Tensorflow 简明教程

TensorFlow - XOR Implementation

在本章中，我们将了解使用 TensorFlow 的 XOR 实现。在开始使用 TensorFlow 中的 XOR 实现之前，让我们看看 XOR 表值。这将帮助我们理解加密和解密过程。

A

B

A XOR B

0

0

0

0

1

1

1

0

1

1

1

0

XOR 密码加密方法基本上用来加密难以用蛮力方法（即通过生成与适当密钥匹配的随机加密密钥来）破解的数据。

使用 XOR 密码实现的概念是定义一个 XOR 加密密钥，然后对指定字符串中的字符执行与该密钥的 XOR 操作，这是用户尝试进行加密的操作。现在，我们将专注于使用 TensorFlow 的 XOR 实现，如下所述：

#Declaring necessary modules
import tensorflow as tf
import numpy as np
"""
A simple numpy implementation of a XOR gate to understand the backpropagation
algorithm
"""

x = tf.placeholder(tf.float64,shape = [4,2],name = "x")
#declaring a place holder for input x
y = tf.placeholder(tf.float64,shape = [4,1],name = "y")
#declaring a place holder for desired output y

m = np.shape(x)[0]#number of training examples
n = np.shape(x)[1]#number of features
hidden_s = 2 #number of nodes in the hidden layer
l_r = 1#learning rate initialization

theta1 = tf.cast(tf.Variable(tf.random_normal([3,hidden_s]),name = "theta1"),tf.float64)
theta2 = tf.cast(tf.Variable(tf.random_normal([hidden_s+1,1]),name = "theta2"),tf.float64)

#conducting forward propagation
a1 = tf.concat([np.c_[np.ones(x.shape[0])],x],1)
#the weights of the first layer are multiplied by the input of the first layer

z1 = tf.matmul(a1,theta1)
#the input of the second layer is the output of the first layer, passed through the
   activation function and column of biases is added

a2 = tf.concat([np.c_[np.ones(x.shape[0])],tf.sigmoid(z1)],1)
#the input of the second layer is multiplied by the weights

z3 = tf.matmul(a2,theta2)
#the output is passed through the activation function to obtain the final probability

h3 = tf.sigmoid(z3)
cost_func = -tf.reduce_sum(y*tf.log(h3)+(1-y)*tf.log(1-h3),axis = 1)

#built in tensorflow optimizer that conducts gradient descent using specified
   learning rate to obtain theta values

optimiser = tf.train.GradientDescentOptimizer(learning_rate = l_r).minimize(cost_func)

#setting required X and Y values to perform XOR operation
X = [[0,0],[0,1],[1,0],[1,1]]
Y = [[0],[1],[1],[0]]

#initializing all variables, creating a session and running a tensorflow session
init = tf.global_variables_initializer()
sess = tf.Session()
sess.run(init)

#running gradient descent for each iteration and printing the hypothesis
   obtained using the updated theta values
for i in range(100000):
   sess.run(optimiser, feed_dict = {x:X,y:Y})#setting place holder values using feed_dict
   if i%100==0:
      print("Epoch:",i)
      print("Hyp:",sess.run(h3,feed_dict = {x:X,y:Y}))

上面这一行代码生成的输出如以下截图所示 −

xor implementation using tensorflow