Add or modify constants

Constants are time-independent variables that do not change over the course of a simulation. constant() adds or changes a constant variable. This is a convenience wrapper around update() with type = "constant". See the Constants section of update() for more details.

Usage

constant(object, name, eqn = 0, label = name, doc = "", non_negative = FALSE)

Arguments

object

Stock-and-flow model, object of class stockflow.

name

Variable name. Accepts a bare symbol (e.g., population), a string ("population"), or a vector via c() (e.g., c(a, b) or c("a", "b")). Use !! to inject from a variable.

eqn

Equation (or initial value in the case of stocks). Accepts a bare expression (e.g., a * b + 1), a string ("a * b + 1"), or a numeric value. Use !! to inject from a variable. Defaults to 0.

label

Name of variable used for plotting. Defaults to the same as name.

doc

Description of variable. Defaults to "" (no description).

non_negative

If TRUE, variable is enforced to be non-negative (i.e., strictly 0 or positive). Defaults to FALSE.

Value

A stock-and-flow model object of class stockflow

See also

update(), discard(), change_name()

Examples

# Create constants for model parameters
sfm <- stockflow() |>
  constant(growth_rate, eqn = 0.1, label = "Growth Rate") |>
  constant(carrying_capacity, eqn = 1000, label = "Carrying Capacity")