms of ππ ππ
ππ ππ and ππ ππ can be easily derived since we have it as a function of ππ and ππ in closed form
πππ‘π‘ = 1 β πππ‘π‘1+π π π΄π΄(πππ‘π‘)1βπππ‘π‘+π π πππ‘π‘
, where πππ‘π‘ β πΆπΆπ‘π‘/πππ‘π‘
πππ‘π‘ = πππ‘π‘1+π π π΄π΄(πππ‘π‘)1βπππ‘π‘+π π πππ‘π‘
Remark:One can obtain the moneyless equilibrium with ππ ππ = 0by setting ππππ = βππ (in models with real risk-free debt) Why? recall ππππππ = [ Ξ¦ ππ β πΏπΏ β ππππ]ππππ + ππ + ππππ ππππ
We never used the drift to solve the model. To make money, risk-free asset we have to set ππππ = βππ 30
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Roadmap
Changes in solution procedure in a setting with idiosyncratic risk and money Compare to lecture 03 without idiosyncratic risk and money
Simple two sector model1. Real Debt
2. Money/Nominal Debt
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Two Sector Model Setup
Expert sectorOutput: π¦π¦π‘π‘ = πππππ‘π‘ Consumption rate: πππ‘π‘ Investment rate: πππ‘π‘πππππ‘π‘
οΏ½οΏ½π€
πππ‘π‘οΏ½οΏ½π€
= Ξ¦ πππ‘π‘ βπΏπΏ πππ‘π‘+πππππππ‘π‘+οΏ½ππππ οΏ½πππ‘π‘οΏ½οΏ½π€+ππΞπ‘π‘
ππ,οΏ½οΏ½π€
πΈπΈ0[β«0β ππβπππ‘π‘ log πππ‘π‘ ππππ]
Friction: Can only issue Risk-free debt Equity, but most hold πππ‘π‘ β₯ πΌπΌ 32
Household sectorOutput: π¦π¦π‘π‘ = πππππ‘π‘ Consumption rate: πππ‘π‘ Investment rate: πππ‘π‘πππππ‘π‘
οΏ½οΏ½π€
πππ‘π‘οΏ½οΏ½π€
= Ξ¦ πππ‘π‘ βπΏπΏ πππ‘π‘+πππππππ‘π‘+οΏ½ππππ οΏ½πππ‘π‘οΏ½οΏ½π€+ππΞπ‘π‘
ππ,οΏ½οΏ½π€
πΈπΈ0[β«0βππβπππ‘π‘ log πππ‘π‘ ππππ]
ππ = ππ
ππ = ππ
πΏπΏ = πΏπΏοΏ½ππ β€ οΏ½ππ
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Two Sector Model with & without Money
Idio risk without money and real debt
Expertsβ idio risk οΏ½ππ can depress πππ‘π‘ππ, which hurts households
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A L
Capitalπππ‘π‘πππ‘π‘πΎπΎπ‘π‘
πππ‘π‘
A L
Capital1 β πππ‘π‘ πππ‘π‘πΎπΎπ‘π‘
Net worthπππ‘π‘
Real DebtClaimsReal Debt
Poll 33: Increasing experts idiosyncratic risk οΏ½ππa) Lowers experts wealth share drift ππππb) Increases experts wealth share drift ππππ, as
they earn some extra risk premiumc) Hurts the households, as it depresses πππ‘π‘
ππ
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Two Sector Model with & without Money
Idio risk without money and real debt
Idio risk with money (and nominal short-term debt)
Value of money covaries with πΎπΎ-shocks β implicit insurance 34
A L
Capitalπππ‘π‘πππ‘π‘πΎπΎπ‘π‘
πππ‘π‘
A L
Capital1 β πππ‘π‘ πππ‘π‘πΎπΎπ‘π‘
Net worthπππ‘π‘
Outside Money Outside Money
A L
Capitalπππ‘π‘πππ‘π‘πΎπΎπ‘π‘
πππ‘π‘
A L
Capital1 β πππ‘π‘ πππ‘π‘πΎπΎπ‘π‘
Net worthπππ‘π‘
Real DebtClaimsReal Debt
Nominal DebtClaims
Inside Money/Nominal Debt
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Solution Procedure for Both Settings
