代码：
import tensorflow as tf
from tensorflow.examples.tutorials.mnist import input_data
#载入数据集
mnist = input_data.read_data_sets("MNIST_data",one_hot=True)
运行结果：
Extracting MNIST_data/train-images-idx3-ubyte.gz Extracting MNIST_data/train-labels-idx1-ubyte.gz Extracting MNIST_data/t10k-images-idx3-ubyte.gz Extracting MNIST_data/t10k-labels-idx1-ubyte.gz
代码：
#每个批次100张照片
batch_size = 100
#计算一共有多少个批次
n_batch = mnist.train.num_examples // batch_size
#定义两个placeholder
x = tf.placeholder(tf.float32,[None,784])
y = tf.placeholder(tf.float32,[None,10])
#创建一个简单的神经网络，输入层784个神经元，输出层10个神经元
W = tf.Variable(tf.zeros([784,10]))
b = tf.Variable(tf.zeros([10]))
prediction = tf.nn.softmax(tf.matmul(x,W)+b)
#二次代价函数
# loss = tf.reduce_mean(tf.square(y-prediction))
loss = tf.reduce_mean(tf.nn.softmax_cross_entropy_with_logits(labels=y,logits=prediction))
#使用梯度下降法
train_step = tf.train.GradientDescentOptimizer(0.2).minimize(loss)
#初始化变量
init = tf.global_variables_initializer()
#结果存放在一个布尔型列表中
correct_prediction = tf.equal(tf.argmax(y,1),tf.argmax(prediction,1))#argmax返回一维张量中最大的值所在的位置
#求准确率
accuracy = tf.reduce_mean(tf.cast(correct_prediction,tf.float32))
# 定义一个saver
saver = tf.train.Saver()
with tf.Session() as sess:
sess.run(init)
for epoch in range(11):
for batch in range(n_batch):
batch_xs,batch_ys = mnist.train.next_batch(batch_size)
sess.run(train_step,feed_dict={x:batch_xs,y:batch_ys})
acc = sess.run(accuracy,feed_dict={x:mnist.test.images,y:mnist.test.labels})
print("Iter " + str(epoch) + ",Testing Accuracy " + str(acc))
#保存模型
saver.save(sess,'net/my_net.ckpt')
运行结果：
Iter 0,Testing Accuracy 0.8237 Iter 1,Testing Accuracy 0.8937 Iter 2,Testing Accuracy 0.9018 Iter 3,Testing Accuracy 0.906 Iter 4,Testing Accuracy 0.9089 Iter 5,Testing Accuracy 0.9111 Iter 6,Testing Accuracy 0.9118 Iter 7,Testing Accuracy 0.9128 Iter 8,Testing Accuracy 0.9147 Iter 9,Testing Accuracy 0.916 Iter 10,Testing Accuracy 0.9168