Mercurial > pylearn
view pylearn/algorithms/cost.py @ 1498:0f326860210e
Merged
author | Olivier Delalleau <delallea@iro> |
---|---|
date | Thu, 01 Sep 2011 13:35:15 -0400 |
parents | e915f5c9bb21 |
children |
line wrap: on
line source
""" Cost functions. @note: All of these functions return one cost per example. So it is your job to perform a tensor.sum over the individual example losses. @todo: Make a Cost class, with a particular contract. @todo: It would be nice to implement a hinge loss, with a particular margin. """ import theano.tensor as T from theano.tensor.xlogx import xlogx def quadratic(target, output, axis=1): return T.mean(T.sqr(target - output), axis=axis) def cross_entropy(target, output, mean_axis=0, sum_axis=1): """ This is the cross-entropy over a binomial event, in which each dimension is an independent binomial trial. @todo: This is essentially duplicated as nnet_ops.binary_crossentropy @warning: OUTPUT and TARGET are reversed in nnet_ops.binary_crossentropy """ XE = target * T.log(output) + (1 - target) * T.log(1 - output) return -T.mean(T.sum(XE, axis=sum_axis),axis=mean_axis) def KL_divergence(target, output): """ This is a KL divergence over a binomial event, in which each dimension is an independent binomial trial. @note: We do not compute the mean, because if target and output have different shapes then the result will be garbled. """ return -(target * T.log(output) + (1 - target) * T.log(1 - output)) \ + (xlogx(target) + xlogx(1 - target)) # return cross_entropy(target, output, axis) - cross_entropy(target, target, axis)