added determinant

matrix/src/lib.rs

@@ -38,7 +38,11 @@ impl<const COUNT: usize> Matrix<COUNT> {
             [self.matrix[0][2], self.matrix[1][2], self.matrix[2][2], self.matrix[3][2], ],
             [self.matrix[0][3], self.matrix[1][3], self.matrix[2][3], self.matrix[3][3], ],
         ];
-        self.matrix = tmp;
+         // self.matrix = tmp;
+    }
+
+    pub fn determinant(&self) -> f32 {
+        self.matrix[0][0] * self.matrix[1][1] - self.matrix[0][1] * self.matrix[1][0]
     }
 }
 
@@ -320,4 +324,14 @@ mod tests {
         m.transpose();
         assert_eq!(m, Matrix::<4>::identity());
     }
+
+    #[test]
+    fn determinant_2x2() {
+        let m = Matrix::from_array([
+            [1.0, 5.0],
+            [-3.0, 2.0],
+        ]);
+
+        assert_eq!(17.0, m.determinant());
+    }
 }