tf.nn.dynamic_rnn返回值详解

函数原型

tf.nn.dynamic_rnn(cell,inputs,sequence_length=None,initial_state=None,dtype=None,parallel_iterations=None,swap_memory=False,time_major=False,scope=None
)

实例讲解：

import tensorflow as tf
import numpy as npn_steps = 2
n_inputs = 3
n_neurons = 5X = tf.placeholder(tf.float32, [None, n_steps, n_inputs])
basic_cell = tf.contrib.rnn.BasicRNNCell(num_units=n_neurons)seq_length = tf.placeholder(tf.int32, [None])
outputs, states = tf.nn.dynamic_rnn(basic_cell, X, dtype=tf.float32,sequence_length=seq_length)init = tf.global_variables_initializer()X_batch = np.array([# step 0     step 1[[0, 1, 2], [9, 8, 7]], # instance 1[[3, 4, 5], [0, 0, 0]], # instance 2 (padded with zero vectors)[[6, 7, 8], [6, 5, 4]], # instance 3[[9, 0, 1], [3, 2, 1]], # instance 4])
seq_length_batch = np.array([2, 1, 2, 2])with tf.Session() as sess:init.run()outputs_val, states_val = sess.run([outputs, states], feed_dict={X: X_batch, seq_length: seq_length_batch})print("outputs_val.shape:", outputs_val.shape, "states_val.shape:", states_val.shape)print("outputs_val:", outputs_val, "states_val:", states_val)

log info:

outputs_val.shape: (4, 2, 5) states_val.shape: (4, 5)
outputs_val:
[[[ 0.53073734 -0.61281306 -0.5437517   0.7320347  -0.6109526 ][ 0.99996936  0.99990636 -0.9867181   0.99726075 -0.99999976]][[ 0.9931584   0.5877845  -0.9100412   0.988892   -0.9982337 ][ 0.          0.          0.          0.          0.        ]][[ 0.99992317  0.96815354 -0.985101    0.9995968  -0.9999936 ][ 0.99948144  0.9998127  -0.57493806  0.91015154 -0.99998355]][[ 0.99999255  0.9998929   0.26732785  0.36024097 -0.99991137][ 0.98875254  0.9922327   0.6505734   0.4732064  -0.9957567 ]]]
states_val:[[ 0.99996936  0.99990636 -0.9867181   0.99726075 -0.99999976][ 0.9931584   0.5877845  -0.9100412   0.988892   -0.9982337 ][ 0.99948144  0.9998127  -0.57493806  0.91015154 -0.99998355][ 0.98875254  0.9922327   0.6505734   0.4732064  -0.9957567 ]]

首先输入X是一个 [batch_size，step，input_size] = [4，2，3] 的tensor，注意我们这里调用的是BasicRNNCell，只有一层循环网络，outputs是最后一层每个step的输出，它的结构是[batch_size，step，n_neurons] = [4，2，5]，states是每一层的最后那个step的输出，由于本例中，我们的循环网络只有一个隐藏层，所以它就代表这一层的最后那个step的输出，因此它和step的大小是没有关系的，我们的X有4个样本组成，输出神经元大小n_neurons是5，因此states的结构就是[batch_size，n_neurons] = [4，5]，最后我们观察数据，states的每条数据正好就是outputs的最后一个step的输出。

下面我们继续讲解多个隐藏层的情况，这里是三个隐藏层，注意我们这里仍然是调用BasicRNNCell

import tensorflow as tf
import numpy as npn_steps = 2
n_inputs = 3
n_neurons = 5
n_layers = 3X = tf.placeholder(tf.float32, [None, n_steps, n_inputs])
seq_length = tf.placeholder(tf.int32, [None])layers = [tf.contrib.rnn.BasicRNNCell(num_units=n_neurons,activation=tf.nn.relu)for layer in range(n_layers)]
multi_layer_cell = tf.contrib.rnn.MultiRNNCell(layers)
outputs, states = tf.nn.dynamic_rnn(multi_layer_cell, X, dtype=tf.float32, sequence_length=seq_length)init = tf.global_variables_initializer()X_batch = np.array([# step 0     step 1[[0, 1, 2], [9, 8, 7]], # instance 1[[3, 4, 5], [0, 0, 0]], # instance 2 (padded with zero vectors)[[6, 7, 8], [6, 5, 4]], # instance 3[[9, 0, 1], [3, 2, 1]], # instance 4])seq_length_batch = np.array([2, 1, 2, 2])with tf.Session() as sess:init.run()outputs_val, states_val = sess.run([outputs, states], feed_dict={X: X_batch, seq_length: seq_length_batch})print("outputs_val.shape:", outputs, "states_val.shape:", states)print("outputs_val:", outputs_val, "states_val:", states_val)

