Keras中具有LSTM的多层Seq2Seq模型 [英] Multilayer Seq2Seq model with LSTM in Keras

问题描述

我正在喀拉拉邦建立一个seq2seq模型.我建立了单层编码器和解码器，它们工作正常.但是现在我想将其扩展到多层编码器和解码器. 我正在使用Keras Functional API进行构建.

I was making a seq2seq model in keras. I had built single layer encoder and decoder and they were working fine. But now I want to extend it to multi layer encoder and decoder. I am building it using Keras Functional API.

encoder_input=Input(shape=(None,vec_dimension))
encoder_lstm=LSTM(vec_dimension,return_state=True,return_sequences=True)(encoder_input)
encoder_lstm=LSTM(vec_dimension,return_state=True)(encoder_lstm)
encoder_output,encoder_h,encoder_c=encoder_lstm

解码器代码:-

encoder_state=[encoder_h,encoder_c]
decoder_input=Input(shape=(None,vec_dimension))
decoder_lstm= LSTM(vec_dimension,return_state=True,return_sequences=True (decoder_input,initial_state=encoder_state)
decoder_lstm=LSTM(vec_dimension,return_state=True,return_sequences=True)(decoder_lstm)
decoder_output,_,_=decoder_lstm

用于测试:-

encoder_model=Model(inputs=encoder_input,outputs=encoder_state)
decoder_state_input_h=Input(shape=(None,vec_dimension))
decoder_state_input_c=Input(shape=(None,vec_dimension))
decoder_states_input=[decoder_state_input_h,decoder_state_input_c]
decoder_output,decoder_state_h,decoder_state_c =decoder_lstm #(decoder_input,initial_state=decoder_states_input)
decoder_states=[decoder_state_h,decoder_state_c]
decoder_model=Model(inputs=[decoder_input]+decoder_states_input,outputs=[decoder_output]+decoder_states)

现在，当我尝试增加编号时.解码器中用于训练的层数，然后训练效果很好，但是对于测试来说，它无效且会引发错误.

Now when I try to increase the no. of layers in the decoder for training then training works fine but for testing it dosen't works and throws error.

实际上，问题是当将其设置为多层时，我已经将initial_state移到了通常在末尾指定的中间层. 在测试过程中调用它时，会引发错误.

Actually the problem is when making it multi layer i had shifted the initial_state to a middle layer which used to be specified at the end.So when I am calling it during testing, it is throwing errors.

RuntimeError: Graph disconnected: cannot obtain value for tensor Tensor("input_64:0", shape=(?, ?, 150), dtype=float32) at layer "input_64".The following previous layers were accessed without issue: []

如何传递用于输入层的initial_state=decoder_states_input，以免引发错误. 我应该如何在最后一个输入层的最后一层传递initial_state=decoder_states_input?

How should I pass the initial_state=decoder_states_input which is for the input layer so that it doesn't throws error. How should I pass the initial_state=decoder_states_input in the end layer for for the first Input layer??

在该代码中，我尝试制作多层解码器LSTM.但这给了错误. 当使用单层时.正确的代码是:-

In that code I have tried to make multiple layers of decoder LSTM. But that's giving error. When working with single layer.The correct codes are:-

encoder_input=Input(shape=(None,vec_dimension))
encoder_lstm =LSTM(vec_dimension,return_state=True)(encoder_input)
encoder_output,encoder_h,encoder_c=encoder_lstm

解码器(训练):-

encoder_state=[encoder_h,encoder_c]
decoder_input=Input(shape=(None,vec_dimension))
decoder_lstm= LSTM(vec_dimension, return_state=True, return_sequences=True)
decoder_output,_,_=decoder_lstm(decoder_input,initial_state=encoder_state)

解码器(测试)

decoder_output,decoder_state_h,decoder_state_c=decoder_lstm( decoder_input, initial_state=decoder_states_input)
decoder_states=[decoder_state_h,decoder_state_c]
decoder_output,decoder_state_h,decoder_state_c=decoder_lstm (decoder_input,initial_state=decoder_states_input)
decoder_model=Model(inputs=[decoder_input]+decoder_states_input,outputs=[decoder_output]+decoder_states)

