new: Implement Sub trait

src/lib.rs

@@ -13,11 +13,13 @@ mod tests {
     }
 
     #[test]
-    fn add_test() {
+    fn add_sub_test() {
         let a = Matrix::from(vec![vec![1, 2, 3], vec![0, 1, 2]]).unwrap();
         let b = Matrix::from(vec![vec![0, 0, 1], vec![2, 1, 3]]).unwrap();
         let c = Matrix::from(vec![vec![1, 2, 4], vec![2, 2, 5]]).unwrap();
-        assert_eq!(a + b, c);
+        let d = Matrix::from(vec![vec![1, 2, 2], vec![-2, 0, -1]]).unwrap();
+        assert_eq!(a.clone() + b.clone(), c);
+        assert_eq!(a - b, d);
     }
 
     #[test]

src/matrix.rs

@@ -5,7 +5,7 @@ use std::{
     result::Result,
 };
 
-#[derive(PartialEq, Debug)]
+#[derive(PartialEq, Debug, Clone)]
 pub struct Matrix<T: Mul + Add + Sub> {
     entries: Vec<Vec<T>>,
 }
@@ -162,3 +162,20 @@ impl<T: Add<Output = T> + Sub + Mul + Copy + Zero> Add for Matrix<T> {
         }
     }
 }
+
+impl<T: Add + Sub<Output = T> + Mul + Copy + Zero> Sub for Matrix<T> {
+    type Output = Self;
+    fn sub(self, other: Self) -> Self {
+        if self.height() == other.height() && self.width() == other.width() {
+            let mut out = self.entries.clone();
+            for (i, row) in self.rows().iter().enumerate() {
+                for (j, entry) in other.rows()[i].iter().enumerate() {
+                    out[i][j] = row[j] - *entry;
+                }
+            }
+            Matrix { entries: out }
+        } else {
+            panic!("Both matrices must be of same dimensions.");
+        }
+    }
+}