通过MNIST数据集构建网络模型

男娘i 2021-10-30 00:50 413阅读 0赞

# -*- coding: utf-8 -*-
    #@Time    :2019/8/18 21:07
    #@Author  :XiaoMa
    import struct
    import gzip
    import os
    from six.moves.urllib.request import urlretrieve
    import numpy as np
    import tensorflow as tf
    
    def maybe_download(url, filename, expected_bytes, force=False):
      """如果不存在，请下载文件，并确保其大小合适."""
      if force or not os.path.exists(filename):
        print('试图下载文件:', filename)
        filename, _ = urlretrieve(url + filename, filename)
        print('\n已完成文件下载!')
      statinfo = os.stat(filename)
      if statinfo.st_size == expected_bytes:
        print('找到并验证', filename)
      else:
        raise Exception(
          '无法验证' + filename + '. 你能用浏览器找到它吗?')
      return filename
    
    
    def read_mnist(fname_img, fname_lbl):
        print('\n读取文件 %s 和 %s' % (fname_img, fname_lbl))
    
        with gzip.open(fname_img) as fimg:
            magic, num, rows, cols = struct.unpack(">IIII", fimg.read(16))
            print(num, rows, cols)
            img = (np.frombuffer(fimg.read(num * rows * cols), dtype=np.uint8)
                                    .reshape(num, rows * cols)).astype(np.float32)
            print('(Images) 返回张量的形状 ', img.shape)
    
            img = (img - np.mean(img)) / np.std(img)
    
        with gzip.open(fname_lbl) as flbl:
            # flbl.read(8) 读取最多8个字节
            magic, num = struct.unpack(">II", flbl.read(8))
            lbl = np.frombuffer(flbl.read(num), dtype=np.int8)
            print('（标签）返回一个张量的形状: %s' % lbl.shape)
            print('样例标签: ', lbl[:10])
    
        return img, lbl
    
    # 如果需要，下载数据
    url = 'http://yann.lecun.com/exdb/mnist/'
    # training data
    maybe_download(url,'train-images-idx3-ubyte.gz',9912422)
    maybe_download(url,'train-labels-idx1-ubyte.gz',28881)
    # testing data
    maybe_download(url,'t10k-images-idx3-ubyte.gz',1648877)
    maybe_download(url,'t10k-labels-idx1-ubyte.gz',4542)
    
    # 读取训练数据和测试数据
    train_inputs, train_labels = read_mnist('train-images-idx3-ubyte.gz', 
                                                        'train-labels-idx1-ubyte.gz')
    test_inputs, test_labels = read_mnist('t10k-images-idx3-ubyte.gz', 
                                                        't10k-labels-idx1-ubyte.gz')
    
    WEIGHTS_STRING = 'weights'
    BIAS_STRING = 'bias'
    
    batch_size = 100
    
    img_width, img_height = 28,28
    input_size = img_height * img_width
    num_labels = 10
    
    # 重置默认图形，否则会引发有关已初始化变量的错误
    tf.reset_default_graph()
    
    # 定义输入和输出
    tf_inputs = tf.placeholder(shape=[batch_size, input_size], dtype=tf.float32, 
                    name = 'inputs')
    tf_labels = tf.placeholder(shape=[batch_size, num_labels], dtype=tf.float32, 
                    name = 'labels')
    
    
    # 定义Tensorflow 变量
    def define_net_parameters():
        with tf.variable_scope('layer1'):
            tf.get_variable(WEIGHTS_STRING, shape=[input_size, 500],
                            initializer=tf.random_normal_initializer(0, 0.02))
            tf.get_variable(BIAS_STRING, shape=[500],
                            initializer=tf.random_uniform_initializer(0, 0.01))
    
        with tf.variable_scope('layer2'):
            tf.get_variable(WEIGHTS_STRING, shape=[500, 250],
                            initializer=tf.random_normal_initializer(0, 0.02))
            tf.get_variable(BIAS_STRING, shape=[250],
                            initializer=tf.random_uniform_initializer(0, 0.01))
    
        with tf.variable_scope('output'):
            tf.get_variable(WEIGHTS_STRING, shape=[250, 10],
                            initializer=tf.random_normal_initializer(0, 0.02))
            tf.get_variable(BIAS_STRING, shape=[10],
                            initializer=tf.random_uniform_initializer(0, 0.01))
    
