A vector is defined as having three dimensions as being represented by an ordered collection of three numbers:   (X, Y, Z).

If you imagine a graph with the   x   and   y   axis being at right angles to each other and having a third,   z   axis coming out of the page, then a triplet of numbers,   (X, Y, Z)   would represent a point in the region,   and a vector from the origin to the point.

Given the vectors:

        A = (a1,  a2,  a3) 
        B = (b1,  b2,  b3) 
        C = (c1,  c2,  c3) 

then the following common vector products are defined:

 The dot product       (a scalar quantity)
  A • B = a1b1   +   a2b2   +   a3b3  
 The cross product       (a vector quantity)
  A x B = (a2b3  -   a3b2,     a3b1   -   a1b3,     a1b2   -   a2b1)  
 The scalar triple product       (a scalar quantity)
  A • (B x C) 
 The vector triple product       (a vector quantity)
  A x (B x C) 


Task

Given the three vectors:

        a = ( 3,    4,    5)
        b = ( 4,    3,    5)
        c = (-5,  -12,  -13)

 Create a named function/subroutine/method to compute the dot product of two vectors.
 Create a function to compute the cross product of two vectors.
 Optionally create a function to compute the scalar triple product of three vectors.
 Optionally create a function to compute the vector triple product of three vectors.
 Compute and display: a • b
 Compute and display: a x b
 Compute and display: a • (b x c), the scalar triple product.
 Compute and display: a x (b x c), the vector triple product.


References

   A starting page on Wolfram MathWorld is   Vector Multiplication .
   Wikipedia   dot product. 
   Wikipedia   cross product. 
   Wikipedia   triple product.


Related tasks

   Dot product
   Quaternion type


import Foundation
 
infix operator • : MultiplicationPrecedence
infix operator × : MultiplicationPrecedence
 
public struct Vector {
  public var x = 0.0
  public var y = 0.0
  public var z = 0.0
 
  public init(x: Double, y: Double, z: Double) {
    (self.x, self.y, self.z) = (x, y, z)
  }
 
  public static func • (lhs: Vector, rhs: Vector) -> Double {
    return lhs.x * rhs.x + lhs.y * rhs.y + lhs.z * rhs.z
  }
 
  public static func × (lhs: Vector, rhs: Vector) -> Vector {
    return Vector(
      x: lhs.y * rhs.z - lhs.z * rhs.y,
      y: lhs.z * rhs.x - lhs.x * rhs.z,
      z: lhs.x * rhs.y - lhs.y * rhs.x
    )
  }
}
 
let a = Vector(x: 3, y: 4, z: 5)
let b = Vector(x: 4, y: 3, z: 5)
let c = Vector(x: -5, y: -12, z: -13)
 
print("a: \(a)")
print("b: \(b)")
print("c: \(c)")
print()
print("a • b = \(a • b)")
print("a × b = \(a × b)")
print("a • (b × c) = \(a • (b × c))")
print("a × (b × c) = \(a × (b × c))")