Unable to interface LHAPDF with MadGraph

Asked by Lalit Kumar Saini on 2018-11-15

Dear Madgraph team

I am having problem during the linking of LHAPDF with the Madgraph. It is able to find the path to the LHAPDF but it doesn't download the required pdf from the source. Suppose I take a SM process as

generate p p > a
output a

There I changed the pdlabel as lhapdf with 230000 as the lhaid, but the following error occured :

INFO: Update the dependent parameter of the param_card.dat
Generating 10000 events with run name run_01
survey run_01
INFO: compile directory
INFO: Using LHAPDF v6.2.1 interface for PDFs
INFO: Trying to download NNPDF23_nlo_as_0119
ERROR: Unable to download /cvmfs/sft.cern.ch/lcg/external/lhapdfsets/current/NNPDF23_nlo_as_0119.tar.gz
ERROR: Unable to download /afs/cern.ch/sw/lcg/external/lhapdfsets/current/NNPDF23_nlo_as_0119.tar.gz
Traceback (most recent call last):
  File "/usr/local/bin/lhapdf", line 504, in <module>
    if download_file(tar_filename, options.PDFDIR, dryrun=suboptions.DRYRUN):
  File "/usr/local/bin/lhapdf", line 427, in download_file
    if download_url(source + filename, dest_dir, dryrun):
  File "/usr/local/bin/lhapdf", line 280, in download_url
    file_size = int(u.info().get('Content-Length')[0])
TypeError: 'NoneType' object has no attribute '__getitem__'
Error detected in "generate_events run_01"
write debug file /home/lalit/MG5_aMC_v2_6_3_2/a/run_01_tag_1_debug.log
If you need help with this issue please contact us on https://answers.launchpad.net/mg5amcnlo
MadGraph5Error : Could not download NNPDF23_nlo_as_0119 into /usr/local/share/LHAPDF. Please try to install it manually.

Thank You

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This is a bug of lhapdf/hepforge that make their official API to download PDF not working. (due to a change in hepforge)
As far as i have understood they do not plan to fix it (even in the latest version of lhapdf).

So starting with 2.6.4 version of MG5aMC (already released), I will try to use the official API but if fails, I will try to do it myself.
(So this issue should be fixed in 2.6.4) However It might exists cases where I do not guess the path to the PDF correctly/... since this is not an official API of lhapdf anymore in that case.



PS: Do not hesitate to contact lhpadf author about this in order
1) to convince them that auto-download of pdf is a usefull feature (they do not agree on that)
2) to convince them to fix it in their next version

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