error while generating events.

Hi,

This is a zero division error.
This either means that Ntry or Nacc are zero.
Ntry is the number of generated events that you get before pythia. So it should be bigger than one.
Nacc can on the other hand be zero, if Ntry is small and if the double counting due to the matching is very large.

In other word, you have a matching issue and you probably want to change your value of xqcut/qcut.

Cheers,

Olivier

PS: If you need more info on the matching: https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/IntroMatching

On 22 Sep 2015, at 08:22, Juhi Dutta <email address hidden> wrote:

> New question #271655 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/271655
>
> Hi,
>
> I am recurrently obtaining an error while generating events for some processes which I am unable to decode and correct. The following contains the error message :
>
> generate_events -f
> Traceback (most recent call last):
> File "/home/juhi/Juhi_Docs/MG5_aMC_v2_2_3/P4gogo/bin/internal/extended_cmd.py", line 879, in onecmd
> return self.onecmd_orig(line, **opt)
> File "/home/juhi/Juhi_Docs/MG5_aMC_v2_2_3/P4gogo/bin/internal/extended_cmd.py", line 872, in onecmd_orig
> return func(arg, **opt)
> File "/home/juhi/Juhi_Docs/MG5_aMC_v2_2_3/P4gogo/bin/internal/madevent_interface.py", line 1946, in do_generate_events
> self.exec_cmd('pythia --no_default', postcmd=False, printcmd=False)
> File "/home/juhi/Juhi_Docs/MG5_aMC_v2_2_3/P4gogo/bin/internal/extended_cmd.py", line 919, in exec_cmd
> stop = Cmd.onecmd_orig(current_interface, line, **opt)
> File "/home/juhi/Juhi_Docs/MG5_aMC_v2_2_3/P4gogo/bin/internal/extended_cmd.py", line 872, in onecmd_orig
> return func(arg, **opt)
> File "/home/juhi/Juhi_Docs/MG5_aMC_v2_2_3/P4gogo/bin/internal/madevent_interface.py", line 2827, in do_pythia
> error_m = math.sqrt((error * Nacc/Ntry)**2 + sigma_m**2 *(1-Nacc/Ntry)/Nacc)
> ZeroDivisionError: float division by zero
>
> How do I correct this?
>
> Looking forward to your advise in this matter.
>
> Thanks & Regards,
>
> Juhi Dutta
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi,

I varied the matching scale considerably and receive: MadEventError : Error gensym run not successful

Juhi

Hi,

I varied the matching scale considerably and receive: MadEventError : Error gensym run not successful

Juhi

Dear Juhi,

I have put a fix to avoid the division by zero, such that you get nicely a zero cross-section for such cut.

Cheers,

Olivier

Hi,

Ok. that sounds good.

I have another naive query related to this thread. Some time the run stops during Creation of plots after parton level run. On pressing enter the run resumes correctly to run Pythia . At the end of the run, the pythia plots (even matching plots if any) are correctly generated . however the parton plots do not get generated.

Since I am finally interested in the pythia level plots , i have them and do not worry much about parton level plots. but i haven't really found a possible reason why this occurs .Have you encountered anything of this sort or can help out ?

Regards,
Juhi

HI,

Never face that.

Cheers,

Olivier