vignettes/examples/02_SIMEX.R

In gamrot/godley: Stock-Flow-Consistent Model Simulator

# model SIMEX

# Create empty model
model_simex <- create_model(name = "SFC SIMEX")

# Add variables
model_simex <- model_simex |>
  add_variable("C_d", desc = "Consumption demand by households") |>
  add_variable("C_s", desc = "Consumption supply") |>
  add_variable("G_s", desc = "Government supply") |>
  add_variable("T_d", desc = "Taxes, demand") |>
  add_variable("T_s", desc = "Taxes, supply") |>
  add_variable("N_d", desc = "Demand for labor") |>
  add_variable("N_s", desc = "Supply of labor") |>
  add_variable("H_h", desc = "Cash money held by households") |>
  add_variable("H_s", desc = "Cash money supplied by the government") |>
  add_variable("H_d", desc = "Cash money demanded by the government") |>
  add_variable("Y", desc = "Income = GDP") |>
  add_variable("Yd", desc = "Disposable income of households") |>
  add_variable("Yd_e", desc = "Expected disposable income of households") |>
  add_variable("alpha1", init = 0.6, desc = "Propensity to consume out of income") |>
  add_variable("alpha2", init = 0.4, desc = "Propensity to consume out of wealth") |>
  add_variable("theta", init = 0.2, desc = "Tax rate") |>
  add_variable("G_d", init = 20, desc = "Government demand") |>
  add_variable("W", init = 1, desc = "Wage rate")


# Add equations
model_simex <- model_simex |>
  add_equation("C_s = C_d", desc = "Consumption") |>
  add_equation("G_s = G_d") |>
  add_equation("T_s = T_d") |>
  add_equation("N_s = N_d") |>
  add_equation("Yd = W * N_s - T_s") |>
  add_equation("T_d = theta * W * N_s") |>
  add_equation("C_d = alpha1 * Yd_e + alpha2 * H_h[-1]") |>
  add_equation("H_s = G_d - T_d + H_s[-1]") |>
  add_equation("H_h = Yd - C_d + H_h[-1]") |>
  add_equation("Y = C_s + G_s") |>
  add_equation("N_d = Y/W") |>
  add_equation("H_d = Yd_e - C_d + H_h[-1]") |>
  add_equation("Yd_e = Yd[-1]") |>
  add_equation("H_s = H_h", desc = "Money equilibrium", hidden = TRUE)

# Simulate model
model_simex <- simulate_scenario(model_simex,
  scenario = "baseline", max_iter = 350, periods = 100,
  hidden_tol = 0.1, tol = 1e-05, method = "Newton"
)

# Plot results
plot_simulation(
  model = model_simex, scenario = c("baseline"), from = 1, to = 50,
  expressions = c("Y", "C_d", "C_s / alpha1")
)

# Create empty shock
shock_simex <- create_shock()

# Add shock equation with increased government expenditures
shock_simex <- add_shock(shock_simex,
  variable = "G_d", value = 25,
  desc = "Increase in government expenditures", start = 5, end = 50
)

# Create new scenario with this shock
model_simex <- add_scenario(model_simex,
  name = "expansion", origin = "baseline", shock = shock_simex
)

# Simulate shock
model_simex <- simulate_scenario(model_simex,
  scenario = "expansion", max_iter = 350, periods = 100,
  hidden_tol = 0.1, tol = 1e-05, method = "Newton"
)

# Plot results
plot_simulation(
  model = model_simex, scenario = c("baseline", "expansion"), from = 1, to = 50,
  expressions = c("Y")
)

plot_simulation(
  model = model_simex, scenario = c("baseline", "expansion"), from = 1, to = 50,
  expressions = c("C_d")
)

plot_simulation(
  model = model_simex, scenario = c("baseline", "expansion"), from = 1, to = 50,
  expressions = c("C_s / alpha1")
)