On 01/23/2014 09:25 AM, Jan Blechta wrote:
> On Thu, 23 Jan 2014 18:19:45 +0100
> Jan Blechta <[email protected]> wrote:
> 
>> On Thu, 23 Jan 2014 08:53:13 -0800
>> Nikolaus Rath <[email protected]> wrote:
>>
>>> On 01/23/2014 04:19 AM, Jan Blechta wrote:
>>>> On Wed, 22 Jan 2014 11:39:30 -0800
>>>> Nikolaus Rath <[email protected]> wrote:
>>>>
>>>>> Hi Jan,
>>>>>
>>>>> It was my impression from the other thread that I could handle
>>>>> the problem of multiple solutions by giving the nullspace to the
>>>>> solver. But I'll try the Laplace constraint as well.
>>>>>
>>>>> But then, even with u constrained, I still need to somehow put
>>>>> the same constraint on the test functions, don't I? That's the
>>>>> part I'm struggling with.
>>>>
>>>> Sure. This is why it seems logical to me to constraint both trial
>>>> and test space by Laplace equation. Nevertheless I did not think
>>>> it over a much.
>>>
>>>
>>> For what it's worth, it seems logical to me as well... I just don't
>>> know how to impose the second constraint.
>>
>> Check
>> http://fenicsproject.org/documentation/dolfin/1.3.0/python/demo/documented/neumann-poisson/python/documentation.html
>>
>> Testing by (v, 0) and (v + c, 0) gives linearly dependent equations -
>> in fact, the same. Similar construction can apply to your problem.
> 
> Here, I meant (v, 0) and (v + arbitrary_constant, 0). And it holds
> because "the sufficient condition"
>   \int f \dx + \int g \ds = c |\Omega|
> is fulfilled.


I'm afraid I'm completely lost. What do you mean with "Testing by (v, 0)
and (v + arbitrary_constant, 0)", and what is |\Omega|? The sufficient
condition on the above link doesn't have this term...



Thanks,
Nikolaus

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