minor fix for early stop

Author: jhj0411jhj

docs/en/advanced_usage/early_stop.md

@@ -95,7 +95,7 @@ The output of early stopping is as follows:
 ```
 [Early Stop] EI less than the threshold! min_improvement_percentage=0.05, 
 default_obj=0.03334620334620342, best_obj=0.022310167310167328, 
-threshold=0.0005518018018018045, max_EI=[0.00051861]
+threshold=0.0005518018018018045, max_EI=0.0005186128080311961
 
 Early stop triggered at iter 41!
 ```

docs/zh_CN/advanced_usage/early_stop.md

@@ -80,7 +80,7 @@ print(history)
 ```
 [Early Stop] EI less than the threshold! min_improvement_percentage=0.05, 
 default_obj=0.03334620334620342, best_obj=0.022310167310167328, 
-threshold=0.0005518018018018045, max_EI=[0.00051861]
+threshold=0.0005518018018018045, max_EI=0.0005186128080311961
 
 Early stop triggered at iter 41!
 ```

openbox/core/generic_advisor.py

@@ -524,7 +524,7 @@ def get_suggestion(self, history: History = None, return_list: bool = False):
 
             # early stop
             if self.early_stop:
-                max_acq_value = max(self.acquisition_function(challengers))
+                max_acq_value = np.max(self.acquisition_function(challengers)).item()
                 if self.early_stop_algorithm.decide_early_stop_after_suggest(
                         history=history, max_acq_value=max_acq_value):
                     self.early_stop_algorithm.set_already_early_stopped(history)