Package: pyjet
pyjethas been maintained minimalistically over the past couple of years.
In the meantime a new project started, to provide a modern Pythonic jet-finding package in the Scikit-HEP ecosystem.fastjetprovides official FastJet bindings to Python and Awkward Array.Refer to the GitHub repository for details.pyjet: the interface between FastJet and NumPypyjet allows you to perform jet clustering withFastJetonNumPyarrays. By default pyjet only depends on
NumPy and internally uses FastJet’s standalone fjcore release. The interface
code is written inCythonthat then becomes compiled
C++, so it’s fast. Remember that if you use pyjet then you are using FastJet
and should cite the papers listedhere.Strict dependenciesPython(3.7+)NumpyGetting startedpyjet provides thecluster()function that takes a NumPy array as input
and returns aClusterSequencefrom which you can access the jets:frompyjetimportclusterfrompyjet.testdataimportget_eventvectors=get_event()sequence=cluster(vectors,R=1.0,p=-1)jets=sequence.inclusive_jets()# list of PseudoJetsexclusivejets=sequence.exclusive_jets(3)# Find the cluster history when there are 3 jetsThe input is given in the form of astructured arrayin numpy. The first four fields of the input arrayvectorsmust be either:np.dtype([('pT','f8'),('eta','f8'),('phi','f8'),('mass','f8')])or ifcluster(...,ep=True):np.dtype([('E','f8'),('px','f8'),('py','f8'),('pz','f8')])Note that the field names of the input array need not match ‘pT’, ‘eta’, ‘phi’,
‘mass’ etc. pyjet only assumes that the first four fields are those quantities.
This array may also have additional fields of any type. Additional fields will
then become attributes of thePseudoJetobjects.See theexamplesto
get started:Standalone InstallationTo simply use the built-in FastJet source, from your virtual environment, run:python -m pip install pyjetAnd you’re good to go! If you have a old version of pip (<10), you will need to have Cython and Numpy already installed to build from source - however on most systems, you should get a binary wheel.Get example.py and run it:curl -O https://raw.githubusercontent.com/scikit-hep/pyjet/master/examples/example.py
    python example.py
    jet#          pT        eta        phi       mass  #constit.
    1        983.280     -0.868      2.905     36.457         34
    2        901.745      0.221     -0.252     51.850         34
    3         67.994     -1.194     -0.200     11.984         32
    4         12.465      0.433      0.673      5.461         13
    5          6.568     -2.629      1.133      2.099          9
    6          6.498     -1.828     -2.248      3.309          6

    The 6th jet has the following constituents:
    PseudoJet(pt=0.096, eta=-2.166, phi=-2.271, mass=0.000)
    PseudoJet(pt=2.200, eta=-1.747, phi=-1.972, mass=0.140)
    PseudoJet(pt=1.713, eta=-2.037, phi=-2.469, mass=0.940)
    PseudoJet(pt=0.263, eta=-1.682, phi=-2.564, mass=0.140)
    PseudoJet(pt=1.478, eta=-1.738, phi=-2.343, mass=0.940)
    PseudoJet(pt=0.894, eta=-1.527, phi=-2.250, mass=0.140)

    Get the constituents as an array (pT, eta, phi, mass):
    [( 0.09551261, -2.16560157, -2.27109083,   4.89091390e-06)
     ( 2.19975694, -1.74672746, -1.97178728,   1.39570000e-01)
     ( 1.71301882, -2.03656511, -2.46861524,   9.39570000e-01)
     ( 0.26339374, -1.68243005, -2.56397904,   1.39570000e-01)
     ( 1.47781519, -1.7378898 , -2.34304346,   9.39570000e-01)
     ( 0.89353864, -1.52729244, -2.24973202,   1.39570000e-01)]

    or (E, px, py, pz):
    [( 0.42190436, -0.06155242, -0.07303395, -0.41095089)
     ( 6.50193926, -0.85863306, -2.02526044, -6.11692764)
     ( 6.74203628, -1.33952806, -1.06775374, -6.45273802)
     ( 0.74600384, -0.22066287, -0.1438199 , -0.68386087)
     ( 4.43164941, -1.0311407 , -1.05862485, -4.07096881)
     ( 2.15920027, -0.56111108, -0.69538886, -1.96067711)]

Reclustering the constituents of the hardest jet with the kt algorithm
[PseudoJet(pt=983.280, eta=-0.868, phi=2.905, mass=36.457)]

Go back in the clustering sequence to when there were two jets
PseudoJet(pt=946.493, eta=-0.870, phi=2.908, mass=20.117)
PseudoJet(pt=36.921, eta=-0.800, phi=2.821, mass=4.119)

Ask how many jets there are with a given dcut
There are 9 jets with a dcut of 0.5

Get the jets with the given dcut
1 PseudoJet(pt=308.478, eta=-0.865, phi=2.908, mass=2.119)
2 PseudoJet(pt=256.731, eta=-0.868, phi=2.906, mass=0.140)
3 PseudoJet(pt=142.326, eta=-0.886, phi=2.912, mass=0.829)
4 PseudoJet(pt=135.971, eta=-0.870, phi=2.910, mass=0.140)
5 PseudoJet(pt=91.084, eta=-0.864, phi=2.899, mass=1.530)
6 PseudoJet(pt=30.970, eta=-0.831, phi=2.822, mass=2.124)
7 PseudoJet(pt=7.123, eta=-0.954, phi=2.939, mass=1.017)
8 PseudoJet(pt=5.951, eta=-0.626, phi=2.818, mass=0.748)
9 PseudoJet(pt=4.829, eta=-0.812, phi=3.037, mass=0.384)Using an External FastJet InstallationTo take advantage of the full FastJet library, including the jet area
calculations and the optimized O(NlnN) kt and anti-kt algorithms,
you can first build and install FastJet and then install
pyjet with the--external-fastjetflag. Before building FastJet you will
need to installCGALandGMP.On a Debian-based system (Ubuntu):sudo apt-get install libcgal-dev libcgal11v5 libgmp-dev libgmp10On an RPM-based system (Fedora):sudo dnf install gmp.x86_64 gmp-devel.x86_64 CGAL.x86_64 CGAL-devel.x86_64On Mac OS:brew install cgal gmp wgetThen run pyjet’sinstall-fastjet.shscript:curl -O https://raw.githubusercontent.com/scikit-hep/pyjet/master/install-fastjet.sh
chmod +x install-fastjet.sh
sudo ./install-fastjet.shNow install pyjet like:python -m pip install numpy Cython
python setup.py install --external-fastjetpyjet will now use the external FastJet installation on your system.Note on unitsThe package is indifferent to particular units, which are merely “propagated”
through the code. We do recommend that the HEP units be used, as defined
in theunitsmodule of thehepunits package.It is worth noting that the azimuthal angle phi is expressed in radians
and varies from pi to pi.DevelopingIf you want to setup for development:python3 -m venv .env
source .env/bin/activate
pip install -e .[dev]
pytest