view cost.py @ 479:fbfd3932fd00

typo
author James Bergstra <bergstrj@iro.umontreal.ca>
date Mon, 27 Oct 2008 17:28:48 -0400
parents d99fefbc9324
children 3daabc7f94ff
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.
"""

import theano.tensor as T
from xlogx import xlogx

def quadratic(target, output, axis=1):
    return T.mean(T.sqr(target - output), axis)

def cross_entropy(target, output, axis=1):
    """
    @todo: This is essentially duplicated as nnet_ops.binary_crossentropy
    @warning: OUTPUT and TARGET are reversed in nnet_ops.binary_crossentropy
    """
    return -T.mean(target * T.log(output) + (1 - target) * T.log(1 - output), axis=axis)

def KL_divergence(target, output):
    """
    @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)