[Gate-users] problem with random number seed?
David Boersma
david.boersma at physics.uu.se
Mon Feb 1 17:29:04 CET 2016
Hi,
Den 01/02/2016 kl. 17:08, skrev Andrej:
> A quick and dirty fix is to set the randomSeed to some run related
> number. I know that in geant people would sometimes start each event
> with a seed equal to that event number. Here you only have to do it
> run-wise.
Unfortunately when we try that we still get identical outputs for
successive runs.
I think that the problem is not in how Gate obtains a seed (from
/dev/random with "auto" or reading a literal user-supplied value from
the macro), but rather in how Gate communicates that seed to (a
multithreaded version of) the geant4 library.
David
>
> Cheers
>
> Andrej
>
> surabhi balagopal nair je 2/1/2016 ob 4:40 PM napisal:
>> Hello,
>>
>> Can anyone tell me whether the Virtual Gate is built on GEANT4
>> multithread ON or OFF?
>>
>> Thank you,
>> SN
>>
>> On 1 February 2016 at 10:14, David Boersma
>> <david.boersma at physics.uu.se <mailto:david.boersma at physics.uu.se>> wrote:
>>
>> Hi,
>>
>> 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.
>>
>> HTH,
>> 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
>> <mailto:loic.grevillot at medaustron.at>>
>> *To:* hediye acun <acunhediye at yahoo.com
>> <mailto:acunhediye at yahoo.com>>;
>> "gate-users at lists.opengatecollaboration.org
>> <mailto:gate-users at lists.opengatecollaboration.org>"
>> <gate-users at lists.opengatecollaboration.org
>> <mailto: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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>> *On Behalf
>> Of *hediye acun
>> *Sent:* Friday, January 29, 2016 3:46 PM
>> *To:* gate-users at lists.opengatecollaboration.org
>> <mailto: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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