Re: [fluka-discuss]: Numerical precision in FLUKA

From: paola sala <paola.sala_at_cern.ch>
Date: Fri, 16 Oct 2015 09:21:25 +0200

Dear Roberta,
looking better at your message:
the write statement is not compatible with the format, Jtrack is an
integer, not a real. Also, the output unit (42 in your case) must be an
integer number. Depending on the compiler, these instructions can
trigger a crash, or output a nonsense number for Jtrack, or... could you
please specify which compiler did you use, and, better correct the
statements, for instance

200 FORMAT(1x,A,I5,4E25.15)

WRITE(42,200)'333333',JTRACK,ETRACK-AM(JTRACK),
      $ CXTRCK,CYTRCK,CZTRCK


Paola
On 10/16/2015 07:23 AM, Paola Sala wrote:
> Dear Roberta
> strange. Could you please send me the input and the user routines?
> Thanks
> Paola
>> Dear Paola,
>> thank for your suggestion, indeed in my modified mgdraw.f I was using an
>> unfitting format in writing the txt file.
>>
>> Anyway, now, I fixed it, using:
>> 200 FORMAT(' ',A,5E25.15)
>> ......
>> WRITE(42.0,200),'333333',JTRACK,ETRACK-AM(JTRACK),
>> $ CXTRCK,CYTRCK,CZTRCK
>>
>> And the values I get for CZTRCK (for angle < 0.4mrad ) are:
>> CZTRCK=1 or CZTRCK=0.999999940395355E+00
>> and nothing between these values.
>>
>> See, as an example for angle grater than 0 and less than 0.4mrad, few
>> output lines below (*).
>>
>> So, now it doesn't seem a numerical precision issue anymore.
>> Do you have any idea on how to cope with that?
>> Thank you,
>> Roberta
>>
>> (*)
>> 333333 0.700000000000000E+01 0.489577674865723E+02
>> -0.379900448024273E-03 0.734752029529773E-04 0.999999940395355E+00
>> 333333 0.100000000000000E+01 0.398913940429688E+03
>> 0.243720045546070E-03 0.187961297342554E-03 0.999999940395355E+00
>> 333333 0.100000000000000E+01 0.378580841064453E+03
>> 0.240417313762009E-03 0.217997265281156E-03 0.999999940395355E+00
>> 333333 0.100000000000000E+01 0.398872375488281E+03
>> -0.289755815174431E-03 -0.169058344908990E-03 0.999999940395355E+00
>> 333333 0.100000000000000E+01 0.398769622802734E+03
>> -0.195283661014400E-03 -0.303217006148770E-03 0.999999940395355E+00
>> 333333 0.100000000000000E+01 0.398898071289062E+03
>> 0.582441571168602E-04 0.355932890670374E-03 0.999999940395355E+00
>> 333333 0.100000000000000E+01 0.398916778564453E+03
>> -0.868009956320748E-04 0.254166428931057E-03 0.999999940395355E+00
>>
>> 2015-10-13 7:36 GMT+02:00 Paola Sala <paola.sala_at_mi.infn.it>:
>>
>>> Hi
>>> it looks like there is some single precision variable, either in the
>>> writing or reading procedure, that cuts your rounding.
>>> Please check all the steps, and be sure to use double precision
>>> variables
>>> (the default in FLUKA) and to write them with enough decimals.
>>> You might also want to try the predefined FLUKA scoring options.
>>> Ciao
>>> Paola
>>>> Dear experts,
>>>> I have a question on the numerical precision which FLUKA can get on
>>> the
>>>> angular distributions.
>>>> I simulated a 400 GeV proton beam incident on a thick Be target, 50 cm
>>>> long.
>>>> I modified the mgdraw.f routine in order to get an ASCII file with the
>>>> information I need.
>>>> I am interested in the particles produced and going out of the target
>>> at
>>>> very small angle, say less than 0.2 mrad. I simulated my geometry with
>>>> cylindrical symmetry along z axis, so I am interested in particles
>>> with
>>>> ZSCO close to 1.
>>>> I see that the next value less than 1 is ZSCO=0.99999994,
>>> corresponding
>>> to
>>>> an angle of 0.00034641 rad. So I cannot get a continuous distribution
>>> in
>>>> that angle range.
>>>> I am attaching two plots to show you the issue, they show the polar
>>> angle
>>>> vs kinetic energy for neutrons, one is with angle less than 10 mrad,
>>> and
>>> I
>>>> suppose that the distribution is reasonable, and the other is for
>>> angle<1
>>>> mrad.
>>>> I am wondering if there is any way to increase the precision.
>>>> Also, can you please tell me if the distribution I get is the expected
>>> one
>>>> or if you see further issues with that?
>>>> Thank you,
>>>> best regards,
>>>> Roberta Volpe
>>>>
>>>
>>> Paola Sala
>>> INFN Milano
>>> tel. Milano +39-0250317374
>>> tel. CERN +41-227679148
>>>
>>>
>
> Paola Sala
> INFN Milano
> tel. Milano +39-0250317374
> tel. CERN +41-227679148
>
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Received on Fri Oct 16 2015 - 10:24:25 CEST

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