Restructure IFP lectures: separate transient shocks into new lecture

[jstac]

Summary

This PR reorganizes the Income Fluctuation Problem (IFP) lecture series to improve pedagogical clarity by separating content into distinct lectures of increasing complexity.

Changes

1. Split into two lectures

New Lecture III (): Simplified model without transient shocks

• Income specification: y(z) = exp(z) (deterministic given state)
• No Monte Carlo integration needed
• Cleaner introduction to the Endogenous Grid Method
• Faster computation and easier to understand

New Lecture IV (): Full model with transient shocks

• Income specification: y(z, η) = exp(a_y * η + z * b_y)
• Includes Monte Carlo integration over η draws
• Shows wealth inequality analysis (Gini coefficient, top 1% share)
• Demonstrates how inequality varies with interest rate

2. Updated lecture numbering

• ifp_egm.md: The Income Fluctuation Problem III: The Endogenous Grid Method
• ifp_egm_transient_shocks.md: The Income Fluctuation Problem IV: Transient Income Shocks (NEW)
• ifp_advanced.md: The Income Fluctuation Problem V: Stochastic Returns on Assets (changed from IV)

3. Code improvements

• Increased savings_grid_size from 50 to 200 for better accuracy
• Converted utility functions to lambda expressions for conciseness
• Reorganized References section placement
• All code tested and verified to run successfully

4. Updated table of contents

• Added ifp_egm_transient_shocks in proper sequence
• Maintains logical progression: discrete → OPI → EGM (simple) → EGM (transient shocks) → stochastic returns

Performance

Both lectures run successfully:

• ifp_egm: JAX is 7.77x faster than NumPy
• ifp_egm_transient_shocks: JAX is 19.51x faster than NumPy (Monte Carlo integration benefits significantly from JAX optimization)

Pedagogical Benefits

1. Clearer learning path: Students first learn EGM with a simpler model, then add complexity
2. Better understanding of timing: The simpler model makes it easier to see why the new timing is efficient
3. Motivation for next lecture: Students can see how transient shocks complicate the problem and why they matter for inequality

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com

[jstac]

Fixed the duplicate equation label warnings by renaming labels in ifp_egm_transient_shocks.md:

• eqst → eqst_ts
• eqeul1 → eqeul1_ts
• cfequ → cfequ_ts

All references to these equations have been updated accordingly. The build should now pass without warnings.

[github-actions]

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📚 Changed Lecture Pages: ifp_advanced, ifp_egm, ifp_egm_transient_shocks