Build Your First Model

This example creates a simple accumulating stock.

1. Place the primitives

In Primitives:

1. Select Stock, then click the canvas. Name it Population.
2. Add a Flow entering the stock. Name it Births.
3. Add an Auxiliary. Name it Birth rate.

You can also Shift-drag from a node to begin a flow. Move and resize objects directly on the canvas. Double-click a label to rename it.

2. Connect the model

Select Connector, click Birth rate, then click Births.

Connectors communicate dependency. A referenced variable should normally have a connector into the equation that uses it. The inspector warns when an equation reference and its connectors do not agree and can offer Add Connector.

3. Enter equations

Select each object and use Model Inspector > Behavior:

• Population: enter an initial value such as 100.
• Birth rate: enter a constant such as 0.05.
• Births: enter Population * Birth rate.

Add compatible units, for example People, 1/Year, and People/Year. Stock equations are initial values; connected flows change the stock during simulation.

4. Configure and run

Open Model Settings and set:

• Time Unit: Year
• Start Time: 0
• Stop Time: 20
• DT: for example 0.25
• Integration Method: select the method appropriate for the model

Select Simulate. When the run completes, add Population to a plot or inspect it in the Workspace.

See Working on the canvas, Editing behavior and style, and Simulation settings.