Something for (almost) nothing: improving deep ensemble calibration using unlabeled data

We present a method to improve the calibration of deep ensembles in the small training data regime in the presence of unlabeled data. Our approach is extremely simple to implement: given an unlabeled set, for each unlabeled data point, we simply fit a different randomly selected label with each ensemble member. We provide a theoretical analysis based on a PAC-Bayes bound which guarantees that if we fit such a labeling on unlabeled data, and the true labels on the training data, we obtain low negative log-likelihood and high ensemble diversity on testing samples. Empirically, through detailed experiments, we find that for low to moderately-sized training sets, our ensembles are more diverse and provide better calibration than standard ensembles, sometimes significantly.

$\nu$-ensembles are trained based on the following algorithm

Below we see some results on the CIFAR-10 and CIFAR-100 datasets

🔖 Usage.

• utils/models implements all the models used for the evaluation
• utils/metrics implements all the metrics used for the evaluation
• utils/train implements both the $\nu$-ensembles and standard ensembles
• utils/benchmarking_algorithms impements dice-ensembles, masegosa ensembles and agree to disagree ensembles

The code is currently launched from ablation_studies and ablation_studies_other_benchmarks.

The experiment folders are structured as training_set_#1@#2_..._ens_size#3 where #1 is the size of the training set #2 is the size of the unlabeled set, and #3 is the size of the ensemble. Experimental runs are configured through hydra. The configuration files exist in the conf folders of each experiment.

• train_models.py trains a model according to the hydra configuration in conf.
• evaluate_models.py evaluates trained models on the test set
• evaluate_corruptions.py evaluates trained models on common image corruptions with 5 levels of intensity (this script works only for the CIFAR-10 dataset).

The hyperparameter ranges used to recreate the experiments of the paper can be found as train_....slurm and tune_....slurm files in each experiment folder. tune_....slurm files were used for optimizing the hyperparameters (without storing the weights), while train_....slurm were used to store the final weights.

An example python command to train a LeNet architecture with the $\nu$-ensembles algorithm is

python train_models.py --multirun hyperparameters=diverse server=jeanzay hyperparameters.model='LeNet' optimizer=adamw hyperparameters.epochs=100 optimizer.learning_rate=0.001 hyperparameters.beta=0.01 hydra.sweeper.direction=minimize hydra.job.chdir=True hydra/sweeper=optuna hydra/sweeper/sampler=grid hydra.sweep.dir='multirun/train_diverse_lenet'

note that in the above command, even though the Optuna hyperparameter is invoked only a single instance is given for each hyperparameter. Thus only a single network is finally trained.

📝 Citation

When citing this repository on your scientific publications please use the following BibTeX citation:

@article{pitas2023something,
  title={Something for (almost) nothing: Improving deep ensemble calibration using unlabeled data},
  author={Pitas, Konstantinos and Arbel, Julyan},
  journal={arXiv preprint arXiv:2310.02885},
  year={2023}
}

✉️ Contact Information

You can contact me at any of my social network profiles:

• 💼 Linkedin: https://www.linkedin.com/in/konstantinos-pitas-lts2-epfl/
• Github: https://github.com/konstantinos-p

Or via email at cwstas2007@hotmail.com

⚠️ Disclaimer

This Python package has been made for research purposes.