Merge pull request #1950 from Haichao-Zhang/beam_search_doc_error_fix

fixed error in beam_search example and documents

python/paddle/trainer_config_helpers/layers.py

@@ -3563,9 +3563,15 @@ def beam_search(step,
                 simple_rnn += last_time_step_output
             return simple_rnn
 
+        generated_word_embedding = GeneratedInput(
+                               size=target_dictionary_dim,
+                               embedding_name="target_language_embedding",
+                               embedding_size=word_vector_dim)
+
         beam_gen = beam_search(name="decoder",
                                step=rnn_step,
-                               input=[StaticInput(encoder_last)],
+                               input=[StaticInput(encoder_last),
+                                      generated_word_embedding],
                                bos_id=0,
                                eos_id=1,
                                beam_size=5)
@@ -3584,7 +3590,8 @@ def beam_search(step,
                  You can refer to the first parameter of recurrent_group, or
                  demo/seqToseq/seqToseq_net.py for more details.
     :type step: callable
-    :param input: Input data for the recurrent unit
+    :param input: Input data for the recurrent unit, which should include the
+                  previously generated words as a GeneratedInput object.
     :type input: list
     :param bos_id: Index of the start symbol in the dictionary. The start symbol
                    is a special token for NLP task, which indicates the