How to write cost function formula from Andrew Ng assignment in Octave?

Question

My implementation (see below) gives the scalar value 3.18, which is not the right answer. The value should be 0.693. Where does my code deviate from the equation?

Her

Answer 1

This is the code for the sigmoid function which I think you have made mistake in:

function g = sigmoid(z)
   g = zeros(size(z));
   temp=1+exp(-1.*z);
   g=1./temp;
end


function [J, grad] = costFunction(theta, X, y)
   m = length(y); 
   J = 0;
   grad = zeros(size(theta));
   h=X*theta;
   xtemp=sigmoid(h);
   temp1=(-y'*log(xtemp));
   temp2=(1-y)'*log(1-xtemp);
   J=1/m*sum(temp1-temp2);
   grad=1/m*(X'*(xtemp-y));
end

And I think it should be (1-y)' as shown in temp2=(1-y)'