import_desolve: Import a deSolve model

Description

Convert a model written for deSolve into a stock-and-flow model of class stockflow.

Usage

import_desolve(model, params, init, times, method = "lsoda", name = NULL)

Value

A stock-and-flow model of class stockflow.

Arguments

model: A deSolve-style ODE function with arguments (t, state, parameters).
params: Named numeric vector of model parameters (constants).
init: Named numeric vector of initial state values (stocks).
times: Numeric vector of time points. Must be evenly spaced (e.g., from seq(start, stop, by = dt)).
method: Integration method. Defaults to "lsoda". See sim_methods().
name: Optional model name. Character scalar.

Details

The model function must follow the canonical deSolve convention:

model <- function(t, state, parameters) {
  with(as.list(c(state, parameters)), {
    dX <- <rate expression>   # d<VarName> for each state in init
    list(c(dX))
  })
}

State variable names are taken from names(init), parameter names from names(params). Each d<VarName> assignment inside the with() block is parsed as the net rate of change for stock VarName and becomes a flow in the sfm. Any other assignments in the with() block (intermediate calculations) are imported as auxiliary variables in the order they appear.

Examples

Run this code

logistic_model <- function(t, state, parameters) {
  with(as.list(c(state, parameters)), {
    dN <- r * N * (1 - N / K)
    list(c(dN))
  })
}
sfm <- import_desolve(
  model  = logistic_model,
  params = c(r = 0.3, K = 100),
  init   = c(N = 10),
  times  = seq(0, 50, by = 0.1),
  method = "lsoda",
  name   = "Logistic growth"
)
# \dontshow{
sfm <- sim_settings(sfm, save_at = 5)
# }
sim <- simulate(sfm)
plot(sim)