推荐答案

编辑-更新为在Keras与RNN中使用功能性API模型

EDIT - Updated to use the functional API model in Keras vs. the RNN

from keras.models import Model
from keras.layers import Input, LSTM, Dense, RNN
layers = [256,128] # we loop LSTMCells then wrap them in an RNN layer

encoder_inputs = Input(shape=(None, num_encoder_tokens))

e_outputs, h1, c1 = LSTM(latent_dim, return_state=True, return_sequences=True)(encoder_inputs) 
_, h2, c2 = LSTM(latent_dim, return_state=True)(e_outputs) 
encoder_states = [h1, c1, h2, c2]

decoder_inputs = Input(shape=(None, num_decoder_tokens))

out_layer1 = LSTM(latent_dim, return_sequences=True, return_state=True)
d_outputs, dh1, dc1 = out_layer1(decoder_inputs,initial_state= [h1, c1])
out_layer2 = LSTM(latent_dim, return_sequences=True, return_state=True)
final, dh2, dc2 = out_layer2(d_outputs, initial_state= [h2, c2])
decoder_dense = Dense(num_decoder_tokens, activation='softmax')
decoder_outputs = decoder_dense(final)


model = Model([encoder_inputs, decoder_inputs], decoder_outputs)

model.summary()

这是推理设置:

encoder_model = Model(encoder_inputs, encoder_states)

decoder_state_input_h = Input(shape=(latent_dim,))
decoder_state_input_c = Input(shape=(latent_dim,))
decoder_state_input_h1 = Input(shape=(latent_dim,))
decoder_state_input_c1 = Input(shape=(latent_dim,))
decoder_states_inputs = [decoder_state_input_h, decoder_state_input_c, 
                         decoder_state_input_h1, decoder_state_input_c1]
d_o, state_h, state_c = out_layer1(
    decoder_inputs, initial_state=decoder_states_inputs[:2])
d_o, state_h1, state_c1 = out_layer2(
    d_o, initial_state=decoder_states_inputs[-2:])
decoder_states = [state_h, state_c, state_h1, state_c1]
decoder_outputs = decoder_dense(d_o)
decoder_model = Model(
    [decoder_inputs] + decoder_states_inputs,
    [decoder_outputs] + decoder_states)

decoder_model.summary()

最后，如果您遵循Keras seq2seq示例，则必须更改预测脚本，因为需要管理多个隐藏状态，而在单层示例中只有两个.层隐藏状态的数量将是原来的2倍

Lastly, if you are following the Keras seq2seq example, you will have to change the prediction script as there are multiple hidden states that need to be managed vs. just two of them in the single-layer example. There will be 2x the number of layer hidden states

# Reverse-lookup token index to decode sequences back to
# something readable.
reverse_input_char_index = dict(
    (i, char) for char, i in input_token_index.items())
reverse_target_char_index = dict(
    (i, char) for char, i in target_token_index.items())

def decode_sequence(input_seq):
    # Encode the input as state vectors.
    states_value = encoder_model.predict(input_seq)

    # Generate empty target sequence of length 1.
    target_seq = np.zeros((1, 1, num_decoder_tokens))
    # Populate the first character of target sequence with the start character.
    target_seq[0, 0, target_token_index['\t']] = 1.

    # Sampling loop for a batch of sequences
    # (to simplify, here we assume a batch of size 1).
    stop_condition = False
    decoded_sentence = ''
    while not stop_condition:
        output_tokens, h, c, h1, c1 = decoder_model.predict(
            [target_seq] + states_value) #######NOTICE THE ADDITIONAL HIDDEN STATES

        # Sample a token
        sampled_token_index = np.argmax(output_tokens[0, -1, :])
        sampled_char = reverse_target_char_index[sampled_token_index]
        decoded_sentence += sampled_char

        # Exit condition: either hit max length
        # or find stop character.
        if (sampled_char == '\n' or
           len(decoded_sentence) > max_decoder_seq_length):
            stop_condition = True

        # Update the target sequence (of length 1).
        target_seq = np.zeros((1, 1, num_decoder_tokens))
        target_seq[0, 0, sampled_token_index] = 1.

        # Update states
        states_value = [h, c, h1, c1]#######NOTICE THE ADDITIONAL HIDDEN STATES

    return decoded_sentence


for seq_index in range(100):
    # Take one sequence (part of the training set)
    # for trying out decoding.
    input_seq = encoder_input_data[seq_index: seq_index + 1]
    decoded_sentence = decode_sequence(input_seq)
    print('-')
    print('Input sentence:', input_texts[seq_index])
    print('Target sentence:', target_texts[seq_index])
    print('Decoded sentence:', decoded_sentence)

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