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# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
import math
import torch
import torch.nn.functional as F
from fairseq import utils
from fairseq.criterions import FairseqCriterion, register_criterion
@register_criterion("sentence_prediction_r3f")
class SentencePredictionR3F(FairseqCriterion):
def __init__(
self,
task,
eps,
r3f_lambda,
noise_type,
classification_head_name,
regression_target,
):
super().__init__(task)
self.eps = eps
self.r3f_lambda = r3f_lambda
self.noise_type = noise_type
self.classification_head_name = classification_head_name
self.regression_target = regression_target
if self.noise_type in {"normal"}:
self.noise_sampler = torch.distributions.normal.Normal(
loc=0.0, scale=self.eps
)
elif self.noise_type == "uniform":
self.noise_sampler = torch.distributions.uniform.Uniform(
low=-self.eps, high=self.eps
)
else:
raise Exception(f"unrecognized noise type {self.noise_type}")
@staticmethod
def add_args(parser):
# fmt: off
parser.add_argument('--eps', type=float, default=1e-5,
help='noise eps')
parser.add_argument('--r3f-lambda', type=float, default=1.0,
help='lambda for combining logistic loss and noisy KL loss')
parser.add_argument('--noise-type', type=str, default='uniform',
choices=['normal', 'uniform'],
help='type of noises for RXF methods')
parser.add_argument('--classification-head-name',
default='sentence_classification_head',
help='name of the classification head to use')
parser.add_argument('--regression-target', action='store_true')
# fmt: on
def _get_symm_kl(self, noised_logits, input_logits):
return (
F.kl_div(
F.log_softmax(noised_logits, dim=-1, dtype=torch.float32),
F.softmax(input_logits, dim=-1, dtype=torch.float32),
None,
None,
"sum",
)
+ F.kl_div(
F.log_softmax(input_logits, dim=-1, dtype=torch.float32),
F.softmax(noised_logits, dim=-1, dtype=torch.float32),
None,
None,
"sum",
)
) / noised_logits.size(0)
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
"""
assert (
hasattr(model, "classification_heads")
and self.classification_head_name in model.classification_heads
), "model must provide sentence classification head for --criterion=sentence_prediction"
token_embeddings = model.encoder.sentence_encoder.embed_tokens(
sample["net_input"]["src_tokens"]
)
input_logits, _ = model(
**sample["net_input"],
features_only=True,
classification_head_name=self.classification_head_name,
token_embeddings=token_embeddings,
)
if model.training and self.noise_sampler:
noise = self.noise_sampler.sample(sample_shape=token_embeddings.shape).to(
token_embeddings
)
noised_embeddings = token_embeddings.detach().clone() + noise
noised_logits, _ = model(
**sample["net_input"],
features_only=True,
classification_head_name=self.classification_head_name,
token_embeddings=noised_embeddings,
)
symm_kl = self._get_symm_kl(noised_logits, input_logits)
else:
symm_kl = 0
targets = model.get_targets(sample, [input_logits]).view(-1)
sample_size = targets.numel()
if not self.regression_target:
loss = F.nll_loss(
F.log_softmax(input_logits, dim=-1, dtype=torch.float32),
targets,
reduction="sum",
)
if model.training:
symm_kl = symm_kl * sample_size
loss = loss + self.r3f_lambda * symm_kl
else:
logits = input_logits.squeeze().float()
targets = targets.float()
loss = F.mse_loss(logits, targets, reduction="sum")
logging_output = {
"loss": utils.item(loss.data) if reduce else loss.data,
"ntokens": sample["ntokens"],
"nsentences": sample_size,
"sample_size": sample_size,
}
if not self.regression_target:
preds = input_logits.max(dim=1)[1]
logging_output.update(ncorrect=(preds == targets).sum().item())
if model.training and self.noise_sampler:
logging_output.update(
symm_kl=utils.item(symm_kl.data) if reduce else symm_kl.data
)
return loss, sample_size, logging_output
@staticmethod
def aggregate_logging_outputs(logging_outputs):
"""Aggregate logging outputs from data parallel training."""
loss_sum = sum(log.get("loss", 0) for log in logging_outputs)
symm_kl_sum = sum(log.get("symm_kl", 0) for log in logging_outputs)
ntokens = sum(log.get("ntokens", 0) for log in logging_outputs)
nsentences = sum(log.get("nsentences", 0) for log in logging_outputs)
sample_size = sum(log.get("sample_size", 0) for log in logging_outputs)
agg_output = {
"loss": loss_sum / sample_size / math.log(2),
"symm_kl": symm_kl_sum / sample_size,
"ntokens": ntokens,
"nsentences": nsentences,
"sample_size": sample_size,
}
if len(logging_outputs) > 0 and "ncorrect" in logging_outputs[0]:
ncorrect = sum(log.get("ncorrect", 0) for log in logging_outputs)
agg_output.update(accuracy=ncorrect / nsentences)
if sample_size != ntokens:
agg_output["nll_loss"] = loss_sum / ntokens / math.log(2)
return agg_output
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