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最新推荐文章于 2022-10-20 07:45:00 发布

weixin_30340745

最新推荐文章于 2022-10-20 07:45:00 发布

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CC 4.0 BY-SA版权

文章标签：人工智能 python

原文链接：http://www.cnblogs.com/superxuezhazha/p/9531932.html

本文介绍了一种使用TensorFlow构建多层神经网络的方法，通过增加神经网络层数而非卷积层，实现对MNIST手写数字数据集的分类。文章详细展示了如何定义神经网络层、设置超参数、训练模型以及评估模型准确性。

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不做卷积，只是增加多层神经网络层。

#-*- encoding:utf-8 -*-
#!/usr/local/env python

import numpy as np
import tensorflow as tf
from tensorflow.examples.tutorials.mnist import input_data

def add_layer(inputs, in_size, out_size, activation_function=None):
    W = tf.Variable(tf.random_normal([in_size, out_size]))
    b = tf.Variable(tf.zeros([1, out_size]) + 0.01)

    Z = tf.matmul(inputs, W) + b
    if activation_function is None:
        outputs = Z
    else:
        outputs = activation_function(Z)

    return outputs


if __name__ == "__main__":

    MNIST = input_data.read_data_sets("mnist", one_hot=True)

    learning_rate = 0.01
    batch_size = 128
    n_epochs = 70

    X = tf.placeholder(tf.float32, [batch_size, 784])
    Y = tf.placeholder(tf.float32, [batch_size, 10])

    layer_dims = [784, 500, 500, 10]
    layer_count = len(layer_dims)-1 # 不算输入层
    layer_iter = X

    for l in range(1, layer_count): # layer [1,layer_count-1] is hidden layer
        layer_iter = add_layer(layer_iter, layer_dims[l-1], layer_dims[l], activation_function=tf.nn.relu)
    prediction = add_layer(layer_iter, layer_dims[layer_count-1], layer_dims[layer_count], activation_function=None)

    entropy = tf.nn.softmax_cross_entropy_with_logits(labels=Y, logits=prediction)
    loss = tf.reduce_mean(entropy)

    optimizer = tf.train.GradientDescentOptimizer(learning_rate).minimize(loss)

    init = tf.initialize_all_variables()

    with tf.Session() as sess:
        sess.run(init)

        n_batches = int(MNIST.test.num_examples/batch_size)
        for i in range(n_epochs):
            for j in range(n_batches):
                X_batch, Y_batch = MNIST.train.next_batch(batch_size)
                _, loss_ = sess.run([optimizer, loss], feed_dict={X: X_batch, Y: Y_batch})
                if i % 10 == 5 and j == 0:
                    print( "Loss of epochs[{0}]: {1}".format(i, loss_))

        # test the model
        n_batches = int(MNIST.test.num_examples/batch_size)
        total_correct_preds = 0
        for i in range(n_batches):
            X_batch, Y_batch = MNIST.test.next_batch(batch_size)
            preds = sess.run(prediction, feed_dict={X: X_batch, Y: Y_batch})
            correct_preds = tf.equal(tf.argmax(preds, 1), tf.argmax(Y_batch, 1))
            accuracy = tf.reduce_sum(tf.cast(correct_preds, tf.float32))

            total_correct_preds += sess.run(accuracy)

        print ("Accuracy {0}".format(total_correct_preds/MNIST.test.num_examples))