深度学习和神经网络对很多初学者来说都是摸不着头脑,今天分享一个完整的手写识别的实例,学习和理解了这个实例代码和过程就基本上掌握了神经网络。
1、构建神经网络类 network_claas.py
- #!/usr/bin/env python3
- # -*- coding: utf-8 -*-
- # neural network class definition
- import scipy.special
- import numpy
- # library for plotting arrays
- import matplotlib.pyplot
- # helper to load data from PNG image files# helpe
- import imageio
- # glob helps select multiple files using patterns
- import glob
- class neuralNetwork :
- # initialise the neural network
- def __init__(self, inputnodes, hiddennodes, outputnodes, learningrate) :
- #set number of nodes in each input , hidden , output
- #初始化网络,设置输入层,中间层,和输出层节点数
- self.inodes = inputnodes
- self.hnodes = hiddennodes
- self.onodes = outputnodes
- # link weight matrices, wih and who
- # weights inside the arrays are w_ i_ j, where link is from node i to node j in the next layer
- # w11 w21
- # w12 w22 etc
- # 初始化权重矩阵,我们有两个权重矩阵,一个是wih表示输入层和中间层节点间链路权重形成的矩阵一个是who,表示中间层和输出层间链路权重形成的矩阵
- self. wih = numpy.random.normal( 0.0, pow( self. hnodes, -0.5), (self. hnodes, self. inodes))
- self. who = numpy.random.normal( 0.0, pow( self. onodes, -0.5), (self. onodes, self. hnodes))
- # learning rate
- self.lr = learningrate
- # activation function is the sigmoid function
- # 设置激活函数的反函数
- self.activation_function = lambda x:scipy.special.expit(x)
- pass
- # train the neural network
- def train(self, inputs_list, targets_list) :
- # convert inputs list to 2d array
- #根据输入的训练数据更新节点链路权重
- #把inputs_list, targets_list转换成numpy支持的二维矩阵.T表示做矩阵的转置
- inputs = numpy.array(inputs_list, ndmin=2).T
- targets = numpy.array(targets_list, ndmin=2).T
- # calculate signals into hidden layer
- #计算信号经过输入层后产生的信号量
- hidden_inputs = numpy.dot(self.wih, inputs)
- # calculate the signals emerging from hidden layer
- #中间层神经元对输入的信号做激活函数后得到输出信号
- hidden_outputs = self.activation_function(hidden_inputs)
- # calculate signals into final output layer
- #输出层接收来自中间层的信号量
- final_inputs = numpy.dot(self.who, hidden_outputs)
- # calculate the signals emerging from final output layer
- #输出层对信号量进行激活函数后得到最终输出信号
- final_outputs = self.activation_function(final_inputs)
- # output layer error is the (target - actual)
- #计算误差
- output_errors = targets - final_outputs
- # hidden layer error is the output_errors, split by weights, recombined at hidden nodes
- hidden_errors = numpy.dot(self.who.T, output_errors)
- #根据误差计算链路权重的更新量,然后把更新加到原来链路权重上
- # update the weights for the links between the hidden and output layers
- self.who += self.lr * numpy.dot((output_errors * final_outputs * (1.0 - final_outputs)), numpy.transpose(hidden_outputs))
- # update the weights for the links between the input and hidden layers
- self.wih += self.lr * numpy.dot((hidden_errors * hidden_outputs * (1.0 - hidden_outputs)), numpy.transpose(inputs))
- pass
- # query the neural network
- def query(self, inputs_list) :
- #根据输入数据计算并输出答案
- # convert inputs list to 2d array
- inputs = numpy.array(inputs_list, ndmin=2).T
- #计算中间层从输入层接收到的信号量
- # calculate signals into hidden layer
- hidden_inputs = numpy.dot(self.wih, inputs)
- #计算中间层经过激活函数后形成的输出信号量
- # calculate the signals emerging from hidden layer
- hidden_outputs = self.activation_function(hidden_inputs)
- #计算最外层接收到的信号量
- # calculate signals into final output layer
- final_inputs = numpy.dot(self.who, hidden_outputs)
- # calculate the signals emerging from final output layer
- final_outputs = self.activation_function(final_inputs)
- return final_outputs
2、初始化及训练测试该网络
- #!/usr/bin/env python3
- # -*- coding: utf-8 -*-
- from network_claas import neuralNetwork
- import numpy
- import matplotlib
- import glob
- import imageio
- # library for plotting arrays
- import matplotlib.pyplot as plt
- import pylab
- # ensure the plots are inside this notebook, not an external window
- #初始化网络
- # number of input, hidden and output nodes
