def METHOD_NAME(self, *args, **kwargs):
    """
    :returns: loss estimated using validation batch
    :rtype: float
    Calculates loss on validation batch. If no validation batch is set,
    will set one by calling `set_validation_batch`. Can be used to track
    the loss in a less noisy way during training.
    Arguments are passed to the model and guide.
    """
    if self.validation_batch is None:
        self.set_validation_batch(*args, **kwargs)
    return self.loss_and_grads(False, self.validation_batch, *args, **kwargs)