From: Alberto Fasso' (fasso@SLAC.Stanford.EDU)
Date: Tue May 30 2006 - 20:04:02 CEST
Dear Dr. Fan,
first one remark that is valid for you as well as for any other user who
wants an explanation about some results: please send always your input
file and your user routines (if any), and send them as text attachments.
In general, the person who asks "sees" only a small part of the problem,
which most often is located somewhere else. In your case, for instance,
nobody can know what you have coded into your mgdraw file: what is printed as
"track length of each step" could be correct, or could have been
misunderstood. And your input could contain commands that have an effect
on that track length.
Having said that, I would like to warn you that the user is not supposed
to change the default stepsize, UNLESS THERE ARE MAGNETIC FIELDS.
The idea that you could use the STEPSIZE command to reduce calculation time
is not a good idea. In principle, you could gain some (small) amount of time
by setting a maximum energy loss per step by means of commands EMFFIX
and FLUKAFIX. But the first is only for electrons, and both commands anyway
assure you only that each step is SMALLER than a certain length, not that
all steps have a given length. And this maximum length cannot be larger
than that corresponding to a 20% energy loss.
You need to remember that FLUKA has a very sophisticated algorithm to manage
the step length, which is already optimized for both accuracy and time, and
using STEPSIZE you can only do worse. The reason STEPSIZE is available
is only to make sure that a small region is not missed when tracking IN
A MAGNETIC FIELD, and that a particle of very low energy does not spiral
unnecessarily IN A MAGNETIC FIELD.
Best regards,
Alberto
On Tue, 30 May 2006, Fan, Ph.D., Jiajin wrote:
> Hi all,
>
> I'm working on proton and carbon dose calculation. I tried to use STEPSIZE
> card to change charged particles' stepsize to reduce calculation time. And I
> use mgdraw.f to output particle track info to test it. But I found what ever
> minimum step size I gave to input file, particle track is always same. Can
> anybody tell me what's wrong in my input? Thank you.
>
> Stepsize input card (no other input cards which will affect particle step
> size):
>
> * minimum 1.0 cm, maximum 10.0 cm in region 3
> STEPSIZE 1. 10.0 3.0 0.0 0.0 0.0
>
> Track info:
>
> * First column: track length of each step; Second column: energy
> deposit in this step
> * Last column: (carbon) total kinetic energy
> 0.019366 2.216800 1.000000 0.000000 0.000000 0.000000 0 0
> -30 3597.783447
> 0.012749 1.459835 1.000000 0.000000 0.000000 0.000000 0 1
> -30 3596.324463
> 0.019322 2.213185 1.000000 0.000000 0.999730 -0.023238 0 0
> -30 3593.977539
> 0.008135 0.932023 1.000000 0.000345 0.999730 -0.023238 0 0
> -30 3593.045654
> 0.010283 1.178353 1.000000 0.000000 0.999730 -0.023238 0 0
> -30 3591.866943
> 0.003214 0.368304 1.000000 0.000000 0.999730 -0.023238 0 0
> -30 3591.498779
> 0.002584 0.296127 1.000000 0.000000 0.999730 -0.023238 0 1
> -30 3591.203125
>
> The minimum step size is much smaller than 1.0 cm set in input file, and
> output info is always same whatever minimum stepsize value set in input
> file. I don't know why. Thanks again.
>
> *******************************************
> Jiajin Fan, Ph.D.
> Research Associate, Radiation Oncology
> Fox Chase Cancer Center
> 432 Rhawn Street, Philadelphia, PA 19111
> Tel: (215) 214-1711
> Fax:(215) 728-1148
> Email: jiajin.fan@fccc.edu
> *******************************************
>
>
-- Alberto Fassò SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025 Phone: (1 650) 926 4762 Fax: (1 650) 926 3569 fasso@slac.stanford.edu
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