Re: Random Seeds in G4_VMC

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
>>