def val_dataloader(self) -> ArithmeticIterator:  # type: ignore
        """
        Used by pytorch_lighting

        :returns: an iterator for self.train_dataset
        """
        device = self.transformer.embedding.weight.device
        iterator = ArithmeticIterator(
            self.val_dataset,
            device,
            batchsize_hint=-1,  # no need to batch validation data
        )
        return iterator

        Used by pytorch_lighting

        :returns: an iterator for self.train_dataset
        
grok/training.py