TensorFlow中的Seq2Seq没有嵌入

时间:2018-01-11 22:24:28

标签: python tensorflow autoencoder

我试图创建一个非常基本的多变量时间序列自动编码器。 我希望能够重建我传入的确切两个信号。

我正在查看的大多数参考文献都使用旧版本的API或使用嵌入。 我试图使用最新的更高级别的API,但是如何将它们拼凑在一起并不明显。

class Seq2SeqConfig():

     def __init__(self):
          self.sequence_length = 15 # num of time steps
          self.hidden_units = 64 # ?
          self.num_features = 2
          self.batch_size = 10 

# Expect input as batch major. 
encoder_inputs = tf.placeholder(shape=(None, config.sequence_length, config.num_features), dtype=tf.float32)
decoder_inputs = tf.placeholder(shape=(None, config.sequence_length, config.num_features), dtype=tf.float32))

# Convert inputs to time major
encoder_inputs_tm = tf.transpose(encoder_inputs, [1, 0, 2])
decoder_inputs_tm = tf.transpose(decoder_inputs, [1, 0, 2])

# setup encoder
encoder_cell = tf.contrib.rnn.LSTMCell(config.hidden_units)
encoder_outputs, encoder_final_state = tf.nn.dynamic_rnn(
    cell=encoder_cell,
    inputs=encoder_inputs_tm,
    time_major=True)

# setup decoder
decoder_cell = tf.contrib.rnn.LSTMCell(config.hidden_units)

# The sequence length is mandatory. Not sure what the expectation is here? 
helper = tf.contrib.seq2seq.TrainingHelper(
     decoder_inputs_tm, 
     sequence_length=tf.constant(config.sequence_length, dtype=tf.int32, shape=[config.batch_size]),
     time_major=True)
decoder = tf.contrib.seq2seq.BasicDecoder(decoder_cell, helper, encoder_final_state)
decoder_outputs, _, _ = tf.contrib.seq2seq.dynamic_decode(decoder, output_time_major=True)

# loss calculation
loss_op = tf.reduce_mean(tf.square(decoder_outputs.rnn - decoder_targets_tm)

由于形状不同,损失操作失败。 decoder_targets is (?, 15, 2) and decoder_outputs.rnn is (?, ?, 64).

问题1: 我在重塑解码器输出的地方错过了一个操作吗? 我松散地遵循了这个张量流教程:https://www.tensorflow.org/tutorials/seq2seq

有一个projection_layer操作传递到基本解码器。这是为了这个目的吗? projection_layer = layers_core.Dense(tgt_vocab_size, use_bias=False)

我在任何地方都没有看到layers_core.Dense()函数。我认为它已弃用或内部。

问题2: 不使用嵌入时,哪个帮助器用于推理?

问题3: 隐藏单位的理想大小是多少? 我假设因为我们想要减少潜在空间中的尺寸,它需要小于输入的大小。当序列长度= 15且要素数量为2的输入时,如何转换。

隐藏单位的数量是否应< 15,&lt; 2或者&lt; 15 * 2?

2 个答案:

答案 0 :(得分:1)

找出问题1

的答案
from tensorflow.python.layers.core import Dense
output_layer = Dense(config.num_features)
decoder = tf.contrib.seq2seq.BasicDecoder(decoder_cell, helper, encoder_final_state, output_layer)

参考:https://github.com/udacity/deep-learning/blob/master/seq2seq/sequence_to_sequence_implementation.ipynb

其他两个问题仍然存在。

答案 1 :(得分:1)

关于问题3:我建议您使用不同的超参数运行多个培训和验证周期,以找出最适合您的数据和要求的内容。您可以在这里查看我的实施(https://github.com/fritzfitzpatrick/tensorflow-seq2seq-generic-example),在那里我构建了一个非常简单的培训&amp;验证循环,一旦验证损失没有停止多个周期就停止,以防止过度拟合。

关于问题2:我目前仍在进行CustomHelper实现,看起来它正在某个地方。您可以在此处找到完整的示例代码(https://github.com/fritzfitzpatrick/tensorflow-seq2seq-generic-example/blob/master/tensorflow_custom_helper.ipynb)。

batch_size = 5
features_dec_inp = 2 # number of features in target sequence
go_token = 2
end_token = 3
sess = tf.InteractiveSession()

def initialize_fn():
    finished = tf.tile([False], [batch_size])
    start_inputs = tf.fill([batch_size, features_dec_inp], go_token)
    return (finished, start_inputs)

def next_inputs_fn(time, outputs, state, sample_ids):
    del time, sample_ids

    # finished needs to update after last step.
    # one could use conditional logic based on sequence length
    # if sequence length is known in advance
    finished = tf.tile([False], [batch_size])

    # next inputs should be the output of the dense layer
    # unless the above finished logic returns [True]
    # in which case next inputs can be anything in the right shape
    next_inputs = tf.fill([batch_size, features_dec_inp], 0.5)

    return (finished, next_inputs, state)

helper = tf.contrib.seq2seq.CustomHelper(
    initialize_fn = initialize_fn,
    sample_fn = tf.identity,                      
    next_inputs_fn = next_inputs_fn)

print(helper)

关于问题1:这是我用来将解码器输出的维数降低到目标序列中的特征数量的代码:

train_output_dense = tf.layers.dense(
    train_dec_out_logits, # [batch_size x seq_length x num_units]
    features_dec_exp_out) # [batch_size x seq_length x num_target_features]