Re: Random Seeds in G4_VMC

From: Mohammad Al-Turany <m.al-turany_at_gsi.de>
Date: Mon, 5 Oct 2009 15:54:11 +0200

Hi,

For me it is ok, I never used this method, for G3 it is also not really needed because in the ctor of the TVirtualMC the fRandom is set to gRandom and usually I set up my random number generator before creating the montecarlo engine.

Regards

Mohammad

On 10/5/09 3:15 PM, "Ivana Hrivnacova" <Ivana.Hrivnacova_at_cern.ch> wrote:

> 
> I think much simpler, and more transparent to the user
> would be to change the current TVirtualMC function:
>     virtual void SetRandom(TRandom* random);
> to
>     virtual void SetRandomSeed(Long_t seed);
> 
> Ivana
> 
> 
> Mohammad Al-Turany wrote:
>> Hallo Ivana,
>> 
>> Ok, I agree it is more complicated than what I expected! But all what I want
>> is to be able to set the seed myself in a consistence way, without really
>> caring which random generator is running behind.
>> 
>> So what about implementing something in the init of VMC which simply put the
>> gRandom::GetSeed() in an ASCII (current.rnd) file that is read by default in
>> the g4config.in with
>> 
>> /random/resetEngineFrom    current.rnd
>>  
>> And for the advanced users who would like to restore or re-process a run
>> they have to change the config.in. But at least for the normal use one has
>> the control over the random seed whatever generator is setting behind,
>> because originally we had the problem with G4_VMC that it always uses the
>> same seed and that is way we need to control it specially on the grid and
>> batch farms.
>> 
>> 
>> Regards
>> 
>> Mohammad
>> 
>> 
>> On 10/5/09 11:33 AM, "Ivana Hrivnacova" <Ivana.Hrivnacova_at_cern.ch> wrote:
>> 

>>> Hi Mohammad,
>>>
>>> Geant4 does not use the random number generator from Root,
>>> but from CLHEP, that's why I considered it as misleading
>>> to implement setting its seed via gRandom.
>>>
>>> The reason is that this way would not allow you
>>> to re-process a run or event from a previous simulation
>>> by storing gRandom status and restoring it in a new
>>> simulation, as gRandom status has nothing to do with
>>> the random generator used by Geant4.
>>>
>>> The command
>>> /random/resetEngineFrom current.rnd
>>> should be used together with a file stored via Geant4
>>> commands
>>> /random/saveThisRun
>>> /random/saveThisEvent
>>> If you try the command and look at the file, you
>>> will see that there is more data than just one long number.
>>>
>>> You can use gRandom->GetSeed() (=mySeed) number for setting
>>> initial seed:
>>> /random/setSeeds mySeed mySeed
>>> (G4 setSeeds requires at least two long values)
>>> but a question is what it will be good for.
>>>
>>> A possible solution to handle the different random generators
>>> in a common way via VMC could be to interface the appropriate
>>> functions for storing/restoring the generator status.
>>>
>>> Best regards,
>>>
>>> Ivana
>>>
>>>
>>> Mohammad Al-Turany wrote:

>>>> Hallo,
>>>> 
>>>> As you all know to set the Random seed in G3_VMC it is enough to use
>>>>  gRandom->SetSeed(seed), in G4_VMC this does not work, and what I do to
>>>> set the seed is to go via the g4config.in macro  and put there:
>>>> 
>>>>     /random/resetEngineFrom    seed.rnd
>>>> 
>>>> Where seed.rnd is an ASCII file containing my seeds.
>>>> 
>>>> Is it possible to unify this behavior and to pass the seed from gRandom
>>>> to the G4_VMC in the initialization? Or do you have any other suggestion?
>>>> 
>>>> Regards
>>>> 
>>>> Mohammad
>>>> 
>> 

Received on Mon Oct 05 2009 - 15:54:14 CEST