Press "Enter" to skip to content

tensorflow2搭建基础神经网络模型

2021年12月9日

tensorflow2.0搭建基础NN

 

1. sequenial()

 

用Tensorflow API:tf. keras

 

六步法搭建神经网络

第一步：import相关模块，如import tensorflow as tf。
第二步：指定输入网络的训练集和测试集，如指定训练集的输入x_train和标签y_train，测试集的输入x_test和标签y_test。
第三步：逐层搭建网络结构，model = tf.keras.models.Sequential()。
第四步：在model.compile()中配置训练方法，选择训练时使用的优化器、损失函数和最终评价指标。
第五步：在model.fit()中执行训练过程，告知训练集和测试集的输入值和标签、每个batch的大小（batchsize）和数据集的迭代次数（epoch）。
第六步：使用model.summary()打印网络结构，统计参数数目。

1.1 Sequential()容器

 

Sequential()可以认为是个容器，这个容器里封装了一个神经网络结构。

 

model = tf.keras.models.Sequential ([网络结构]) #描述各层网络

 

在Sequential()中，要描述从输入层到输出层每一层的网络结构。每一层的网络结构可以是：

拉直层：tf.keras.layers.Flatten( )
这一层不含计算，只是形状转换，把输入特征拉直变成一维数组
全连接层：tf.keras.layers.Dense(神经元个数，activation= "激活函数“，kernel_regularizer=哪种正则化)
activation (字符串给出)可选: relu、softmax、sigmoid、tanh
kernel_regularizer可 选:tf.keras.regularizers.l1()
、tf.keras.regularizers.12()

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()

1.2 compile配置神经网络的训练方法

 

告知训练时选择的优化器、损失函数和评测指标

 

model.compile(optimizer = 优化器, loss = 损失函数, metrics = ["准确率"] )

 

优化器可以是以字符串形式给出的优化器名字

 

Optimizer（优化器）可选:

'sgd'
ortf.keras optimizers.SGD (lr=学习率,momentum=动量参数)
'adagrad'
ortf.keras.optimizers.Adagrad (lr=学习率)
’adadelta'
ortf.keras.optimizers.Adadelta (lr=学习率)
'adam'
ortf.keras.optimizers.Adam (lr=学习率，beta_ 1=0.9, beta_ 2=0.999)

loss是（损失函数）可选:

'mse'
ortf.keras losses MeanSquaredError()
'sparse_ categorical_crossentropy
ortf.keras.losses.SparseCategoricalCrossentropy(from_logits =False)
from_logits
参数：有些神经网络的输出是经过了softmax等函数的概率分布，有些则不经概率分布直接输出，from_logits
参数是在询问是否是原始输出，即没有经概率分布的输出。
如果神经网络预测结果输出前经过了概率分布，这里是False
如果神经网络预测结果输出前没有经过了概率分布，直接输出，这里是True

Metrics(评测指标)可选:

 

'accuracy'
: y_ 和y都是数值，如y_=[1] y=[1]

 

'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]

 

'sparse_ categorical_accuracy'
: y_ 是数值，y是独热码(概率分布)，如y_ =[1] y=[0 256,0.695,0.048]

 

1.3 fit()执行训练过程

 

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)

batch_ size
：每次喂入神经网络的样本数，推荐个数为：2^n
epochs
：要迭代多少次数据集
validation_data
和validation_split
二选一
validation_freq
：每多少次epoch迭代使用测试集验证一次结果

1.4 model.summary()打印和统计

 

summary()
可以打印出网络的结构和参数统计

 

1.5 鸢尾花示例

 

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()

 

运行结果

 

......
 32/120 [=======>......................] - ETA: 0s - loss: 0.3005 - sparse_categorical_accuracy: 0.9375
120/120 [==============================] - 0s 83us/sample - loss: 0.3336 - sparse_categorical_accuracy: 0.9667
Epoch 499/500
 32/120 [=======>......................] - ETA: 0s - loss: 0.3630 - sparse_categorical_accuracy: 0.9688
120/120 [==============================] - 0s 125us/sample - loss: 0.3486 - sparse_categorical_accuracy: 0.9583
Epoch 500/500
 32/120 [=======>......................] - ETA: 0s - loss: 0.3122 - sparse_categorical_accuracy: 0.9688
120/120 [==============================] - 0s 142us/sample - loss: 0.3333 - sparse_categorical_accuracy: 0.9667 - val_loss: 0.4002 - val_sparse_categorical_accuracy: 1.0000
Model: "sequential"
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
dense (Dense)                multiple                  15        
=================================================================
Total params: 15
Trainable params: 15
Non-trainable params: 0
_________________________________________________________________

 

鸢尾花分类神经网络，是四输入三输出的一层神经网络，参数12个w和3个b，共计15个参数，这一层是Dense全连接。

 

2. 搭建网络模型class

 

Sequential搭建神经网络的方法，用Sequential可以搭建出上层输出就是下层输入的顺序网络结构,但是无法写出一些带有跳连的非顺序网络结构。这个时候我们可以选择用class搭建神经网络结构。

 

六步法搭建神经网络

 

 

    1. import

 

    1. train，test

 

    1. class MyModel(Model) model=MyMode

 

    1. model.compile

 

    1. model.fit

 

    1. model.summary

 

