Update Shubert

Update shubert as the number of each iteration is multiplied by cos function and one element of input array is multiplied by cos function as defined by the definition.

Thank you!

With kind regards.

Author: umair-nasir14

pybenchfunction/function.py

@@ -2348,7 +2348,8 @@ def get_global_minimum(self, d):
 
     def __call__(self, X):
         d = X.shape[0]
-        res = np.prod(np.sum([np.cos((j+1)*X + j) for j in range(1, 5+1)]))
+        for i in range(0,d):
+            res = np.prod(np.sum([i * np.cos((j+1)*X[i] + j) for j in range(1, 5+1)]))
         return res
 
 class ShubertN3: