added cofactor

matrix/src/lib.rs

@@ -67,9 +67,7 @@ impl<const H: usize, const W: usize> Matrix<H, W> {
         }
     }
 
-    pub fn minor(&self, row: usize, col: usize) -> f32 where
-        [(); H - 1]: ,
-        [(); W - 1]: ,
+    pub fn minor(&self, row: usize, col: usize) -> f32
     {
         let t = self.zero_skip(row);
         let b = self.bound_skip(row, H - 1);
@@ -84,6 +82,15 @@ impl<const H: usize, const W: usize> Matrix<H, W> {
         tl * br - tr * bl
     }
 
+    pub fn cofactor(&self, row: usize, col: usize) -> f32 {
+        self.minor(row, col) * if row + col % 1 == 0 {
+            1.0
+        }
+        else {
+            -1.0
+        }
+    }
+
     pub fn sub_matrix(&self, skip_row: usize, skip_col: usize) -> Matrix<{H - 1}, {W - 1}>
     {
         let mut idx_row: usize = 0;
@@ -438,4 +445,18 @@ mod tests {
         assert_eq!(25.0, s.determinant());
         assert_eq!(25.0, m.minor(1, 0));
     }
+
+    #[test]
+    fn cofactor_3x3() {
+        let m = Matrix::from_array([
+            [3.0, 5.0, 0.0],
+            [2.0, -1.0, -7.0],
+            [6.0, -1.0, 5.0],
+        ]);
+        assert_eq!(-12.0, m.minor(0, 0));
+        assert_eq!(-12.0, m.cofactor(0, 0));
+        assert_eq!(25.0, m.minor(1, 0));
+        assert_eq!(-25.0, m.cofactor(1, 0));
+
+    }
 }