本片文章的目的是:利用Tensorflow API tf.keras搭建网络八股(六步法)
六步法:
- 导入相关的模块,也就是 import
- 加载训练集和测试集,也就是加载train(x_train数据、y_train标签)、test(x_test数据、y_test标签)数据
- 前向传播(搭建神经网络结构,逐层描述每层网络),也就是model = tf.keras.models.Sequential
- 配置训练时所用的方法(也就是优化器,损失函数,评测指标的选择),也就是model.compile
- 进行数据的训练(告诉训练集和测试集的输入特征和标签,batch的值,以及迭代多少次数据集),也即是model.fit
- 利用summary()函数打印出网络的结构和参数统计
对上述用到的tf.keras模块中的函数进行进一步的介绍
- model = tf.keras.models.Sequential([网络结构]) #描述各层网络
网络结构举例:- 拉直层:tf.keras.layers.Flatten()
- 全连接层:tf.keras.layers.Dense(神经元个数,activation=“激活函数”,kernel_regularizer=“正则化函数”)
activation可选的字符串:“relu”、“softmax”、“sigmoid”、“tanh”
kernel_regularizer可选:tf.keras.regularizers.l1()、tf.keras.regularizers.l2() - 卷积层:tf.keras.layers.Conv2D(filters = 卷积核个数,kernel_size = 卷积核尺寸,strides = 卷积步长,padding = “valid”or“same”)
- LSTM层:tf.keras.layers.LSTM()
- model.compile(optimizer=优化器,loss=损失函数,metrics=[“准确率”])
- Optimizer可选:
i. ‘sgd’ or tf.keras.optimizers.SGD(lr=学习率,momentum=动量参数)
ii. 'adagrad’or tf.keras.optimizers.Adagrad(lr=学习率)
iii. 'adadelta’or tf.keras.optimizers.Adadelta(lr=学习率)
iv. 'adam’or tf.keras.optimizers.Adam(lr=学习率,beta_1=0.9,beta_1=0.999) - loss可选:
i. ‘mse’ or tf.keras.losses.MeanSquaredError()
ii. ‘sparse_categorical_crossentropy’ or tf.keras.losses.SparseCategoricalCrossentropy(from_logots=False) - Metrics可选:
i. ‘accuracy’:y_和y都是数值,如y_=[1] y=[1]
ii. ‘categorical_accuracy’:y_和y都是独热码(概率分布),如y_=[0,1,0] y=[0.256,0.695,0.048]
iii. ‘sparse_categorical_accuracy’:y_是数值,y是独热码(概率分布),y_=[1] y=[0.256,0.695,0.048]
- Optimizer可选:
- model.fit(训练集的输入特征,训练集的标签,batch_size=,epochs=,validation_data=(测试集的输入特征,测试集的标签),validation_split=从训练集划分多少比例给测试集,validation_freq=多少次epoch测试一次)
- model.summary() 打印出网络的结构和参数统计
案例实战
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案例1:利用tf.keras实现鸢尾花分类
import tensorflow as tf from sklearn import datasets import numpy as np x_train = datasets.load_iris().data y_train = datasets.load_iris().target np.random.seed(116) np.random.shuffle(x_train) np.random.seed(116) np.random.shuffle(y_train) tf.random.set_seed(116) model = tf.keras.models.Sequential([ tf.keras.layers.Dense(3,activation = 'softmax',kernel_regularizer = tf.keras.regularizers.l2()) ]) model.compile(optimizer = tf.keras.optimizers.SGD(lr = 0.1), loss = tf.keras.losses.SparseCategoricalCrossentropy(from_logits = False), metrics = ['sparse_categorical_accuracy']) model.fit(x_train,y_train,batch_size = 32,epochs = 500,validation_split = 0.2,validation_freq = 20) model.summary()
将上述代码封装成class
import tensorflow as tf from tensorflow.keras.layers import Dense from tensorflow.keras import Model from sklearn import datasets import numpy as np x_train = datasets.load_iris().data y_train = datasets.load_iris().target np.random.seed(116) np.random.shuffle(x_train) np.random.seed(116) np.random.shuffle(y_train) tf.random.set_seed(116) class IrisModel(Model): def __init__(self): super(IrisModel,self).__init__() self.dl = Dense(3,activation = 'sigmoid',kernel_regularizer = tf.keras.regularizers.l2()) def call(self,x): y = self.dl(x) return y model = IrisModel() model.compile(optimizer = tf.keras.optimizers.SGD(lr = 0.1), loss = tf.keras.losses.SparseCategoricalCrossentropy(from_logits = False), metrics = ['sparse_categorical_accuracy']) model.fit(x_train,y_train,batch_size = 32,epochs = 500,validation_split = 0.2,validation_freq = 20) model.summary()
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案例2:利用tf.keras实现mnist手写数字识别
import tensorflow as tf mnist = tf.keras.datasets.mnist (x_train,y_train),(x_test,y_test) = mnist.load_data() x_train,x_test = x_train / 255.0,x_test / 255.0 model = tf.keras.models.Sequential([ tf.keras.layers.Flatten(), tf.keras.layers.Dense(128,activation = 'relu'), tf.keras.layers.Dense(10,activation = 'softmax') ]) model.compile(optimizer = 'adam', loss = tf.keras.losses.SparseCategoricalCrossentropy(from_logits = False), metrics = ['sparse_categorical_accuracy']) model.fit(x_train,y_train,batch_size = 32,epochs = 5,validation_data = (x_test,y_test),validation_freq=1) model.summary()
将上述代码封装成class
import tensorflow as tf from tensorflow.keras.layers import Dense,Flatten from tensorflow.keras import Model mnist = tf.keras.datasets.mnist (x_train,y_train),(x_test,y_test) = mnist.load_data() x_train,x_test = x_train / 255.0,x_test / 255.0 class MnistModel(Model): def __init__(self): super(MnistModel,self).__init__() self.flatten = Flatten() self.d1 = Dense(128,activation = 'relu') self.d2 = Dense(10,activation = 'softmax') def call(self,x): x = self.flatten(x) x = self.d1(x) y = self.d2(x) return y model = MnistModel() model.compile(optimizer = 'adam', loss = tf.keras.losses.SparseCategoricalCrossentropy(from_logits = False), metrics = ['sparse_categorical_accuracy']) model.fit(x_train,y_train,batch_size = 32,epochs = 5,validation_data = (x_test,y_test),validation_freq=1) model.summary()
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