sim_specs: Modify simulation specifications

In sdbuildR: Easily Build, Simulate, and Visualise Stock-and-Flow Models

Modify simulation specifications

Description

Simulation specifications are the settings that determine how the model is simulated, such as the integration method (i.e. solver), start and stop time, and timestep. Modify these specifications for an existing stock-and-flow model.

Usage

sim_specs(
  sfm,
  method = "euler",
  start = "0.0",
  stop = "100.0",
  dt = "0.01",
  save_at = dt,
  save_from = start,
  seed = NULL,
  time_units = "s",
  language = "R"
)

Arguments

sfm	Stock-and-flow model, object of class sdbuildR_xmile.
method	Integration method. Defaults to "euler".
start	Start time of simulation. Defaults to 0.
stop	End time of simulation. Defaults to 100.
dt	Timestep of solver; controls simulation accuracy. Smaller = more accurate but slower. Defaults to 0.01.
save_at	Timestep at which to save computed values; controls output size. Must be >= dt. Use larger than dt to reduce memory without sacrificing accuracy. Example: dt = 0.01, save_at = 1 gives accurate simulation but only saves every 100th point. Defaults to dt (save everything).
save_from	Time at which to start saving values. Use to discard initial transient behavior. Must be >= start. Defaults to start.
seed	Seed number to ensure reproducibility across runs in case of random elements. Must be an integer. Defaults to NULL (no seed).
time_units	Simulation time unit, e.g. 's' (second). Defaults to "s".
language	Coding language in which to simulate model. Either "R" or "Julia". Julia is necessary for using units or delay functions. Defaults to "R".

Value

A stock-and-flow model object of class sdbuildR_xmile

See Also

solvers()

Examples

sfm <- xmile("predator_prey") |>
  sim_specs(start = 0, stop = 50, dt = 0.1)
sim <- simulate(sfm)
plot(sim)

# Change the simulation method to "rk4"
sfm <- sim_specs(sfm, method = "rk4")

# Change the time units to "years", such that one time unit is one year
sfm <- sim_specs(sfm, time_units = "years")

# To save storage but not affect accuracy, use save_at and save_from
sfm <- sim_specs(sfm, save_at = 1, save_from = 10)
sim <- simulate(sfm)
head(as.data.frame(sim))

# Add stochastic initial condition but specify seed to obtain same result
sfm <- sim_specs(sfm, seed = 1) |>
  build(c("predator", "prey"), eqn = "runif(1, 20, 50)")

# Change the simulation language to Julia to use units
sfm <- sim_specs(sfm, language = "Julia")

sdbuildR documentation built on Nov. 19, 2025, 5:07 p.m.