Dear All,
thank you Stefan. I might just add a detail:
The procedure described by Stefan assumes an obvious prerequisite: the
fluka runs must be "independent", meaning that they must start with
different random numbers. The Fluka ($FLUPRO/flutil/rfluka ) and flair
procedures ensure this independence by input/output of the first/last
random number in each cycle.
However, if several runs are sent in parallel on different CPUs, or the
same run is restarted from zero in a different disk area, the user has
to be sure that the initial random for the runs are different, by
changing the RANDOMIZE card. Otherwise, results from the parallel runs
will be identical. In this case, statistical errors will be magically
zero or negligible (can be, due to rounding when writing results to disk).
Again, fluka and flair provide utilities (a script in $FLUPRO/flutil, or
the loop menu of flair) to handle this automatically.
Regards
Paola
On 3/15/24 09:34, Stefan E. Mueller wrote:
> Dear Amandeep Sharma,
>
> the FLUKA postprocessing routines (either invoked from FLAIR's
> "Process"-Button in the "Run"->"Data" menu, or using directly the
> executables in $FLUPRO/flutil/*suw) use the Central Limit Theorem to
> express the statistical uncertainty of the scorer result as the standard
> deviation (sigma) of a normal distribution. For this, the
> postprocessing routines need at least 5 independent FLUKA runs.
>
> See e.g.
>
> https://indico.cern.ch/event/753612/contributions/3121551/attachments/1974578/3285956/MC_2019.pdf
>
> (slides 20ff)
>
> As a (crude) rule of thumb, the simulation has converged if this
> uncertainty is better then 5 percent.
>
> All other uncertainties (often called "systematic uncertainties")
> unfortunately have to be (gu)es(s)timated by the user.
>
> Cheers,
>
> Stefan
>
> --
> Stefan E. Mueller
> Department of Information Services and Computing - Computational Science
> and Institute of Radiation Physics
> Helmholtz-Zentrum Dresden-Rossendorf
> Tel: +49 (0351) 260 3847
> Stefan.Mueller_at_hzdr.de
> http://www.hzdr.de
>
> Vorstand: Prof. Dr. Sebastian M. Schmidt, Dr. Diana Stiller
> Vereinsregister: VR 1693 beim Amtsgericht Dresden
>
> On Thu, 14 Mar 2024, Amandeep Sharma wrote:
>
>> Whether it represents the statistical uncertainity in results or it is
>> different from statistical uncertainity?
>> Regards !
>>
>> On Thu, 14 Mar, 2024, 10:15 pm Stefan E. Mueller,
>> <stefan.mueller_at_hzdr.de>
>> wrote:
>> Dear Imen Hammami,
>>
>> judging from your screenshot, I would say that your uncertainty
>> is
>> on the order of 0.014% for all your results. No need to multiply
>> by 100.
>> These are already percentage errors.
>>
>> Cheers,
>>
>> Stefan
>>
>> --
>> Stefan E. Mueller
>> Department of Information Services and Computing - Computational
>> Science
>> and Institute of Radiation Physics
>> Helmholtz-Zentrum Dresden-Rossendorf
>> Tel: +49 (0351) 260 3847
>> Stefan.Mueller_at_hzdr.de
>> http://www.hzdr.de
>>
>> Vorstand: Prof. Dr. Sebastian M. Schmidt, Dr. Diana Stiller
>> Vereinsregister: VR 1693 beim Amtsgericht Dresden
>>
>> On Thu, 14 Mar 2024, imen hammami wrote:
>>
>> > Hi, Could someone provide guidance on how to calculate the
>> Monte Carlo
>> > error from the output of the USRBIN card, given that we've
>> utilized 5*10^7
>> > primaries for 5 cycles to calculate the dose? Do I need to
>> multiply the
>> > values in the red box by 100 to get the exact error value in
>> percentage? Any
>> > insights would be greatly appreciated.
>> >
>> > Regards
>> >
>> >
>> >
>> >
>> >
>> >
>> > image.png
>> >
>> >
>>
>>
>>
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Received on Fri Mar 15 2024 - 17:51:54 CET