Recursive Methods and Dynamic Optimization, Summaries of Economics

An introduction to dynamic optimization, focusing on the sequence problem and the bellman equation. It outlines the principle of optimality, which allows the use of the bellman equation to find the value function and optimal plan. The document also discusses why this approach is beneficial, including intuition, notation, analysis, and computation. It then presents a proof of theorem 4.3, which shows that the value function defined by the sequence problem is the same as the solution to the bellman equation. Finally, the document introduces the bellman equation as a fixed point problem and discusses the needed tools, including basic real analysis, the contraction mapping theorem, and the theorem of the maximum.

Typology: Summaries

2021/2022

Uploaded on 08/03/2024

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Recursive

Methods

Introduction

to

Dynamic

Optimization

Nr.

1

Outline

Today’s

Lecture

housekeeping:

ps#

and

recitation

day/

theory

general

web

page

fi

nish

Principle

of

Optimality:

Sequence

Problem

(for

values

and

plans)

solution

to

Bellman

Equation

begin

study

of

Bellman

equation

with

bounded

and

continuous

F

tools:

contraction

mapping

and

theorem

of

the

maximum

Introduction

to

Dynamic

Optimization

Nr.

2

Principle

of

Optimality

IDEA:

use

BE

to

fi

nd

value

function

V

and

optimal

plan

x

Thm

V

de

fi

ned

by

SP

V

solves

FE

Thm

V

solves

FE

and

V

V

Thm

x

x

0

is

optimal

V

x

∗ t

F

x

∗ t

, x

∗ t

βV

x

∗ t

Thm

x

x

0

satis

fi

es

V

x

∗ t

F

x

∗ t

, x

∗ t

βV

x

∗ t

and

x

is

optimal

Introduction

to

Dynamic

Optimization

Nr.

4

Why is this Progress?

intuition:

breaks

planning

horizon

into

two:

‘now’

and

‘then’

notation:

reduces

unnece

s

sary

notation

(especially

with

uncertainty)

analysis:

prove

existence,

uniqueness

and

properties

of

optimal

policy

(e.g.

continuity,

montonicity,

etc...)

computation:

associated

numerical

algorithm

are

powerful

for

many

applications

Introduction

to

Dynamic

Optimization

Nr.

5

Continue

this

way

V

x

0

n

X

t

=

β

t

F

x

t

, x

t

β

n

V

x

n

for

all

x

x

0

n

X

t

=

β

t

F

x

∗ t

, x

∗ t

β

n

V

x

∗ n

for

some

x

x

0

Since

β

T

V

x

T

taking

the

limit

n

on

both

sides

of

both

expres

sions

we

conclude

that:

V

x

0

u

x

for

all

x

x

0

V

x

0

u

x

for

some

x

x

0

Introduction

to

Dynamic

Optimization

Nr.

7

Bellman

Equation

as

a

Fixed

Point

de

fi

ne

operator

T

f

x

max

y

Γ

(

x

)

F

x,

y

βf

y

V

solution

of

BE

V

fi

xed

point

of

T

[i.e.

T V

V

]

Bounded

Returns:

if

k

F

k

< B

and

F

and

are

continuos:

T

maps

continuous

bounded

functions

into

continuous

bounded

functions

bounded

returns

T

is

a

Contraction

Mapping

unique

fi

xed

point

many

other

bonuses

Introduction

to

Dynamic

Optimization

Nr.

8