```eval_rst .. _apfelcomb: ``` # 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](../data/exp-data-files.html#exp-data-files). APFELcomb depends on the following libraries * [APFEL](https://github.com/scarrazza/apfel) * [nnpdf](https://github.com/NNPDF/nnpdf) * [APPLgrid](https://github.com/NNPDF/external/tree/master/applgrid-1.4.70-nnpdf) and data files from * [applgrids](https://github.com/NNPDF/applgrids) There are various ways of generating the latter, as explained in [How to generate applgrids](../tutorials/APPLgrids.md). 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 `-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](../tutorials/apfelcomb.md).