Cheers for feed back. The cost/error function is simply the 1/2(a-y)^2 ...(I think its called the square cost function). I wrote all the code myself (no libs) so people like yourself can see all steps required to train an ANN. I was thinking of getting things working for GPU, which should even make cython look slow. All depends on how much attention I get. Right now it's still got quite a few bugs, and in general is under done.