From 97a0b2fee5dd9d9db19e80bf59cd9f13e7a34301 Mon Sep 17 00:00:00 2001
From: That-One-Nerd <crazymailbro2@yahoo.com>
Date: Mon, 10 Jul 2023 16:34:07 -0400
Subject: [PATCH] Fixed some blunders and finished #31.

---
 Changelog.md                              | 11 +++++++++++
 Nerd_STF/Mathematics/Abstract/IMatrix.cs  |  1 +
 Nerd_STF/Mathematics/Algebra/Matrix.cs    |  7 ++++++-
 Nerd_STF/Mathematics/Algebra/Matrix2x2.cs |  4 ++--
 4 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/Changelog.md b/Changelog.md
index 66fb4ad..4440fd6 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -6,10 +6,21 @@ Here's the full changelog:
 ```
 * Nerd_STF
     * Mathematics
+        * Abstract
+            * IMatrix
+                + Cofactor()
+        * Algebra
+            * Matrix
+                = Fixed a blunder in `SignGrid(Int2)` with signs being incorrectly placed on matrixes with even column count.
+            * Matrix2x2
+                = Fixed a blunder in `Cofactor()` with the position of elements.
         * NumberSystems
             * Complex
                 + operator Complex(SystemComplex)
                 + operator SystemComplex(Complex)
+            * Quaternion
+                + operator Quaternion(SystemQuaternion)
+                + operator SystemQuaternion(Quaternion)
         * Float3
             = Added a setter to `XY`
             = Added a setter to `XZ`
diff --git a/Nerd_STF/Mathematics/Abstract/IMatrix.cs b/Nerd_STF/Mathematics/Abstract/IMatrix.cs
index 84429c2..34974f5 100644
--- a/Nerd_STF/Mathematics/Abstract/IMatrix.cs
+++ b/Nerd_STF/Mathematics/Abstract/IMatrix.cs
@@ -6,6 +6,7 @@ public interface IMatrix<T> : IAbsolute<T>, ICeiling<T>, IClamp<T>, IDivide<T>,
     where T : IMatrix<T>
 {
     public T Adjugate();
+    public T Cofactor();
     public float Determinant();
     public T? Inverse();
     public T Transpose();
diff --git a/Nerd_STF/Mathematics/Algebra/Matrix.cs b/Nerd_STF/Mathematics/Algebra/Matrix.cs
index 3d13abc..b48d138 100644
--- a/Nerd_STF/Mathematics/Algebra/Matrix.cs
+++ b/Nerd_STF/Mathematics/Algebra/Matrix.cs
@@ -20,7 +20,12 @@ public class Matrix : IMatrix<Matrix, Matrix>
         return m;
     }
     public static Matrix One(Int2 size) => new(size, 1);
-    public static Matrix SignGrid(Int2 size) => new(size, Fills.SignFill);
+    public static Matrix SignGrid(Int2 size) => new(size, delegate (int x)
+    {
+        float sgnValue = Fills.SignFill(x);
+        if (size.y % 2 == 0 && x / size.y % 2 == 1) sgnValue *= -1;
+        return sgnValue;
+    });
     public static Matrix Zero(Int2 size) => new(size);
 
     public bool HasMinors => Size.x > 1 && Size.y > 1;
diff --git a/Nerd_STF/Mathematics/Algebra/Matrix2x2.cs b/Nerd_STF/Mathematics/Algebra/Matrix2x2.cs
index 620b6a2..f842a94 100644
--- a/Nerd_STF/Mathematics/Algebra/Matrix2x2.cs
+++ b/Nerd_STF/Mathematics/Algebra/Matrix2x2.cs
@@ -223,8 +223,8 @@ public record class Matrix2x2 : IStaticMatrix<Matrix2x2>
     {
         Matrix2x2 swapped = new(new[,]
         {
-            { r2c2, r1c2 },
-            { r2c1, r1c1 }
+            { r2c2, r2c1 },
+            { r1c2, r1c1 }
         });
         return swapped ^ SignGrid;
     }