Update df.py (#684)

Correction of DF11 Pareto front calculation

Author: ahcheriet

pymoo/problems/dynamic/df.py

@@ -318,10 +318,10 @@ def _calc_pareto_front(self, *args, n_pareto_points=100, **kwargs):
         y1 = np.pi * G / 6 + (np.pi / 2 - np.pi * G / 3) * x1
         y2 = np.pi * G / 6 + (np.pi / 2 - np.pi * G / 3) * x2
 
-        f1 = np.sin(y1)
-        f2 = np.dot(np.multiply(1, np.sin(y2)), np.cos(y1))
-        f3 = np.dot(np.multiply(1, np.cos(y2)), np.cos(y1))
-
+        f1 = (1 + G) * np.sin(y1)
+        f2 = (1 + G) * np.sin(y2) * np.cos(y1)  # Correct element-wise multiplication
+        f3 = (1 + G) * np.cos(y2) * np.cos(y1)  # Correct element-wise multiplication
+        
         return get_PF(np.array([f1, f2, f3]), False)