Tensorflow 中多层感知器的问题

Question

我在带有一个隐藏层（带有 RELU 激活函数）的 Tensorflow 中创建了一个感知器（即具有完全连接层的神经网络），并且运行它在 MNIST 数据上成功地获得了 90%+准确率。但是，当我添加第二个隐藏层时，即使经过许多小批量的随机梯度下降，我的准确率也很低 (10%)。为什么会发生这种情况的任何想法？如果有帮助，我可以将我的 Python 代码添加到此 post。

这是我的图形代码（使用 Udacity 课程的起始代码，但添加了额外的层）。请注意，为了简单起见，某些方面被注释掉了——但即使使用这个更简单的版本，症状仍然相同（即使经过多次迭代，准确率仍然很低，约为 10%）：

import tensorflow as tf

batch_size = 128
hidden_size = 256
train_subset = 10000

graph = tf.Graph()
with graph.as_default():

  # Input data. For the training data, we use a placeholder that will be fed
  # at run time with a training minibatch.
  tf_train_dataset = tf.placeholder(tf.float32,
                                    shape=(batch_size, image_size * image_size))
  tf_train_labels = tf.placeholder(tf.float32, shape=(batch_size, num_labels))
  #tf_train_dataset = tf.constant(train_dataset[:train_subset, :])
  #tf_train_labels = tf.constant(train_labels[:train_subset])  

  tf_valid_dataset = tf.constant(valid_dataset)
  tf_test_dataset = tf.constant(test_dataset)

  # Variables.
  weightsToHidden1 = tf.Variable(
    tf.truncated_normal([image_size * image_size, hidden_size]))
  biasesToHidden1 = tf.Variable(tf.zeros([hidden_size]))

  weightsToHidden2 = tf.Variable(
    tf.truncated_normal([hidden_size, hidden_size]))
  biasesToHidden2 = tf.Variable(tf.zeros([hidden_size]))

  weightsToOutput = tf.Variable(
    tf.truncated_normal([hidden_size, num_labels]))
  biasesToOutput = tf.Variable(tf.zeros([num_labels]))

  # Training computation.    
  logitsToHidden1 = tf.nn.relu(tf.matmul(tf_train_dataset, weightsToHidden1) 
                          + biasesToHidden1)

  validLogitsToHidden1 = tf.nn.relu(tf.matmul(tf_valid_dataset, weightsToHidden1) 
                          + biasesToHidden1)

  testLogitsToHidden1 = tf.nn.relu(tf.matmul(tf_test_dataset, weightsToHidden1) 
                          + biasesToHidden1)

  logitsToHidden2 = tf.nn.relu(tf.matmul(logitsToHidden1, weightsToHidden2) 
                          + biasesToHidden2)

  validLogitsToHidden2 = tf.nn.relu(tf.matmul(validLogitsToHidden1, weightsToHidden2) 
                          + biasesToHidden2)

  testLogitsToHidden2 = tf.nn.relu(tf.matmul(testLogitsToHidden1, weightsToHidden2) 
                          + biasesToHidden2)


  logitsToOutput = tf.matmul(logitsToHidden2, weightsToOutput) + biasesToOutput
  validLogitsToOutput = tf.matmul(validLogitsToHidden2, weightsToOutput) + biasesToOutput
  testLogitsToOutput = tf.matmul(testLogitsToHidden2, weightsToOutput) + biasesToOutput


  loss = (tf.reduce_mean(
    tf.nn.softmax_cross_entropy_with_logits(logitsToOutput, tf_train_labels))) #+
   # tf.nn.l2_loss(weightsToHidden1) * 0.002 + 
    #tf.nn.l2_loss(weightsToHidden2) * 0.002 + 
    #tf.nn.l2_loss(weightsToOutput) * 0.002)

  # Optimizer.
  optimizer = tf.train.GradientDescentOptimizer(0.5).minimize(loss)

  # Predictions for the training, validation, and test data.
  train_prediction = tf.nn.softmax(logitsToOutput)
  valid_prediction = tf.nn.softmax(validLogitsToOutput)
  test_prediction = tf.nn.softmax(testLogitsToOutput)

Answer 1

将您的学习率更改为 0.01 或更小的值。它有帮助，但在我的情况下，准确性仍然比两层感知器差

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