Re: [fluka-discuss]: About statistical error

From: Santana, Mario <msantana_at_slac.stanford.edu>
Date: Tue, 24 Sep 2013 12:37:09 -0700

On 9/24/13 1:35 AM, "pkrai_at_barc.gov.in" <pkrai_at_barc.gov.in> wrote:

>I have made two run for a same input file.
>
>1) With number of histories=1000000 and 10 statistically independent run.
>
>2) With number of histories=10000000, with only 1 run
>
>
>I am getting same result for usrbdx detector in both cases with only
>difference of statistical error.

This is normal. If you look at the end of your long simulation there will
be a random seed file ranYYY002 which will be identical to that after the
10th cycle of your short simulation, ranYYY011.

>
>so what is the use of 10 independent run, only for calculation for error?

Please note that what you are describing are not 'independent' runs. Each
of these runs starts with a seed generated at the end of the previous run,
i.e.. ranYYYnnn
Yes, it allows computing the error. Also, you could compute higher order
momenta of your estimators.
Also, by splitting a long simulation in shorter runs you could start to
analyze your output after the fist few runs and decide to stop your
simulation if you have enough statistics or if you have done something
wrong. Moreover, if the system crashes for any reason, you will have some
results.

However, the most common use of shorter runs is to send 'truly'
independent simulations (each with a different seed number in the input
file) to different CPUS, so that you can 'parallelize' your calculation.

>
>what is mean by a vector of 97 seed? how it initialises random number
>generator?

The seed file is used to start your next simulation (when you use the -N n
-M m flags in the running script)

FLUKA uses an updated version of the Marsaglia random generator algorithm
to 64-bit pseudo-random sequences with a periodicity of about 10^44


>
>
>
>
>
Received on Tue Sep 24 2013 - 22:48:04 CEST

This archive was generated by hypermail 2.3.0 : Tue Sep 24 2013 - 22:48:09 CEST