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python實(shí)現(xiàn)簡(jiǎn)單神經(jīng)網(wǎng)絡(luò)算法

 更新時(shí)間：2018年03月10日 12:37:19   作者：由硬到軟  
這篇文章主要為大家詳細(xì)介紹了python實(shí)現(xiàn)簡(jiǎn)單神經(jīng)網(wǎng)絡(luò)算法，具有一定的參考價(jià)值，感興趣的小伙伴們可以參考一下

python實(shí)現(xiàn)簡(jiǎn)單神經(jīng)網(wǎng)絡(luò)算法，供大家參考，具體內(nèi)容如下

python實(shí)現(xiàn)二層神經(jīng)網(wǎng)絡(luò)

包括輸入層和輸出層

import numpy as np 
 
#sigmoid function 
def nonlin(x, deriv = False): 
  if(deriv == True): 
    return x*(1-x) 
  return 1/(1+np.exp(-x)) 
 
#input dataset 
x = np.array([[0,0,1], 
       [0,1,1], 
       [1,0,1], 
       [1,1,1]]) 
 
#output dataset 
y = np.array([[0,0,1,1]]).T 
 
np.random.seed(1) 
 
#init weight value 
syn0 = 2*np.random.random((3,1))-1 
 
for iter in xrange(100000): 
  l0 = x             #the first layer,and the input layer  
  l1 = nonlin(np.dot(l0,syn0))  #the second layer,and the output layer 
 
 
  l1_error = y-l1 
 
  l1_delta = l1_error*nonlin(l1,True) 
 
  syn0 += np.dot(l0.T, l1_delta) 
print "outout after Training:" 
print l1 

import numpy as np 
 
#sigmoid function 
def nonlin(x, deriv = False): 
  if(deriv == True): 
    return x*(1-x) 
  return 1/(1+np.exp(-x)) 
 
#input dataset 
x = np.array([[0,0,1], 
       [0,1,1], 
       [1,0,1], 
       [1,1,1]]) 
 
#output dataset 
y = np.array([[0,0,1,1]]).T 
 
np.random.seed(1) 
 
#init weight value 
syn0 = 2*np.random.random((3,1))-1 
 
for iter in xrange(100000): 
  l0 = x             #the first layer,and the input layer  
  l1 = nonlin(np.dot(l0,syn0))  #the second layer,and the output layer 
 
 
  l1_error = y-l1 
 
  l1_delta = l1_error*nonlin(l1,True) 
 
  syn0 += np.dot(l0.T, l1_delta) 
print "outout after Training:" 
print l1

這里，
l0:輸入層

l1:輸出層

syn0:初始權(quán)值

l1_error:誤差

l1_delta:誤差校正系數(shù)

func nonlin:sigmoid函數(shù)

可見(jiàn)迭代次數(shù)越多，預(yù)測(cè)結(jié)果越接近理想值，當(dāng)時(shí)耗時(shí)也越長(zhǎng)。

python實(shí)現(xiàn)三層神經(jīng)網(wǎng)絡(luò)

包括輸入層、隱含層和輸出層

import numpy as np 
 
def nonlin(x, deriv = False): 
  if(deriv == True): 
    return x*(1-x) 
  else: 
    return 1/(1+np.exp(-x)) 
 
#input dataset 
X = np.array([[0,0,1], 
       [0,1,1], 
       [1,0,1], 
       [1,1,1]]) 
 
#output dataset 
y = np.array([[0,1,1,0]]).T 
 
syn0 = 2*np.random.random((3,4)) - 1 #the first-hidden layer weight value 
syn1 = 2*np.random.random((4,1)) - 1 #the hidden-output layer weight value 
 
for j in range(60000): 
  l0 = X            #the first layer,and the input layer  
  l1 = nonlin(np.dot(l0,syn0)) #the second layer,and the hidden layer 
  l2 = nonlin(np.dot(l1,syn1)) #the third layer,and the output layer 
 
 
  l2_error = y-l2    #the hidden-output layer error 
 
  if(j%10000) == 0: 
    print "Error:"+str(np.mean(l2_error)) 
 
  l2_delta = l2_error*nonlin(l2,deriv = True) 
 
  l1_error = l2_delta.dot(syn1.T)   #the first-hidden layer error 
 
  l1_delta = l1_error*nonlin(l1,deriv = True) 
 
  syn1 += l1.T.dot(l2_delta) 
  syn0 += l0.T.dot(l1_delta) 
print "outout after Training:" 
print l2 
import numpy as np 
 
def nonlin(x, deriv = False): 
  if(deriv == True): 
    return x*(1-x) 
  else: 
    return 1/(1+np.exp(-x)) 
 
#input dataset 
X = np.array([[0,0,1], 
       [0,1,1], 
       [1,0,1], 
       [1,1,1]]) 
 
#output dataset 
y = np.array([[0,1,1,0]]).T 
 
syn0 = 2*np.random.random((3,4)) - 1 #the first-hidden layer weight value 
syn1 = 2*np.random.random((4,1)) - 1 #the hidden-output layer weight value 
 
for j in range(60000): 
  l0 = X            #the first layer,and the input layer  
  l1 = nonlin(np.dot(l0,syn0)) #the second layer,and the hidden layer 
  l2 = nonlin(np.dot(l1,syn1)) #the third layer,and the output layer 
 
 
  l2_error = y-l2    #the hidden-output layer error 
 
  if(j%10000) == 0: 
    print "Error:"+str(np.mean(l2_error)) 
 
  l2_delta = l2_error*nonlin(l2,deriv = True) 
 
  l1_error = l2_delta.dot(syn1.T)   #the first-hidden layer error 
 
  l1_delta = l1_error*nonlin(l1,deriv = True) 
 
  syn1 += l1.T.dot(l2_delta) 
  syn0 += l0.T.dot(l1_delta) 
print "outout after Training:" 
print l2

以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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