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[8_markov_jump_lq]_correction #175

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shlff
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@shlff shlff commented Jan 6, 2021

Hi @jstac , as I commented in #174 , there is a further issue in a Bellman equation in section Linked-Ricatti-equations-for-Markov-LQ-dynamic-programming of lecture markov_jump_lq and this PR corrects that issue:

  • $-x' P_i x - \rho_i & = \max_u - [x'R_i x + u' Q_i u + 2 u' W_i x - \beta \sum_j \Pi_{ij}E ((A_i x + B_i u + C_i w)' P_j(A_i x + B_i u + C_i w) x + \rho_j)$ -->> $-x' P_i x - \rho_i & = \max_u - [x'R_i x + u' Q_i u + 2 u' W_i x + \beta \sum_j \Pi_{ij}E ((A_i x + B_i u + C_i w)' P_j(A_i x + B_i u + C_i w) x + \rho_j)$
  • i.e., - -->> +

We should correct it because, in the setups above, we have

  • $\min_{{u_t}{t=0}^\infty} E \sum{t=0}^{\infty} \beta^t r(x_t, s_t, u_t)$ with $r(x_t, s_t, u_t) = x_t' R_{s_t} x_t + u_t' Q_{s_t} u_t + 2 u_t' W_{s_t} x_t$
  • the Bellman equation I modified is just obtained by turning the minimization problem in the above setting into a maximization problem
  • so in the Bellman equation, we should only add a minus sign, -, in the front of the objective function from the minimization problem.

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github-actions bot commented Jan 6, 2021

@mmcky mmcky requested a review from jstac April 20, 2021 03:11
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mmcky commented Apr 20, 2021

@jstac would you be able to review and confirm this change?

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jstac commented May 7, 2021

Hi @mmcky , I confirm this is correct. Please go ahead.

mmcky added a commit to QuantEcon/lecture-python-advanced.myst that referenced this pull request May 7, 2021
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mmcky commented May 7, 2021

Closing this as I have migrated this to https://github.com/QuantEcon/lecture-python-advanced.myst

@mmcky mmcky closed this May 7, 2021
mmcky added a commit to QuantEcon/lecture-python-advanced.myst that referenced this pull request May 17, 2021
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3 participants