Fix the beam_search in test_machine_translation.py

python/paddle/fluid/tests/book/high-level-api/machine_translation/test_machine_translation.py

@@ -127,9 +127,19 @@ def decode(context, is_sparse):
         current_score = pd.fc(input=current_state_with_lod,
                               size=target_dict_dim,
                               act='softmax')
-        topk_scores, topk_indices = pd.topk(current_score, k=topk_size)
+        topk_scores, topk_indices = pd.topk(current_score, k=beam_size)
+        # calculate accumulated scores after topk to reduce computation cost
+        accu_scores = pd.elementwise_add(
+            x=pd.log(topk_scores), y=pd.reshape(
+                pre_score, shape=[-1]), axis=0)
         selected_ids, selected_scores = pd.beam_search(
-            pre_ids, topk_indices, topk_scores, beam_size, end_id=10, level=0)
+            pre_ids,
+            pre_score,
+            topk_indices,
+            accu_scores,
+            beam_size,
+            end_id=10,
+            level=0)
 
         pd.increment(x=counter, value=1, in_place=True)
 
@@ -141,7 +151,7 @@ def decode(context, is_sparse):
         pd.less_than(x=counter, y=array_len, cond=cond)
 
     translation_ids, translation_scores = pd.beam_search_decode(
-        ids=ids_array, scores=scores_array)
+        ids=ids_array, scores=scores_array, beam_size=beam_size, end_id=10)
 
     # return init_ids, init_scores