# Difference between revisions of "Example 1: Simple Population Model"

A simple system dynamics model can be used to show unrestricted exponential growth over time.

## Viewing this model in Nova

To run this model:

1. Launch Nova
2. Select Menu Item File | Browse Model Library
3. Open folder 1-Population Models and double-click SimplePopModel

The model displays in Nova as shown

In the model, population is a stock called pop whose change is specified by a flow called birth. The birth rate is provided by the component expression rate * pop. Here rate is a term which represents the constant or computed quantity contained in its component expression. In this model rate is provided by a slider called birth_rate, which is visible in the dashboard.
The mathematical model represented here is given by the differential equation: d pop/dt = rate * pop