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本文实现了一种图像分类算法,它采用支持向量机与直方图相交核和随机梯度下降法。我到目前为止的代码:支持向量机与直方图相交核使用梯度下降
import numpy as np
# calculate the kernel matrix for x and examples
# kernel is (n_samples x 1) matrix
# n_samples number of the examples
def histogram_intersection_kernel(x,u):
n_samples , n_features = x.shape
K = np.zeros(shape=(n_samples,1),dtype=np.float)
for d in xrange(n_samples):
K[d][0] = np.sum(np.minimum(x[d],u),axis =1)
return K
# related to the hinge loss
# returns 1 if y*f_{t-1}(xt) < 1
# 0 otherwise
def get_sigma(self,y,y_prediction) :
if np.dot(y,y_prediction) <1 :
return 1
else :
return 0
# alpha is a predicted matrix for f = alpha *K(x,.)
# returns the predicted value y' for given x
def get_prediction(self,X,alpha,n_samples,u):
y_predict = np.dot(alpha.T,self.get_kernel(X,u))
return np.sign(y_predict.item(0))
# calculate the update for gradient descent function
# alpha is the parameter of the equation that i try to find
# eta is the learning rate
# (xt,yt) is the t^th example
# update rule : f = (1-lambda*eta)*f_{t-1} + eta*sigma*yt*K(xt,.)
def update_rule(self,alpha,eta,lmbda,y,X,n_samples,xt,yt):
param1 = (1-lmbda * eta)*alpha
y_prediction = self.get_prediction(X,alpha,n_samples,xt)
kernel_value = self.get_kernel(X,xt)
param2 = eta * self.get_sigma(yt,y_prediction)*yt.item(0)*kernel_value
return param1 + param2
# go through all of the examples
# try to find minimum
def gradient_descent(self,n_samples,X,y,alpha,eta,lmbda):
for i in xrange(n_samples):
alpha = self.update_rule(alpha,eta,lmbda,y,X,n_samples,X[i],y[i])
return alpha
此程序不适用于我的数据。看来我错过了一些东西。我想知道这个基本想法是否属实。
- 这就像是一个梯度下降的实现。为了找到支持向量,我应该计算向量,其中0为预测函数?
- 我应该如何更新eta?
谢谢。
Alpha是(features_number×1)的矩阵是吗? – yossarianlives
@yossarianlives alpha是一个具有数据集编号长度(xi,n数)的向量 – lennon310
ok然后在代码中使用alpha是真实的,但是我仍然不明白为什么我的代码没有给出好的分类 – yossarianlives