Now that you've got a taste of how the
NetLogo interface works...

we're going to spend some time talking
about the basic objects of NetLogo.

And of course one of the main basic
objects is the <i>turtle</i>...

the basic agent of the model.

So the first thing we should do is
create some turtles.

What you have here is a blank model that
I've just opened up,

and this is what you get when you open up
NetLogo normally,

and what I can do is go down to this
space that says 'observer'...

underneath the 'Command Center'...

and here I can type commands in that will
go straight to NetLogo.

So one of the most basic commands and one
of the first commands you'll often write...

is <i>create-turtles</i>. And what <i>create-turtles</i>
does, as you might expect, is create turtles,

and you have to give it the number of
turtles,

so I can create 100 turtles

and when I do that, you'll see that in the
middle of the world..

there are 100 little triangles piled up on
top of each other.

It might not be obvious that there <i>are</i> 100
little triangles there,

so what I can do is, I can talk directly
to the turtles,

There are two ways to do this in NetLogo.

One of them is much more common, but let
me show you the less common way...

which is - this little 'observer' thing is
actually highlightable,

and I can instead select 'turtles',

and so now, rather than talking to the 
<i>observer</i>, which is the all-seeing 'deity',

I'm now talking directly to the <i>turtles</i>.

And I can tell the turtles to all go
forward 10 steps,

And when I do that, as you can see, we
spread the turtles out around the world,

and now you might be able to see that
there's 100 of them...

they're all pointing in slightly different
directions,

and they are have slightly different
colors, to differentiate them.

That's the less common way of talking to
the turtles.

The more common way - because it's the
way we do it from the code tab -

is we <i>ask</i> the turtles to do something.

So I can <i>ask turtles</i>, and then I have to
use these square brackets...

to tell it the message I want to ask the
turtles.

I can ask the turtles, for instance, to go
<i>back</i> 5 steps...

and when I do that you can see they go
back 5 steps.

You're going to be using <i>ask turtles</i> a lot

because <i>ask turtles</i> is the basic way that
NetLogo's observer communicates with turtles.

In addition to having them go forward and
back...

I can also have them go <i>left 90</i> degrees...

and I can have them go <i>right 90</i> degrees...

or any arbitrary number, so <i>right 9</i>
degrees, for instance.

Then I can put these commands all together

and I can ask them to <i>repeat</i> them, to put
together a set of coordinated movements.

So, for instance, I can ask the turtles to
<i>repeat 4</i> times a particular step...

in this case, let's have them go <i>forward 
10</i>, <i>right 90</i> degrees...

and you didn't see anything, because, if
you think about it, if I repeat 4 times...

'forward 10 right 90 degrees' what I'm
doing is drawing a box,

and that means the turtles are returning
to the same place.

However, as we learned in the previous
talk we can use the <i>speed slider</i>...

to control the speed at which they do this
and then maybe we could see them.

So I turn the speed slider down, and now,
sure enough...

you can see each individual turtle doing 
the actions that we asked it to do.

It'll take quite a while if you leave it at
this slower speed, so we'll speed it up.

We've talked about basic commands for
the turtles.

Turtles also have a variety of <i>properties</i>

For instance, they have the <i>color</i> that 
you can see,

and we can ask the turtles to change their
color,

we can <i>set color blue</i> for all the turtles,
for instance...

oop! - this is a nice notion - I created 
an error here...

I left a bracket out...

and NetLogo will tell me what that error
is...

it will tell me there is no closing bracket
for this open bracket...

So I put the bracket in, and once I do 
that it works.

I can also ask the turtles to change
their <i>size</i>,

the default size is 1, I can change it
to 2, so I can make them all bigger.

And I can change where they are located
in the world

They have an x coordinate (<i>xcor</i>) and a
y coordinate (<i>ycor</i>)

And rather than setting their xcor and
ycor to particular values...

I'm going to set them to random values.

So I can set their <i>xcor</i> to a <i>random-xcor</i>
and their <i>ycor</i> to a <i>random-ycor</i>,

<i>random-xcor</i> and <i>random-ycor</i> are
built-in NetLogo primitives...

that generate a random value for those
particular settings.

That gives you some basic introductions
to the properties,

if you want to find out more about the 
properties...

you can right-click (or control-click on 
a Mac) on any of the different turtles,

and if you go down there's a little 'turtle
menu 92', which will highlight that turtle,

here, '92' specifies that specific turtle,

and we can <i>inspect</i> the turtle, and we can 
see that particular turtle's properties,

so you can see '92' - its identifier, its
color, its heading, xcor, ycor, shape...

and we'll go over all these as we continue
through the model discussions.