Created
March 26, 2020 06:37
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| import numpy as np | |
| import math | |
| import matplotlib.pyplot as plt | |
| #----------Pegasos Code definition------------------------# | |
| def pegasos(feature_matrix,labels,T): | |
| theta=np.array([0]*feature_matrix.shape[1]) | |
| theta_0=0 | |
| count=0 | |
| L=2 #value for lambda | |
| for i in range(T): | |
| for j in range(len(feature_matrix)): | |
| count+=1 | |
| eta=1/math.sqrt(count) #decreasing eta value as iteration increase | |
| z=labels[j]*(np.dot(feature_matrix[j],theta)+theta_0) | |
| if(z<=1): | |
| theta=theta+eta*labels[j]*feature_matrix[j]-eta*L*theta | |
| theta_0=theta_0+eta*labels[j] | |
| else: | |
| theta=theta-eta*L*theta | |
| return theta,theta_0 | |
| #---------------Ends Pegsos----------------------------------# | |
| if __name__=="__main__": | |
| x=np.array([[1,2],[2,3],[3,4],[4,5]]) | |
| y=np.array([1,1,-1,-1]) | |
| theta,theta_0=pegasos(x,y,100) | |
| print("theta ={} theta_0= {}".format(theta,theta_0)) | |
| #----------visualization-----------------------------# | |
| pos=[[],[]] | |
| neg=[[],[]] | |
| for i in range(len(x)): | |
| if(y[i]==1): | |
| pos[0].append(x[i][0]) | |
| pos[1].append(x[i][1]) | |
| else: | |
| neg[0].append(x[i][0]) | |
| neg[1].append(x[i][1]) | |
| plt.scatter(neg[0],neg[1]) | |
| plt.scatter(pos[0],pos[1]) | |
| print(x,y) | |
| x=[i for i in range(0,5)] | |
| y=[-(theta[0]*i+theta_0)/theta[1] for i in x] | |
| plt.plot(x,y) | |
| plt.show() |
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