Goods market clearingππ πππ‘π‘ + πππ‘π‘ = ππ β πππ‘π‘ divide by ππ and use ππ = 1 + π π ππ
ππ1
1 β πππ‘π‘=ππ β ππ1 + π π ππ
πππ‘π‘ = 1βπππ‘π‘ ππβππ1βπππ‘π‘+π π ππ
πππ‘π‘ = 1 + π π πππ‘π‘ = 1 β πππ‘π‘1+π π ππ
1βπππ‘π‘+π π ππ
πππ‘π‘ = πππ‘π‘πππ‘π‘
1βπππ‘π‘= πππ‘π‘
1+π π ππ1βπππ‘π‘+π π ππ
Capital market clearing (defines πππ‘π‘ for planner)1 β πππ‘π‘ = πππ‘π‘
πππ‘π‘(1 β πππ‘π‘) 1 β πππ‘π‘ = 1βπππ‘π‘
1βπππ‘π‘(1 β πππ‘π‘)
Money market clearing by Walras law35
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Solution Procedure for Both Settings
Goods market clearingππ πππ‘π‘ + πππ‘π‘ = ππ β πππ‘π‘ divide by ππ and use ππ = 1 + π π ππ
ππ1
1 β πππ‘π‘=ππ β ππ1 + π π ππ
πππ‘π‘ = 1βπππ‘π‘ ππβππ1βπππ‘π‘+π π ππ
πππ‘π‘ = 1 + π π πππ‘π‘ = 1 β πππ‘π‘1+π π ππ
1βπππ‘π‘+π π ππ
πππ‘π‘ = πππ‘π‘πππ‘π‘
1βπππ‘π‘= πππ‘π‘
1+π π ππ1βπππ‘π‘+π π ππ
Capital market clearing (defines πππ‘π‘ for planner)1 β πππ‘π‘ = πππ‘π‘
πππ‘π‘(1 β πππ‘π‘) 1 β πππ‘π‘ = 1βπππ‘π‘
1βπππ‘π‘(1 β πππ‘π‘)
Money market clearing by Walras law36
Poll 36: How would equations change if ππ β ππa) Replace ππ with π΄π΄ πππ‘π‘b) Nothing c) Whole approach has to be different.
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Solution Procedure for Both Settings
Goods market clearingππ πππ‘π‘ + πππ‘π‘ = ππ β πππ‘π‘ divide by ππ and use ππ = 1 + π π ππ
ππ1
1 β πππ‘π‘=ππ β ππ1 + π π ππ
πππ‘π‘ = 1βπππ‘π‘ ππβππ1βπππ‘π‘+π π ππ
πππ‘π‘ = 1 + π π πππ‘π‘ = 1 β πππ‘π‘1+π π ππ
1βπππ‘π‘+π π ππ
πππ‘π‘ = πππ‘π‘πππ‘π‘
1βπππ‘π‘= πππ‘π‘
1+π π ππ1βπππ‘π‘+π π ππ
Capital market clearing (defines πππ‘π‘ for planner)1 β πππ‘π‘ = πππ‘π‘
πππ‘π‘(1 β πππ‘π‘) 1 β πππ‘π‘ = 1βπππ‘π‘
1βπππ‘π‘(1 β πππ‘π‘)
Money market clearing by Walras law37
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Solution Procedure for Both Settings
Price-taking Social Planner Problemmax
πππ‘π‘πππ‘π‘πΈπΈ πππ‘π‘ππ + 1 β πππ‘π‘ πΈπΈ πππ‘π‘πΎπΎ
β(πππ‘π‘πππ‘π‘ + πππ‘π‘(1 β πππ‘π‘))(ππ + πππ‘π‘ππ+ππ)
β( πππ‘π‘πππ‘π‘ οΏ½ππ + ππ 1 β πππ‘π‘ οΏ½ππ)
FOC: πππ‘π‘ππ + πππ‘π‘ οΏ½ππ = πππ‘π‘ππ + ππ οΏ½ππ (prices of risks adjust for interior solution)
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Poll 38: Does πΈπΈπ‘π‘[πππ‘π‘πΎπΎ] depend on ππ?a) Yesb) No
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Solution Procedure for Both Settings
Price-taking Social Planner Problemmax
πππ‘π‘πππ‘π‘πΈπΈ πππ‘π‘ππ + 1 β πππ‘π‘ πΈπΈ πππ‘π‘πΎπΎ
β(πππ‘π‘πππ‘π‘ + πππ‘π‘(1 β πππ‘π‘))(ππ + πππ‘π‘ππ+ππ)
β( πππ‘π‘πππ‘π‘ οΏ½ππ + ππ 1 β πππ‘π‘ οΏ½ππ)
FOC: πππ‘π‘ππ + πππ‘π‘ οΏ½ππ = πππ‘π‘ππ + ππ οΏ½ππ (prices of risks adjust for interior solution)
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1. Real Debt Setting: ππ, ππ, Plannerβs prob.
