Bug #16936

Zero length steps during LArG4

Added by Jason Stock over 3 years ago. Updated about 2 years ago.

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Running Dune's standard_g4_dune10kt_1x2x6.fcl on /pnfs/dune/scratch/users/jstock/GeneratedBugSample.root
produces a divide by zero error.
To reproduce, run the above with a breakpoint at larsim/LArG4/ISCalculationSeparate.cxx: 106

Using Allinea I have tracked the bug as far as larsim/LArG4/ISCalculationSeparate.cxx line 106. dx=0. The issue is that the g4 step it is looking at is apparently length 0 (G4Step Step->GetPreStepPoint->GetPosition()==ste->GetPostStepPoint()->GetPosition() ).


#1 Updated by Jason Stock over 3 years ago

  • Subject changed from larsim/LArG4/ISCalculationSeparate.cxx to Zero length steps during LArG4

Changing bug name

#2 Updated by Jason Stock over 3 years ago

I find the following will reliably produce the bug on a dunegpvm.

source /cvmfs/
setup larsoft v06_40_01 -q e14:prof
setup dunetpc v06_40_01 -q e14:prof
lar -c prod_Ar39.fcl -n 10 -o gen.root ###(Available from dunetpc feature/JStock_Ar39Test
lar -c standard_g4_dune10kt_1x2x6.fcl -n 10 -o g4.root gen.root

#3 Updated by Jason Stock over 3 years ago

Bug does not appear in v06_39_00.

I should also note, when the bug is noticed, the PreStepPoint and PostStepPoint are the same, and the energy deposited is extremely small (~10^-14).

#4 Updated by Lynn Garren over 3 years ago

  • Status changed from New to Assigned
  • Assignee set to Hans-Joachim Wenzel

Hans, can you have a look?

#5 Updated by Hans-Joachim Wenzel about 2 years ago

  • Status changed from Assigned to Resolved
  • % Done changed from 0 to 100

I tried if I could reproduce the 0 step length problem using the new larg4 module where voxel read out is replaced with a simple step limiter. I ran a million single particle event and never ran into the problem. So my recommendation is to move to the new larg4

#6 Updated by Jason Stock about 2 years ago

Alex, is DUNE able to move to the new LArG4 yet?

#7 Updated by Alexander Himmel about 2 years ago

No. Certainly from the photon detector side, we will not have any cycles to validate major changes in infrastructure until we are past the TDR studies. I would estimate next March or April would be the right time to bring this discussion back up.

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