- input_nodes = 784
- hidden_nodes = 100
- output_nodes = 10
- #初始化学习率
- # learning rate is 0.3
- learning_rate = 0.3
- # create instance of neural network
- # 初始化神经网络
- n = neuralNetwork(input_nodes,hidden_nodes,output_nodes, learning_rate)
- # load the mnist training data CSV file into a list
- training_data_file = open("mnist_dataset/mnist_train_100.csv", 'r')
- training_data_list = training_data_file.readlines()
- training_data_file.close()
- # train the neural network
- # epochs is the number of times the training data set is used for training
- epochs = 5
- for e in range( epochs):
- # go through all records in the training data set
- for record in training_data_list:
- # split the record by the ',' commas
- all_values = record.split(',')
- # scale and shift the inputs
- inputs = (numpy.asfarray( all_values[1:]) / 255.0 * 0.99) + 0.01
- # create the target output values (all 0.01, except the desired label which is 0.99)
- targets = numpy.zeros(output_nodes) + 0.01
- # all_values[0] is the target label for this record
- targets[int(all_values[0])] = 0.99
- n.train(inputs, targets)
- pass
- # load the mnist test data CSV file into a list
- test_data_file = open("mnist_dataset/mnist_test_10.csv", 'r')
- test_data_list = test_data_file.readlines()
- test_data_file.close()
- # test the neural network
- # scorecard for how well the network performs, initially empty
- scorecard = []
- # go through all the records in the test data set
- for record in test_data_list:
- # split the record by the ',' commas
- all_values = record.split(',')
- # correct answer is first value
- correct_label = int( all_values[ 0])
- # scale and shift the inputs
- inputs = (numpy.asfarray( all_values[ 1:]) / 255.0 * 0.99) + 0.01
- # query the network
- outputs = n.query( inputs)
- # the index of the highest value corresponds to the label
- label = numpy.argmax( outputs)
- # append correct or incorrect to list
- if (label == correct_label):
- # network' s answer matches correct answer, add 1 to scorecard
- scorecard.append( 1)
- else:
- # network' s answer doesn' t match correct answer, add 0 to scorecard
- scorecard.append( 0)
- pass
- pass
- # calculate the performance score, the fraction of correct answers
- scorecard_array = numpy.asarray( scorecard)
- print ("performance = ", scorecard_array.sum() / scorecard_array.size)
- # our own image test data set# our o
- our_own_dataset = []
- # load the png image data as test data set
- for image_file_name in glob.glob('my_own_images/2828_my_own_?.png'):
- # use the filename to set the correct label
- label = int(image_file_name[-5:-4])
- # load image data from png files into an array
- print ("loading ... ", image_file_name)
- img_array = imageio.imread(image_file_name, as_gray=True)
- # reshape from 28x28 to list of 784 values, invert values
- img_data = 255.0 - img_array.reshape(784)
- # then scale data to range from 0.01 to 1.0
- img_data = (img_data / 255.0 * 0.99) + 0.01
- print(numpy.min(img_data))
- print(numpy.max(img_data))
- # append label and image data to test data set
- record = numpy.append(label,img_data)
- our_own_dataset.append(record)
- pass
- # record to test
- item = 2
- # plot image
- plt.imshow(our_own_dataset[item][1:].reshape(28,28), cmap='Greys', interpolation='None')
- # correct answer is first value
- correct_label = our_own_dataset[item][0]
- # data is remaining values
- inputs = our_own_dataset[item][1:]
- # query the network
- outputs = n.query(inputs)
- print (outputs)
- # the index of the highest value corresponds to the label
- label = numpy.argmax(outputs)
- print("network says ", label)
- # append correct or incorrect to list
- if (label == correct_label):
- print ("match!")
- else:
- print ("no match!")
- pass
- pylab.show()
3,输出如下:
4,完整代码如下:
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