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Description:

pyhf 0.7.6

pure-python fitting/limit-setting/interval estimation HistFactory-style

The HistFactory p.d.f. template
[CERN-OPEN-2012-016] is per-se
independent of its implementation in ROOT and sometimes, it’s useful to
be able to run statistical analysis outside of ROOT, RooFit, RooStats
framework.
This repo is a pure-python implementation of that statistical model for
multi-bin histogram-based analysis and its interval estimation is based
on the asymptotic formulas of “Asymptotic formulae for likelihood-based
tests of new physics”
[arXiv:1007.1727]. The aim is also
to support modern computational graph libraries such as PyTorch and
TensorFlow in order to make use of features such as autodifferentiation
and GPU acceleration.

User Guide
For an in depth walkthrough of usage of the latest release of pyhf visit the pyhf tutorial.

Hello World
This is how you use the pyhf Python API to build a statistical model and run basic inference:
>>> import pyhf
>>> pyhf.set_backend("numpy")
>>> model = pyhf.simplemodels.uncorrelated_background(
... signal=[12.0, 11.0], bkg=[50.0, 52.0], bkg_uncertainty=[3.0, 7.0]
... )
>>> data = [51, 48] + model.config.auxdata
>>> test_mu = 1.0
>>> CLs_obs, CLs_exp = pyhf.infer.hypotest(
... test_mu, data, model, test_stat="qtilde", return_expected=True
... )
>>> print(f"Observed: {CLs_obs:.8f}, Expected: {CLs_exp:.8f}")
Observed: 0.05251497, Expected: 0.06445321
Alternatively the statistical model and observational data can be read from its serialized JSON representation (see next section).
>>> import pyhf
>>> import requests
>>> pyhf.set_backend("numpy")
>>> url = "https://raw.githubusercontent.com/scikit-hep/pyhf/main/docs/examples/json/2-bin_1-channel.json"
>>> wspace = pyhf.Workspace(requests.get(url).json())
>>> model = wspace.model()
>>> data = wspace.data(model)
>>> test_mu = 1.0
>>> CLs_obs, CLs_exp = pyhf.infer.hypotest(
... test_mu, data, model, test_stat="qtilde", return_expected=True
... )
>>> print(f"Observed: {CLs_obs:.8f}, Expected: {CLs_exp:.8f}")
Observed: 0.35998409, Expected: 0.35998409
Finally, you can also use the command line interface that pyhf provides
$ cat << EOF | tee likelihood.json | pyhf cls
{
"channels": [
{ "name": "singlechannel",
"samples": [
{ "name": "signal",
"data": [12.0, 11.0],
"modifiers": [ { "name": "mu", "type": "normfactor", "data": null} ]
},
{ "name": "background",
"data": [50.0, 52.0],
"modifiers": [ {"name": "uncorr_bkguncrt", "type": "shapesys", "data": [3.0, 7.0]} ]
}
]
}
],
"observations": [
{ "name": "singlechannel", "data": [51.0, 48.0] }
],
"measurements": [
{ "name": "Measurement", "config": {"poi": "mu", "parameters": []} }
],
"version": "1.0.0"
}
EOF
which should produce the following JSON output:
{
"CLs_exp": [
0.0026062609501074576,
0.01382005356161206,
0.06445320535890459,
0.23525643861460702,
0.573036205919389
],
"CLs_obs": 0.05251497423736956
}

What does it support

Implemented variations:

☑ HistoSys
☑ OverallSys
☑ ShapeSys
☑ NormFactor
☑ Multiple Channels
☑ Import from XML + ROOT via uproot
☑ ShapeFactor
☑ StatError
☑ Lumi Uncertainty
☑ Non-asymptotic calculators

Computational Backends:

☑ NumPy
☑ PyTorch
☑ TensorFlow
☑ JAX

Optimizers:

☑ SciPy (scipy.optimize)
☑ MINUIT (iminuit)

All backends can be used in combination with all optimizers.
Custom user backends and optimizers can be used as well.

