Add NNPDF4.0 FK table importer

[cschwan]

Specification is available here: https://docs.nnpdf.science/data/th-data-files.html.

[alecandido]

I believe this not to be relevant any longer, do you agree @cschwan?

It would be not a simple task, because of everything we found out in the meanwhile, and we didn't schedule any conversion at this point.

[cschwan]

@alecandido I don't think it's a priority Issue right now or even in the forseeable future, but I'd like to keep this open. Having the option of converting an FK table to a PineAPPL grid might be useful for debugging purposes in the future.

I think writing a converter would be quite easy, why do you think it wouldn't be?

[alecandido]

Of course you have to take into account DIS vs hadronic, but I believe this is already included in what you call "quite easy".

But on top of what is currently inside a PineAPPL FkTable as well, you have to add at list the concatenation, that for 4.0 grids is inside, and for PineAPPL ones is outside (in the yaml recipe, together with compound).

Then, from my personal point of view, since the more this shifts to the future, the more PineAPPL FkTables will establish and replace 4.0 FkTables, I don't see a window in which this feature will be useful.
In any case, this is my point of view, so if you have a different feeling, keeping this open doesn't hurt.

[cschwan]

@alecandido I don't quite follow what you said, but what I mean is simply a converter that takes FK tables in this format, https://docs.nnpdf.science/data/th-data-files.html, and converts them into PineAPPL grids, just like APPLgrids or fastNLO tables.

[alecandido]

Ok, if you're able to do it, so much the better.

Just take into account that one old-style FkTable may correspond to multiple new FkTables.

[cschwan]

@alecandido that's OK, I mainly need it for the positivity support for which we don't have any grids.