The Fishing Fleet, Year by Year

Solow model · capital accumulation · depreciation · simulation · update order

The fishing town of Corrow measures its capital in boats per fisher, k. Each year every fisher lands

y_t = A\,k_t^{\alpha}

crates of fish (output per worker, with 0 < \alpha < 1). The town follows the Solow model of capital accumulation:

  • a fixed share s of each year's output is saved and turned into new boats (investment per worker s\,y_t);
  • a share delta of the boats wears out during the year (depreciation);
  • the number of fishers grows by a share n a year, so the existing boats are spread over more people.

Capital per worker therefore moves from year t to year t+1 by

k_{t+1} = k_t + s\,y_t - (\delta + n)\,k_t

where both y_t and the last term use year t's capital. All three rates are fractions: 5 % is 0.05.

Write fleet_path(A, alpha, s, delta, n, k0, T) that returns the list [k_0, k_1, \ldots, k_T] (so T + 1 numbers, starting with k0). Press Run with plot(path) to watch it level off.

Examples

Input:  A = 1, alpha = 0.5, s = 0.2, delta = 0.05, n = 0.05, k0 = 1, T = 3
Output: [1, 1.1, 1.19976177, 1.29885287]
Explanation: in year 0, y = 1, so k1 = 1 + 0.2 * 1 - 0.1 * 1 = 1.1.
In year 1, y = sqrt(1.1) = 1.0488, so k2 = 1.1 + 0.20976 - 0.11 = 1.19976.

Input:  A = 2, alpha = 0.3, s = 0.25, delta = 0.06, n = 0.01, k0 = 20, T = 2
Output: [20, 19.82822803, 19.66530590]
Explanation: the town starts with more boats than its saving can keep up,
so wear and newcomers outrun new boats and capital per worker falls.

Constraints

  • answers are compared with a tolerance of 1e-6; do not round

Goals

  • Simulate capital per worker with the Solow accumulation rule
  • Use this year's output for this year's investment (state timing exactly)
  • See capital rise from below its long-run level and fall from above it
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