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Tree Growth Simulation
an experiment in emergence
created with NetLogo
view/download model file: tree.nlogo
WHAT IS IT?
In an attempt to learn a bit about how Netlogo works, I decided to try to model the growth of a tree.
HOW IT WORKS
The model begins with a single agent at the bottom of the screen, which moves upwards (grows toward the sun), branches (creates a second agent), and possibly dies on each step of growth.
HOW TO USE IT
There are several controls to play with.
THINGS TO NOTICE
Note the slider at the top of the screen is all the way to the right. This makes the tree draw immediately. As you slide it to the left, it slows down the program so that you can observe the tree 'growing.'
Notice that when a new branch is created, it and the branch it came from are each slightly smaller in width.
WARNING: Since branches multiply exponentially, it's best to clear the screen and start over with the Setup button after creating a tree. This is why the Grow_Until button only goes up to 10 - your computer may lock up trying to complete more cycles.
THINGS TO TRY
Try setting the Growth_Rate very low and the Branching_Frequency to 1. Notice that sometimes the tree grows down and out the top of the screen. The primitive I used in the code was towards-nowrap, which returns the direction of the goal patch without accounting for the screen wrapping (which can be the shortest path). Yet in some extreme examples, the tree still grows roots. I haven't yet figured out why - maybe you can.
EXTENDING THE MODEL
I'd be interested in knowing if anyone adds anything interesting.
I considered starting the tree in the center of the screen and starting with 2 agents doing the exact same thing, except that one will aim down for roots at the same time that one aims up for branches. It might be interesting to see what kind of symmetry occurs. I once heard that a tree's roots spread out as far as its branches. Perhaps the same would happen with our virtual tree.
CREDITS AND REFERENCES