tensorflow_backend.py 文件源码

def categorical_crossentropy(output, target, from_logits=False):
    '''Categorical crossentropy between an output tensor
    and a target tensor, where the target is a tensor of the same
    shape as the output.
    '''
    # Note: tf.nn.softmax_cross_entropy_with_logits
    # expects logits, Keras expects probabilities.
    if not from_logits:
        # scale preds so that the class probas of each sample sum to 1
        output /= tf.reduce_sum(output,
                                reduction_indices=len(output.get_shape()) - 1,
                                keep_dims=True)
        # manual computation of crossentropy
        epsilon = _to_tensor(_EPSILON, output.dtype.base_dtype)
        output = tf.clip_by_value(output, epsilon, 1. - epsilon)
        return - tf.reduce_sum(target * tf.log(output),
                               reduction_indices=len(output.get_shape()) - 1)
    else:
        return tf.nn.softmax_cross_entropy_with_logits(output, target)