Set πππ‘π‘ = 0, β ππ = 0
ππ = 1+π π ππ1+π π ππ
βππ β ππππ = ππππ+ππ = 0 (as in Basak Cuoco)
Prices of Risk
πππ‘π‘ = πππ‘π‘ππ = 1 β πππ‘π‘ ππ = πππ‘π‘πππ‘π‘ππ, πππ‘π‘ = πππ‘π‘
ππ = 1 β πππ‘π‘ ππ = 1βπππ‘π‘1βπππ‘π‘
ππ
πππ‘π‘ = οΏ½πππ‘π‘ππ = 1 β πππ‘π‘ οΏ½ππ = πππ‘π‘πππ‘π‘οΏ½ππ, πππ‘π‘ = οΏ½πππ‘π‘
ππ = 1 β πππ‘π‘ οΏ½ππ = 1βπππ‘π‘1βπππ‘π‘
οΏ½ππ
Plug in planners FOC: πππ‘π‘ππ2 + πππ‘π‘ οΏ½ππ = πππ‘π‘ππ + ππ οΏ½ππ
πππ‘π‘ =πππ‘π‘(ππ2 + οΏ½ππ2)
ππ2 + 1 β πππ‘π‘ οΏ½ππ2 + πππ‘π‘ οΏ½ππ2
πππ‘π‘ππ = β― ,πππ‘π‘
ππ = β―40
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1. Real Debt Setting: ππ-Evolution
πππ‘π‘ππ = 1 β πππ‘π‘ πππ‘π‘ππ β πππ‘π‘ππ = 1 β πππ‘π‘
πππ‘π‘πππ‘π‘β 1βπππ‘π‘
1βπππ‘π‘ππ =
= πππ‘π‘βπππ‘π‘πππ‘π‘
ππ
πππ‘π‘ππ = 1 β πππ‘π‘ πππ‘π‘ β πππ‘π‘
οΏ½ππ πππ‘π‘ππ β πππ‘π‘ππ β (1 β πππ‘π‘) πππ‘π‘ β πππ‘π‘
οΏ½ππ πππ‘π‘ππβ πππ‘π‘ππ
+ 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘ππ β 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘ππ β πΆπΆπ‘π‘
πππ‘π‘β πΆπΆπ‘π‘+πΆπΆπ‘π‘
πππ‘π‘+πππ‘π‘ πΎπΎπ‘π‘
Benchmark asset is risk-free asset in ππ-numeraire πππ‘π‘ππ = βππ because πππ‘π‘
οΏ½ππ = ππ (since ππππ = 0), πΆπΆππ
= ππ
πππ‘π‘ππ = 1 β πππ‘π‘ πππ‘π‘ β ππ πππ‘π‘
ππ + ππ β (1 β πππ‘π‘) πππ‘π‘ β ππ πππ‘π‘ππ
+ ππ+ 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘ππ β 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘
ππ
πππ‘π‘ππ = πππ‘π‘βπππ‘π‘
πππ‘π‘
πππ‘π‘β2πππ‘π‘πππ‘π‘+πππ‘π‘2
πππ‘π‘(1βπππ‘π‘)ππ2 + 1 β πππ‘π‘
πππ‘π‘πππ‘π‘
2οΏ½ππ2 β 1βπππ‘π‘
1βπππ‘π‘
2οΏ½ππ2
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1. Real Debt Setting: risk free rate
ππβππππ
+ Ξ¦ ππ β πΏπΏ = πππ‘π‘ππ + πππ‘π‘ππ + πππ‘π‘ οΏ½ππ
πππ‘π‘ππ = ππ + Ξ¦ ππ β πΏπΏ β πππ‘π‘
πππ‘π‘ππ2 + οΏ½ππ2 , where πππ‘π‘
πππ‘π‘= (ππ2+οΏ½ππ2)
ππ2+ 1βπππ‘π‘ οΏ½ππ2+πππ‘π‘οΏ½ππ2
πππ‘π‘ππ = ππ + Ξ¦ ππ β πΏπΏ β
ππ2 + οΏ½ππ2 ππ2 + οΏ½ππ2
ππ2 + 1 β πππ‘π‘ οΏ½ππ2 + πππ‘π‘ οΏ½ππ2
Proposition: πππ‘π‘ππ is decreasing in οΏ½ππ2
HH suffer from expertsβ idiosyncratic risk exposure via a lower πππ‘π‘ππ
Experts have more idio risk, but benefit from lower πππ‘π‘ππ
(since they have to earn risk premium for idio risk)
Difference to Basak-Cuoco: limited participation ππ = 1,
