From: Jamshid Soltani (jsoltani@physics.pub.ro)
Date: Tue Dec 11 2007 - 18:51:38 CET
Hi Vasilis,
Thank you for your kindly respond.
I did your and Konstantin suggestion and generate 5 cycles .
in attach file there is a new graph for Bragg Peak.you see statistical
fluctuations for photon interaction have been reduced but there is yet.If
I
define Zero bins in X and Y direction it takes error.I had to define
USRBIN card as in attach file for photon interaction.
I am waiting for your suggestion.
thanks
jamshid
> Hi jamshid,
>
> welcome to the wonderful world of monte carlo.
> This zig-zag has a name (and a family-name :) and is called statistical
> fluctuations and you will have to learn to live with it. Actually is a
> very useful information that tells you how well you should trust your
> result.
>
> However a better quantity to plot, is the statistical mean of each bin
> together with the error on the mean. In principle MC is a counting
> experiment and should follow a Poisson distribution, therefore the error
> is the square root of the counts in each bin, which is no longer true if
> you are using biasing or other techniques. Therefore FLUKA exploits the
> Central Limit Theorem to get the correct mean and error on the mean. For
> this reason you need to perform a few cycles and based on the CLT the
> final distribution on the average will tend to be Normal (for infinite
> cycles) no matter what was the original distribution. Actually it
> converges very quickly and 5 cycles are enough.
>
> Please give a look on the FLUKA course material and especially the
> presentations about the monte carlo and estimators.
>
> Regards
> Vasilis
>
> Jamshid Soltani wrote:
>> Dear fluka Users,
>>
>> I made a graph for interaction of Photon with 1.3 Mev with water as
>> attach input file.there is my graph in attach file too.there is more
>> widspreding(Zig-zag) in the graph. I changed DEFAULTS to PRECISIOn and
>> EM-CASCAde but there is zig-zag yet.Can I omit it or not? what is the
>> reasons of these event?
>>
>> thanks
>> jamshid Soltani
>>
>>
>>
>>
>
>
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