WEBVTT

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hi and welcome to modeling with turtle

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graphics in this video we'll be learning

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about graphing with Tracy the turtle so

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this is Tracy Tracy is a turtle and

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Tracy is really good at drawing lines

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and shapes on the screen we'll see some

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examples of that in a second you can

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tell Tracy to do things using commands

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Tracy understands commands written in a

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programming language called Python right

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above Tracy is an example of a command

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this command tells Tracy to move to the

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location X Y and Tracy's world as Tracy

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moves to this point Tracy will draw a

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line on the screen that represents the

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path the Tracy took programming or

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coding is giving commands to a computer

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will be writing programs for Tracy where

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we give Tracy sequences of commands to

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follow let's learn about some things

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that Tracy can do Tracy lives in a world

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called a canvas because we'll be using

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Tracy to create graphs we'll want to set

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up some axes and labels this will be

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done for us in our programs to graph

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with Tracy will be using the set

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position command the set position

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command takes two arguments X and Y and

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then sends Tracy to the place on the

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canvas with the coordinates x and y 2sin

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Tracy to a specific location we need to

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set x and y to be numerical values like

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0 and 5 or 10 and 10's Tracy moves to

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the coordinate point Tracy will leave a

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trail showing the path taken which is

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going to be the line in our graph so to

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draw a graph we'll use the set position

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command to send Tracy to a series of XY

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coordinates to do this we'll use a

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for-loop code inside a for loop will

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execute repeatedly we set how many times

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the code executes by putting a number in

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parentheses so if I wanted to run

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something 100 times I would say

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X in range 100 making sure to put the

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number 100 in parenthesis and then

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ending with a colon then whatever code I

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put indented below that line will repeat

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100 times the value of x will start at 0

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and each time the for loop runs it will

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increase the value of X until it reaches

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the maximum value which is the number we

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put in parenthesis so in this case 100

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so to graph an equation we can make it

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so every time X updates we calculate the

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value of y and then use the set position

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command to send Traci to the position X

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comma Y let's take a look at an example

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so this is the editor page and the

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editor page is set up so that our

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program or our code is written on the

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left side and then our canvas where we

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can see Traci run the code is on the

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right side and anytime we want to run

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the code we can just click this green

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Run code button so you can see that this

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code that's written already sets up

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Traci with axes and labels on the canvas

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so I'm going to click stop to clear the

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canvas while we code our graph so we

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want to make sure not to modify any of

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the code that sets up Traci's axes and

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we'll just graph below all of that so

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I'll start with a for loop for X in

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range 50 so I want to make sure that the

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number 50 is in parentheses and that I

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put a colon after this statement now I

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want to make sure that all the code I

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want repeated is indented under this

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loop every time my x value updates i

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want to recalculate my y value and go to

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the position x comma y let's say i want

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to graph the equation y equals x divided

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by 4 so i've written my equation and now

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i need to use set position to send traci

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to the coordinate pair XY ok let's try

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running our program now

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okay so we got an error here and so the

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issue here is that I used set position

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with a capital S when I should have used

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a lowercase s Python is very picky and

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so if you make a small typo like

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forgetting to close your parentheses or

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using upper case instead of lowercase it

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won't work and it's going to give you an

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error

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luckily on the left hand side of our

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editor page we have some documentation

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and this just has a list of the commands

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we might use so if you forget exactly

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how to write something just check here

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and so I can see that set position

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should have a lowercase s now let's run

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the code again awesome so this graph is

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linear but Tracy can plot all kinds of

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two variable relationships here you can

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see Tracy is plotting a sinusoidal wave

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graph now it's your turn to make graphs

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with Tracy