How to reproduce an NNPDF4.0 fit

Here we describe how to reproduce the NNPDF4.0 PDF sets that are publicly available through LHAPDF as discussed in section 10 of the NNPDF4.0 paper [BallCarrazzaCruzMartinez+21].

The files needed to reproduce the results are available in the folder n3fit/runcards/reproduce_nnpdf40 of the project repository on Github. The .yml files that folder are the following:

nnpdf40_env.yml # conda environment

NNPDF40_hyperopt.yml # hyperoptimization runcard

# Fit runcards:

NNPDF40_nnlo_as_0118_hessian.yml # Hessian conversion runcard

Below we will describe how these runcards can be used to generate the NNPDF4.0 PDF grids.

Setting up the NNPDF4.0 conda envirnoment

The exact conda environment, including all transitive dependencies, used to produce all the publicly released PDF fits has been preserved to ensure precise reproducibility. The environment can be found in the project repository It can be generated and activated by running

conda env create --file nnpdf40_env.yaml
conda activate nnpdf40

Alternatively, we provide a ready to run docker image with a pre-installed environment. After setting it up, you can download and open the environment by running

docker run -it bash

Hyperoptimization for NNPDF4.0

The NNPDF40_hyperopt.yml runcard can be used to run the hyperoptimization with the exact same settings used to identify the NNPDF4.0 architecture. This step can be skipped if the aim is simply to reproduce the NNPDF4.0 grids, which requires using the exact same architecture as was used to create the NNPDF4.0 grids. Nevertheless, this runcard is made available to provide a complete overview of each step in the production of the NNPDF4.0 sets.

Producing the NNPDF4.0 fits

After setting up the conda environment, we can use it to produce the fits in the usual way. The names of the “fit runcards” listed in the textblock above are the same as those of the corresponding (public) LHAPDF grids of the same name. For example, baseline fit with \(\alpha_s(m_Z)=0.118\) and a variable-flavor-number scheme with up to five active flavors can be generated with NNPDF40_nnlo_as_0118_1000.yml.

Hessian conversion, compression, bundled sets and flavor number variations

Among the released PDF sets of NNPDF4.0 are also some sets that are the result of a transformation or combination of the fits produced using the “fit runcards”, these PDF grids are:

# Baseline NNDPF4.0 sets:

# PDF sets with :math:`\alpha_s` variations:

# PDF sets with flavor-number variations:

Section 10 of the NNPDF4.0 states how these can be obtained from the fits produced using the method discussion under Producing the NNPDF4.0 fits, but we will again give some pointers here.

Both NNPDF40_nnlo_as_0118 and NNPDF40_nnlo_as_0118_hessian are based on a 1000 replica PDF set NNPDF40_nnlo_as_0118_1000. Specifically, NNPDF40_nnlo_as_0118 is the result of a compression of NNPDF40_nnlo_as_0118_1000 using the pycompressor package, while NNPDF40_nnlo_as_0118_hessian can be created by running

validphys NNPDF40_nnlo_as_0118_hessian.yml

For more information, see the tutorial on how to transform a Monte Carlo PDF set into a Hessian PDF set.

The bundled PDF + \(\alpha_s\) variation set NNPDF40_nnlo_pdfas can be generated using the runcard NNPDF40_nnlo_as_0118_1000.yml, again, for more information on how to bundle PDFs with \(\alpha_s\) replicas, see the relevant tutorial.

The PDF sets released as part of NNPDF4.0 also includes sets in which the maximum value of nf differs from the baseline value of nf=5. To produce these sets, the steps described in How to create PDF sets with flavor-number variations. In particular, the ID’s of the required theories can be found in the theory dabase, where the id’s of the theories used to do the flavor-number variations are 218-227.


Please note that the Hessian and _pdfas conversion runcards won’t work with the 4.0.3 version of the code (and thus the fixed enviroment) and instead require a version 4.0.4 or newer.