MadGraph5_aMC@NLO

Reweight PDF option requires to use pdf sets associated to lhapdf

Asked by Maura Barros

Dear experts,

I am trying to generate some monotop events using v2.3.4 of MadGraph. It is an older version of MG but I am trying to compare generations of events at NLO with LO generation and the code is written for this version.

I want to take into account scale variations. However, I have to enable this option on the MG run card. So, I did:

True = reweight_scale
True = reweight_PDF
260001 = PDF_set_min
260100 = PDF_set_max

And I am using the 260000 lhaid. The run decay card is using the 244600 lhaid with:

244601 = PDF_set_min
244700 = PDF_set_max

On the input/mg5_configuration.txt, I defined the path to an installation that I have of LHAPDF version 6.3.0:

lhapdf = /afs/cern.ch/work/m/mbarrost/AFP/LHAPDF_installation/bin/lhapdf-config

This version is well-installed since I use it in other contexts. On the shared folder of LHAPDF, I have both NNPDF23_nlo_as_0118_qed and NNPDF30_nlo_as_0118 that correspond to the lhaid mentioned above.

When I run the code, I have the following error:

Reweight PDF option requires to use pdf sets associated to lhapdf. Please either change the pdlabel or set reweight_pdf to False.

I am not sure why this is happening. If I am doing something wrong or if I have a too older version of MG interfaced with a more recent version of LHAPDF.

Can you help me with this?

Thank you! Best regards,
Maura

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Solved by:
Olivier Mattelaer
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Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

The check is that you need to have set "pdlabel" to lhapdf and not to one of the internal pdf.
The reason is that if you use an internal pdf code, then our code will not be linked to lhapdf at all
and the reweighting module need that module.

So you need to set pdlabel to lhapdf and set the lhaid to the value that you want.

This being said, I have no clue if this is going to work on 2.3.4 since we do not provide support for such version that are not compiling anymore on any of test infrastructure (we do not even have a python version compatible with such old code). Those days we strongly suggest to migrate at least to our Long Term Stable version (2.9.13).

Cheers,

Olivier

> On 2 Feb 2023, at 11:35, Maura Barros <email address hidden> wrote:
>
> Reweight PDF option requires to use pdf sets associated to lhapdf. Please either change the pdlabel or set reweight_pdf to False.

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Maura Barros (maurabarros) said : 		#2

Thanks Olivier Mattelaer, that solved my question.

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Maura Barros (maurabarros) said : 		#3

Hi Olivier,

Just a follow-up on this. What you suggested solved my problem but now I got the following error:

Error detected in "launch auto "
write debug file /afs/cern.ch/work/m/mbarrost/MonoTop/NLO_new_20072022/MonoTop/proc_msigma4000.0_mchi10.0_lam0.6_y0.4_energy13.0TeV_PS_0/decay/run_01_tag_1_debug.log
If you need help with this issue please contact us on https://answers.launchpad.net/madgraph5
aMCatNLOError : An error occurred during the collection of results.
 Please check the .log files inside the directories which failed:
 /afs/cern.ch/work/m/mbarrost/MonoTop/NLO_new_20072022/MonoTop/proc_msigma4000.0_mchi10.0_lam0.6_y0.4_energy13.0TeV_PS_0/decay/SubProcesses/P0_sig3_n1t/all_G1/log.txt

And on the P0_sig3_n1t/all_G1/log.txt file, I got:

ERROR from dummy "initpdf()": cannot do pdf reweighting without LHAPDF

Do you think this could be related to the old version of MG?

Thank you!

Cheers,
Maura

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Maura Barros (maurabarros) said : 		#4
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Olivier Mattelaer (olivier-mattelaer) said : 		#5

Hi,

I do not know here, seems that the issue is related to lhapdf.
I do not know which lhapdf version was supported by that old version of the code.
So maybe the issue is that you are using a version of lhapdf which is not compatible with our code

For the UpdatesNotes, I can see that support for lhapdf6.2 was added to version 2.6.1
So this is not too surprising that your lhapdf is not working correctly.

So maybe you might even need to use lhapdf5. Support for lhapdf6.1 was quite chaotic and some version of MG5aMC are only compatible with lhapdf6.1.6/...

But on that you might need try and error to find the good combination of lhapdf and MG5aMC (and potentially compiler too, since none of those will compile with modern compiler)

Cheers,

Olivier

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Maura Barros (maurabarros) said : 		#6

Hi Olivier,

Thanks a lot for your help! I will try to find the correct combination for this.

Cheers,
Maura