 

class MyModel(Model):
    # 需要继承Model
def __init__ (self):
super(MyModel, self).__init__()
# 定义网络结构块,super继承要与类名一致
def cal(self, x):
# 调用网络结构块，实现前向传播
return y
model = MyModel()

 

__init__()

 

代码示例

 

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.d1 = Dense(3, activation='softmax', kernel_regularizer=tf.keras.regularizers.l2())
    def call(self, x):
        y = self.d1(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()

 

运行结果

 

......
 32/120 [=======>......................] - ETA: 0s - loss: 0.3630 - sparse_categorical_accuracy: 0.9688
120/120 [==============================] - 0s 108us/sample - loss: 0.3486 - sparse_categorical_accuracy: 0.9583
Epoch 500/500
 32/120 [=======>......................] - ETA: 0s - loss: 0.3122 - sparse_categorical_accuracy: 0.9688
120/120 [==============================] - 0s 158us/sample - loss: 0.3333 - sparse_categorical_accuracy: 0.9667 - val_loss: 0.4002 - val_sparse_categorical_accuracy: 1.0000
Model: "iris_model"
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
dense (Dense)                multiple                  15        
=================================================================
Total params: 15
Trainable params: 15
Non-trainable params: 0
_________________________________________________________________

 

3. MNIST数据集

 

提供6万张28*28
像素点的0~9手写数字图片和标签，用于训练。

 

提供1万张28*28
像素点的0~9手写数字图片和标签，用于测试。

 

代码示例：

 

import tensorflow as tf
from matplotlib import pyplot as plt
mnist = tf.keras.datasets.mnist
(x_train, y_train), (x_test, y_test) = mnist.load_data()
# 可视化训练集输入特征的第一个元素
plt.imshow(x_train[0], cmap='gray')  # 绘制灰度图
plt.show()
# 打印出训练集输入特征的第一个元素
print("x_train[0]:
", x_train[0])
# 打印出训练集标签的第一个元素
print("y_train[0]:
", y_train[0])
# 打印出整个训练集输入特征形状
print("x_train.shape:
", x_train.shape)
# 打印出整个训练集标签的形状
print("y_train.shape:
", y_train.shape)
# 打印出整个测试集输入特征的形状
print("x_test.shape:
", x_test.shape)
# 打印出整个测试集标签的形状
print("y_test.shape:
", y_test.shape)

 

运行结果

 

y_train[0]:
 5
x_train.shape:
 (60000, 28, 28)
y_train.shape:
 (60000,)
x_test.shape:
 (10000, 28, 28)
y_test.shape:
 (10000,)

 

3.1 Sequential实现手写数字识别训练

 

import tensorflow as tf
mnist = tf.keras.datasets.mnist
(x_train, y_train), (x_test, y_test) = mnist.load_data()
# 对输入网络的输入特征进行归一化
# 使原本0到255之间的灰度值，变为0到1之间的数值
# 把输入特征的数值变小更适合神经网络吸收
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'),   # 128个神经元为超参数
    tf.keras.layers.Dense(10, activation='softmax')  # 10分类的任务，所以输出层有10个节点
])
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()

 

运行结果

 

......
58848/60000 [============================>.] - ETA: 0s - loss: 0.0480 - sparse_categorical_accuracy: 0.9854
59328/60000 [============================>.] - ETA: 0s - loss: 0.0480 - sparse_categorical_accuracy: 0.9854
59776/60000 [============================>.] - ETA: 0s - loss: 0.0479 - sparse_categorical_accuracy: 0.9854
60000/60000 [==============================] - 6s 94us/sample - loss: 0.0478 - sparse_categorical_accuracy: 0.9854 - val_loss: 0.0730 - val_sparse_categorical_accuracy: 0.9776
Model: "sequential"
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
flatten (Flatten)            multiple                  0         
_________________________________________________________________
dense (Dense)                multiple                  100480    
_________________________________________________________________
dense_1 (Dense)              multiple                  1290      
=================================================================
Total params: 101,770
Trainable params: 101,770
Non-trainable params: 0
_________________________________________________________________

 

对于结果，后半部部分才是测试集中运行结果。

 

6s 94us/sample - loss: 0.0478 - sparse_categorical_accuracy: 0.9854 - val_loss: 0.0730 - val_sparse_categorical_accuracy: 0.9776

 

3.2 calss实现手写数字识别训练

 

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()

 

运行结果

 

......
57824/60000 [===========================>..] - ETA: 0s - loss: 0.0440 - sparse_categorical_accuracy: 0.9866
58528/60000 [============================>.] - ETA: 0s - loss: 0.0440 - sparse_categorical_accuracy: 0.9866
59264/60000 [============================>.] - ETA: 0s - loss: 0.0440 - sparse_categorical_accuracy: 0.9866
60000/60000 [==============================] - 5s 88us/sample - loss: 0.0439 - sparse_categorical_accuracy: 0.9866 - val_loss: 0.0752 - val_sparse_categorical_accuracy: 0.9766
Model: "mnist_model"
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
flatten (Flatten)            multiple                  0         
_________________________________________________________________
dense (Dense)                multiple                  100480    
_________________________________________________________________
dense_1 (Dense)              multiple                  1290      
=================================================================
Total params: 101,770
Trainable params: 101,770
Non-trainable params: 0
_________________________________________________________________

Categories:机器学习

Be First to Comment

发表回复

您的电子邮箱地址不会被公开。 必填项已用*标注