How much experience do you have creating agent-based models?

Which NetLogo platform are you using?

Note: The core functionality of NetLogo Web and NetLogo Desktop are the same, so it doesn't really matter for the purpose of this lesson, but it makes sense to learn on the platform you intend to use with students:

• If your students have chromebooks, you will want to use NetLogo Web. (Everything will be here in the browser so just continue ahead)

• If your students have laptops that can download desktop applications, you may want to use the desktop version because it is faster and has some features that haven't been added to the web version yet. You can download NetLogo Desktop here.

Moving Turtles

Now let's ask the turtles to move. In the Command Center, type ask turtles [forward 10]. There is an abbreviation for this one too. You can just type ask turtles [fd 10], and it will do the same thing. To clear everything away, type clear-all, or ca for short (not every command has an abbreviation, but a lot of the most common ones do).

What does it look like when you create a bunch of turtles and ask them to all move forward the same distance? Why is this?

The command random number will produce a random integer greater than 0 and less than number. So random 10 will output a random integer greater than 0 and less than 10. The command random-float number does the same thing, except the output will be a decimal number instead of an integer.

Try creating a bunch of turtles and asking them to move forward a random distance.  What does it look like?  Does it look different if you use random vs random-float? Does it look different as you add more turtles? Try to explain why you see what you do for each question. 

Moving individual turtles and turning

• You can also ask individual turtles to do things. Try typing ask turtle 1 [fd 5]. Each turtle has a number. Go ahead and move a few turtles individually. 
• To have turtles turn, you have to ask them to turn a number of degrees. For example, rt 90  to turn right by 90 degrees, or lt 30 to turn left by 30 degrees (rt stands for right turn and lt for left turn). Try asking some turtles individually and as a group to turn and move.

Using just the commands you've learned, how might you make a turtle move in a circle?

Buttons

To make things even easier, we can create a button to call a procedure. 

• If you are using NetLogo Web, first click the lock button that looks like this:  so that you enter authoring mode. Then you can right click on the green area and click Create Button. A window for creating a button will appear. In the commands box type move-turtles and press okay.
• If you are using NetLogo Desktop, you can just right click on the white area next to the model "view" and click Button. A window for creating a button will appear. In the commands box type move-turtle and press okay. 

Now you can click the button to call the procedure. 

The Go Procedure

As a convention, almost every NetLogo model also has a go procedure and an accompanying button. This is generally the procedure used to make a model run continuously. It makes sense to have a unit of time in a model when it runs continuously. In NetLogo this unit is called a tick.

• To reset the clock in our model add the command reset-ticks  to your setup procedure.
• Create a procedure called go. For now just call your move-turtles procedure and the tick command. 
• Create a button for your go procedure. In the window for creating the button, check the box that says "forever" and also check the box that says "disable until ticks start". (If you closed the box, you can right click on the button and click "edit" to open it again).

When you click the go button, it should now call the go procedure repeatedly. Each time the go procedure is executed, the ticks increase by 1, because you called the tick command inside the go procedure. 

What behavior do you see? Were you surprised by it? Why is this behavior occurring? Answer in the box below.  

Integrative Understanding

Change your move-turtles procedure so that turtles move forward slightly more each tick (something like 0.22). What pattern emerges? (You can use the Model Speed slider at the top of the model to make the model run faster or slower).

Most people do not predict the resulting pattern. Some predict that the turtles will move in a smaller or larger pattern, but rarely the actual emergent pattern of a pulsating circle. This illustrates one of the difficulties in understanding emergent systems. It is difficult to predict how a small change enacted by many agents will "integrate" to form a larger pattern. This is sometimes called "integrative understanding," as it parallels the cumulative integration of small differences in calculus.

Can you think of a real world system in which integrative understanding is difficult?

If you are using NetLogo Web, copy your code here, because when you leave this page the code you entered in the NetLogo Code tab won't be saved. If you are using NetLogo Desktop, still copy your code here, but you can also save your model on your computer if you want to.

Asking Neighbors for Things

Patches can ask other patches to do things (Turtles can too). This is one way to have patches interact with on another.

• Ask a specific patch to ask its neighbors to set their pcolor like this ask patch 5 3 [ask neighbors [set pcolor color]]. (where color is a specific color). 
• Whenever you ask a patch to do something, any properties inside the brackets (like pcolor) belong to the patch being asked. So, in the code in the previous bullet point, each neighbor of patch 5 3 was asked to set its own pcolor. But what if patch 5 3 wants to ask its neighbors to change their pcolor to match its own? For this, it can ask the neighbors to set their pcolor to [pcolor] of myself. This is like saying "set (your) pcolor to the pcolor of me." 
• Try asking a specific patch to ask its neighbors to set their pcolor to its pcolor. Copy and paste the code you used to accomplish this.

Go procedure

• Now write a go procedure that asks patches to ask their neighbors to change their color. You can ask all 8 neighbors with neighbors, or just the east, west, north and south neighbors with neighbors4. You can also ask just one of these neighbors by asking one-of neighbors to do something.
• Make a button for the go procedure. Have it run forever, and also disable it until ticks start.

Copy the code of your go procedure below.

What behavior do you see? Why does this happen? Describe below.

Approximately how long did you spend on this entire lesson? How many sessions did you do it in?