def cost(self, Y, Y_hat, batch_axis):
        raise NotImplementedError(
            str(type(self)) + " does not implement cost function.")
See :meth:`I18n.format_percent`.
dataset/ETHPy150Open lisa-lab/pylearn2/pylearn2/models/mlp.py/ConvNonlinearity.cost--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/lib/webapp2-2.3/webapp2_extras/i18n.py/format_percent