minor without calling submatrix

matrix/src/lib.rs

@@ -51,11 +51,37 @@ impl<const H: usize, const W: usize> Matrix<H, W> {
         self.matrix[0][0] * self.matrix[1][1] - self.matrix[0][1] * self.matrix[1][0]
     }
 
+    fn zero_skip(&self, val: usize) -> usize {
+        if val == 0 {
+            1
+        } else {
+            0
+        }
+    }
+
+    fn bound_skip(&self, val: usize, bound: usize) -> usize {
+        if val < bound {
+            bound
+        } else {
+            bound - 1
+        }
+    }
+
     pub fn minor(&self, row: usize, col: usize) -> f32 where
         [(); H - 1]: ,
         [(); W - 1]: ,
     {
-        self.sub_matrix(row, col).determinant()
+        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];
+
+        tl * br - tr * bl
     }
 
     pub fn sub_matrix(&self, skip_row: usize, skip_col: usize) -> Matrix<{H - 1}, {W - 1}>