mag(x, y, [z])
Calculates the magnitude (or length) of a vector. A vector is a direction in space commonly used in computer graphics and linear algebra. Because it has no “start” position, the magnitude of a vector can be thought of as the distance from coordinate (0,0) to its (x,y) value. Therefore, mag() is a shortcut for writing dist(0, 0, x, y).
Type: function
Parameter(s):
- x {Number}:Coordinate. 
- y {Number}:Coordinate. 
- z {Number} Optional:Coordinate, optional. 
Returns:
- 
    {Number}:
 The magnitude.