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Revise the two supply and demand lectures - #845

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Sep 15, 2026
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@jstac jstac commented Sep 12, 2026

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Revisions by @thomassargent30 to supply_demand_multiple_goods.md, supply_demand_heterogeneity.md, and a small forward pointer in cons_smooth.md (branch tom_sept, see Tom's email "tom_sept branch(es)").

Corrections

  • Fix the sign and restore the missing $\mu$ in the matrix of demand curve slopes, which is $-\mu (\Pi' \Pi)^{-1}$.
  • Separate Frisch from Hicksian demand curves: holding $\mu$ fixed gives a Frisch demand curve, and the claim that freezing $\mu$ leaves $p'e + w$ unaltered was false.
  • Restrict the monopoly output comparison to the single-good case, since with several goods cross effects can raise one good's output.
  • Correct the two-good cross-slope explanation: preference substitution, rather than the shift in the demand intercept, drives the larger fall in the second quantity.
  • Label the consumption vector correctly in the risk section; write $h'c$ rather than $hc$ in the welfare criterion.
  • State the budget constraint $p'(c_i - e_i) = W_i$ that defines $\mu_i$.
  • Replace a cross-document equation reference that could not resolve.
  • Fix two code bugs: Ws is None, and np.isclose for the wealth sum.

New material

  • Derive welfare criterion $= CS + PS - b'b/(2\mu)$, tying the planning problem to the surplus measure in intro_supply_demand.
  • New section on Negishi weights: a competitive equilibrium allocation solves a planning problem with welfare weights $1/\mu_i$ and $\eta = p$.
  • Seven new exercises with dropdown solutions, plus solutions for the four existing exercises that had none.
  • Cross-links to cons_smooth (where $\beta R = 1$ is assumed and here derived), pv, olg, lp_intro and linear_equations.
  • Concluding remarks added to both lectures.

cons_smooth.md gains a forward pointer noting that it takes $R$ as given while supply_demand_multiple_goods determines $R$.

Per the commit message, all code cells execute and every number reported in the text has been verified.

🤖 Generated with Claude Code

https://claude.ai/code/session_01UZWhdWQnrKdbgHbyvX4UYs

Corrections to supply_demand_multiple_goods.md and
supply_demand_heterogeneity.md:

* fix the sign and restore the missing mu in the matrix of demand curve
  slopes, which is -mu (Pi' Pi)^{-1}
* separate Frisch from Hicksian demand curves; holding mu fixed gives a
  Frisch demand curve, and the claim that freezing mu leaves p'e + w
  unaltered was false
* restrict the monopoly output comparison to the single good case, since
  with several goods cross effects can raise one good's output
* correct the two good cross slope explanation; preference substitution
  rather than the shift in the demand intercept drives the larger fall
  in the second quantity
* label the consumption vector correctly in the risk section
* write h' c rather than h c in the welfare criterion
* replace a cross document equation reference that could not resolve
* state the budget constraint p'(c_i - e_i) = W_i that defines mu_i
* fix two code bugs: Ws is None, and np.isclose for the wealth sum

New material:

* derive welfare criterion = CS + PS - b'b/(2 mu), which ties the
  planning problem to the surplus measure of intro_supply_demand
* add a section on Negishi weights: a competitive equilibrium allocation
  solves a planning problem with welfare weights 1/mu_i and eta = p
* add seven exercises with dropdown solutions, and supply solutions for
  the four exercises that had none
* connect the lectures to cons_smooth, where beta R = 1 is assumed and
  here derived, and to pv, olg, lp_intro and linear_equations
* add concluding remarks to both lectures

cons_smooth.md gains a forward pointer recording that it takes R as
given while supply_demand_multiple_goods determines R.

All code cells execute and every number reported in the text is verified.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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github-actions Bot temporarily deployed to pull request September 12, 2026 21:18 Inactive
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github-actions Bot temporarily deployed to pull request September 12, 2026 21:19 Inactive
Continuation sentences under a./b./c. exercise parts were indented by
four spaces; since those markers are not CommonMark list items, the
parser rendered the indented lines as literal code blocks.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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@jstac

jstac commented Sep 15, 2026

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Many thanks for these edits @thomassargent30 . Everything looks good. I made very minor cosmetic changes to match the style guide (e.g., capitalization of section titles). I'll merge now.

@jstac
jstac merged commit eb32f13 into main Sep 15, 2026
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jstac deleted the tom_sept branch September 15, 2026 09:53

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