From f1988b5579dd00ae27ad5c6f089881d8ee5e6248 Mon Sep 17 00:00:00 2001 From: tomeichlersmith <eichl008@umn.edu> Date: Thu, 26 Oct 2023 15:27:31 -0500 Subject: [PATCH] longer comment about process ordering trying to point future developers in the right direction --- src/SimCore/GammaPhysics.cxx | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/src/SimCore/GammaPhysics.cxx b/src/SimCore/GammaPhysics.cxx index b75bf48..ed65361 100644 --- a/src/SimCore/GammaPhysics.cxx +++ b/src/SimCore/GammaPhysics.cxx @@ -31,7 +31,24 @@ void GammaPhysics::ConstructProcess() { modelParameters); pn->removeExistingModel(processManager); pn->ConstructGammaProcess(processManager); - // put the PN process first in the ordering in case PN biasing is happening + /** + * Put the PN process first in the ordering in case PN biasing is happening. + * + * Process ordering is a complicated concept and unfortunately + * its affect on biasing is poorly documented. What has been said is + * that some processes _need_ to be called _last_[1]. In addition, + * the practical experience of working on defining a custom + * process for + * [G4DarkBreM](https://github.com/LDMX-Software/G4DarkBreM) + * showed that sometimes Geant4 does + * not get through the full list of processes but it always starts + * at the beginning. For these reasons, we put the PN process first + * in the ordering so that we can insure it is always check by Geant4 + * before continuing. + * + * [1] + * https://indico.cern.ch/event/58317/contributions/2047449/attachments/992300/1411062/PartDef-ProcMan-AS.pdf + */ const auto processes{processManager->GetProcessList()}; for (int i{0}; i < processes->size(); i++) { const auto process{(*processes)[i]};