log info:

outputs_val.shape:
Tensor("rnn/transpose_1:0", shape=(?, 2, 5), dtype=float32) states_val.shape:
(<tf.Tensor 'rnn/while/Exit_3:0' shape=(?, 5) dtype=float32>, <tf.Tensor 'rnn/while/Exit_4:0' shape=(?, 5) dtype=float32>, <tf.Tensor 'rnn/while/Exit_5:0' shape=(?, 5) dtype=float32>)outputs_val:[[[0.         0.         0.         0.         0.        ][0.         0.18740742 0.         0.2997518  0.        ]][[0.         0.07222144 0.         0.11551574 0.        ][0.         0.         0.         0.         0.        ]][[0.         0.13463384 0.         0.21534224 0.        ][0.03702604 0.18443246 0.         0.34539366 0.        ]][[0.         0.54511094 0.         0.8718864  0.        ][0.5382122  0.         0.04396425 0.4040263  0.        ]]] states_val:(array([[0.        , 0.83723307, 0.        , 0.        , 2.8518028 ],[0.        , 0.1996038 , 0.        , 0.        , 1.5456247 ],[0.        , 1.1372368 , 0.        , 0.        , 0.832613  ],[0.        , 0.7904129 , 2.4675028 , 0.        , 0.36980057]],dtype=float32), array([[0.6524607 , 0.        , 0.        , 0.        , 0.        ],[0.25143963, 0.        , 0.        , 0.        , 0.        ],[0.5010576 , 0.        , 0.        , 0.        , 0.        ],[0.        , 0.3166597 , 0.4545995 , 0.        , 0.        ]],dtype=float32), array([[0.        , 0.18740742, 0.        , 0.2997518 , 0.        ],[0.        , 0.07222144, 0.        , 0.11551574, 0.        ],[0.03702604, 0.18443246, 0.        , 0.34539366, 0.        ],[0.5382122 , 0.        , 0.04396425, 0.4040263 , 0.        ]],dtype=float32))

我们说过，outputs是最后一层的输出，即 [batch_size，step，n_neurons] = [4，2，5]

states是每一层的最后一个step的输出，即三个结构为 [batch_size，n_neurons] = [4，5] 的tensor

继续观察数据，states中的最后一个array，正好是outputs的最后那个step的输出

下面我们继续讲当由BasicLSTMCell构造单元工厂的时候，只讲多层的情况，我们只需要将上面的BasicRNNCell替换成BasicLSTMCell就行了，打印信息如下：

