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Exphormers: Sparse Transformers for Graphs

In this work we introduce new sparse transformers for graph data, and use them in the GraphGPS framework. Our sparse transformers outperform BigBird and Performer in all cases we tried, which have been mainly designed for the natural language processing context; in many cases, we even get better results than full (dense attention) transformers. Our sparse transformer has three components: actual edges, expander graphs, and universal connectors or virtual nodes. We combine these components into a single sparse attention mechanism.

Python environment setup with Conda

conda create -n exphormer python=3.9
conda activate exphormer

conda install pytorch=1.10 torchvision torchaudio -c pytorch -c nvidia
conda install pyg=2.0.4 -c pyg -c conda-forge

# RDKit is required for OGB-LSC PCQM4Mv2 and datasets derived from it.  
conda install openbabel fsspec rdkit -c conda-forge

pip install torchmetrics
pip install performer-pytorch
pip install ogb
pip install tensorboardX
pip install wandb

conda clean --all

Running Exphormer

conda activate exphormer

# Running Exphormer for LRGB Datasets
python main.py --cfg configs/Exphormer_LRGB/peptides-struct-EX.yaml  wandb.use False

# Running Exphormer for Cifar10
python main.py --cfg configs/Exphormer/cifar10.yaml  wandb.use False

You can also set your wandb settings and use wandb.

Guide on configs files

Most of the configs are shared with GraphGPS code. You can change the following parameters in the config files for different parameters and variants of the Exphormer:

prep:
  exp: True  # Set True for using expander graphs, set False otherwise. 
    # Alternatively you can set use_exp_edges to False.
    # In this case expander graphs will be calculated but not used in the Exphormer. 
  exp_deg: 5 # Set the degree of the expander graph.
    # Please note that if you set this to d, the algorithm will use d permutations 
    # or d Hamiltonian cycles, so the actual degree of the expander graph will be 2d
  exp_algorithm: 'Random-d' # Options are ['Random-d', 'Random-d2', 'Hamiltonian].
    # Default value is 'Random-d'
  add_edge_index: True # Set True if you want to add real edges beside expander edges
  num_virt_node: 1 # Set 0 for not using virtual nodes 
    # otherwise set the number of virtual nodes you want to use.

Citation

Our work can be cited using the following bibtex:

@inproceedings{shirzad2023exphormer,
  title={Exphormer: Sparse transformers for graphs},
  author={Shirzad, Hamed and Velingker, Ameya and Venkatachalam, Balaji and Sutherland, Danica J and Sinop, Ali Kemal},
  booktitle={International Conference on Machine Learning},
  eprinttype={arXiv}, eprint={2303.06147},
  year={2023}
}