『TensorFlow』读书笔记_降噪自编码器

ゝ一世哀愁。 2022-03-29 15:52 239阅读 0赞

[『TensorFlow』降噪自编码器设计][TensorFlow]

之前学习过的代码，又敲了一遍，新的收获也还是有的，因为这次注释写的比较详尽，所以再次记录一下，具体的相关知识查阅之前写的文章即可（见上面链接）。

# Author : Hellcat
    # Time   : 2017/12/6
    
    import numpy as np
    import sklearn.preprocessing as prep
    import tensorflow as tf
    from tensorflow.examples.tutorials.mnist import input_data
    
    def xavier_init(fan_in,fan_out, constant = 1):
        '''
        xavier 权重初始化方式
        :param fan_in: 行数
        :param fan_out: 列数
        :param constant: 常数权重，调节初始化范围的倍数
        :return: 初始化后的权重tensor
        '''
        low = -constant * np.sqrt(6.0 / (fan_in + fan_out))
        high = constant * np.sqrt(6.0 / (fan_in + fan_out))
        return tf.random_uniform((fan_in, fan_out),
                                 minval=low, maxval=high)
    
    class AdditiveGaussianNoiseAutoencoder():
    
        def __init__(self, n_input, n_hidden,
                     transfer_function=tf.nn.softplus,
                     optimizer=tf.train.AdamOptimizer(),scale=0.1):
            '''
            初始化自编码器
            :param n_input: 输入层结点数
            :param n_hidden: 隐藏层节点数
            :param transfer_function: 隐藏层激活函数
            :param optimizer: 优化器，是实例化的对象
            :param scale: 高斯噪声系数
            '''
            self.n_input = n_input
            self.n_hidden = n_hidden
            self.transfer = transfer_function
            self.scale = tf.placeholder(tf.float32) # 实际网络中调用的
            self.training_scale = scale # 训练用噪声系数
            network_weights = self._initialize_weights()
            self.weights = network_weights
    
            self.x = tf.placeholder(tf.float32, [None, self.n_input])
            self.hidden = \
                self.transfer(
                    tf.add(
                        tf.matmul(
                            self.x + self.scale * tf.random_normal((n_input,)),
                            self.weights['w1']),
                        self.weights['b1']))
    
            # 重建部分没有使用激活函数
            self.reconstruction = \
                tf.add(
                    tf.matmul(
                        self.hidden, self.weights['w2']),
                    self.weights['b2'])
    
            self.cost = 0.5 * tf.reduce_sum(tf.pow(tf.subtract(self.reconstruction,self.x),2.0))
            # 可以将类的实例过程作为实参传入函数
            self.optimizer = optimizer.minimize(self.cost)
    
            init = tf.global_variables_initializer()
            self.sess = tf.Session()
            self.sess.run(init)
    
        def _initialize_weights(self):
            '''
            初始化全部变量
            :return: 装有变量的字典
            '''
            all_weights = dict()
            all_weights['w1'] = tf.Variable(xavier_init(self.n_input, self.n_hidden))
            all_weights['b1'] = tf.Variable(tf.zeros([self.n_hidden], dtype=tf.float32))
            all_weights['w2'] = tf.Variable(tf.zeros([self.n_hidden, self.n_input], dtype=tf.float32))
            all_weights['b2'] = tf.Variable(tf.zeros([self.n_input], dtype=tf.float32))
            return all_weights
    
        def partial_fit(self, X):
            '''
            进行单次训练并返回loss
            :param X: 训练数据
            :return: 本次损失函数值
            '''
            cost, opt = self.sess.run((self.cost, self.optimizer),
                                      feed_dict={self.x:X, self.scale:self.training_scale})
            return cost
    
        def calc_totul_cost(self, X):
            '''
            计算损失函数，不触发训练
            :param X: 训练数据
            :return: 损失函数
            '''
            return self.sess.run(self.cost, feed_dict={self.x:X, self.scale:self.training_scale})
    
        def transform(self, X):
            '''
            返回隐藏层输出结果，目的是获取抽象后的特征
            :param X: 训练数据
            :return: 隐藏层输出
            '''
            return self.sess.run(self.hidden, feed_dict={self.x:X, self.scale:self.training_scale})
    
        def generate(self, hidden=None):
            '''
            通过隐藏层特征重建
            :param hidden: 隐藏层特征
            :return: 重建数据
            '''
            if hidden is None:
                hidden = np.random.normal(size=[self.n_input])
            return self.sess.run(self.reconstruction, feed_dict={self.hidden:hidden})
    
        def reconstruct(self,X):
            '''
            从原始数据重建
            :param X: 训练数据
            :return: 重建数据
            '''
            return self.sess.run(self.reconstruction,
                                 feed_dict={self.x:X, self.scale:self.training_scale})
    
        def getWeights(self):
            '''
            获取参数值
            :return: 隐藏层权重
            '''
            return self.sess.run(self.weights['w1'])
    
        def getBaises(self):
            '''
            获取参数值
            :return: 隐藏层偏置
            '''
            return self.sess.run(self.weights['b1'])
    
    def standard_scale(X_train, X_test):
        '''
        标准化数据
        :param X_train: 训练数据
        :param X_test: 测试数据
        :return: 标准化之后的训练、测试数据
        '''
        preprocessor = prep.StandardScaler().fit(X_train)
        X_train = preprocessor.transform(X_train)
        X_test = preprocessor.transform(X_test)
        return X_train, X_test
    
    def get_random_block_from_data(data, batch_size):
        start_index = np.random.randint(0, len(data) - batch_size)
        return data[start_index:(start_index + batch_size)]
    
    if __name__ == '__main__':
        mnist = input_data.read_data_sets('../../../Mnist_data/',one_hot=True)
        X_train, X_test = standard_scale(mnist.train.images, mnist.test.images)
    
        n_samples = int(mnist.train.num_examples)
        train_epochs = 20
        batch_size = 20
        display_step = 1
    
        autoencoder = AdditiveGaussianNoiseAutoencoder(
            n_input=784,
            n_hidden=200,
            transfer_function=tf.nn.softplus,
            optimizer=tf.train.AdamOptimizer(learning_rate=0.001),
            scale=0.01)
    
        for epoch in range(train_epochs):
            avg_cost = 0.
            totu_batch = int(n_samples / batch_size)
            for i in range(totu_batch):
                batch_xs = get_random_block_from_data(X_train, batch_size)
    
                # 单数据块训练并计算损失函数
                cost = autoencoder.partial_fit(batch_xs)
                avg_cost += cost / n_samples * batch_size
    
                if epoch % display_step == 0:
                    print('epoch : %04d, cost = %.9f' % (epoch + 1,avg_cost))
    
                # 计算测试集上的cost
        print('Total coat:',str(autoencoder.calc_totul_cost(X_test)))

部分输出如下：

> ……
> 
> epoch : 0020, cost = 1509.876800515  
> epoch : 0020, cost = 1510.107261985  
> epoch : 0020, cost = 1510.332509055  
> epoch : 0020, cost = 1510.551538707  
> Total coat: 768927.0

1.xavier初始化权重方法

2.函数实参可以是class()，即实例化的类

[TensorFlow]: http://www.cnblogs.com/hellcat/p/6957434.html