Re: Random Seeds in G4_VMC

This is not good because random number classes may have a seed that is an int, a longlong or an array.

Rene

Ivana Hrivnacova 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 - 17:56:16 CEST