# CSCE 782: Problem Set 0

## Due: Never

Figure 1: A picture of what your final program should look like. Click on the picture to see the applet and get the source code.

### The turtles in the world go round and round

This is a simple exercise to help you get started working with netlogo. Your goal is to implement a program which looks like Figure 1 where all the turtles are moving around in a circle. The program itself should not be any longer than about half a page of code. The turtles can use the locations of the others in order to calculate their move, but each turtle's decision must be made independently, that is, without communicating with other turtles. The buttons have the following function:

• setup randomly places num-turtles on the field.
• update moves the turtles one step, they should move a distance of exactly speed at each time step.
• num-turtles is just that. If you change it while the turtles are moving their number should still be adjusted accordingly.
• clockwise determines wether the turtles should move clockwise or counter-clockwise
• shake shakes all the turtles somewhat. They should then be able to find their way back to the circle

Your turtles should do form the circle without using the absolute coordinate grid. That is, you cannot specify, for example, that the center of the circle is at 0,0. In fact, the circle will probably move around the screen if you have a correct implementation.

In order to keep everyone's programs roughly the same, you should implement a turtle function called move which does the actual work. The update function will simply ask turtles [move] and the turtles will move exactly speed.

### Further Research

• Is your program as short as it can be? What is the smallest possible program?
• If you instandiated someone else's turtles, will the resulting population still form a circle?
• Can you get your turtles to run around in a square? a figure eight?
• What peculiarities can you observe and can you explain them? For example, in my implementation I noticed that the turtles can contract the circle a lot faster than they can expand it (when I change the radius). I don't know why this happens, yet.

José M. Vidal