Add the square_singlet activation function

[scarlehoff]

With a check so that it can only be used as the final layer.

[RoyStegeman]

Ah wait, this is applied before the basis rotation so maybe a check should be added that you're indeed squaring the singlet elements?

[scarlehoff]

I can add that, yes.
That would make it not work if one uses something like the flavour basis, but that's probably a good thing.

[scarlehoff]

@RoyStegeman can I take the previous green tick as still applying?

This has been used for this fit: https://vp.nnpdf.science/TsABd61tS_OOMbRYxCcmlA==/

[RoyStegeman]

This has been used for this fit: https://vp.nnpdf.science/TsABd61tS_OOMbRYxCcmlA==/

Did you also check in evol basis? Since there it's easier to see the impact of this activation function

[scarlehoff]

What do you mean? It can only be used in the evolution basis.

[RoyStegeman]

But the plots in the report are all flavor basis, so they don't really help to see if this PR does what you want

[RoyStegeman]

Thanks for adding the checks

[scarlehoff]

so they don't really help to see if this PR does what you want

Ah! That's what you mean. Yes: https://vp.nnpdf.science/RqocL3BvSL698F2-3ytrAw==/Scales0_pdf_report_report.html#Scales0_pdf_report_PDFnormalize0_Basespecs1_PDFscalespecs1_plot_pdfs_Sigma

(although it only makes a real difference for the gluon tbh)

[RoyStegeman]

Thanks, I'm happy to merge