Question 1

In the last paragraph there is probably a mistake.
The distributive rule with 2 scalars, 1 vector: (n∗m)∗v⃗ =n∗v⃗ +m∗v⃗ 
Between n and m should be a plus sign instead of a multiplication sign. So: 
The distributive rule with 2 scalars, 1 vector: (n+m)∗v⃗ =n∗v⃗ +m∗v⃗

Accepted Answer

Such problems can be reported using the 'Report a mistake in the article' button at the top-right of the discussion panel, possibly even leading to the 'Fact Checker' moon badge. Someone else already reported this mistake.

Question 2

in the first example couldn't you just do this

var draw = function() {
    
background(255, 255, 255);
    stroke(255, 0, 0);
    strokeWeight(3);
    line(200, 200, mouseX, mouseY);
};

Accepted Answer

Yes, that would work, but it uses techniques that you already knew before learning about vectors.  The point of the example is to illustrate subtraction of vectors.  The subtraction occurs when the center of the canvas (vector *center*) is subtracted from the mouse position (vector *mouse*).  Vector mouse represents the mouse position, but it's now relative to the center of the canvas (meaning position (0,0) is the canvas center).  
If the coordinate system used for storing a mouse position is changed to make (0,0) the center of the canvas, the way it's drawn must also be changed.  This was done in the example by using translate so that the drawing coordinate system is also at the center of the canvas.

Question 3

Operations over vectors like .`add(), sub(), mult()` etc. change the vectors themselves. What if I wanted to introduce a new variable, a new PVector and  assign it to for example a sum of two other vectors, but not change them?
Like *newVector* = *a* + *b*

Accepted Answer

What you ask shall be answered, use static methods of the functions that come with the `PVector();`, here's an example: `var newVector = PVector.add(a, b);`.

Here's more about it: https://www.khanacademy.org/computing/computer-programming/programming-natural-simulations/programming-vectors/a/static-functions-vs-instance-methods.

Question 4

Can someone pleas help me on the next challenge i don't get it

Accepted Answer

var  v = new PVector(50, 75);

var drawSaber = function() {
    background(0, 0, 0);
    // glow
    strokeWeight(8);
    stroke(107, 206, 219, 150);
    line(0, 400, v.x, 400-v.y);
    // blade
    stroke(255, 255, 255);
    strokeWeight(4);var v = new PVector(50, 75);

var drawSaber = function() {
background(0, 0, 0);
// glow
strokeWeight(8);
stroke(107, 206, 219, 150);
line(0, 400, v.x, 400-v.y);
// blade
stroke(255, 255, 255);
strokeWeight(4);
line(0, 400, v.x, 400-v.y);
};

keyPressed = function(){
if (keyCode === UP){
v.mult(2);
} else if(keyCode === DOWN){
if (keyCode === DOWN){
v.div(2);
}
}
drawSaber();
};

line(0, 400, v.x, 400-v.y);
};

drawSaber();

Question 5

I don't understand what resetMatrix() does, can anybody explain it to me?

Accepted Answer

Let's think of it this way.
You have a program consisting of a tree and a snowflake; and you want to rotate the snowflake by 20 degrees.
You _could_ put the `rotate(20)` line in front of the code, but that would rotate both the snowflake and the tree, because the `draw` function repeats itself for the program lifetime. On the other hand, if you omit the function, you don't have animation.
----------------------------------------------------------------------------------------------------------------------
There's a solution!
You just "enclose" the snowflake drawing code and its `rotate` function in a chunk of code.
The first line is:
`pushMatrix();`
That "activates" the matrix, anything after will be affected by transformations.
`rotate(20);`
Then you have the snowflake drawing code (here).
And then:
`popMatrix();`
That line "disactivates" the matrix. Anything after or before that chunk of code (from the "push" to the "pop" will not be rotated).
-----------------------------------------------------------------------------------------------------------------------
But let's assume that you have a really big program and you want to save code.
You would write the above code this way:
`rotate(20);`
Aha, the computer got a command to rotate the canvas by 20 degrees.
Here - the snowflake drawing command.
`resetMatrix();` 
This function serves the same purpose as the `popMatrix()` function -- except that you don't need the "push" anymore. The "reset" function, as it says, resets the canvas to a neutral state.
Hope that helped,
- SapFire13

Question 6

What is the difference between `dist();` and `mag();`

Accepted Answer

The `.mag()` method of a PVector finds the magnitude of the vector, which is the distance between the vector and (0, 0, 0).  `PVector.dist(vector2)` finds the distance between the vector and `vector2`.

Question 7

could someone help me on the ```LightSaber Challenge```? Thanks!

Accepted Answer

Also, make sure you move the drawSaber function inside the keyPressed function. If you don't, the drawing won't update when you multiple/divide the vector.

Question 8

In the two example programs, what does " translate (width/2, height/2) " mean? It isn't mentioned in the operator list at the start of the article.

Accepted Answer

Ok, in JS, translate moves an object according to the amount of pixels entered into the arguments. In this case, `width/2` and `height/2` were used. So, instead of saying `translate(200,200);` which would only be centered for a 400x400 canvas, `translate(width/2,height/2);` was used to center it on _all_ canvases.

Question 9

I used  v = mult(v);  but It says mult is not defined. Is there something I'm missing?

Accepted Answer

The correct syntax is

```        myVector.mult(_scale_)```
If your vector is called `v` and you want to scale it up by a factor of 4, you would write

```        v.mult(4);```

Question 10

why is vector math so important just stick to easy math

Accepted Answer

If you just stick to easy math, you won't learn very much and you won't gain the abilities that come with new math knowledge!

Computer programming

Course: Computer programming > Unit 5

More vector math

Vector Subtraction

Vector Multiplication

More Number Properties with Vectors

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