vignettes/examples/03_PC.R

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

# model PC

# Create empty model
model_pc <- create_model(name = "SFC PC")

# Add variables
model_pc <- model_pc |>
  add_variable("B_cb", desc = "") |>
  add_variable("H_s", desc = "") |>
  add_variable("B_s", desc = "") |>
  add_variable("B_h", desc = "") |>
  add_variable("H_h1", desc = "") |>
  add_variable("H_h", desc = "") |>
  add_variable("C", desc = "") |>
  add_variable("V", desc = "") |>
  add_variable("T_x", desc = "") |>
  add_variable("Y", desc = "Income = GDP") |>
  add_variable("Yd", desc = "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("r", init = 0.025, desc = "") |>
  add_variable("G", init = 20, desc = "Government demand") |>
  add_variable("lambda0", init = 0.635, desc = "") |>
  add_variable("lambda1", init = 0.05, desc = "") |>
  add_variable("lambda2", init = 0.01, desc = "")

# Add equations
model_pc <- model_pc |>
  add_equation("Y = C + G", desc = "") |>
  add_equation("Yd = Y - T_x + r[-1] * B_h[-1]") |>
  add_equation("T_x = theta * (Y + r[-1] * B_h[-1])") |>
  add_equation("V = V[-1] + (Yd - C)") |>
  add_equation("C = alpha1 * Yd + alpha2 * V[-1]") |>
  add_equation("H_h = V - B_h") |>
  add_equation("H_h1 = V * ((1 - lambda0) - lambda1 * r + lambda2 * ( Yd/V ))") |>
  add_equation("B_h = V * (lambda0 + lambda1 * r - lambda2 * ( Yd/V ))") |>
  add_equation("B_s = B_s[-1] + (G + r[-1] * B_s[-1]) - (T_x + r[-1] * B_cb[-1])") |>
  add_equation("H_s = H_s[-1] + B_cb - B_cb[-1]") |>
  add_equation("B_cb = B_s - B_h") |>
  add_equation("H_h = H_s", hidden = T)

# Simulate model
model_pc <- simulate_scenario(
  model_pc,
  scenario = "baseline", max_iter = 350, periods = 100,
  hidden_tol = 0.1, tol = 1e-08, method = "Gauss"
)
# Plot results
plot_simulation(
  model = model_pc, scenario = c("baseline"), from = 1, to = 50,
  expressions = c("B_h / V")
)

# Plot results
plot_simulation(
  model = model_pc, scenario = c("baseline"), from = 1, to = 50,
  expressions = c("H_h / V")
)

# Create shock - increased rate of interest on bills
shock_pc <- create_shock()

shock_pc <- shock_pc |>
  add_shock(variable = "r", value = 0.035, desc = "Increase in the rate of interest on bills", start = 5, end = 50)

model_pc <- model_pc |>
  add_scenario(name = "expansion", origin = "baseline", origin_start = 1, origin_end = 100, shock = shock_pc)

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

# Plot results
plot_simulation(
  model = model_pc, scenario = "expansion", from = 1, to = 50,
  expressions = c("B_h / V")
)

plot_simulation(
  model = model_pc, scenario = "expansion", from = 1, to = 50,
  expressions = c("H_h / V")
)