    
    # 定义从输入到logits的神经网络中的各类计算
    # logits是将softmax应用于最终输出之前的值
    
    def inference(x):
        # 第1层的计算
        with tf.variable_scope('layer1', reuse=True):
            w, b = tf.get_variable(WEIGHTS_STRING), tf.get_variable(BIAS_STRING)
            tf_h1 = tf.nn.relu(tf.matmul(x, w) + b, name='hidden1')
    
        # 第2层的计算
        with tf.variable_scope('layer2', reuse=True):
            w, b = tf.get_variable(WEIGHTS_STRING), tf.get_variable(BIAS_STRING)
            tf_h2 = tf.nn.relu(tf.matmul(tf_h1, w) + b, name='hidden1')
    
        # 输出层的计算
        with tf.variable_scope('output', reuse=True):
            w, b = tf.get_variable(WEIGHTS_STRING), tf.get_variable(BIAS_STRING)
            tf_logits = tf.nn.bias_add(tf.matmul(tf_h2, w), b, name='logits')
    
        return tf_logits
    
    define_net_parameters()
    
    # 定义损失(loss)
    tf_loss = tf.reduce_mean(tf.nn.softmax_cross_entropy_with_logits_v2(logits=inference(tf_inputs), 
                                                                        labels=tf_labels))
    
    # 定义优化函数
    tf_loss_minimize = tf.train.MomentumOptimizer(momentum=0.9,learning_rate=0.01).minimize(tf_loss)
    
    # 定义预测
    tf_predictions = tf.nn.softmax(inference(tf_inputs))
    
    session = tf.InteractiveSession()
    
    tf.global_variables_initializer().run()
    
    NUM_EPOCHS = 50
    
    def accuracy(predictions, labels):
        ''' 度量某些预测（softmax输出）和标签（整数类标签）的分类准确度'''
        return np.sum(np.argmax(predictions,axis=1).flatten()==labels.flatten())/batch_size
    
    test_accuracy_over_time = []
    train_loss_over_time = []
    
    for epoch in range(NUM_EPOCHS):
        train_loss = []
    
        # 训练阶段
        for step in range(train_inputs.shape[0] // batch_size):
            # 使用标签创建one-hot编码标签
            # 10级（类）mnist数据集的one-hot编码的DIGHT为3的结果为[0,0,0,1,0,0,0,0,0]
            labels_one_hot = np.zeros((batch_size, num_labels), dtype=np.float32)
            labels_one_hot[np.arange(batch_size), train_labels[step * batch_size:(step + 1) *
                                                             batch_size]] = 1.0
    
            # 打印one-hot标签
            if epoch == 0 and step == 0:
                print('样例标签 (one-hot)')
                print(labels_one_hot[:10])
                print()
    
            # 进行优化处理
            loss, _ = session.run([tf_loss, tf_loss_minimize], feed_dict={
                tf_inputs: train_inputs[step * batch_size: (step + 1) * batch_size, :],
                tf_labels: labels_one_hot}
                                  )
            train_loss.append(loss)  # 用于平均单个epoch的损失
    
        test_accuracy = []
        # 测试阶段
        for step in range(test_inputs.shape[0] // batch_size):
            test_predictions = session.run(tf_predictions, feed_dict={
                tf_inputs: test_inputs[step * batch_size: (step + 1) * batch_size, :]})
            batch_test_accuracy = accuracy(test_predictions, test_labels[step * batch_size:
                                                             (step + 1) * batch_size])
            test_accuracy.append(batch_test_accuracy)
    
        print(' 第 %d 个epoch上训练数据的平均损失: %.3f\n' % (epoch + 1, np.mean(train_loss)))
        train_loss_over_time.append(np.mean(train_loss))
        print('\t 第 %d 个epoch上测试数据的平均准确率: %.2f\n' % (epoch + 1, np.mean(test_accuracy) * 100.0))
        test_accuracy_over_time.append(np.mean(test_accuracy) * 100)
    
    session.close()
    
    
    x_axis = np.arange(len(train_loss_over_time))
    
    fig, ax = plt.subplots(nrows=1, ncols=2)
    fig.set_size_inches(w=25,h=5)
    ax[0].plot(x_axis, train_loss_over_time)
    ax[0].set_xlabel('Epochs',fontsize=18)
    ax[0].set_ylabel('训练数据的平均损失',fontsize=18)
    ax[0].set_title('训练数据的损失随时间的变化',fontsize=20)
    ax[1].plot(x_axis, test_accuracy_over_time)
    ax[1].set_xlabel('Epochs',fontsize=18)
    ax[1].set_ylabel('测试数据的准确率',fontsize=18)
    ax[1].set_title('测试数的准确率随时间的变化',fontsize=20)
    fig.savefig('mnist_stats.jpg')