[aspect-devel] Aspect logical operators

[FELIPE ORELLANA ROVIROSA]

Hola Rene, thanks for replying.

   Yesterday there were some email bugs, as I initially sent an image and
the system rejected it, then I resent copy-pasting the text only, but I am
not sure if you could read the whole.

   I am not using any plugin. I am simply using an IF conditional statement
on the
subsection Boundary velocity model. And yeah, it seems that Aspect
automatically discards any value application inside the domain (where the
ELSE would act).

   Still, the parser obliges one to write something (a value) for the ELSE.

Thanks Rene.

This was yesterday's complete text:

   I used an IF for the boundary conditions using the coordinates x<=0 ||
x>=1e6 || z>=5e5, and had set the ELSE value to 0, which under the logic of
the IF would have meant 0 velocity_x inside the domain. It worked well !!!
my plot looks just as I wanted the system to behave in this case.
   Somehow Aspect knows that even if the velocity is set to 0 inside the
domain on the subsection Boundary velocity model, it has to be discarded,
as inside the domain the Stokes eqs. are solved.

  Anyways I think it is a good practice to use a 'very wrong' value (like
-1e99) in case we wanna catch a bug.

Felipe

On Thu, Jan 5, 2017 at 1:59 AM, Rene Gassmoeller <
rene.gassmoeller at mailbox.org> wrote:

> Hi Felipe,
>
> from your description it looks like you are assigning a velocity boundary
> condition via the function plugin, is this correct? In this case ASPECT
> 'knows' not to apply the boundary condition to anything inside the domain,
> because the function is not  evaluated (and the corresponding constraint is
> not applied) for anything but the boundary. Therefore, you do not need to
> manually exclude the interior of the domain in your function, which makes
> writing the function much simpler.
>
> Nice to know that your model is working now.
>
> Best,
>
> Rene
>
>
> On 01/04/2017 10:01 PM, FELIPE ORELLANA ROVIROSA wrote:
>
> Hi Wolfgang,
>
>   Thanks for replying.
>
>    I used an IF for the boundary conditions using the coordinates x<=0 ||
> x>=1e6 || z>=5e5, and had set the ELSE value to 0, which under the logic of
> the IF would have meant 0 velocity_x inside the domain. It worked well !!!
> the attached plot looks just as I wanted the system to behave in this case.
>
>    Somehow Aspect knows that even if the velocity is set to 0 inside the
> domain on the subsection Boundary velocity model, it has to be discarded,
> as inside the domain the Stokes eqs. are solved.
>
>   Anyways I think it is a good practice to use a 'very wrong' value (like
> -1e99) in case we wanna catch a bug.
>
> thanks,
>
> Felipe
>
> On Wed, Jan 4, 2017 at 5:29 AM, Wolfgang Bangerth < <bangerth at tamu.edu>
> bangerth at tamu.edu> wrote:
>
>> On 01/04/2017 12:06 AM, FELIPE ORELLANA ROVIROSA wrote:
>>
>>>
>>>     Now that you specify your point of view, I realize that this is a
>>> broad
>>> problem concerning logic and physics.
>>>
>>>     What you wrote is essentially true, but I think you are missing some
>>> possible cases.
>>>
>>>      As a note: Several codes use simple IF statements without ELSE
>>> (just to
>>> do something in a weird case, or so..), but this all depends on how one
>>> builds
>>> the program.
>>>
>>>     I am trying to use a conditional statement to specify the value of a
>>> variable (using an IF over the coordinates to specify a Boundary
>>> Condition,
>>> say x<=0), but otherwise, when the condition is not true (for example
>>> inside
>>> the domain) not to specify anything (cause there Stokes' fluid equations
>>> are
>>> solved).
>>>
>>>    What should I do in that case for the ELSE?   -1,..Nan..?
>>>
>>
>> If I need to specify a value that I know should not be used, I try to use
>> something that is *so wrong* that I will immediately know if it happens to
>> be used anywhere (although I *believed* that it would not be used).
>>
>> NaN is a good candidate in those cases, but I'm not sure that you can
>> specify it in the formula parser. -1e100 is also a good candidate.
>>
>>
>>  I have tried and tested, but I am not getting physically reasonable
>>> outcomes.
>>>
>>
>> But that must not have anything to do with the other problem above since
>> you say that whatever happens in the ELSE branch should not matter.
>>
>>
>> Best
>>  W.
>>
>> --
>> ------------------------------------------------------------------------
>> Wolfgang Bangerth          email:
>> <bangerth at colostate.edu>bangerth at colostate.edu
>>                            www:
>> <http://www.math.colostate.edu/%7Ebangerth/>
>> http://www.math.colostate.edu/~bangerth/
>>
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>
>
>
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