Evaluate and extend set of included PDFs and / or grid files

[Christian Speckner]

Now that #368 is closed with built-in PDFs being implemented, I create this ticket for discussion of the list of included PDFs. At the moment, I am supporting CTEQ6L/L1/D/M and MRST2004QED (both proton and neutron), with grids being shipped for CTEQ6L and both (proton / neutron) MRST2004QED sets. The default PDF being CTEQ6L. We could improve upon this status in the following ways:

• Activate the other "special" PDF sets from the CTEQ6 bunch (take a look at src/pdf_builtin/cteq6pdf.f. Doing this would be trivial, but I see little worth in it apart from bloating the table in the manual.
• Include the other CTEQ6 grids as well. Each grid is around 200k and swells the tarball by about 70k, so this is not exactly a lot, but downloading the grids is no big problem either for those who need them. So, I have no definite opinion here :)
• Add other sets --- MRSTW2008 and friends come to my mind, and we could also add at least one photon and one pion set.
• ...

Adding new PDFs is semi-trivial and boils down to a few semi-trivial modifications to the provided code and augmenting the wrapper in src/pdf_builtin, so I am open to all suggestions :)

[Juergen Reuter]

We should discuss and decide on this question as quick as possible in order to have this ticket not too long lingering around. For CTEQ only numbers 1-4 are in question, in principle they are already approved by CS. What about CTEQ65, so I mean, is CTEQ6 not already outdated!? MRST2004QED is also fine. MSTW2008 we should include the most relevant set. I guess thats it. Otherwise the users can use LHAPDF. So that would be 4 CTEQ, 1-2 MRST2004QED (correct?), and how many MSTW2008??? Please add your opinions in order to settle this open issue rather quickly.

[Juergen Reuter]

Guys, (WK/TO),please give your opinion to that topic such that CS can proceed accordingly and we can close this ticket.

[Juergen Reuter]

Discussed this von CS. We will include the four CTEQ6 PDFs, the MRST2004QED and the relevant MWST2008. That's it. CS will do it next week.

[Christian Speckner]

As of r2965, MSTW2008LO/NLO/NNLO and CT10 are implemented and the grids are included. I've left the default as CTEQ6L - we also use this for LHApdf, and it is leading order. I've run a detailed comparison for all included sets between the builtin versions and LHApdf, and the results look OK. I'm not completely content with the agreement, but after comparing the PDFs directly, I am convinced that the difference only signifies WHIZARD underestimating the integration error. I will run some more tests, and if I find anything suspicious, I'll reopen the ticket.