Todo

☐ StatConfig

results obtained from this package are validated against output computed
from HistFactory workspaces

A one bin example
import pyhf
import numpy as np
import matplotlib.pyplot as plt
from pyhf.contrib.viz import brazil

pyhf.set_backend("numpy")
model = pyhf.simplemodels.uncorrelated_background(
signal=[10.0], bkg=[50.0], bkg_uncertainty=[7.0]
)
data = [55.0] + model.config.auxdata

poi_vals = np.linspace(0, 5, 41)
results = [
pyhf.infer.hypotest(
test_poi, data, model, test_stat="qtilde", return_expected_set=True
)
for test_poi in poi_vals
]

fig, ax = plt.subplots()
fig.set_size_inches(7, 5)
brazil.plot_results(poi_vals, results, ax=ax)
fig.show()
pyhf

ROOT

A two bin example
import pyhf
import numpy as np
import matplotlib.pyplot as plt
from pyhf.contrib.viz import brazil

pyhf.set_backend("numpy")
model = pyhf.simplemodels.uncorrelated_background(
signal=[30.0, 45.0], bkg=[100.0, 150.0], bkg_uncertainty=[15.0, 20.0]
)
data = [100.0, 145.0] + model.config.auxdata

poi_vals = np.linspace(0, 5, 41)
results = [
pyhf.infer.hypotest(
test_poi, data, model, test_stat="qtilde", return_expected_set=True
)
for test_poi in poi_vals
]

fig, ax = plt.subplots()
fig.set_size_inches(7, 5)
brazil.plot_results(poi_vals, results, ax=ax)
fig.show()
pyhf

ROOT

Installation
To install pyhf from PyPI with the NumPy backend run
python -m pip install pyhf
and to install pyhf with all additional backends run
python -m pip install pyhf[backends]
or a subset of the options.
To uninstall run
python -m pip uninstall pyhf

Documentation
For model specification, API reference, examples, and answers to FAQs visit the pyhf documentation.

Questions
If you have a question about the use of pyhf not covered in the
documentation, please ask a question
on the GitHub Discussions.
If you believe you have found a bug in pyhf, please report it in the
GitHub
Issues.
If you’re interested in getting updates from the pyhf dev team and release
announcements you can join the pyhf-announcements mailing list.

Citation
As noted in Use and Citations,
the preferred BibTeX entry for citation of pyhf includes both the
Zenodo archive and the
JOSS paper:
@software{pyhf,
author = {Lukas Heinrich and Matthew Feickert and Giordon Stark},
title = "{pyhf: v0.7.6}",
version = {0.7.6},
doi = {10.5281/zenodo.1169739},
url = {https://doi.org/10.5281/zenodo.1169739},
note = {https://github.com/scikit-hep/pyhf/releases/tag/v0.7.6}
}

@article{pyhf_joss,
doi = {10.21105/joss.02823},
url = {https://doi.org/10.21105/joss.02823},
year = {2021},
publisher = {The Open Journal},
volume = {6},
number = {58},
pages = {2823},
author = {Lukas Heinrich and Matthew Feickert and Giordon Stark and Kyle Cranmer},
title = {pyhf: pure-Python implementation of HistFactory statistical models},
journal = {Journal of Open Source Software}
}

Authors
pyhf is openly developed by Lukas Heinrich, Matthew Feickert, and Giordon Stark.
Please check the contribution statistics for a list of
contributors.

Milestones

2022-09-12: 2000 GitHub issues and pull requests. (See PR #2000)
2021-12-09: 1000 commits to the project. (See PR #1710)
2020-07-28: 1000 GitHub issues and pull requests. (See PR #1000)

Acknowledgements
Matthew Feickert has received support to work on pyhf provided by NSF
cooperative agreements OAC-1836650
and PHY-2323298 (IRIS-HEP)
and grant OAC-1450377 (DIANA/HEP).
pyhf is a NumFOCUS Affiliated Project.