[FEAT] Add Submatrix

tests/03_matrix.cpp

@@ -239,3 +239,41 @@ TEST_CASE("[Matrix] Calculating the determinant of a 2x2 matrix", "[Matrix]")
 
     REQUIRE(a.determinant() == 17);
 }
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("[Matrix] A submatrix of a 3x3 matrix is a 2x2 matrix", "[Matrix]")
+{
+    Matrix a = {
+        { 1, 5,  0},
+        {-3, 2,  7},
+        { 0, 6, -3}
+    };
+
+    Matrix b = {
+        {-3, 2},
+        { 0, 6}
+    };
+
+    REQUIRE(a.sub_matrix(0, 2) == b);
+}
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("[Matrix] A submatrix of a 4x4 matrix is a 3x3 matrix", "[Matrix]")
+{
+    Matrix a = {
+        {-6, 1,  1, 6},
+        {-8, 5,  8, 6},
+        {-1, 0,  8, 2},
+        {-7, 1, -1, 1}
+    };
+
+    Matrix b = {
+        {-6,  1, 6},
+        {-8,  8, 6},
+        {-7, -1, 1}
+    };
+
+    REQUIRE(a.sub_matrix(2, 1) == b);
+}