[Gate-users] problem with random number seed?

David Boersma david.boersma at physics.uu.se
Mon Feb 1 16:14:57 CET 2016


It looks like Thomas Deschler was right: random number seeding in Gate 
(current develop version, but I suspect the conclusions also hold for 
release 7.1) only works correctly if the Geant4 10.1 libraries were 
compiled with multithreading OFF. By "correctly" we mean: with "auto" 
seeding you get a different seed every time you run it, and therefore 
statistically independent outputs. If you use a geant4 installation 
built with multithreading=ON, then successive Gate runs will give 
identical outputs.

We verified this (on Linux and on MacOSX) by compiling Geant4 with and 
without multithreading, and then building Gate with it. We ran Hediye's 
minimal RT macro (shoot electrons on a target foil, and collect a 
phasespace of the particles after it, stored in a ROOT output file). We 
ran the macro twice (renaming the output directory in between). "Ekine" 
histograms of the two runs were numerically identical when we ran *with* 
multithreading and they were clearly different *without* multithreading.

Short term action item: it would be good to document this clearly in the 
README file and/or the 7.1 installation guide on the wiki.

Medium/long term action item: fix Gate to work correctly with 
multithreaded geant4.

I have more comments, but they are more technical, will submit them as 
"issues" on GitHub.

David B.

Den 01/02/2016 kl. 11:18, skrev hediye acun:
> Hello Loic,
> We tried your recommendations with David Boersma.  First we run main
> macro file for 20 particles and stored output in PhS_new.root file. We
> got particle's properties(location and energy) in root with Scan command
> and then we closed root to make sure root will not remember the first
> output file due to the same tree's name. We run main macro second time
> with same particle number(20) to get second output file which called
> PhS_try.root.  In root with scan we obtained particle's properties again
> for second run. After that we compared two text files which include
> particle's location and energies and there was no difference between them.
> David Boersma run same macro file in his computer which has Geant4
> compiled with multithread OFF, and he obtained different results for
> same number of primaries. My Geant4 compiled with multithread ON.  We
> are going to try to compile on my computer with multitherad OFF and on
> David's computer multithread ON to investigate whether it really depends
> on the multithreading.
> Best regards.
> Hediye acun
> PS. It looks like the mailing list not working today. David didn't
> receive your reply and we didn't see on the archive either.
> ------------------------------------------------------------------------
> *From:* Grevillot Loic <loic.grevillot at medaustron.at>
> *To:* hediye acun <acunhediye at yahoo.com>;
> "gate-users at lists.opengatecollaboration.org"
> <gate-users at lists.opengatecollaboration.org>
> *Sent:* Monday, February 1, 2016 9:20 AM
> *Subject:* RE: [Gate-users] problem with random number seed?
> Hello,
> In my experience the command"/gate/random/setEngineSeed auto"works.
> In your example you are looking at histograms, but to verify that issue
> I was thinking about something different:
> -If the seed did not change as you suspect, the physical properties from
> every single particle stored in your Phase Space one after the other
> shall be exactly the same (position, direction, energy, etc.) for 2
> simulations.
> -Could you check that on a particle basis for 10 or 20 particles?
> You could even try a very simple example where you could randomly sample
> 10 particles and look if they are the same for 2 simulations.
> Let us know!
> Thanks
> Image:Uncle_Sam_pointing_finger_small.jpgImage:We-Need-You1-324x500.jpgImage:superdupont-we-need-you.jpgImage:gsam_want_gnu_small.jpg
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> *From:*gate-users-bounces at lists.opengatecollaboration.org
> [mailto:gate-users-bounces at lists.opengatecollaboration.org] *On Behalf
> Of *hediye acun
> *Sent:* Friday, January 29, 2016 3:46 PM
> *To:* gate-users at lists.opengatecollaboration.org
> *Subject:* [Gate-users] problem with random number seed?
> Hello All,
> I have Gate "develop" version and at the same time geant4.10.1.0 and
> root_v5.34.32 on the GPU. My operating system is Linux Mint 17.2 .
> I am triying to simulate a linac head to get Phase Space of photons.
> Just for an example I run Gate for a basic geometry which include only
> electron beam, target filter and Phase space plane inside a linac
> geometry. When I run Gate two or more times for same "number of
> primaries" I got the exactly the same Phase Space distributions
> (histogram of Ekine completely identical). But I am using
> "/gate/random/setEngineSeed auto" command and according to the
> documentation that should give me the different seed every time when I
> run it. I would expect some random differences between PhS's from
> different runs.
> Does anyone have any idea about this issue? Thank you in advance.
> Hediye Acun
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