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Tom's Feb 6 morning edits of cons_smooth lecture
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lectures/cons_smooth.md

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@@ -24,9 +24,9 @@ In this lecture, we'll study what is often called the "consumption-smoothing mo
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Formulas presented in {doc}`present value formulas<pv>` are at the core of the consumption smoothing model because we shall use them to define a consumer's "human wealth".
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The key idea that inspired Milton Friedman was that a person's non-financial income, i.e., his or
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her wages from working, could be viewed as a dividend stream from that person's ``human capital''
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her wages from working, could be viewed as a dividend stream from that person's ''human capital''
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and that standard asset-pricing formulas could be applied to compute a person's
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``non-financial wealth'' that capitalizes the earnings stream.
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''non-financial wealth'' that capitalizes the earnings stream.
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```{note}
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As we'll see in this quantecon lecture {doc}`equalizing difference model <equalizing_difference>`,
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### Experiments
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In this section we experiment consumption smoothing behavior under different setups.
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In this section we decribe how a consumption sequence would optimally respond to different sequences sequences of non-financial income.
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First we write a function `plot_cs` that generate graphs above based on a consumption smoothing model `cs_model`.
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First we create a function `plot_cs` that generate graphs for different instances of the consumption smoothing model `cs_model`.
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This helps us repeat the steps shown above
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This will help us avoid rewriting code to plot outcomes for different non-financial income sequences.
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```{code-cell} ipython3
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def plot_cs(model, # consumption smoothing model
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plt.show()
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```
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In the experiments below, please study how consumption and financial asset sequences vary accross different sequences for non-financial income.
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#### Experiment 1: one-time gain/loss
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We first assume a one-time windfall of $W_0$ in year 21 of the income sequence $y$.
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We'll make $W_0$ big - positive to indicate a one-time windfall, and negative to indicate a one-time "disaster".
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```{code-cell} ipython3
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# Windfall W_0 = 20
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# Windfall W_0 = 2.5
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y_seq_pos = np.concatenate(
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[np.ones(21), np.array([20]), np.ones(44)])
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[np.ones(21), np.array([2.5]), np.ones(44)])
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plot_cs(cs_model, a0, y_seq_pos)
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```
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```{code-cell} ipython3
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# Disaster W_0 = -20
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# Disaster W_0 = -2.5
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y_seq_neg = np.concatenate(
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[np.ones(21), np.array([-20]), np.ones(44)])
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[np.ones(21), np.array([-2.5]), np.ones(44)])
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plot_cs(cs_model, a0, y_seq_neg)
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```
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#### Experiment 2: permanent wage gain/loss
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Now we assume a permanent increase in income of $W$ in year 21 of the $y$-sequence.
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Now we assume a **permanent** increase in income of $W$ in year 21 of the $y$-sequence.
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Again we can study positive and negative cases
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What happens when $\lambda$ is negative
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```{code-cell} ipython3
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λ = -0.05
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λ = -0.95
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geo_seq = λ ** np.arange(t_max) * y_0
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y_seq_geo = np.concatenate(

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