def forward(self, model, sample, reduce=True):
        """Compute the loss for the given sample.

        Returns a tuple with three elements:
        1) the loss
        2) the sample size, which is used as the denominator for the gradient
        3) logging outputs to display while training
        """
        net_output = model(**sample["net_input"])
        loss, nll_loss = self.compute_loss(model, net_output, sample, reduce=reduce)
        sample_size = (
            sample["target"].size(0) if self.sentence_avg else sample["ntokens"]
        )
        logging_output = {
            "loss": loss.data,
            "nll_loss": nll_loss.data,
            "ntokens": sample["ntokens"],
            "nsentences": sample["target"].size(0),
            "sample_size": sample_size,
        }
        if self.report_accuracy:
            n_correct, total = self.compute_accuracy(model, net_output, sample)
            logging_output["n_correct"] = utils.item(n_correct.data)
            logging_output["total"] = utils.item(total.data)
        return loss, sample_size, logging_output
Compute the loss for the given sample.

        Returns a tuple with three elements:
        1) the loss
        2) the sample size, which is used as the denominator for the gradient
        3) logging outputs to display while training
        
decoding/IAD/fairseq/fairseq/criterions/label_smoothed_cross_entropy.py