What is the explicit solution for the DSGE model with one unique solution?

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In summary, the lecturer is trying to find the stable eigenvalues of the matrix A and the solution is premultiplied by Q^{-1} and then defined as: p_{t}= -\gamma/1-\lambda\beta m_{t}+\beta^t\left( \frac{\gamma}{1-\lambda\beta}u_{t+1}+p_{0} \right) and m_{t}=\frac{\lambda}{1-\lambda\beta}p_{t+1}+\left(\frac{1}{1-\lambda\beta} \right)^t\left( \frac{1}{\lambda}w
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Charlotte87
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Homework Statement


I have understood the point with the Blanchard Kahn condition, my problem is to find the explicit solution when I know there exists one unique solution to the problem. The problem comes from a DSGE model.


Homework Equations


[itex]\begin{pmatrix} p_{t} \\ m_{t} \\ \end{pmatrix} = \begin{pmatrix} \beta & \gamma/\lambda \\ 0 & 1/\gamma \\ \end{pmatrix} \begin{pmatrix} p_{t+1} \\ m_{t+1} \\ \end{pmatrix} + \begin{pmatrix} \gamma/\lambda & \beta \\ 1/\lambda & 0 \\ \end{pmatrix} \begin{pmatrix} u_{t+1} \\ w_{t+1} \\ \end{pmatrix} [/itex]

I have found the diagonal matrix of the matrix in front of p(t+1) and m(t+1). Let Q be the matrix of eigenvectors from A and [itex]\Lambda[/itex] be the diagonal matrix of A, we then have [itex]A=Q\Lambda Q^{-1}[/itex]:

[itex] \begin{pmatrix} \beta & \gamma/\lambda \\ 0 & 1/\gamma \\ \end{pmatrix} = \begin{pmatrix} 1 & 1 \\ 0 & (1-\lambda\beta)/\gamma \\ \end{pmatrix} \begin{pmatrix} \beta & 0 \\ 0 & 1/\lambda \\ \end{pmatrix} \begin{pmatrix} 1 & -\gamma/(1-\lambda\beta) \\ 0 & \gamma/(1-\lambda\beta) \\ \end{pmatrix} [/itex].


The Attempt at a Solution


I have followed the lecture notes where the lecturer starts by taking expectations such that:

[itex] \begin{pmatrix} p_{t} \\ m_{t} \\ \end{pmatrix} = A E_{t} \begin{pmatrix} p_{t+1} \\ m_{t+1} \\ \end{pmatrix} [/itex]

Then we premultiply by [itex]Q^{-1}[/itex] and define [itex] Q^{-1} \begin{pmatrix} p_{t} \\ m_{t} \\ \end{pmatrix} = \begin{pmatrix} z_{t}^{1} \\ z_{t}^{2} \\ \end{pmatrix} [/itex]. We then get:

[itex] \begin{pmatrix} z_{t}^{1} \\ z_{t}^{2} \\ \end{pmatrix} = \begin{pmatrix} \beta & 0 \\ 0 & 1/\lambda \\ \end{pmatrix} E_{t} \begin{pmatrix} z_{t+1}^{1} \\ z_{t+1}^{2} \\ \end{pmatrix} [/itex]

The stable eigenvalue in the diagonal matrix of A is [itex] \beta [/itex] and the unstable one [itex] 1/\lambda [/itex]. I have tried to follow theoretical papers I have found online but I just do not manage to do it.

The solution is supposed to be:
[itex] p_{t} = \frac{-\gamma}{1-\lambda\beta}m_{t} [/itex]
 
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+ \beta^t \left( \frac{\gamma}{1-\lambda\beta} u_{t+1} + p_{0} \right) and m_{t} = \frac{\lambda}{1-\lambda\beta}p_{t+1} + \left(\frac{1}{1-\lambda\beta} \right)^t \left( \frac{1}{\lambda} w_{t+1} + m_{0} \right) .
 

Related to What is the explicit solution for the DSGE model with one unique solution?

What is the Blanchard Kahn condition?

The Blanchard Kahn condition is a mathematical concept used in macroeconomics to determine the stability of a dynamic economic model. It states that for a model to have a unique and stable solution, the number of predetermined variables must be equal to or larger than the number of jump variables.

What does the Blanchard Kahn condition tell us about a model?

The Blanchard Kahn condition tells us whether a model has a unique and stable solution. If the condition is met, then the model is said to be locally stable, meaning that it will converge to a steady state. If the condition is not met, the model is considered to be unstable and may have multiple solutions.

Why is the Blanchard Kahn condition important?

The Blanchard Kahn condition is important because it helps economists determine whether a dynamic economic model is valid and can be used to make accurate predictions. It also provides insight into the behavior of economic systems and their stability.

How is the Blanchard Kahn condition calculated?

The Blanchard Kahn condition is calculated by counting the number of predetermined variables and jump variables in a model. Predetermined variables are those that are determined in the past and cannot be changed, while jump variables are those that can change abruptly in the future. If the number of predetermined variables is equal to or greater than the number of jump variables, then the condition is met.

What are some real-life applications of the Blanchard Kahn condition?

The Blanchard Kahn condition is used in many macroeconomic models to study the behavior of various economic systems, such as business cycles, monetary policy, and fiscal policy. It is also used in forecasting economic outcomes and evaluating the effectiveness of economic policies.

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