注释讲解版:
# Classifier example
import numpy as np
# for reproducibility
np.random.seed(1337)
# from keras.datasets import mnist
from keras.utils import np_utils
from keras.models import Sequential
from keras.layers import Dense, Activation
from keras.optimizers import RMSprop
# 程序中用到的数据是经典的手写体识别mnist数据集
# download the mnist to the path if it is the first time to be called
# X shape (60,000 28x28), y
# (X_train, y_train), (X_test, y_test) = mnist.load_data()
# 下载minst.npz:
# 链接: https://pan.baidu.com/s/1b2ppKDOdzDJxivgmyOoQsA
# 提取码: y5ir
# 将下载好的minst.npz放到当前目录下
path='./mnist.npz'
f = np.load(path)
X_train, y_train = f['x_train'], f['y_train']
X_test, y_test = f['x_test'], f['y_test']
f.close()
# data pre-processing
# 数据预处理
# normalize
# X shape (60,000 28x28),表示输入数据 X 是个三维的数据
# 可以理解为 60000行数据,每一行是一张28 x 28 的灰度图片
# X_train.reshape(X_train.shape[0], -1)表示:只保留第一维,其余的纬度,不管多少纬度,重新排列为一维
# 参数-1就是不知道行数或者列数多少的情况下使用的参数
# 所以先确定除了参数-1之外的其他参数,然后通过(总参数的计算) / (确定除了参数-1之外的其他参数) = 该位置应该是多少的参数
# 这里用-1是偷懒的做法,等同于 28*28
# reshape后的数据是:共60000行,每一行是784个数据点(feature)
# 输入的 x 变成 60,000*784 的数据,然后除以 255 进行标准化
# 因为每个像素都是在 0 到 255 之间的,标准化之后就变成了 0 到 1 之间
X_train = X_train.reshape(X_train.shape[0], -1) / 255
X_test = X_test.reshape(X_test.shape[0], -1) / 255
# 分类标签编码
# 将y转化为one-hot vector
y_train = np_utils.to_categorical(y_train, num_classes = 10)
y_test = np_utils.to_categorical(y_test, num_classes = 10)
# Another way to build your neural net
# 建立神经网络
# 应用了2层的神经网络,前一层的激活函数用的是relu,后一层的激活函数用的是softmax
#32是输出的维数
model = Sequential([
Dense(32, input_dim=784),
Activation('relu'),
Dense(10),
Activation('softmax')
])
# Another way to define your optimizer
# 优化函数
# 优化算法用的是RMSprop
rmsprop = RMSprop(lr=0.001, rho=0.9, epsilon=1e-08, decay=0.0)
# We add metrics to get more results you want to see
# 不自己定义,直接用内置的优化器也行,optimizer='rmsprop'
#激活模型:接下来用 model.compile 激励神经网络
model.compile(
optimizer=rmsprop,
loss='categorical_crossentropy',
metrics=['accuracy']
)
print('Training------------')
# Another way to train the model
# 训练模型
# 上一个程序是用train_on_batch 一批一批的训练 X_train, Y_train
# 默认的返回值是 cost,每100步输出一下结果
# 输出的样式与上一个程序的有所不同,感觉用model.fit()更清晰明了
# 上一个程序是Python实现Keras搭建神经网络训练回归模型:
# https://blog.csdn.net/weixin_45798684/article/details/106503685
model.fit(X_train, y_train, nb_epoch=2, batch_size=32)
print('\nTesting------------')
# Evaluate the model with the metrics we defined earlier
# 测试
loss, accuracy = model.evaluate(X_test, y_test)
print('test loss:', loss)
print('test accuracy:', accuracy)
运行结果:
Using TensorFlow backend.
Training------------
Epoch 1/2
32/60000 [..............................] - ETA: 5:03 - loss: 2.4464 - accuracy: 0.0625
864/60000 [..............................] - ETA: 14s - loss: 1.8023 - accuracy: 0.4850
1696/60000 [..............................] - ETA: 9s - loss: 1.5119 - accuracy: 0.6002
2432/60000 [>.............................] - ETA: 7s - loss: 1.3151 - accuracy: 0.6637
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48416/60000 [=======================>......] - ETA: 1s - loss: 0.3732 - accuracy: 0.8966
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50688/60000 [========================>.....] - ETA: 0s - loss: 0.3669 - accuracy: 0.8983
51264/60000 [========================>.....] - ETA: 0s - loss: 0.3654 - accuracy: 0.8988
51872/60000 [========================>.....] - ETA: 0s - loss: 0.3636 - accuracy: 0.8992
52608/60000 [=========================>....] - ETA: 0s - loss: 0.3618 - accuracy: 0.8997
53376/60000 [=========================>....] - ETA: 0s - loss: 0.3599 - accuracy: 0.9003
54048/60000 [==========================>...] - ETA: 0s - loss: 0.3583 - accuracy: 0.9006
54560/60000 [==========================>...] - ETA: 0s - loss: 0.3568 - accuracy: 0.9010
55296/60000 [==========================>...] - ETA: 0s - loss: 0.3548 - accuracy: 0.9016
56064/60000 [===========================>..] - ETA: 0s - loss: 0.3526 - accuracy: 0.9021
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57376/60000 [===========================>..] - ETA: 0s - loss: 0.3499 - accuracy: 0.9029
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59584/60000 [============================>.] - ETA: 0s - loss: 0.3444 - accuracy: 0.9043
60000/60000 [==============================] - 5s 87us/step - loss: 0.3435 - accuracy: 0.9046
Epoch 2/2
32/60000 [..............................] - ETA: 11s - loss: 0.0655 - accuracy: 1.0000
736/60000 [..............................] - ETA: 4s - loss: 0.2135 - accuracy: 0.9389
1408/60000 [..............................] - ETA: 4s - loss: 0.2217 - accuracy: 0.9361
1984/60000 [..............................] - ETA: 4s - loss: 0.2316 - accuracy: 0.9390
2432/60000 [>.............................] - ETA: 4s - loss: 0.2280 - accuracy: 0.9379
3040/60000 [>.............................] - ETA: 4s - loss: 0.2374 - accuracy: 0.9368
3808/60000 [>.............................] - ETA: 4s - loss: 0.2251 - accuracy: 0.9386
4576/60000 [=>............................] - ETA: 4s - loss: 0.2225 - accuracy: 0.9379
5216/60000 [=>............................] - ETA: 4s - loss: 0.2208 - accuracy: 0.9377
5920/60000 [=>............................] - ETA: 4s - loss: 0.2173 - accuracy: 0.9383
6656/60000 [==>...........................] - ETA: 4s - loss: 0.2217 - accuracy: 0.9370
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8800/60000 [===>..........................] - ETA: 3s - loss: 0.2235 - accuracy: 0.9358
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58560/60000 [============================>.] - ETA: 0s - loss: 0.1951 - accuracy: 0.9440
59360/60000 [============================>.] - ETA: 0s - loss: 0.1947 - accuracy: 0.9440
60000/60000 [==============================] - 5s 76us/step - loss: 0.1946 - accuracy: 0.9440
Testing------------
32/10000 [..............................] - ETA: 15s
1248/10000 [==>...........................] - ETA: 0s
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9984/10000 [============================>.] - ETA: 0s
10000/10000 [==============================] - 0s 47us/step
test loss: 0.17407772153392434
test accuracy: 0.9513000249862671