How to code cross entropy error function in matlab

Question

Can someone help me in coding the cross entropy loss function in Matlab. I want to code it in single line using @ i.e function handle. The error function is

E(w) = 1/N* summation(n=1..N) ln(1+ exp( -y(n)*w*x(n) ) )

N is the total number of training examples. 'w' are the parameters of the function. 'x' is a vector containing features of a training example and 'y' is the corresponding label.

Each evaluation of 'E' requires processing of all the training examples.

Thank you very much

Answer 1

I'm not sure why this is so hard, but here's one version

E = @(w)mean(log1p(exp(-y.*w.*x)));

without knowing the dimensions of x, w, and y, I can't be sure that one or more of them don't need to be transposed (or if w is even a vector).