线性回归（Gradient descent update） - 训练集err不仅仅是测试

Question

我的算法就像：

数据存储为：

data = [record1, record2, ... ]
    where record1 is [1, x1, x2 ..., x_m] m feature values for that record
theta is parameter of linear regression function, theta is vector of size m+1
y is true label, again array of length, len(data). (y[0] is true value for record 0)

线性回归随机更新：

while True:
    for i in range(len(data)):
        x = data[i]
        for t in range(0, m):
            theta[t] = theta[t] - my_lambda * (np.dot(theta, x) - y[i]) * x[t]
        j_theta = compute_J_of_theta(data, y, theta)
    print "Iteration #: ", iterations, " j_theta ", j_theta
    if j_theta < 5000:
        #print "******************** FINALLY CONVERGED!!!! ********************" 
        break

compute_j_of_theta(data, y, theta):
"""
Convergence criteria,
compute J(theta) = 1/2M sum (h_theta(x_t) - y_t)**2
"""
temp = 0
for i in range(0, len(data)):
    x = data[i]
    temp += (np.dot(theta, x) - y[i])**2
return temp/2*M

my_lambda非常小 最初theta是0矢量，大小为m + 1

Que：训练集错误不只是测试...为什么？这有什么问题？ 编辑1： 在计算错误

时，这是我的愚蠢错误