From 75f882f860fdc65723d5263d0df033ceae1131d4 Mon Sep 17 00:00:00 2001
From: Jon Janzen <jonjanzen@me.com>
Date: Fri, 2 Apr 2021 15:58:25 -0600
Subject: [PATCH] determinants can not function

const_generics are not done and I can not use 2 methods in one due to the errors
---
 matrix/src/lib.rs | 79 ++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 64 insertions(+), 15 deletions(-)

diff --git a/matrix/src/lib.rs b/matrix/src/lib.rs
index 3fd5409..7e28e5c 100644
--- a/matrix/src/lib.rs
+++ b/matrix/src/lib.rs
@@ -47,8 +47,19 @@ impl<const H: usize, const W: usize> Matrix<H, W> {
         }
     }
 
-    pub fn determinant(&self) -> f32 {
-        self.matrix[0][0] * self.matrix[1][1] - self.matrix[0][1] * self.matrix[1][0]
+    pub fn determinant(&self) -> f32 where
+        [(); H - 1]: ,
+        [(); W - 1]: ,
+    {
+        if W == 2 {
+            self.matrix[0][0] * self.matrix[1][1] - self.matrix[0][1] * self.matrix[1][0]
+        } else {
+            let mut sum = 0.0;
+            for (col, val) in self.matrix[0].iter().enumerate().take(W) {
+                sum += val * self.cofactor(0, col);
+            }
+            sum
+        }
     }
 
     fn zero_skip(&self, val: usize) -> usize {
@@ -67,24 +78,34 @@ impl<const H: usize, const W: usize> Matrix<H, W> {
         }
     }
 
-    pub fn minor(&self, row: usize, col: usize) -> f32
+    pub fn minor(&self, row: usize, col: usize) -> f32 where
+        [(); H - 1]: ,
+        [(); W - 1]: ,
+        [(); H - 1]: ,
+        [(); W - 1]: ,
     {
-        let t = self.zero_skip(row);
-        let b = self.bound_skip(row, H - 1);
-        let l = self.zero_skip(col);
-        let r = self.bound_skip(col, W - 1);
+        let m = self.sub_matrix(row, col);
+        let det = m.determinant();
+        det
+       // let t = self.zero_skip(row);
+       // let b = self.bound_skip(row, H - 1);
+       // let l = self.zero_skip(col);
+       // let r = self.bound_skip(col, W - 1);
 
-        let tl = self.matrix[t][l];
-        let br = self.matrix[b][r];
-        let tr = self.matrix[t][r];
-        let bl = self.matrix[b][l];
+       // let tl = self.matrix[t][l];
+       // let br = self.matrix[b][r];
+       // let tr = self.matrix[t][r];
+       // let bl = self.matrix[b][l];
 
-        tl * br - tr * bl
+       // tl * br - tr * bl
     }
 
-    pub fn cofactor(&self, row: usize, col: usize) -> f32 {
+    pub fn cofactor(&self, row: usize, col: usize) -> f32 where
+        [(); H - 1]: ,
+        [(); W - 1]: ,
+    {
         let minor = self.minor(row, col);
-        if row + col % 1 == 0 {
+        if (row + col) & 0x1 == 0 {
             minor
         } else {
             minor * -1.0
@@ -457,6 +478,34 @@ mod tests {
         assert_eq!(-12.0, m.cofactor(0, 0));
         assert_eq!(25.0, m.minor(1, 0));
         assert_eq!(-25.0, m.cofactor(1, 0));
-
     }
+
+    #[test]
+    fn determinant_3x3() {
+        let m = Matrix::from_array([
+            [1.0, 2.0, 6.0],
+            [-5.0, 8.0, -4.0],
+            [2.0, 6.0, 4.0],
+        ]);
+        assert_eq!(56.0, m.cofactor(0, 0));
+        assert_eq!(12.0, m.cofactor(0, 1));
+        assert_eq!(-46.0, m.cofactor(0, 2));
+        assert_eq!(-196.0, m.determinant());
+    }
+
+    #[test]
+    fn determinant_4x4() {
+        let m = Matrix::from_array([
+            [-2.0, -8.0, 3.0, 5.0],
+            [-3.0, 1.0, 7.0, 3.0],
+            [1.0, 2.0, -9.0, 6.0],
+            [-6.0, 7.0, 7.0, -9.0],
+        ]);
+        assert_eq!(690.0, m.cofactor(0, 0));
+        assert_eq!(447.0, m.cofactor(0, 1));
+        assert_eq!(210.0, m.cofactor(0, 2));
+        assert_eq!(51.0, m.cofactor(0, 3));
+        assert_eq!(-4071.0, m.determinant());
+    }
+
 }