Re: FLUKA: Max. number of USRBIN binnings

[Alberto Fasso' <fasso@slac.stanford.edu>]

On Fri, 24 Nov 2000, Laurent APHECETCHE wrote:

> By the way, I also debugged my geometry and I have some :
> 
>   *** Region # 27 Dnear according to    no    overlapping ORs ***
>   *** Region # 53 Dnear according to possible overlapping ORs ***
>   *** Region # 56 Dnear according to possible overlapping ORs ***
>   
> messages. Are those errors or just warnings ?

They are neither errors nor warnings, just information.
Overlapping ORs (i.e. overlapping subregions in a region definition)
are perfectly legitimate. The reason why this information is printed out
is that when there are overlapping subregions, special precautions must
be taken if the user wishes to reproduce exactly a given run using
the same random number sequence.

See an explanation in the manual, under command GLOBAL:

DNEAR designates the distance between the current particle position and
the nearest boundary (or a lower bound to that distance), and it is used
by FLUKA to optimize the step length of charged particles. The concept and
the name have been borrowed from the EGS4 code, but the FLUKA
implementation is very different because it is fully automatic rather than
left to the user, and it is tailored for Combinatorial Geometry, where a
region can be described by partially overlapping bodies. The sequential
order in which the overlapping bodies are considered when evaluating DNEAR
is irrelevant from the point of view of particle tracking, but can affect
the random number sequence. This does not have any effect on the average
results of the calculation, but the individual histories can differ due
the different random number sequence used. Option GLOBAL can be used in
those cases where the user wants to reproduce exactly each particle
history, or on the contrary to forgo it in order to get a better step
optimization.


Alberto

PS In the above explanation, probably "overlapping bodies" should be
replaced by "overlapping subregions"


--------------------------------------------------
Alberto Fasso'
Stanford Linear Accelerator Center
Radiation Physics Dept. ms 48
2575 Sand Hill Road
Menlo Park, CA 94025   

Tel. +1 650 926 4062        Fax: +1 650 926 3569