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This repository contains the source code accompanying the paper:

Group Equivariant Stand-Alone Self-Attention For Vision [Slides] [Demos]
David W. Romero & Jean-Baptiste Cordonnier, ICLR 2021.

We provide a general self-attention formulation to impose group equivariance to arbitrary symmetry groups. This is achieved by defining positional encodings that are invariant to the action of the group considered. Since the group acts on the positional encoding directly, group equivariant self-attention networks (GSA-Nets) are steerable by nature. Our experiments on vision benchmarks demonstrate consistent improvements of GSA-Nets over non-equivariant self-attention networks.

This repository is organized as follows:

• g_selfatt contains the main PyTorch library of our model.

• datasets implements Dataset wrappers for the datasets used.

• demo includes some minimalistic examples on the usage of our approach as well as the construction of Group Equivariant Self-Attention Networks (GSA-Nets). These files also demonstrate empirically the equivariance properties of our model.

• models contains the models used throughout our experiments.

• runs contains the command lines used to obtain the results reported in our experiments.

• saved contains various pretrained models.

In order to reproduce our results, please first install the required dependencies. This can be done by:

conda env create -f conda_requirements.txt

This will create the conda environment g_selfatt with the correct dependencies.

The same conda environment can be created with pip by running:

conda create -n g_selfatt python=3.7
conda activate g_selfatt
conda install pytorch==1.6.0 torchvision==0.7.0 cudatoolkit=10.1 -c pytorch
pip install -r requirements.txt

When running experiments on rotMNIST or CIFAR10, the data will be downloaded automatically. For the PCam dataset, though, this needs to be done manually (Dataset size = ~7GB).

We use an ImageFolder structure for our experiments. A file containing the entire dataset in this format can be downloaded from: https://drive.google.com/file/d/1THSEUCO3zg74NKf_eb3ysKiiq2182iMH/view?usp=sharing (~7GB). Once downloaded, please extract the data in ./data.

The dataset structure should look as follows:

./data
+-> PCam
    +--> test
    |     +--> no_tumor
    |     +--> tumor
    +--> train
    |     +--> no_tumor
    |     +--> tumor
    +--> valid
         +--> no_tumor
         +--> tumor

To reproduce the experiments in the paper, please follow the configurations given in runs/README.md

Specifications on the parameters specified via the argsparser can be found in the corresponding config.py file.

To use pretrained models, please add the argument --config.pretrained=True to the corresponding execution line.

We leveraged atomatic mixed precision (AMP) torch.cuda.amp in some of our experiments , i.e., on the rotMNIST dataset. We observed that using AMP simultaneously with learning rate schedulers made all our models diverge. Therefore, we disable AMP whenever learning rate schedulers are used.

Our initial experiments used a torch.nn.Embedding layer as positional encoding. However, this type of layer does not allow for rotations finer than 90 degrees. We solve this by replacing torch.nn.Embedding layers with a small MLP.

We provide a simplified version of the code used to construct GSA-Nets, which you can easily incorporate in your own project in demo/Construct_your_own_GSA-Net.ipynb.

If you found this work useful in your research, please consider citing:

@inproceedings{romero2021group,
  title={Group Equivariant Stand-Alone Self-Attention For Vision},
  author={David W. Romero and Jean-Baptiste Cordonnier},
  booktitle={International Conference on Learning Representations},
  year={2021},
  url={https://openreview.net/forum?id=JkfYjnOEo6M}
}

We gratefully acknowledge Robert-Jan Bruintjes, Fabian Fuchs, Erik Bekkers, Andreas Loukas, Mark Hoogendoorn and our anonymous reviewers for their valuable comments on early versions of this work. David W. Romero is financed as part of the Efficient Deep Learning (EDL) programme (grant number P16-25), partly funded by the Dutch Research Council (NWO) and Semiotic Labs. Jean-Baptiste Cordonnier is financed by the Swiss Data Science Center (SDSC). Both authors are thankful to everyone involved in funding this work. This work was carried out on the Dutch national e-infrastructure with the support of SURF Cooperative.