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Title: DivideMix: Learning with Noisy Labels as Semi-supervised Learning

Paper content:
Deep neural networks are known to be annotation-hungry.
Numerous efforts have been devoted to reducing the annotation cost when learning with deep networks.
Two prominent directions include learning with noisy labels and semi-supervised learning by exploiting unlabeled data.
In this work, we propose DivideMix, a novel framework for learning with noisy labels by leveraging semi-supervised learning techniques.
In particular, DivideMix models the per-sample loss distribution with a mixture model to dynamically divide the training data into a labeled set with clean samples and an unlabeled set with noisy samples, and trains the model on both the labeled and unlabeled data in a semi-supervised manner.
To avoid confirmation bias, we simultaneously train two diverged networks where each network uses the dataset division from the other network.
During the semi-supervised training phase, we improve the MixMatch strategy by performing label co-refinement and label co-guessing on labeled and unlabeled samples, respectively.
Experiments on multiple benchmark datasets demonstrate substantial improvements over state-of-the-art methods.
Code is available at https://github.com/LiJunnan1992/DivideMix .
The remarkable success in training deep neural networks (DNNs) is largely attributed to the collection of large datasets with human annotated labels.
However, it is extremely expensive and time-consuming to label extensive data with high-quality annotations.
On the other hand, there exist alternative and inexpensive methods for mining large-scale data with labels, such as querying commercial search engines (Li et al., 2017a) , downloading social media images with tags (Mahajan et al., 2018) , leveraging machine-generated labels (Kuznetsova et al., 2018) , or using a single annotator to label each sample (Tanno et al., 2019) .
These alternative methods inevitably yield samples with noisy labels.
A recent study (Zhang et al., 2017) shows that DNNs can easily overfit to noisy labels and results in poor generalization performance.
Existing methods on learning with noisy labels (LNL) primarily take a loss correction approach.
Some methods estimate the noise transition matrix and use it to correct the loss function (Patrini et al., 2017; Goldberger & Ben-Reuven, 2017) .
However, correctly estimating the noise transition matrix is challenging.
Some methods leverage the predictions from DNNs to correct labels and modify the loss accordingly (Reed et al., 2015; Tanaka et al., 2018) .
These methods do not perform well under high noise ratio as the predictions from DNNs would dominate training and cause overfitting.
To overcome this, Arazo et al. (2019) adopt MixUp augmentation.
Another approach selects or reweights samples so that noisy samples contribute less to the loss (Jiang et al., 2018; Ren et al., 2018) .
A challenging issue is to design a reliable criteria to select clean samples.
It has been shown that DNNs tend to learn simple patterns first before fitting label noise (Arpit et al., 2017) .
Therefore, many methods treat samples with small loss as clean ones (Jiang et al., 2018; Arazo et al., 2019) .
Among those methods, Co-teaching (Han et al., 2018) and Co-teaching+ train two networks where each network selects small-loss samples in a mini-batch to train the other.
Another active area of research that also aims to reduce annotation cost is semi-supervised learning (SSL).
In SSL, the training data consists of unlabeled samples in addition to the labeled samples.
Significant progress has been made in leveraging unlabeled samples by enforcing the model to produce low entropy predictions on unlabeled data (Grandvalet & Bengio, 2004) or consistent predictions on perturbed input (Laine & Aila, 2017; Tarvainen & Valpola, 2017; Miyato et al., 2019) .
Recently, Berthelot et al. (2019) propose MixMatch, which unifies several dominant SSL approaches in one framework and achieves state-of-the-art performance.
Despite the individual advances in LNL and SSL, their connection has been underexplored.
In this work, we propose DivideMix, which addresses learning with label noise in a semi-supervised manner.
Different from most existing LNL approaches, DivideMix discards the sample labels that are highly likely to be noisy, and leverages the noisy samples as unlabeled data to regularize the model from overfitting and improve generalization performance.
The key contributions of this work are:
• We propose co-divide, which trains two networks simultaneously.
For each network, we dynamically fit a Gaussian Mixture Model (GMM) on its per-sample loss distribution to divide the training samples into a labeled set and an unlabeled set.
The divided data is then used to train the other network.
Co-divide keeps the two networks diverged, so that they can filter different types of error and avoid confirmation bias in self-training.
• During SSL phase, we improve MixMatch with label co-refinement and co-guessing to account for label noise.
For labeled samples, we refine their ground-truth labels using the network's predictions guided by the GMM for the other network.
For unlabeled samples, we use the ensemble of both networks to make reliable guesses for their labels.
• We experimentally show that DivideMix significantly advances state-of-the-art results on multiple benchmarks with different types and levels of label noise.
We also provide extensive ablation study and qualitative results to examine the effect of different components.
2 RELATED WORK
In this paper, we propose DivideMix for learning with noisy labels by leveraging SSL.
Our method trains two networks simultaneously and achieves robustness to noise through dataset co-divide, label co-refinement and co-guessing.
Through extensive experiments across multiple datasets, we show that DivideMix consistently exhibits substantial performance improvements compared to state-of-the-art methods.
For future work, we are interested in incorporating additional ideas from SSL to LNL, and vice versa.
Furthermore, we are also interested in adapting DivideMix to other domains such as NLP.

assistant: text: We propose a novel semi-supervised learning approach with SOTA performance on combating learning with noisy labels.