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view/download model file: billings3.nlogo


This model is of an agent that can observe things about its environment and, based on the information it gets, change things.

In this scenario, a turtle who can't swim is wandering around the world. If it encounters water, it changes direction to aviod it. However, it eventually looses patience and builds a bridge to cross the water.


The agent has three main behaviors that it does depending on the color of the patch one space in front of it.

If the patch is not blue (a bridge or grass), it moves forward then turns in a random direction (shown in the "wander" function).

Every time the turtle sees a blue patch, it's "wet" variable increases by one (it gets wetter and more annoyed). If it encounters a blue patch while it's wet variable is at or less than three, it turns to avoid the water ("avoid-water" function). If it encounters water with a wet variable above three, it builds a bridge ("build-bridge" function).

The "build-bridge" function is recursive. As long as the patch ahead of the turtle is blue, it continues turning the patches gray and moving forward. This means that it builds an entire bridge from one side of the body of water to the other.


The interface is simple. The "step" button goes through the program once, moving or turnign the turtle, depending on the patch it is facing. The "wander" button allows the turtle to wander around the environment. The "irritation" button shows the turtle's rising and falling irritation, showing when it is going to build a bridge.


There's nothing particularly interesting to notice, except that it's fun to watch the turtle try to find a way around the water then give up and just build a bridge.


There are no sliders or switches.


One extension would be to have the turtle try to find a nearby bridge before creating another one. More or less water could also be added.


One thing discovered was the pcolor-of patch-ahead function, which is what allows the turtle to see if it is about to walk into water and drown itself.


There are no related models that I know of.


Jessica Billings
Emergence - CS361
Spring, 2007