diff --git a/lectures/calvo_machine_learn.md b/lectures/calvo_machine_learn.md index fe73c60a..282b368d 100644 --- a/lectures/calvo_machine_learn.md +++ b/lectures/calvo_machine_learn.md @@ -156,12 +156,6 @@ the linear difference equation {eq}`eq_grad_old2` can be solved forward to get: \theta_t = \frac{1}{1+\alpha} \sum_{j=0}^\infty \left(\frac{\alpha}{1+\alpha}\right)^j \mu_{t+j}, \quad t \geq 0 ``` -```{note} -Equation {eq}`eq_grad_old3` shows that an equivalence class of continuation money growth sequences $\{\mu_{t+j}\}_{j=0}^\infty$ deliver the same $\theta_t$. Consequently, equations {eq}`eq_grad_old1` and {eq}`eq_grad_old3` show that $\theta_t$ intermediates -how choices of $\mu_{t+j}, \ j=0, 1, \ldots$ impinge on time $t$ -real balances $m_t - p_t = -\alpha \theta_t$. Chang {cite}`chang1998credible` exploits this -fact extensively. -``` @@ -1189,9 +1183,9 @@ For example, we could have regressed $\theta_t$ on $\mu_t$ and obtained the same Actually, wouldn't that direction of fit have made more sense? -After all, the Ramsey planner is **choosing** $\vec \mu$ while $\vec \theta$ is the outcome. +After all, the Ramsey planner chooses $\vec \mu$, while $\vec \theta$ is an outcome that reflects the represenative agent's response to the Ramsey planner's choice of $\vec \mu$. -Which is **cause** and which is **effect**? +Isn't it more natural then to expect that we'd learn more about the structure of the Ramsey problem from a regression of components of $\vec \theta$ on components of $\vec \mu$? To answer such questions, we'll have to deploy more economic theory. @@ -1231,4 +1225,15 @@ print(f'(d_0, d_1) = ({clq.d0:.6f}, {clq.d1:.6f})') Evidently, these agree with the relationships that we discovered by running regressions on the Ramsey outcomes $\vec \mu^R, \vec \theta^R$ that we constructed with either of our machine learning algorithms. -We have set the stage for diving into this quantecon lecture {doc}`calvo`. +We have set the stage for this quantecon lecture {doc}`calvo`. + +We close this lecture by giving a hint about an insight of Chang {cite}`chang1998credible` that +underlies much of quantecon lecture {doc}`calvo`. + +Chang noticed how equation {eq}`eq_grad_old3` shows that an equivalence class of continuation money growth sequences $\{\mu_{t+j}\}_{j=0}^\infty$ deliver the same $\theta_t$. + +Consequently, equations {eq}`eq_grad_old1` and {eq}`eq_grad_old3` indicate that $\theta_t$ intermediates how the government's choices of $\mu_{t+j}, \ j=0, 1, \ldots$ impinge on time $t$ +real balances $m_t - p_t = -\alpha \theta_t$. + +In lecture {doc}`calvo`, we'll see how Chang {cite}`chang1998credible` exploits this +insight.