Thank you very much
Regards
El martes, 8 de febrero de 2022 a las 23:40:58 UTC+1, Timo Heister escribió:
> > *L_operator(local_dof_indices[i],local_dof_indices[j]) =
> cell_matrix(i,j);*
>
> *This looks incorrect, because global pairs of indices will happen more
> than once in a normal assembly (with a continuous finite element). You have
> to add the contribution using +=.*
>
>
> On Tue, Feb 8, 2022, 16:52 Hermes Sampedro <hermes...@gmail.com> wrote:
>
>>
>> Dear Wolfgang,
>>
>> Thank you for the clarification. In that case, I am missing some
>> operation somewhere...
>>
>> Let me clarify what I am doing. Apart from building the system_matrix, I
>> save the operator L in the assembling process. But I did not do any
>> distribute_local_to_global nor compress to that operator, as I do for the
>> system matrix. Is that wrong?
>>
>>
>> ________________________________________________________________________________________
>> *for (const auto &cell : dof_handler.active_cell_iterators())*
>> * if (cell->is_locally_owned())*
>> *{*
>> * for (unsigned int i = 0; i < dofs_per_cell; ++i)*
>> * { ......*
>> * for (unsigned int j = 0; j < dofs_per_cell; ++j)*
>> * {. .....*
>> * cell_matrix(i, j)= ....*
>> * ....*
>> * L_operator(local_dof_indices[i],local_dof_indices[j]) =
>> cell_matrix(i,j);*
>> * }*
>> * }*
>>
>> * cell->get_dof_indices(local_dof_indices);*
>> * constraints.distribute_local_to_global(cell_matrix,*
>> * cell_rhs,*
>> * local_dof_indices,*
>> * system_matrix,*
>> * system_rhs);*
>> *}*
>> *system_matrix.compress(VectorOperation::add);*
>> *system_rhs.compress(VectorOperation::add);*
>>
>> ________________________________________________________________________________________
>>
>> I checked the content of the matrics by solving a very small case. I
>> found that indeed system_matrix is different to the saved operator L. Do
>> you have any suggestion where the different is coming from? Both are taken
>> from the same assembling, the difference is that system_matrix applies
>> *distribute_local_to_global()
>> and compress().*
>>
>> Thank you again.
>> Regards
>> El martes, 8 de febrero de 2022 a las 22:22:37 UTC+1, Wolfgang Bangerth
>> escribió:
>>
>>> On 2/8/22 09:06, Hermes Sampedro wrote:
>>> >
>>> > I checked that in both cases, the operators/system_matrix have the
>>> same
>>> > values just in the assemble_system() function. I was wondering if
>>> there
>>> > is something internally that change somehow the systme_matrix. I can
>>> see
>>> > that after checking the values of the operators I have the following
>>> > lines which I am not sure if there is something happening:
>>>
>>> No functions in deal.II touch your linear system unless you specifically
>>> call a function that takes a matrix or vector as argument. So, if you
>>> have the distribute_local_to_global() call for one type of matrix, you
>>> need to call it for the other kind of matrix as well. But these
>>> functions do not internally store some kind of magic pointer to the
>>> matrix and right hand side so that at some later point, when you're not
>>> watching, they do something nefarious to your matrix :-)
>>>
>>> My suggestion would be to make sure that before the solve, the two
>>> matrices and corresponding right hand sides are the same. This is often
>>> awkward if the objects are large, but you can test this by outputting
>>> the norm of these objects.
>>>
>>> Then check that the solution is also the same. My guess is that for some
>>> reason, either the matrix or the rhs are different.
>>>
>>> Best
>>> W.
>>>
>>> --
>>> ------------------------------------------------------------------------
>>> Wolfgang Bangerth email: bang...@colostate.edu
>>> www: http://www.math.colostate.edu/~bangerth/
>>>
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