Dear MG developers, I have a question about weight ID's in HepMC files. First, the setup and what happens. When reweighting and naming various parameter points it would be great to have these names/ids written in the HepMC file. For example, let's say I have an event in an LHEF file (along with the header): set param_card mass 34 1000.0 # orig: 3000.0 set param_card ssmcoup 1 0.9 # orig: 1.0 set param_card mass 34 2000.0 # orig: 3000.0 set param_card ssmcoup 1 0.5 # orig: 1.0 # Number of Events : 5 # Integrated weight (pb) : 0.010046 2212 2212 6.500000e+03 6.500000e+03 0 0 230000 230000 -4 1 1.004600e-02 1.268800e-04 1.016000e-02 0 please cite 1405.0301 5 0 +1.0160000e-02 2.99912800e+03 7.81616400e-03 8.00755700e-02 -2 -1 0 0 0 501 -0.0000000000e+00 +0.0000000000e+00 +9.8323714599e+02 9.8323714599e+02 0.0000000000e+00 0.0000e+00 1.0000e+00 1 -1 0 0 501 0 +0.0000000000e+00 -0.0000000000e+00 -2.2870299871e+03 2.2870299871e+03 0.0000000000e+00 0.0000e+00 -1.0000e+00 -34 2 1 2 0 0 +0.0000000000e+00 +0.0000000000e+00 -1.3037928411e+03 3.2702671331e+03 2.9991284316e+03 0.0000e+00 0.0000e+00 13 1 3 3 0 0 -4.3939456193e+02 +3.0684611657e+02 -2.1790372204e+03 2.2439753404e+03 0.0000000000e+00 0.0000e+00 -1.0000e+00 -14 1 3 3 0 0 +4.3939456193e+02 -3.0684611657e+02 +8.7524437929e+02 1.0262917927e+03 0.0000000000e+00 0.0000e+00 1.0000e+00 +9.6275264e-06 +2.3461820e-06 If I shower this event with Pythia8 and use the default pythia8_card.dat, the HepMC file starts like this: HepMC::Version 2.06.09 HepMC::IO_GenEvent-START_EVENT_LISTING E 0 -1 -1.0000000000000000e+00 -1.0000000000000000e+00 -1.0000000000000000e+00 9999 0 431 1 2 0 3 1.7672388399999997e-05 3.7847199999999997e-06 2.0034000000000002e-03 N 3 "1000.0_#_ORIG:_3000.0 SET_PARAM_CARD_SSMCOUP_1_0.9_#_ORIG:_MERGING=0.000" "2000.0_#_ORIG:_3000.0 SET_PARAM_CARD_SSMCOUP_1_0.5_#_ORIG:_MERGING=0.000" "Weight_MERGING=0.000" U GEV MM C 2.0034000000000002e-03 1.0017000000000000e-02 The important lines are these: N 3 "1000.0_#_ORIG:_3000.0 SET_PARAM_CARD_SSMCOUP_1_0.9_#_ORIG:_MERGING=0.000" "2000.0_#_ORIG:_3000.0 SET_PARAM_CARD_SSMCOUP_1_0.5_#_ORIG:_MERGING=0.000" "Weight_MERGING=0.000" In these lines the weight "names" are encoded and it is rather difficult to decode them back into human-readable form. After some hacking of MG5aMC_PY8_interface.cc I am able to get a much more usable HepMC file that starts like this: HepMC::Version 2.06.09 HepMC::IO_GenEvent-START_EVENT_LISTING E 0 -1 -1.0000000000000000e+00 -1.0000000000000000e+00 -1.0000000000000000e+00 9999 0 207 1 2 0 3 2.0320000000000008e-03 1.9255052800000001e-06 4.6923640000000006e-07 N 3 "Weight_MERGING=0.000" "point1_MERGING=0.000" "point2_MERGING=0.000" U GEV MM Again, the important line is N 3 "Weight_MERGING=0.000" "point1_MERGING=0.000" "point2_MERGING=0.000" which now contains easily readable weight ids in a single line. So, finally, my question is whether there is an "official" way to do this without hacking the MG5aMC_PY8_interface? Also, is there some deeper reason for the current weight naming in HepMC files? Thanks, Simonas

When	Who	Action	New State
2020-10-13	Olivier Mattelaer	Answer	Answered
2020-10-13	Simonas Drauksas	Comment	Answered
2020-10-13	Stefan Prestel	Comment	Answered
2020-10-14	Simonas Drauksas	Comment	Answered

MadGraph5_aMC@NLO

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