未能在 tensorflow 中训练玩具 LSTM

Question

我正在尝试使用一个用于序列分类的玩具问题来熟悉 tensorflow 中的循环网络。

数据：

half_len = 500
pos_ex = [1, 2, 3, 4, 5] # Positive sequence.
neg_ex = [1, 2, 3, 4, 6] # Negative sequence.
num_input = len(pos_ex)
data = np.concatenate((np.stack([pos_ex]*half_len), np.stack([neg_ex]*half_len)), axis=0)
labels = np.asarray([0, 1] * half_len + [1, 0] * half_len).reshape((2 * half_len, -1))

型号：

_, x_width = data.shape
X = tf.placeholder("float", [None, x_width])
Y = tf.placeholder("float", [None, num_classes])

weights = tf.Variable(tf.random_normal([num_input, n_hidden]))
bias = tf.Variable(tf.random_normal([n_hidden]))


def lstm_model():
    from tensorflow.contrib import rnn
    x = tf.split(X, num_input, 1)
    rnn_cell = rnn.BasicLSTMCell(n_hidden)
    outputs, states = rnn.static_rnn(rnn_cell, x, dtype=tf.float32)
    return tf.matmul(outputs[-1], weights) + bias

培训：

logits = lstm_model()
prediction = tf.nn.softmax(logits)

# Define loss and optimizer
loss_op = tf.reduce_mean(tf.nn.softmax_cross_entropy_with_logits(logits=logits, labels=Y))
optimizer = tf.train.AdamOptimizer(learning_rate=learning_rate)
train_op = optimizer.minimize(loss_op)

# Train...

我的训练准确率在 0.5 左右变化，这让我很困惑，因为问题很简单。

Step 1, Minibatch Loss = 82.2726, Training Accuracy = 0.453
Step 25, Minibatch Loss = 6.7920, Training Accuracy = 0.547
Step 50, Minibatch Loss = 0.8528, Training Accuracy = 0.500
Step 75, Minibatch Loss = 0.6989, Training Accuracy = 0.500
Step 100, Minibatch Loss = 0.6929, Training Accuracy = 0.516

将玩具数据更改为：

pos_ex = [1, 2, 3, 4, 5]
neg_ex = [1, 2, 3, 4, 100]

立即收敛到准确性 1. 谁能解释一下为什么这个网络在如此简单的任务上失败了？谢谢。

以上代码基于this tutorial。

Answer 1

您是否尝试过降低学习率？
在第二个例子中，最后一个坐标上的间隔值较大，这应该没有区别，但对学习率的选择有影响。
如果您要对数据进行归一化（将每个坐标的域设置在 -1 和 1 之间），并找到合适的步长，您应该以相同的步数解决这两个问题。

编辑：稍微玩一下你的玩具示例，即使没有规范化，以下内容也可以正常工作

import tensorflow as tf
import numpy as np
from tensorflow.contrib import rnn

# Meta parameters

n_hidden = 10
num_classes = 2
learning_rate = 1e-2
input_dim = 5
num_input = 5



# inputs
X = tf.placeholder("float", [None, input_dim])
Y = tf.placeholder("float", [None, num_classes])

# Model
def lstm_model():
    # input layer
    x = tf.split(X, num_input, 1)

    # LSTM layer
    rnn_cell = rnn.BasicLSTMCell(n_hidden)
    outputs, states = rnn.static_rnn(rnn_cell, x, dtype=tf.float32)

    # final layer - softmax
    weights = tf.Variable(tf.random_normal([n_hidden, num_classes]))
    bias = tf.Variable(tf.random_normal([num_classes]))
    return tf.matmul(outputs[-1], weights) + bias

# logits and prediction
logits = lstm_model()
prediction = tf.nn.softmax(logits)

# Define loss and optimizer
loss_op = tf.reduce_mean(tf.nn.softmax_cross_entropy_with_logits(logits=logits, labels=Y))
optimizer = tf.train.AdamOptimizer(learning_rate=learning_rate)
train_op = optimizer.minimize(loss_op)


# -----------
# Train func
# -----------
def train(data,labels):

    with tf.Session() as session:
        session.run(tf.global_variables_initializer())
        for i in range(1000):
            _, loss, onehot_pred = session.run([train_op, loss_op, prediction], feed_dict={X: data, Y: labels})
            acc = np.mean(np.argmax(onehot_pred,axis=1) == np.argmax(labels,axis=1))
            print('Iteration {} accuracy: {}'.format(i,acc))
            if acc == 1:
                print('---> Finised after {} iterations'.format(i+1))
                break

# -----------
# Train 1
# -----------
# data generation
half_len = 500
pos_ex = [1, 2, 3, 4, 5] # Positive sequence.
neg_ex = [1, 2, 3, 4, 6] # Negative sequence.



data = np.concatenate((np.stack([pos_ex]*half_len), np.stack([neg_ex]*half_len)), axis=0)
labels = np.asarray([0, 1] * half_len + [1, 0] * half_len).reshape((2 * half_len, -1))

train(data,labels)

# -----------
# Train 2
# -----------
# data generation
half_len = 500
pos_ex = [1, 2, 3, 4, 5] # Positive sequence.
neg_ex = [1, 2, 3, 4, 100] # Negative sequence.


data = np.concatenate((np.stack([pos_ex]*half_len), np.stack([neg_ex]*half_len)), axis=0)
labels = np.asarray([0, 1] * half_len + [1, 0] * half_len).reshape((2 * half_len, -1))

train(data,labels)

输出是：

Iteration 0 accuracy: 0.5
Iteration 1 accuracy: 0.5
Iteration 2 accuracy: 0.5
Iteration 3 accuracy: 0.5
Iteration 4 accuracy: 0.5
Iteration 5 accuracy: 0.5
Iteration 6 accuracy: 0.5
Iteration 7 accuracy: 0.5
Iteration 8 accuracy: 0.5
Iteration 9 accuracy: 0.5
Iteration 10 accuracy: 1.0
---> Finised after 11 iterations

Iteration 0 accuracy: 0.5
Iteration 1 accuracy: 0.5
Iteration 2 accuracy: 0.5
Iteration 3 accuracy: 0.5
Iteration 4 accuracy: 0.5
Iteration 5 accuracy: 0.5
Iteration 6 accuracy: 0.5
Iteration 7 accuracy: 0.5
Iteration 8 accuracy: 0.5
Iteration 9 accuracy: 1.0
---> Finised after 10 iterations

祝你好运！