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A two-period overlapping-generations framework linking saving, population growth, and capital accumulation across cohorts.
Phase diagram with 45-degree line
The OLG law of motion k_{t+1} = g(k_t) is a first-order difference equation in capital per worker. Plotting g(k_t) against the 45-degree line reveals steady states as crossings and convergence dynamics as staircase paths -- the canonical visualization for one-dimensional dynamic systems.
Layout
Steady-state capital
0.0050
k∗=(1+ns(1−α))1−α1
Capital per worker at the steady-state crossing of g(k) and the 45-degree line.
Steady-state wage
5.49
w∗=(1−α)(k∗)α
Competitive wage at the steady-state capital stock.
Steady-state return
1.76
r∗=α(k∗)α−1−δ
Net return on capital at steady state. Compare to n to assess dynamic efficiency.
Dynamic efficiency gap
12.98
r∗−n
Positive means dynamically efficient (r > n). Negative means over-accumulation -- the economy saves too much.
s
Share of wage income saved by the young. Under log utility, s = beta / (1 + beta).
0.10.8
Higher saving shifts the g(k) curve upward, raising the steady-state crossing point and increasing k*.
n
Rate at which each new cohort is larger than the last. Higher n dilutes capital per worker.
-0.020.1
Higher n rotates the g(k) curve downward by increasing the denominator, lowering k* and shifting the crossing left.
α
Output elasticity of capital. Governs the curvature of the law-of-motion curve and the wage-capital relationship.
0.20.5
Higher alpha makes the g(k) curve more concave and changes the steady-state k* non-monotonically through opposing wage and return effects.
δ
Fraction of capital that depreciates each period. Full depreciation (delta = 1) is the textbook baseline for the two-period model.
0.51
Lower depreciation raises the effective return on saving, which under log utility does not change saving but shifts the law of motion through the capital accumulation identity.
Kernel: time-series | Viz: Phase diagram with 45-degree line