Sugarscape is an artificial world with life, death, wealth, sex, culture, trade, and disease described in Growing Artificial Societies by Joshua M. Epstein and Robert Axtell, Brookings Institute Press, The MIT Press, 1996. This guide focuses on modelling life, death and wealth as in chapter 2.

This guide was written by Ken Kahn and Howard Noble. Last edited on 6 May, 2014.

We start with a pre-prepared model of the Sugarscape. You will see three prototypical agents have been created called Agent, Sugarscape Environment, and Observer. Each has a number ofNetLogo code fragments we call micro-behaviours (or behaviours for short). You will build on this model by adding more behaviours from the Sugarscape Library.

So let's get started!

If you run your model and look carefully you'll see the you already have one instance of Agent in your model - a small triangle in the bottom-left corner. Now you will make this agent behave as in chapter 2 of the Growing Artificial Societies book. 

• Go to the 'Sugarscape Agents' section within the Sugarscape Library, find the 'Initialise Agent' behaviour and add it to Agent within the Composer area (following a similar process as in the previous step). 
• Go through the same steps to add a behaviour called 'Jump to unoccupied patch' of each agent.
• Give Agent a shape and colour (you will find these in the Appearance and Movement sections of the Library). You can change the shape and colour from their defaults by opening the behaviours and changing the parameters within the NetLogo code on the page (for instance you might want to change the parameter "fish" to "person business" or "circle" in the shape behaviour).

• Add a behaviour to make Agent move to the nearest patch with the most sugar that it can see.
• Run the model a few times (by clicking on the 'Setup' button followed by the 'Go' button) and watch the Agent instance carefully. Think why the agent moves a bit or sometimes doesn't move at all.

• Go to the Composer area and edit the field labelled How many copies for the Agent prototype, to replace the default value of 1 with the variable name: 

• You can now change this value with a slider that was added when you loaded the pre-prepared model in step 1. You should see the agents stop with a pattern similar to this:

• Give the agents the behaviours of collecting and consuming sugar. Note that it is important that the agents move, collect, and then consume sugar in that order so ensure that they are in that order in the Agent prototype. 
• Why do some of them keep moving and others stay still? You should see something like this:

• Make agents die if they have no sugar. Think about the distribution of agents and the way they move. After a while the model will look like the following.

• Add a graph of the total population versus elapsed time - this behaviour should be given to the Observer. Think why the population drops and then levels off. The graph should look like the following:

• Add a histogram of the distribution of sugar/wealth across the population. Note that you need two micro-behaviours for this. Watch how the plot changes as the model runs.

The Lorenz Curve and Gini Coefficient are additional tools for observing the distribution of wealth in the Sugarscape. (See page 36 of Growing Artificial Societies.) 

• Add behaviours create the Lorenz Curve. You will need to add two behaviours, one to create the plotting area and one to draw the graphs. 
• Add a monitor to display the Gini Coefficient as the model runs.

• Give the agents behaviours so they die when they reach their lifespan.
• See how this affects the dynamics of the mean vision level, the mean sugar metabolism, and the wealth distribution. (The way ageing is modelled will begin to have an effect after 60 time steps).
• Be sure that the 'Replace dead agents' behaviour is after these so agents that die of old age are also replaced.

• Add behaviours so that sugar production causes pollution and agents move to avoid polluted areas. 
• Observe the modified dynamics. Note that the production of pollution doesn't begin before 50 time steps. Sugar production is done by the Sugarscape Environment.

• Add behaviours so that sugar consumption causes pollution. This also begins after 50 time steps. Sugar consumption is done by each Agent.

• Add a behaviour to the Sugarscape Environment so that after 100 time steps pollution starts to diffuse to neighbouring sites.