Code review comment for lp:~maddevelopers/mg5amcnlo/v3_syntax_handler

Hi,
I would have the same behaviour in the two cases that Davide considered. I do not see any motivation to have a crash for [QED] (computing NLO3) and a warning for [QCD] (NLO2), when both cases receive mixed QCD-EW corrections.
I would consider QED=99, QCD=99 as a syntax that does not need any warning. In general, this **could** be the case for any order constraint that does not discard any diagram (I am not saying that this should be implemented). The absence of constraint should automatically lead the code to consider the maximally-QCD amplitude (LO1), with the proper squared-order constraints.

Cheers,

Marco

> On 10 May 2021, at 13:18, Olivier Mattelaer <email address hidden> wrote:
>
> Hi,
>
> Yes as I said in our last meeting (and in the merge request), I have weaken a bit the scope in which we crash and provide only a warning for a series of case where the syntax was already possible in 2.x and were the paper 1804.10017 is not an issue per say. Do you think that a warning is not enough?
>
>> Marco: should also QCD=99 AND QED=99 [QCD] or QCD=99 AND QED=99 [QED] raise an error?
>
> In this case they are no ambiguity and therefore I would say that even a warning is not needed.
> This is for me the same case as if the user does not provide anything.
> I strongly believe that we should not put warning if we know that syntaxes between 2.x, 3.x and 3.1.x are the same.
> Useless warning are the best way for people to ignore them.
>
>
> Cheers,
>
> Olivier
>
>
>> On 10 May 2021, at 12:54, davide.pagani.85 <<email address hidden> <mailto:<email address hidden>>> wrote:
>>
>> Hi Olivier,
>>
>> I started to play with it and I noticed that if I do
>>
>> generate p p > t t~ QCD=1 QED=1 [/*QED*/]
>>
>> I get
>>
>>
>> /Interpreting 'QED=1' as 'QED<=1'//
>> //Interpreting 'QCD=1' as 'QCD<=1'//
>> //Command "generate p p > t t~ QCD=1 QED=1 [QED]" interrupted with error://
>> //Exception : Potentially ambigious syntax detected. Note that the
>> syntax of paper 1804.10017 (used in 3.0.x) is not used anymore (since
>> version 3.1.0).//
>> // If you want to follow the syntax of that paper, you can just
>> replace "QED" by "aEW" and "QCD" by "aS".//
>> // More information here: http://amcatnlo.cern.ch/co.htm//
>> // If you know the current meaning of the syntax you can bypass this
>> crash by running (once per machine) this command://
>> // set acknowledged_v3.1_syntax True --global//
>> //Please report this bug on https://bugs.launchpad.net/mg5amcnlo//
>> //More information is found in 'MG5_debug'.//
>> //Please attach this file to your report./
>>
>> and the code stops, that I think it is what we want.
>>
>> If instead I do
>>
>> generate p p > t t~ QCD=1 QED=1 [/*QCD*/]
>>
>> I obtain:
>>
>> /Potentially ambigious syntax detected. Note that the syntax of paper
>> 1804.10017 (used in 3.0.x) is not used anymore (since version 3.1.0).//
>> //If you want to follow the syntax of that paper, you can just replace
>> "QED" by "aEW" and "QCD" by "aS".//
>> //More information here: http://amcatnlo.cern.ch/co.htm//
>> //
>> //Order QED is not constrained as squared_orders. Using: QED^2=2//
>> //Order QCD is not constrained as squared_orders. Using: QCD^2=2//
>> //WARNING: Use of multiparticles is non-trivial for NLO process
>> generation and depends on the orders included, the process considered,
>> as well as the PDF set chosen. See appendix D of arXiv:1804.10017
>> [hep-ph] for some guidance. /
>>
>> and the code keeps running.
>>
>> If I am not wrong, this is not what we wanted. If I remember correctly,
>> the first output should always appear unless one is either not
>> specifying QCD=* QED=* or setting QCD=99 AND QED=99 together with [QCD QED].
>>
>> Marco: should also QCD=99 AND QED=99 [QCD] or QCD=99 AND QED=99 [QED]
>> raise an error?
>>
>> Cheers
>> Davide
>>
>>
>>
>> On 14.04.21 15:15, Olivier Mattelaer wrote:
>>> Any comment on this?
>>>
>>> I think that it does not make that much sense to wait months before releasing it (otherwise this will be even more uglier).
>>>
>>> Olivier
>>
>>
>> --
>> https://code.launchpad.net/~maddevelopers/mg5amcnlo/v3_syntax_handler/+merge/400921
>> Your team MadTeam is subscribed to branch lp:mg5amcnlo.
>
>
> --
> https://code.launchpad.net/~maddevelopers/mg5amcnlo/v3_syntax_handler/+merge/400921 <https://code.launchpad.net/~maddevelopers/mg5amcnlo/v3_syntax_handler/+merge/400921>
> You are requested to review the proposed merge of lp:~maddevelopers/mg5amcnlo/v3_syntax_handler into lp:mg5amcnlo.