'Calculates the average loss of the examples in a mini-batch.
Args:
unused_predictions: a 2-d tensor storing the prediction scores, in which
each row represents a sample in the mini-batch and each column
represents a class.
unused_labels: a 2-d tensor storing the labels, which has the same shape
as the unused_predictions. The labels must be in the range of 0 and 1.
unused_params: loss specific parameters.
Returns:
A scalar loss tensor.'

def calculate_loss(self, unused_predictions, unused_labels, **unused_params):

    raise NotImplementedError()
