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## NetLogo User Community Models

WHAT IS IT?

This is the "Recursive Trees" model from Resnick's "Turtles" book (pp. 110-116).

HOW IT WORKS

'turtle-setup' is the main procedure for setting up the one initial turtle. 'draw-branch' is the procedure that is called once per branch segment.

HOW TO USE IT

Click on 'setup' to initialize the model, and then click on 'go' to start execution of the model.
init-length: The length of the first, longest, branch (the 'trunk' of the tree)
static-tree: If 'on', then the tree will be symmetric. If 'off', then
the length of the branches have a random element.
min-branch-length: The smallest branch length that the model draws.
angle-of-branches: The angle the new branch makes with the heading of the old branch.

THINGS TO TRY

Be sure to try angle-of-branches set to 30, 45, 60, 90, and 120 just to get started. Make init-length as long as you can make it for your screen.

EXTENDING THE MODEL

The 'shrink-factor' could be a slider to change the 'static' value (0.7) and the 'random' value (0.5, 0.1, and 5). For the 'random' value, I'm guessing that you can start with one value (from 0 to 10); suppose that '2' is chosen. Then the values would be 0.2, 0.1, and 8 (notice that 2 and 8 add up to 10). That would be a good place to start.

NETLOGO FEATURES

This model repeatedly generates new turtles so that there are 2^periods turtles.

RELATED MODELS

If you find this of interest, then you should also look in the Mathematics/ Fractals section of the Models Library.

CREDITS AND REFERENCES

This model is described in Resnick, M. (1994) "Turtles, Termites and Traffic Jams: Explorations in Massively Parallel Microworlds." Cambridge, Ma: MIT Press, pp. 88-95. Scott A. Moore (samoore@umich.edu) of the University of Michigan Business School adapted this model to NetLogo.