Using APFELcomb

APFELcomb is the project that allows the user to generate FK tables. These are lookup tables that contain the relevant information to compute theoretical predicitons in the NNPDF framework. Broadly speaking, this is achieved by taking DGLAP evolution kernels from APFEL and combining them with interpolated parton-level observable kernels of various forms. The mechanism behind APFELcomb is presented in arXiv:1605.02070.

APFELcomb is available from

https://github.com/NNPDF/apfelcomb

The various data formats used in APFELcomb are described in Experimental data files.

APFELcomb depends on the following libraries

and data files from

There are various ways of generating the latter, as explained in How to generate applgrids.

Once the above libraries and data files are set up, the APFELcomb project can be compiled as follows

make

Compilation flags and various paths are defined in Makefile.inc. These are mostly inferred from <package>-config files with the exception of

  • RESULTS_PATH (default ./results) Defines the path results are written to.

  • APPL_PATH (default ../applgrids) Defines the path to the applgrid repository.

  • DB_PATH (default .db) Defines the path to the APFELcomb database.

The defaults are configured assuming that both the nnpdf and applgrid repositories are located at ../.

Each FK table is generated piecewise in one or more subgrids. The subgrids implemented in APFELcomb can be displayed by running the script

./scripts/disp_grids.py

Typically DIS and FKGenerator DY tables are made of only one subgrid, whereas FK tables generated from APPLgrids have one subgrid per APPLgrid file. How subgrids are merged into grids, and the generation parameters of each subgrid, is specified in the db/apfelcomb.db database. The database itself is not stored in the repository, but it is built from the sqlite dump at db/apfelcomb.dat. This is done automatically by the APFELcomb makefile. Detailed instructions to generate/implement FK tables for individual experiments and/or a compelte theory are provided in How to generate/implement FK tables.