"""
Cost functions.
"""

import theano.tensor as T

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

def cross_entropy(target, output, axis=1):
    return -T.mean(target * T.log2(output) + (1 - target) * T.log2(1 - output), axis=axis)