Benchmarks: Automatic detection of flavors cancellation

[alecandido]

What

We noticed that there is a common source of differences (rel_err[%]) between us and APFEL coming from Q2 interpolation (or also anything APFEL-like, i.e. Q2 interpolating)

Proposed solution

• in yadmark we can get the numbers for the separate channels from yadism (the "DIS operator") simply calling runner.get_result() and only after calling .apply_pdf() on the result
• once the numbers for the separate channels are available we are able to detect the region, or better the exact ESF where a cancellation between flavors is happening (just looking for the maximum of each flavor channel and computing the absolute ratio with the summed result)
• once that a cancellation is detected raise the absolute error for APFEL comparison

Absolute error value problem

The actual number to choose for the absolute error is difficult to find, because the proper value should be the sum of absolute errors on the individual flavor channels, but in order to find this we should be able to break the APFEL's result as well on the individual flavors, but if these results where available we could have compared directly the channels instead of the recombined sum.

My personal guess for this number is a function of the sum/max(flavors) ratio, protecting for yadism recombined result going to 0 (and so ratio=0 -> rel_err=100%) and protect for the full yadism result where the cancellation is still present but it is more likely APFEL to go to 0 (1%<ratio<20% -> abs_err=yad_result).

[felixhekhorn]

maybe instead of hiding/raising/changing the error, it is sufficient to give an explanation to the user and let him decide on how to adjust the assert

[felixhekhorn]

we decided to only compare in the physical region