So, this question asks us to create a nest

in the center of the world of 9 patches.

We're going to create that nest orange.

So, let's go to the code.

First we'll add a new turtle variable.

So, the first line where it says

"turtles own", type in "return to nest?"

Then we will create a new patch variable

Type in "patches-own [nest?]"

Now we need to add a couple of lines

in the Setup procedure, so in the

"ask turtles" command, let's set

"return to nest?" to "false"

If we don't do this, Netlogo will set any

new variable to "true" by default.

Now we will add a new line

which will become a new procedure

which we will call "set-up nest".

Now, to add that procedure,

begin with a "to set-up nest"

and add "ask patches"

That puts us in the patch context

Whenever a patch falls within a distance

of 2 of the origin. To write that we use

the distance primitive, "distance 0 0"

in parentheses, < 2

If a patch has that criteria,

set pcolor to be orange,

Always end a procedure with end.

Let's see if that is ok.

Looks like I forgot a closing bracket,

let's add that, looks like it's ok now,

Let's go to Interface and press Setup

We can see, it's hard to tell that there

are 9 patches here, but I will assume

that there is. There is an orange nest

in the center of the world.

Next we're asked to write some code that

will have the ants return to the nest

after they eat food,

before they go out and forage again.

There are many ways you could do this.

The way I will do this is the following:

First, I would like to simplify the

"to go" procedure a little bit,

so I am going to create a new procedure,

I am going to call that "look for food",

I am going to copy that section,

write a new procedure line,

and paste it,

and now I will go back to

the "go" procedure, and insert

"ifelse return-to-nest? is false" then

we will look for food, "[look-for-food]",

and consequently "ifelse return-to-nest?"

is true, we will return to nest,

"[return-to-nest]"

We have not yet written the procedure,

return-to-nest. We will do that next.

Before we do that, it is a good idea to

check the code to see

if we have made any mistakes so far.

I am going to press Check.

We see we haven't written

a "return-to-nest" procedure.

I also see that I forgot an equals sign

on this line, so I am going to insert that

We will write the return-to-nest procedure

For this we will simply write

"face patch 0 0" which is the origin and

go forward one, and that will take any ant

that has the return-to-nest variable true,

to turn to face the origin and take a

step in that direction, and then we want

to tell it to go forage again

if it is at the nest,

so if the pcolor is orange, which means

that it has returned home, we will set

return-to-nest "false" because it is

already there, whoops,

So far we don't have any ants with

return-to-nest set to be true,

Obviously we need to do that,

After they have eaten the food, let's set

return-to-nest to be "true".

I will check this code. Looks ok.

Go back to the Interface. Click Setup.

Press Go.

There are quite a few ants.

It's hard to see what they are doing.

Let's reduce the number of ants

to see what they are doing.

Slow it down some.

You may be able to see that they are

behaving as they should --

eating food before returning to the nest

to venture out again.

We could change the color back to red to

make it more obvious,

but let's save that for later.