HH fully at mercy of expertsβ ability to hedge idio risk Here: HH participate in capital holding
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2. Money/Nominal Debt Setting: ππs
Expertsβ price of risk
πππ‘π‘ = πππ‘π‘ππ = ππ + πππ‘π‘ππ + 1 β πππ‘π‘ πππ‘π‘
ππ β πππ‘π‘ππ
= ππ + πππ‘π‘ππ +
πππ‘π‘πππ‘π‘
1 β πππ‘π‘ πππ‘π‘ππ β πππ‘π‘
ππ
πππ‘π‘ = πππ‘π‘οΏ½ππ = 1 β πππ‘π‘ οΏ½ππ = πππ‘π‘πππ‘π‘
(1 β πππ‘π‘) οΏ½ππ
Householdsβ price of risk
πππ‘π‘ = πππ‘π‘ππ = ππ + ππππ + 1 β πππ‘π‘ πππ‘π‘
ππ β ππππ
= ππ + ππππ +1 β πππ‘π‘1 β πππ‘π‘
1 β πππ‘π‘ πππ‘π‘ππ β ππππ
πππ‘π‘ = οΏ½πππ‘π‘ππ = 1 β πππ‘π‘ οΏ½ππ = 1βπππ‘π‘
1βπππ‘π‘(1 β πππ‘π‘) οΏ½ππ
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2. Money Setting: Plannerβs Problem
Conjecture: πππ‘π‘ππ = πππ‘π‘
ππ = 0 βππβ ππ = ππ = ππ = ππ
Proposition: Aggregate risk is perfectly shared! Via inflation risk Stable inflation (targeting) would ruin risk-sharing
Example: Brexit uncertainty. Use inflation reaction to share risks within UK
Plannerβs FOC: ππ οΏ½ππ = ππ οΏ½πππππ‘π‘πππ‘π‘
1 β πππ‘π‘ οΏ½ππ2 = 1βπππ‘π‘1βπππ‘π‘
1 β πππ‘π‘ οΏ½ππ2
ππ(ππ,ππ) does not depend on ππ
ππ ππ =ππ οΏ½ππ2
1 β ππ οΏ½ππ2 + ππ οΏ½ππ244
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2. Money Setting: ππ-Evolution
πππ‘π‘ππ = 1 β πππ‘π‘
πππ‘π‘πππ‘π‘β 1βπππ‘π‘
1βπππ‘π‘πππ‘π‘βπππ‘π‘πππ‘π‘
1 β πππ‘π‘ πππ‘π‘ππ β ππππ
If ππππ = ππππ = 0, then πππ‘π‘ππ = 0 βππ, if πππ‘π‘
ππ = 0, then ππππ = ππππ = 0By Itoβs lemma on ππ(ππ) and ππ(ππ)
πππ‘π‘ππ = 1 β πππ‘π‘ πππ‘π‘ β πππ‘π‘
οΏ½ππ πππ‘π‘ππ β πππ‘π‘ππ β (1 β πππ‘π‘) πππ‘π‘ β πππ‘π‘
οΏ½ππ πππ‘π‘ππβ πππ‘π‘ππ
+ 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘ππ β 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘ππ β πΆπΆπ‘π‘
πππ‘π‘β πΆπΆπ‘π‘+πΆπΆπ‘π‘
πππ‘π‘+πππ‘π‘ πΎπΎπ‘π‘
Benchmark asset is risk-free asset in ππ-numeraire πππ‘π‘ππ = 0 and πππ‘π‘
οΏ½ππ = ππ, πΆπΆππ
= ππ
πππ‘π‘ππ/ 1 β πππ‘π‘ = πππ‘π‘ β ππ πππ‘π‘
ππ β πππ‘π‘ β ππ πππ‘π‘ππ
+ πππ‘π‘πππ‘π‘πππ‘π‘
(1 β πππ‘π‘) οΏ½ππ β πππ‘π‘1βπππ‘π‘1βπππ‘π‘
(1 β πππ‘π‘) οΏ½ππ
πππ‘π‘ππ = 1 β πππ‘π‘ 1 β πππ‘π‘ 2 πππ‘π‘
πππ‘π‘
2οΏ½ππ2 β 1βπππ‘π‘
1βπππ‘π‘
2οΏ½ππ2
