All the activities in this section use the simulation software, NetLogo, which can be downloaded online. Newer versions of NetLogo are no longer compatible with the models for these activities – we recommend using version 4.0.4, with which they were built and tested. All versions of the software are available on the NetLogo site:. The models for all the activities in this free course should be downloaded now from the following links and the models saved to a local disk:
The first activity, Activity 5A, asks you to explore the dynamic behaviour of linear, positive feedback and negative feedback relationships using three simple system dynamics models. In Activity 5B you will begin to investigate the behaviour of a system dynamics model of human population growth where, through the dominance of a positive feedback process, you will be able to visualise exponential growth. Activities 5C and 5D will allow you to explore slightly more complex dynamic behaviours (homeostasis, overshoot and collapse, boom and bust cycles) resulting from the addition of a few basic feedback processes. The final exercise, Activity 5E, will allow you to explore a complex situation of your choice and develop your own system dynamics diagram and investigate the resulting dynamic relationships.
Please don’t feel intimidated by the maths: there is no requirement in this course for any mathematical expertise and I have included the algorithms only for those individuals who wish to follow a comprehensive verbal, visual and mathematical modelling approach. Don’t worry, you won’t need to do any fancy mathematics in your own work.
In activities 5A to 5D, I will try and verbally ‘walk you through’ the various models. However, using verbal descriptions is not the ideal way to do this, so I would encourage you to iterate between my verbal descriptions and playing with the simulations. Although I felt it necessary to describe the very basic mathematics involved, the fundamental point that I would like to get across in these activities is that with just a few dynamic feedback relationships and extremely basic mathematical equations, system behaviours can become very difficult to predict from just looking at the ‘static’ picture of components (stocks and variables) and relationships (links and equations).
The final activity of this section, Activity 5E, will allow you to focus on a few select components of the sign graph you developed in Activity 4A in Understanding the environment: flows and feedback and reinterpret the relationships in a dynamic way. I don’t expect you to actually program and simulate a system dynamics model but, instead, to undertake some of the preparation for doing so by drawing a system dynamics diagram and finding plausible data to support your model.