outputs_val.shape:
Tensor("rnn/transpose_1:0", shape=(?, 2, 5), dtype=float32) states_val.shape:
(LSTMStateTuple(c=<tf.Tensor 'rnn/while/Exit_3:0' shape=(?, 5) dtype=float32>, h=<tf.Tensor 'rnn/while/Exit_4:0' shape=(?, 5) dtype=float32>),
LSTMStateTuple(c=<tf.Tensor 'rnn/while/Exit_5:0' shape=(?, 5) dtype=float32>, h=<tf.Tensor 'rnn/while/Exit_6:0' shape=(?, 5) dtype=float32>),
LSTMStateTuple(c=<tf.Tensor 'rnn/while/Exit_7:0' shape=(?, 5) dtype=float32>, h=<tf.Tensor 'rnn/while/Exit_8:0' shape=(?, 5) dtype=float32>))outputs_val:
[[[1.2949290e-04 0.0000000e+00 2.7623639e-04 0.0000000e+00 0.0000000e+00][9.4675866e-05 0.0000000e+00 2.0214770e-04 0.0000000e+00 0.0000000e+00]][[4.3100454e-06 4.2123037e-07 1.4312843e-06 0.0000000e+00 0.0000000e+00][0.0000000e+00 0.0000000e+00 0.0000000e+00 0.0000000e+00 0.0000000e+00]][[0.0000000e+00 0.0000000e+00 0.0000000e+00 0.0000000e+00 0.0000000e+00][0.0000000e+00 0.0000000e+00 0.0000000e+00 0.0000000e+00 0.0000000e+00]][[0.0000000e+00 0.0000000e+00 0.0000000e+00 0.0000000e+00 0.0000000e+00][0.0000000e+00 0.0000000e+00 0.0000000e+00 0.0000000e+00 0.0000000e+00]]] states_val:
(LSTMStateTuple(
c=array([[0.        , 0.        , 0.04676079, 0.04284539, 0.        ],[0.        , 0.        , 0.0115245 , 0.        , 0.        ],[0.        , 0.        , 0.        , 0.        , 0.        ],[0.        , 0.        , 0.        , 0.        , 0.        ]],dtype=float32),
h=array([[0.        , 0.        , 0.00035096, 0.04284406, 0.        ],[0.        , 0.        , 0.00142574, 0.        , 0.        ],[0.        , 0.        , 0.        , 0.        , 0.        ],[0.        , 0.        , 0.        , 0.        , 0.        ]],dtype=float32)),
LSTMStateTuple(
c=array([[0.0000000e+00, 1.0477135e-02, 4.9871090e-03, 8.2785974e-04,0.0000000e+00],[0.0000000e+00, 2.3306280e-04, 0.0000000e+00, 9.9445322e-05,5.9535629e-05],[0.0000000e+00, 0.0000000e+00, 0.0000000e+00, 0.0000000e+00,0.0000000e+00],[0.0000000e+00, 0.0000000e+00, 0.0000000e+00, 0.0000000e+00,0.0000000e+00]], dtype=float32),
h=array([[0.00000000e+00, 5.23016974e-03, 2.47756205e-03, 4.11730434e-04,0.00000000e+00],[0.00000000e+00, 1.16522635e-04, 0.00000000e+00, 4.97301044e-05,2.97713632e-05],[0.00000000e+00, 0.00000000e+00, 0.00000000e+00, 0.00000000e+00,0.00000000e+00],[0.00000000e+00, 0.00000000e+00, 0.00000000e+00, 0.00000000e+00,0.00000000e+00]], dtype=float32)),
LSTMStateTuple(
c=array([[1.8937115e-04, 0.0000000e+00, 4.0442235e-04, 0.0000000e+00,0.0000000e+00],[8.6200516e-06, 8.4243663e-07, 2.8625946e-06, 0.0000000e+00,0.0000000e+00],[0.0000000e+00, 0.0000000e+00, 0.0000000e+00, 0.0000000e+00,0.0000000e+00],[0.0000000e+00, 0.0000000e+00, 0.0000000e+00, 0.0000000e+00,0.0000000e+00]], dtype=float32),
h=array([[9.4675866e-05, 0.0000000e+00, 2.0214770e-04, 0.0000000e+00,0.0000000e+00],[4.3100454e-06, 4.2123037e-07, 1.4312843e-06, 0.0000000e+00,0.0000000e+00],[0.0000000e+00, 0.0000000e+00, 0.0000000e+00, 0.0000000e+00,0.0000000e+00],[0.0000000e+00, 0.0000000e+00, 0.0000000e+00, 0.0000000e+00,0.0000000e+00]], dtype=float32)))

我们先看看LSTM单元的结构

如果您不查看框内的内容，LSTM单元看起来与常规单元格完全相同，除了它的状态分为两个向量：h（t）和c（t）。你可以将h（t）视为短期状态，将c（t）视为长期状态。

因此我们的states包含三个LSTMStateTuple，每一个表示每一层的最后一个step的输出，这个输出有两个信息，一个是h表示短期记忆信息，一个是c表示长期记忆信息。维度都是[batch_size，n_neurons] = [4，5]，states的最后一个LSTMStateTuple中的h就是outputs的最后一个step的输出

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