Modeling foreign direct aid

[jdebacker]

This PR addresses Issue #1123 by adding a parameter for direct foreign assistance (as a fraction of GDP) that contributes resources to the government.

[Copilot]

Pull request overview

This PR implements Issue #1123 by introducing a new time-varying parameter (alpha_FA) representing direct foreign assistance to the domestic government as a share of GDP, and wiring that flow into the government budget constraint and the economy-wide resource constraint.

Changes:

• Add alpha_FA to default parameters and document it in the book.
• Incorporate foreign aid flows into fiscal policy accounting (debt/spending/transfers) and into the SS/TPI resource constraint calculations.
• Adjust tests/docs around the updated equations and function signatures.

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
ogcore/default_parameters.json	Adds the new alpha_FA parameter definition and validation.
ogcore/fiscal.py	Applies foreign aid flows to government budget arithmetic (SS and time path).
ogcore/aggregates.py	Extends resource_constraint() to include foreign aid.
ogcore/SS.py	Passes SS foreign-aid vector into the resource constraint.
ogcore/TPI.py	Passes TPI foreign-aid path into the resource constraint.
tests/test_fiscal.py	Updates fiscal tests to set alpha_FA and includes a debug print.
tests/test_aggregates.py	Removes old commented-out code in the resource constraint test (but currently misses new arg).
docs/book/content/theory/stationarization.md	Updates stationarized government budget constraint equations to include foreign aid.
docs/book/content/theory/government.md	Updates government budget constraint equations/closure rules to include foreign aid.
docs/book/content/intro/parameters.md	Documents alpha_FA (and includes a couple parameter doc range tweaks).

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.24%. Comparing base (4a8ef99) to head (107301a).

Files with missing lines	Patch %	Lines
ogcore/TPI.py	0.00%	2 Missing ⚠️
ogcore/fiscal.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1126      +/-   ##
==========================================
- Coverage   73.25%   73.24%   -0.02%     
==========================================
  Files          21       21              
  Lines        5242     5251       +9     
==========================================
+ Hits         3840     3846       +6     
- Misses       1402     1405       +3     

Flag	Coverage Δ
unittests	73.24% <72.72%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
ogcore/SS.py	79.02% <100.00%> (+0.09%)	⬆️
ogcore/aggregates.py	100.00% <100.00%> (ø)
ogcore/fiscal.py	97.14% <80.00%> (-0.86%)	⬇️
ogcore/TPI.py	33.85% <0.00%> (-0.16%)	⬇️

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