add spec for determinant

show matrix values in playground

Example/PerspectiveTransform/Visual.playground/Pages/Ovelay.xcplaygroundpage/Contents.swift

@@ -43,13 +43,37 @@ for (index, point) in points.enumerated() {
     label.center = anchorView.center
 }
 
+let transform = start.projectiveTransform(destination: destination)
+
 UIView.animate(withDuration:1.0,
                delay: 0,
                options: [.repeat, .autoreverse],
                animations: {
-                overlayView.layer.transform = start.projectiveTransform(destination: destination)
+                overlayView.layer.transform = transform
 },
                completion:nil)
+print(transform)
+transform.m13 == 0
+transform.m23 == 0
+transform.m31 == 0
+transform.m32 == 0
+transform.m34 == 0
+transform.m43 == 0
 
+transform.m33 == 1
+transform.m44 == 1
 
+transform.m41.rounded() == points[0].x.rounded()
+transform.m42 == points[0].y
+transform.m43 == 0
+transform.m44 == 1
+
+transform.m11.isEqual(to: 16.6798123042149)
+print(transform.m11)
+print(transform.m11.rounded())
+print(transform.m11.rounded(FloatingPointRoundingRule.towardZero))
+transform.m11.magnitude
+transform.m11.magnitude.isEqual(to: CGFloat(16.6798123042149).magnitude)
+transform.m11.significand.isEqual(to: CGFloat(16.6798123042149).significand)
+transform.m11.significand
 //: [Next](@next)

Example/Tests/MatrixSpec.swift

@@ -36,6 +36,23 @@ class MatrixSpec: QuickSpec {
                     expect(m.determinant) == -1
                     expect(m.inverse.determinant) == -1
                 }
+
+                it("should match math word 2x2 example") {
+                    // http://www.mathwords.com/d/determinant.htm
+                    // | 1   2 |
+                    // |       | = 1*4-2*3 = -2
+                    // | 3   4 |
+                    expect(float2x2([float2(1,2), float2(3,4)]).determinant) == -2
+                }
+
+                it("should match math word 3x3 example") {
+                    // http://www.mathwords.com/d/determinant.htm
+                    // | 1 2 3 |
+                    // | 4 5 6 | = (1*5*9+2*6*7+3*4*8)-(3*5*7+2*4*9+1*6*8) = 0
+                    // | 7 8 9 |
+                    // See: https://www.google.com/search?client=safari&rls=en&q=(1*5*9%2B2*6*7%2B3*4*8)-(3*5*7%2B2*4*9%2B1*6*8)+=&ie=UTF-8&oe=UTF-8
+                    expect(Matrix3x3Type([1,2,3,4,5,6,7,8,9]).determinant) == 0
+                }
             }
         }
     }