Symmetry Preserving Attention Networks

A library for training and evaluation SPANets on jet reconstruction tasks. Originally developed for ttbar analysis, this library now supports arbitrary event topologies and symmetry groups.

Version 2 Update

We recently pushed an updated version 2 of this library which adds several new features.

1. New configuration file format with more options on inputs and event topology.
2. Allow for several different inputs, including global inputs for additional context.
3. New Regression and Classification output heads for performing per-event or per-particle predictions.
4. Gated transformers and linear layers for more robust networks. Less hyperparameter optimization.

An example demonstrating these new features may be found here: docs/TTH.md.

Installation

You can install this package to use it outside of the repository after cloning.

git clone https://github.com/Alexanders101/SPANet
cd SPANet
pip install .

Alternatively, you can use pip install -e . to install in an editable mode.

Note

The configuration ini has been deprecated into a configuration yaml. The conversion should just be to change the syntax a bit, the values should remain the same. A conversion script is in the works.

The dataset format has also changed slighty, but old style datasets can be converted into a new style dataset using utils/convert_dataset.py.

The old codebase may always be accesed here: https://github.com/Alexanders101/SPANet/tree/v1.0

Dependencies

A list of the libraries necessary to fully train and evaluate SPANets. These are only the minimum versions that we tested, other versions might work.

Library	Minimum Version
python	3.9
numpy	1.22.1
sympy	1.11
scikit_learn	1.1
pytorch	1.12
pytorch-lightning	1.7
opt_einsum	3.3.0
h5py	2.10
numba	0.53.1

We have updated to using an anaconda environment for simpler dependency management. You can create the environment locally with the following conda / mamba commands:

conda env create -p ./environment --file environment.yaml
conda activate ./environment

Example

We have provided a simple ttbar example in order to demonstrate how to define events, construct datasets, and train & evaluate a network.

Refer to this page for a detailed walk-through for the ttbar example.

The full ttbar dataset may be downloaded here: http://mlphysics.ics.uci.edu/data/2021_ttbar/.

We also have a more advanced example demonstrating some of the additinoal inputs and outputs available on a semi-leptonic ttH event. Refer to this page for a detailed walk-through for the ttH example.

Usage

Using this library requires setting up several components. Refer to the following documentation pages in order to learn about the the different setup components, or just follow the ttbar example.

1. Defining the event topology.
2. Creating a training dataset.
3. Configuring training options.

Training

Once those steps are complete, you can begin training by calling spanet.train with your chosen parameters. For more information simply run python -m spanet.train --help

You can experiment with the provided example configuration and dataset for some ttbar events by calling python -m spanet.train -of options_files/full_hadronic_ttbar/example.json --gpus NUM_GPUS where NUM_GPUS is the number of gpus available on your machine.

Evaluation

Once training is complete, you may evalute a network on a testing dataset by running spanet.test with a path to your previously trained network and a file on which to evalute on.

For example, after running the previous training run on ttbar_example, you can evaluate the network again on the example dataset by running. python -m spanet.test ./spanet_output/version_0 -tf data/full_hadronic_ttbar/example.h5

Note that the included example file is very small and you will likely not see very good performance on it.

Exporting

Once you are happy with your model, you can export it to an ONNX file to use in external applications. This can be done by running spanet.export with the log directory and the desired output file. For example: python -m spanet.export ./spanet_output/version_0 spanet.onnx.

Note that only the neural network is able to be exported, and this network outputs the full reconstruction distributions for every event. Unfortunately, the reconstruction algorithm defined here cannot be exported as part of the ONNX graph. If your target application uses python, then you can simply use SPANet's selection algorithm, but non-python applications must define their own selection algorithm.

You may examine all of the inputs and outputs with the following snippet:

import onnxruntime    # to inference ONNX models, we use the ONNX Runtime

session = onnxruntime.InferenceSession(
    "./spanet.onnx", 
    providers=['CUDAExecutionProvider', 'CPUExecutionProvider']
)

print("Inputs:", [input.name for input in session.get_inputs()])
print("Outputs:", [output.name for output in session.get_outputs()])

Inputs

Input	Shape	DType
{sequential_input_1}_data	(B, N1, D1)	float
{sequential_input_1}_mask	(B, N1)	bool
{sequential_input_2}_data	(B, N2, D2)	float
{sequential_input_2}_mask	(B, N2)	bool
{global_input_1}_data	(B, 1, D1)	float
{global_input_1}_mask	(B, 1)	bool
{global_input_2}_data	(B, 1, D2)	float
{global_input_2}_mask	(B, 1)	bool

The ONNX model expects two inputs for every INPUT defined in the event file. Replace the values in the braces with their appropriate names. The data contains the features for each input. The features must be provided in the exact order that they are defined in the event file. Notice that global inputs require a dummy axis to be added to match the overall shape of the sequential inputs.

Log Features: Any features marked either log or log_normalize must have the following preprocessing transformation applied f(x) -> log(x + 1). You can skip this log preprocessing and have it performed by the network if you specify --input-log-transform. However, this operation is expensive to perform by the graph, so we recommend you apply it during your data pipeline for maximum efficiency.

Outputs

Output	Shape	DType
{event_particle_1}_assignment_probability	(B, N, N, ...)	float
{event_particle_2}_assignment_probability	(B, N, N, ...)	float
{event_particle_1}_detection_probability	(B)	float
{event_particle_2}_detection_probability	(B)	float
{regression_target_1}	(B)	float
{regression_target_2}	(B)	float
{classification_target_1}	(B, C)	float
{classification_target_2}	(B, C)	float

The ONNX model may produce any of the valid output heads. Each event partile defined produces an assignment distribution for its reconstruction. This distribution with be a singlet/doublet/triplet/etc. joint distribution depending on the number of decay products defined for each particle. The shape will reflect this number of products. For example, if a particle has two decay products, then its assignment_log_probability will have a shape of (B, N, N). Each particle also has associated with it a detection probability which indicates how likely the particle is to be reconstructable.

The additional outputs will only be present if you define any REGRESSION or CLASSIFICATION outputs in the event file. Each of the definitions will be add an extra output. The regression outputs simply contain the predicted value for each regression target. The classification outputs contain a distribution over possible classes for each target.

Log Probability vs. Probability For additional numerical stability, you may choose to output the log distributions, log P(x), for all probability outputs instead. If you specify --output-log-transform in the export script, then the *_assignment_probability and *_detection_probability outputs will be replaced with *_assignment_log_probability and *_detection_log_probability. The classification outputs will also be represented as log-probabilities, although the name will not change.

Citation

If you use this software for a publication, please cite the following:

@Article{10.21468/SciPostPhys.12.5.178,
	title={{SPANet: Generalized permutationless set assignment for particle physics  using symmetry preserving attention}},
	author={Alexander Shmakov and Michael James Fenton and Ta-Wei Ho and Shih-Chieh Hsu and Daniel Whiteson and Pierre Baldi},
	journal={SciPost Phys.},
	volume={12},
	pages={178},
	year={2022},
	publisher={SciPost},
	doi={10.21468/SciPostPhys.12.5.178},
	url={https://scipost.org/10.21468/SciPostPhys.12.5.178},
}