前向传播mnist数据集加入训练部分

import os

import lr as lr
import tensorflow as tf
from pyspark.sql.functions import stddev
from tensorflow.keras import datasets

os.environ['TF_CPP_MIN_LOG_LEVEL']='2'   #只打印error的信息
(x,y),(x_test,y_test)=datasets.mnist.load_data()
#x:    [60k,28,28]  [10k,28,28]
#y:    [60k]  [10k]

x=tf.convert_to_tensor(x,dtype=tf.float32)/255     #使x的值从0~255降到0~1
y=tf.convert_to_tensor(y,dtype=tf.int32)

x_test=tf.convert_to_tensor(x_test,dtype=tf.float32)/255     #使x的值从0~255降到0~1
y_test=tf.convert_to_tensor(y_test,dtype=tf.int32)

# print(x.shape,y.shape,x.dtype,y.dtype,x_test.shape,y_test.shape,x_test.dtype,y_test.dtype)
# print(tf.reduce_min(x),tf.reduce_max(x),tf.reduce_min(x_test),tf.reduce_max(x_test))
# print(tf.reduce_min(y),tf.reduce_max(y),tf.reduce_min(y_test),tf.reduce_max(y_test))

train_db=tf.data.Dataset.from_tensor_slices((x,y)).batch(100)   #每次从60k中取100张
test_db=tf.data.Dataset.from_tensor_slices((x_test,y_test)).batch(100)   #每次从10k中取100张
train_iter=iter(train_db)   #迭代器
sample=next(train_iter)
print('batch:',sample[0].shape,sample[1].shape)

#[b,784]=>[b,256]=>[b,128]=>[b,10]
#[dim_in,dim_out],[dim_out]
w1=tf.Variable(tf.random.truncated_normal([784,256],stddev=0.1))    #防止梯度爆炸，需要设定均值和方差的范围，原来是均值为0，方差为1，现在设置方差为0.1
b1=tf.Variable(tf.zeros([256]))
w2=tf.Variable(tf.random.truncated_normal([256,128],stddev=0.1))
b2=tf.Variable(tf.zeros([128]))
w3=tf.Variable(tf.random.truncated_normal([128,10],stddev=0.1))
b3=tf.Variable(tf.zeros([10]))

#h1=x@w1+b1     x指的是之前的一个batch,100个28*28的图片
for epoch in range(50):     #对整个数据集进行50次迭代
    for step,(x,y) in enumerate(train_db):        # x:[100,28,28]  y:[100]    对每个batch进行，整体进度
        x=tf.reshape(x,[-1,28*28])      #[b,28,28]=>[b,28*28]  维度变换
        with tf.GradientTape() as tape:       #tf.Variable
            h1 = x @ w1 + b1  # [b,784]@[784,256]+[256]=>[b,256]
            h1 = tf.nn.relu(h1)  # 加入非线性因素
            h2 = h1 @ w2 + b2  # [b,256]@[256,128]+[128]=>[b,128]
            h2 = tf.nn.relu(h2)
            out = h2 @ w3 + b3  # [b,128]@[128,10]+[10]=>[b,10]      前项计算结束

            # compute loss
            # out:[b,10]
            # y:[b]=>[b,10]
            y_onehot = tf.one_hot(y, depth=10)   #将y  one_hot编码为长度为10的一维数组，好与x*w+b的[b,10]进行相减误差运算

            # mes=mean(sum(y_onehot-out)^2)
            loss = tf.square(y_onehot - out)
            # mean:scalar
            loss = tf.reduce_mean(loss)     #求均值，就是计算100张图片的平均误差
        #compute gradient
        grads=tape.gradient(loss,[w1,b1,w2,b2,w3,b3])    #loss函数中队w1,b1,w2,b2,w3,b3求导
        # print(grads)
        #w1=w1-lr*w1_grad   求下一个w1，梯度下降算法
        # w1 = w1 - lr * grads[0]      #tf.Variable相减之后还是tf.tensor，需要原地更新
        # b1 = b1 - lr * grads[1]
        # w2 = w2 - lr * grads[2]
        # b2 = b2 - lr * grads[3]
        # w3 = w3 - lr * grads[4]
        # b3 = b3 - lr * grads[5]

        lr = 1e-3    #0.001
        w1.assign_sub(lr * grads[0])
        b1.assign_sub(lr * grads[1])
        w2.assign_sub(lr * grads[2])
        b2.assign_sub(lr * grads[3])
        w3.assign_sub(lr * grads[4])
        b3.assign_sub(lr * grads[5])

        # print(isinstance(b3, tf.Variable))
        # print(isinstance(b3, tf.Tensor))

        if step%100==0:      #每进行100个batch输出一次
            print(epoch,step,loss,float(loss))


    #test
    total_correct,total_num=0,0    #总的正确数量和总的测试数量
    for step ,(x,y) in enumerate(test_db):
         x = tf.reshape(x,[-1,28*28])

         h1=tf.nn.relu(x@w1+b1)
         h2=tf.nn.relu(h1@w2+b2)
         out=h2@w3+b3

         #out:[b,10]属于实数范围
         #prob:[b,10]属于0~1范围，概率
         prob=tf.nn.softmax(out,axis=1)  #将out映射到0~1范围的概率上
         pred=tf.argmax(prob,axis=1)  #选取prob中值最大的索引
         pred=tf.cast(pred,dtype=tf.int32)
         #y:[b]
         # print(pred.dtype,y.dtype)
         correct = tf.cast(tf.equal(pred,y),dtype=tf.int32)  #对预测值和真实值进行比较，但是比较之后返回的是bool值，需要转换成0和1  int32位
         #[b],int32
         correct=tf.reduce_sum(correct)   #计算统计对的个数

         total_correct+=int(correct)    #将tensor转换为int，累加起来
         total_num+=x.shape[0]         #总的测试个数

    acc=total_correct/total_num
    print("test acc:",acc)

#对数据集训练50次的acc