"""
Common training criteria.
"""
import theano
import theano.tensor as T
from tags import tags

@tags('cost','binary','cross-entropy')
def binary_crossentropy(output, target):
    """ Compute the crossentropy of binary output wrt binary target.

    .. math::
                L_{CE} \equiv t\log(o) + (1-t)\log(1-o)

    :type output: Theano variable
    :param output: Binary output or prediction :math:`\in[0,1]`
    :type target: Theano variable
    :param target: Binary target usually :math:`\in\{0,1\}`
    """
    return -(target * T.log(output) + (1.0 - target) * T.log(1.0 - output))


# This file seems like it has some overlap with theano.tensor.nnet.  Which functions should go
# in which file?

@tags('cost','binary','cross-entropy', 'sigmoid')
def sigmoid_crossentropy(output_act, target):
    """ Stable crossentropy of a sigmoid activation

    .. math::
                L_{CE} \equiv t\log(\sigma(a)) + (1-t)\log(1-\sigma(a))

    :type output_act: Theano variable
    :param output: Activation
    :type target: Theano variable
    :param target: Binary target usually :math:`\in\{0,1\}`
    """
    return target * (- T.log(1.0 + T.exp(-output_act))) + (1.0 - target) * (- T.log(1.0 + T.exp(output_act)))

@tags('cost','binary','cross-entropy', 'tanh')
def tanh_crossentropy(output_act, target):
    """ Stable crossentropy of a tanh activation

    .. math::
                L_{CE} \equiv t\log(\\frac{1+\\tanh(a)}2) + (1-t)\log(\\frac{1-\\tanh(a)}2)

    :type output_act: Theano variable
    :param output: Activation
    :type target: Theano variable
    :param target: Binary target usually :math:`\in\{0,1\}`
    """
    return sigmoid_crossentropy(2.0*output_act, target)

@tags('cost','binary','cross-entropy', 'tanh', 'abs')
def abstanh_crossentropy(output_act, target):
    """ Stable crossentropy of a absolute value tanh activation

    .. math::
                L_{CE} \equiv t\log(\\frac{1+\\tanh(|a|)}2) + (1-t)\log(\\frac{1-\\tanh(|a|)}2)

    :type output_act: Theano variable
    :param output: Activation
    :type target: Theano variable
    :param target: Binary target usually :math:`\in\{0,1\}`
    """
    return tanh_crossentropy(T.abs_(output_act), target)

@tags('cost','binary','cross-entropy', 'tanh', "normalized")
def normtanh_crossentropy(output_act, target):
    """ Stable crossentropy of a "normalized" tanh activation (LeCun)

    .. math::
                L_{CE} \equiv t\log(\\frac{1+\\tanh(0.6666a)}2) + (1-t)\log(\\frac{1-\\tanh(0.6666a)}2)

    :type output_act: Theano variable
    :param output: Activation
    :type target: Theano variable
    :param target: Binary target usually :math:`\in\{0,1\}`
    """
    return tanh_crossentropy(0.6666*output_act, target)