added schaffer2 function

added output for improvement of fitness
added CMAES algorithm, that requires further testing

functions.py

@@ -17,17 +17,29 @@ class Function:
         X, Y = np.meshgrid(x, y)
         return x, y, self.eval(X, Y)
 
+
 class Rastrigin(Function):
     def __init__(self, A: int = 10):
         super().__init__(
-                xlim=(-5.12, 5.12), 
-                ylim=(-5.12, 5.12), 
+                xlim=(-6.12, 6.12), 
+                ylim=(-6.12, 6.12), 
                 minimum=(0, 0),
                 eval=lambda x, y: self.A * 2 + \
                         (x**2 - self.A * np.cos(2 * np.pi * x)) + \
                         (y**2 - self.A * np.cos(2 * np.pi * y)))
         self.A = A
-    
+
+
+class Schaffer2(Function):
+    def __init__(self):
+        super().__init__(
+                xlim=(-50, 50),
+                ylim=(-50, 50),
+                minimum=(0, 0),
+                eval=lambda x, y: 0.5 + \
+                        (np.sin(x**2 - y**2)**2 - 0.5) / \
+                        ((1 + 0.001 * (x**2 + y**2))**2))
+
 class Sphere(Function):
     def __init__(self):
         super().__init__(