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2. Money Setting: Money Evaluation
Recall βπππ‘π‘ππ= β(1 β ππ)ππππ βπΆπΆπ‘π‘οΏ½πππ‘π‘
+ πππ‘π‘ πππ‘π‘ β πππ‘π‘οΏ½ππ πππ‘π‘
ππ β πππ‘π‘ππ
+ 1 β πππ‘π‘ πππ‘π‘ β πππ‘π‘οΏ½ππ πππ‘π‘
ππβ πππ‘π‘ππ + πππ‘π‘ ππ οΏ½πππ‘π‘ππ + 1 β πππ‘π‘ πππ‘π‘ οΏ½πππ‘π‘
ππ
Plug in ππππ = 0,πΆπΆπ‘π‘οΏ½πππ‘π‘
= ππ, πππ‘π‘ = πππ‘π‘ = ππ, πππ‘π‘οΏ½ππ = ππ
ππ οΏ½πππ‘π‘ππ = 1 β πππ‘π‘ 2 πππ‘π‘πππ‘π‘
2
οΏ½ππ2, πππ‘π‘ = οΏ½πππ‘π‘ππ = 1 β πππ‘π‘ 2 1 β πππ‘π‘
1 β πππ‘π‘
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οΏ½ππ2
βπππ‘π‘ππ= βππ + 1 β πππ‘π‘ 2 πππ‘π‘πππ‘π‘πππ‘π‘
2οΏ½ππ2 + 1 β πππ‘π‘
1βπππ‘π‘1βπππ‘π‘
2οΏ½ππ2
where πππ‘π‘ = πππ‘π‘οΏ½ππ2
1βπππ‘π‘ οΏ½ππ2+πππ‘π‘οΏ½ππ2
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2. Money Setting: Adding Real Debt
Adding Real Debt does not alter the equilibrium, since Markets are complete w.r.t. to aggregate risk
(perfect aggregate risk sharing) Markets are incomplete w.r.t. to idiosyncratic risk only
Note: Result relies on absence of price stickiness
Both Settings: Real Debt and Money/Nominal Debt converge in the long-run to the βI Theory without Iβ steady state model of Lecture 05.
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Example: Real vs. Nominal Debt/Money
ππ = .15,ππ = .03,ππ = .1, π π = 2, πΏπΏ = .03, οΏ½ππ = .2, οΏ½ππ = .3
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Blue: real debt modelRed: nominal model
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Towards the I Theory of Money One sector model with idio risk - βThe I Theory without Iβ
(steady state focus) Store of value Insurance role of money within sector
Money as bubble or not Fiscal Theory of the Price Level Medium of Exchange Role β SDF-Liquidity multiplier β Money bubble
2 sector/type model with money and idio risk Generic Solution procedure (compared to lecture 03) Real debt vs. Money Implicit insurance role of money across sectors
The curse of insurance Reduces insurance premia and net worth gains
I Theory with Intermediary sector Intermediaries as diversifiers
Welfare analysis Optimal Monetary Policy and Macroprudential Policy
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