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import torch
import torch.nn as nn
import torch.nn.functional as F
from .cross_entropy import LabelSmoothingCrossEntropy
class JsdCrossEntropy(nn.Module):
""" Jensen-Shannon Divergence + Cross-Entropy Loss
Based on impl here: https://github.com/google-research/augmix/blob/master/imagenet.py
From paper: 'AugMix: A Simple Data Processing Method to Improve Robustness and Uncertainty -
https://arxiv.org/abs/1912.02781
Hacked together by / Copyright 2020 Ross Wightman
"""
def __init__(self, num_splits=3, alpha=12, smoothing=0.1):
super().__init__()
self.num_splits = num_splits
self.alpha = alpha
if smoothing is not None and smoothing > 0:
self.cross_entropy_loss = LabelSmoothingCrossEntropy(smoothing)
else:
self.cross_entropy_loss = torch.nn.CrossEntropyLoss()
def __call__(self, output, target):
split_size = output.shape[0] // self.num_splits
assert split_size * self.num_splits == output.shape[0]
logits_split = torch.split(output, split_size)
# Cross-entropy is only computed on clean images
loss = self.cross_entropy_loss(logits_split[0], target[:split_size])
probs = [F.softmax(logits, dim=1) for logits in logits_split]
# Clamp mixture distribution to avoid exploding KL divergence
logp_mixture = torch.clamp(torch.stack(probs).mean(axis=0), 1e-7, 1).log()
loss += self.alpha * sum([F.kl_div(
logp_mixture, p_split, reduction='batchmean') for p_split in probs]) / len(probs)
return loss
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