如何使用octave对逻辑回归实现所有列子

Question

我正在学习吴恩达老师的machine learing,在用octave实现逻辑回归时发现代价函数并不能对所有列子都通用，请各位帮帮忙，要实现的函数：

代码：

 function [J, grad] = costFunction(theta, X, y)
 m = length(y);    % number of training examples
 J = 0;
grad = zeros(size(theta));
predictions = 0;

for i = 1:m
    J = J + (-y(i,:) * log(sigmoid (X(i,:)*theta))) - (1-y(i,:)) * log(1-sigmoid (X(i,:)*theta));   
end
predictions = sum(sigmoid (X*theta)) - y;
grad = predictions'* X / m;
J = J/m;

Answer 1

http://blog.sina.com.cn/s/blog_890c6aa301015mya.html