python實現梯度下降法
阿新 • • 發佈:2020-03-25
本文例項為大家分享了python實現梯度下降法的具體程式碼,供大家參考,具體內容如下
使用工具:Python(x,y) 2.6.6
執行環境:Windows10
問題:求解y=2*x1+x2+3,即使用梯度下降法求解y=a*x1+b*x2+c中引數a,b,c的最優值(監督學習)
訓練資料:
x_train=[1,2],[2,1],3],[3,5],[1,[4,[7,[11,[8,7]
y_train=[7,8,10,14,13,20,16,28,26]
測試資料:
x_test = [1,4],[5,1]
# -*- coding: utf-8 -*- """ Created on Wed Nov 16 09:37:03 2016 @author: Jason """ import numpy as np import matplotlib.pyplot as plt # y=2 * (x1) + (x2) + 3 rate = 0.001 x_train = np.array([[1,7] ]) y_train = np.array([7,26]) x_test = np.array([[1,1]]) a = np.random.normal() b = np.random.normal() c = np.random.normal() def h(x): return a*x[0]+b*x[1]+c for i in range(100): sum_a=0 sum_b=0 sum_c=0 for x,y in zip(x_train,y_train): for xi in x: sum_a = sum_a+ rate*(y-h(x))*xi sum_b = sum_b+ rate*(y-h(x))*xi #sum_c = sum_c + rate*(y-h(x)) *1 a = a + sum_a b = b + sum_b c = c + sum_c plt.plot([h(xi) for xi in x_test]) print(a) print(b) print(c) result=[h(xi) for xi in x_train] print(result) result=[h(xi) for xi in x_test] print(result) plt.show()
執行結果:
結論:線段是在逐漸逼近的,訓練資料越多,迭代次數越多就越逼近真實值。
以上就是本文的全部內容,希望對大家的學習有所幫助,也希望大家多多支援我們。