Fix learning rate decay in EAD

Signed-off-by: Beat Buesser <[email protected]>

Author: Beat Buesser

art/attacks/evasion/elastic_net.py

@@ -190,7 +190,7 @@ def _decay_learning_rate(self, global_step: int, end_learning_rate: float, decay
         :return: The decayed learning rate
         """
         learn_rate = self.learning_rate - end_learning_rate
-        decayed_learning_rate = learn_rate * (1 - global_step / decay_steps) ** 2 + end_learning_rate
+        decayed_learning_rate = learn_rate * (1 - global_step / decay_steps) ** 0.5 + end_learning_rate
 
         return decayed_learning_rate