一、TensorFLow完整樣例

在MNIST數據集上，搭建一個簡單神經網絡結構，一個包含ReLU單元的非線性化處理的兩層神經網絡。在訓練神經網絡的時候，使用帶指數衰減的學習率設置、使用正則化來避免過擬合、使用滑動平均模型來使得最終的模型更加健壯。

程序將計算神經網絡前向傳播的部分單獨定義一個函數inference，訓練部分定義一個train函數，再定義一個主函數main。

完整程序：

#!/usr/bin/env python3 # -*- coding: utf-8 -*- """ Created on Thu May 25 08:56:30 2017  @author: marsjhao """  import tensorflow as tf from tensorflow.examples.tutorials.mnist import input_data  INPUT_NODE = 784 # 輸入節點數 OUTPUT_NODE = 10 # 輸出節點數 LAYER1_NODE = 500 # 隱含層節點數 BATCH_SIZE = 100 LEARNING_RETE_BASE = 0.8 # 基學習率 LEARNING_RETE_DECAY = 0.99 # 學習率的衰減率 REGULARIZATION_RATE = 0.0001 # 正則化項的權重系數 TRAINING_STEPS = 10000 # 迭代訓練次數 MOVING_AVERAGE_DECAY = 0.99 # 滑動平均的衰減系數  # 傳入神經網絡的權重和偏置，計算神經網絡前向傳播的結果 def inference(input_tensor, avg_class, weights1, biases1, weights2, biases2):   # 判斷是否傳入ExponentialMovingAverage類對象   if avg_class == None:     layer1 = tf.nn.relu(tf.matmul(input_tensor, weights1) + biases1)     return tf.matmul(layer1, weights2) + biases2   else:     layer1 = tf.nn.relu(tf.matmul(input_tensor, avg_class.average(weights1))                    + avg_class.average(biases1))     return tf.matmul(layer1, avg_class.average(weights2))/              + avg_class.average(biases2)  # 神經網絡模型的訓練過程 def train(mnist):   x = tf.placeholder(tf.float32, [None,INPUT_NODE], name='x-input')   y_ = tf.placeholder(tf.float32, [None, OUTPUT_NODE], name='y-input')    # 定義神經網絡結構的參數   weights1 = tf.Variable(tf.truncated_normal([INPUT_NODE, LAYER1_NODE],                         stddev=0.1))   biases1 = tf.Variable(tf.constant(0.1, shape=[LAYER1_NODE]))   weights2 = tf.Variable(tf.truncated_normal([LAYER1_NODE, OUTPUT_NODE],                         stddev=0.1))   biases2 = tf.Variable(tf.constant(0.1, shape=[OUTPUT_NODE]))    # 計算非滑動平均模型下的參數的前向傳播的結果   y = inference(x, None, weights1, biases1, weights2, biases2)      global_step = tf.Variable(0, trainable=False) # 定義存儲當前迭代訓練輪數的變量    # 定義ExponentialMovingAverage類對象   variable_averages = tf.train.ExponentialMovingAverage(             MOVING_AVERAGE_DECAY, global_step) # 傳入當前迭代輪數參數   # 定義對所有可訓練變量trainable_variables進行更新滑動平均值的操作op   variables_averages_op = variable_averages.apply(tf.trainable_variables())    # 計算滑動模型下的參數的前向傳播的結果   average_y = inference(x, variable_averages, weights1, biases1, weights2, biases2)    # 定義交叉熵損失值   cross_entropy = tf.nn.sparse_softmax_cross_entropy_with_logits(           logits=y, labels=tf.argmax(y_, 1))   cross_entropy_mean = tf.reduce_mean(cross_entropy)   # 定義L2正則化器并對weights1和weights2正則化   regularizer = tf.contrib.layers.l2_regularizer(REGULARIZATION_RATE)   regularization = regularizer(weights1) + regularizer(weights2)   loss = cross_entropy_mean + regularization # 總損失值    # 定義指數衰減學習率   learning_rate = tf.train.exponential_decay(LEARNING_RETE_BASE, global_step,           mnist.train.num_examples / BATCH_SIZE, LEARNING_RETE_DECAY)   # 定義梯度下降操作op，global_step參數可實現自加1運算   train_step = tf.train.GradientDescentOptimizer(learning_rate)/              .minimize(loss, global_step=global_step)   # 組合兩個操作op   train_op = tf.group(train_step, variables_averages_op)   '''''   # 與tf.group()等價的語句   with tf.control_dependencies([train_step, variables_averages_op]):     train_op = tf.no_op(name='train')   '''   # 定義準確率   # 在最終預測的時候，神經網絡的輸出采用的是經過滑動平均的前向傳播計算結果   correct_prediction = tf.equal(tf.argmax(average_y, 1), tf.argmax(y_, 1))   accuracy = tf.reduce_mean(tf.cast(correct_prediction, tf.float32))    # 初始化回話sess并開始迭代訓練   with tf.Session() as sess:     sess.run(tf.global_variables_initializer())     # 驗證集待喂入數據     validate_feed = {x: mnist.validation.images, y_: mnist.validation.labels}     # 測試集待喂入數據     test_feed = {x: mnist.test.images, y_: mnist.test.labels}     for i in range(TRAINING_STEPS):       if i % 1000 == 0:         validate_acc = sess.run(accuracy, feed_dict=validate_feed)         print('After %d training steps, validation accuracy'            ' using average model is %f' % (i, validate_acc))       xs, ys = mnist.train.next_batch(BATCH_SIZE)       sess.run(train_op, feed_dict={x: xs, y_:ys})      test_acc = sess.run(accuracy, feed_dict=test_feed)     print('After %d training steps, test accuracy'        ' using average model is %f' % (TRAINING_STEPS, test_acc))  # 主函數 def main(argv=None):   mnist = input_data.read_data_sets("MNIST_data", one_hot=True)   train(mnist)  # 當前的python文件是shell文件執行的入口文件，而非當做import的python module。 if __name__ == '__main__': # 在模塊內部執行   tf.app.run() # 調用main函數并傳入所需的參數list