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Tom's final edits of advanced lectures, Jan 23
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lectures/cons_news.md

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This lecture studies two consumers who have exactly the same
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nonfinancial income process and who both conform to the linear-quadratic
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permanent income of consumption smoothing model described in the
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permanent income of consumption smoothing model described in this
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[quantecon lecture](https://python-intro.quantecon.org/perm_income_cons.html).
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The two consumers have different information about
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This lecture can be regarded as an introduction to some of the **invertibility** issues that take center stage in
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the analysis of **fiscal foresight** by Eric Leeper, Todd Walker, and Susan Yang {cite}`Leeper_Walker_Yang`.
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## Two Representations of the **Same** Nonfinancial Income Process
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## Two Representations of One Nonfinancial Income Process
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Where $\beta \in (0,1)$, we study consequences of endowing a
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consumer with one of the two alternative representations for the change
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\sigma_a^2 = \sigma_\epsilon^2 + [ 1 + (\beta - \beta^{-1})^2 \sum_{j=0}^\infty \beta^{2j} ] = \beta^{-1} \sigma_\epsilon^2 .
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$$
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### Application of Kalman filter
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## Application of Kalman filter
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We can also obtain representation {eq}`eqn_2` from representation {eq}`eqn_1` by using
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the **Kalman filter**.
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We can also obtain these formulas via the classical filtering theory
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described in {doc}`this lecture <classical_filtering>`.
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### News Shocks and Less Informative Shocks
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## News Shocks and Less Informative Shocks
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Representation {eq}`eqn_1` is cast in terms of a **news shock**
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$\epsilon_{t+1}$ that represents a shock to nonfinancial income
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$d_a(\beta) = \frac{1 -\beta^2}{1 -\beta } = (1 + \beta)$, another
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fact that will be important below.
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### Representation of $\epsilon_t$ in Terms of Future $y$’s
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## Representation of $\epsilon_t$ Shock in Terms of Future $y_t$
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Notice that reprentation {eq}`eqn_1`, namely, $y_{t+1} - y_t = -\beta^{-1} \epsilon_t + \epsilon_{t+1}$
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implies the linear difference equation
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Thus, $\epsilon_t$ contains **exact** information about an
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important linear combination of **future** nonfinancial income.
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### Representation in Terms of $a_t$ Shocks
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## Representation in Terms of $a_t$ Shocks
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Next notice that representation {eq}`eqn_2`, namely, $y_{t+1} - y_t = -
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\beta a_t + a_{t+1}$ implies the linear difference
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E [ y_{t+1} | y^t ] = (1-\beta) \sum_{j=0}^\infty \beta^j y_{t-j}
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$$
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### Permanent Income Consumption-Smoothing Model
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## Permanent Income Consumption-Smoothing Model
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When we computed optimal consumption-saving policies for the two
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representations using formulas obtained with the difference equation
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All the code that we shall use below is presented in that lecture.
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### Computations
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## Computations
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We shall use Python to form **both** of the above two state-space
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representations, using the following parameter values
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plt.legend()
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```
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### Simulating the Income Process and Two Associated Shock Processes
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## Simulating Income Process and Two Associated Shock Processes
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We now describe how we form a **single** $\{y_t\}_{t=0}^T$ realization
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that we will use to simulate the two different decision rules associated
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two consumers having **identical** incomes at each date but at each date
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having **different** information about their future incomes.
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### Calculating Innovations in Another Way
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## Calculating Innovations in Another Way
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Here we use formula {eq}`eqn_3` above to compute $a_{t+1}$ as a function
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of the history
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We can verify that we recover the same $\{a_t\}$ sequence
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computed earlier.
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### Another Invertibility Issue
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## Another Invertibility Issue
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This {doc}`quantecon lecture <hs_invertibility_example>` contains another example of a shock-invertibility issue that is endemic
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to the LQ permanent income or consumption smoothing model.

lectures/dyn_stack.md

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base its choice of $\vec q_1$ on firm 2's choice of
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$\vec q_2$.
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### Abstract Statement of the Leader's and Follower's Problems
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### Statement of Leader's and Follower's Problems
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We can express firm 1's problem as
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We'll put our little duopoly model into a broader class of models with
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the same conceptual structure.
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## The Stackelberg Problem
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## Stackelberg Problem
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We formulate a class of linear-quadratic Stackelberg leader-follower
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problems of which our duopoly model is an instance.
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y_{t+1} = A y_t + B u_t
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```
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### Interpretation of the Second Block of Equations
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### Interpretation of Second Block of Equations
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The Stackelberg follower's best response mapping is summarized by the
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second block of equations of {eq}`new3`.
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as a function of the vector of natural state variables at time $0$,
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$z_0$.
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### Two Bellman Equations
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## Two Bellman Equations
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We now describe Bellman equations for $v(y)$ and $w(z_0)$.
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$\check z^t$ and **not** a corresponding representation cast in
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terms of $z^t$.
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### Dynamic Programming and Time Consistency of Follower's Problem
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## Dynamic Programming and Time Consistency of Follower's Problem
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Given the sequence $\vec q_2$ chosen by the Stackelberg leader in
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our duopoly model, it turns out that the Stackelberg **follower's**
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It follows that the follower's plan is time consistent.
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## Computing the Stackelberg Plan
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## Computing Stackelberg Plan
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Here is our code to compute a Stackelberg plan via a linear-quadratic
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dynamic program as outlined above
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print(f"F = {F}")
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```
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### Implied Time Series for Price and Quantities
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## Time Series for Price and Quantities
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The following code plots the price and quantities
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(v_leader_direct - v_expanded < tol0)[0, 0]
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```
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## Exhibiting Time Inconsistency of Stackelberg Plan
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## Time Inconsistency of Stackelberg Plan
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In the code below we compare two values
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plt.show()
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```
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## Recursive Formulation of the Follower's Problem
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## Recursive Formulation of Follower's Problem
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We now formulate and compute the recursive version of the follower's
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problem.

lectures/lu_tricks.md

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$N$ and factoring it into the $LU$ form, good approximations
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to $c(L)$ and $c(\beta L^{-1})^{-1}$ can be obtained.
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## The Infinite Horizon Limit
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## Infinite Horizon Limit
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For the infinite horizon problem, we propose to discover first-order
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necessary conditions by taking the limits of {eq}`onefour` and {eq}`onefive` as

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