Add or modify flows

Flows move material and information through the system, increasing or decreasing stocks. flow() adds or changes a flow variable. This is a convenience wrapper around update() with type = "flow". See the Flows section of update() for more details.

Usage

flow(
  object,
  name,
  eqn = 0,
  to = NULL,
  from = NULL,
  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.

to

Target of flow. Accepts a bare symbol or string. Must be a stock in the model. Defaults to NULL to indicate no target.

from

Source of flow. Accepts a bare symbol or string. Must be a stock in the model. Defaults to NULL to indicate no source.

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 a flow into a stock
sfm <- stockflow() |>
  stock(population, eqn = 100) |>
  flow(births, eqn = population * 0.1, to = population) |>
  flow(deaths, eqn = population * 0.05, from = population)