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Forum: Multithreading
Re: Question Irreproducible results (Tom Roberts)
Date: 02 Mar, 2015
From: Andrea Dotti <Andrea Dotti>

Dear Tom,
    we have been evaluating your bug report carefully. We have decided to mark it as "won't fix" because we believe this is not the source of the irreproducibility you describe (in addition the change you propose will introduce more non-reproducibility according to our definition, some details at: https://twiki.cern.ch/twiki/bin/view/Geant4/MultiThreadingTaskForce#Reproducibility).

I understand you are using G4 10.1 without multi-threading. This configuration is checked periodically for reproducibility, and as I mentioned, the main production physics lists (with the exclusion of Radioactive Decay and NeutronHP, on both of which we are working) are reproducible: we check both strong and weak reproducibility (e.g. starting again job with the same random number and reproducing a specific event in the middle of a job) and we do not see problems.

I also understand that you are using your own MPI wrapper and the reproducibility issue you report is between an MPI-enabled and an MPI-disabled application (i.e. comparing two jobs running in two different conditions and with different execution paths). I would suggest to first verify and exclude that the problem is in the specific application code: if you still consider the problem to be on our side you should provide a receipt that shows a G4 stand-alone example with breaking of either strong or weak reproducibility.

Regards, Andrea

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