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The interface between FastJet and NumPy

Project description

pyjet allows you to perform jet clustering with FastJet on NumPy arrays.

By default pyjet only depends on NumPy and internally uses FastJet’s standalone fjcore release. The interface code is written in Cython that then becomes compiled C++, so it’s fast.

pyjet provides the cluster() function that takes a NumPy array as input and returns a PyClusterSequence from which you can access the jets:

sequence = cluster(event, R=1.0, p=-1)
jets = sequence.inclusive_jets()  # list of PyPseudoJets

The dtype of the input array can be either:

np.dtype([('pT', 'f8'), ('eta', 'f8'), ('phi', 'f8'), ('mass', 'f8')])

or if cluster(..., ep=True):

np.dtype([('E', 'f8'), ('px', 'f8'), ('py', 'f8'), ('pz', 'f8')])

The input array may have additional fields of any type and this data can be accessed as attributes of the PyPseudoJet objects.

Standalone Installation

To simply use the built-in FastJet source:

pip install --user pyjet

And you’re good to go!

Get and run it:

curl -O
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:
PyPseudoJet(pt=0.096, eta=-2.166, phi=-2.271, mass=0.000)
PyPseudoJet(pt=2.200, eta=-1.747, phi=-1.972, mass=0.140)
PyPseudoJet(pt=1.713, eta=-2.037, phi=-2.469, mass=0.940)
PyPseudoJet(pt=0.263, eta=-1.682, phi=-2.564, mass=0.140)
PyPseudoJet(pt=1.478, eta=-1.738, phi=-2.343, mass=0.940)
PyPseudoJet(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)]

Using an External FastJet Installation

To take advantage of the full FastJet library and optimized O(NlnN) kt and anti-kt algorithms, first install FastJet and then install pyjet with the --external-fastjet flag.

First install CGAL and GMP:

On a Debian-based system (Ubuntu):

sudo apt-get install libcgal-dev libcgal11v5 libgmp-dev libgmp10

On an RPM-based system (Fedora):

sudo dnf install gmp.x86_64 gmp-devel.x86_64 CGAL.x86_64 CGAL-devel.x86_64

On Mac OS:

brew install cgal gmp wget

Then run pyjet’s script:

curl -O
chmod +x
sudo ./

Now install pyjet like:

pip install --user pyjet --install-option="--external-fastjet"

pyjet will now use the external FastJet installation on your system.

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