Najwa,
the relevant code reads something like
const unsigned int n_components = dof.get_fe(0).n_components();
AssertDimension(exact_solution.n_components, n_components);
if (weight != nullptr)
{
Assert((weight->n_components == 1) ||
(weight->n_components == n_components),
ExcDimensionMismatch(weight->n_components, n_components));
}
which means that your exact solution still needs to have as many components
as the FiniteElement object used (and the number of components for
ComponentSelectFunction must also match that).
ComponentSelectFunction then makes sure that all other components are
ignored when computing the error.
Best,
Daniel
On Thu, Jul 20, 2023 at 6:15 AM Najwa Alshehri <najwaalshe...@gmail.com>
wrote:
> Hello again,
>
> I have a follow-up question. Does this ComponentSelectFunction work also
> with vectors that are not written as blocked vectors? I have applied it
> before when I was dealing with blocked vectors and it worked perfectly.
>
> So, I did this,
> const ComponentSelectFunction<dim> primal_mask(0,2);
> Later,
> VectorTools::integrate_difference(omega2_dh,
> u_omega2,
> ExactSolution2<dim>(),
> cellwise_errors2,
> quadrature,
> VectorTools::L2_norm
> ,&primal_mask);
> const double u2_l2_error =
> VectorTools::compute_global_error(triangulation_omega2,
> cellwise_errors2,
> VectorTools::L2_norm);
>
> And I got the following error!!
> An error occurred in line <455> of file
> <../include/deal.II/numerics/vector_tools_integrate_difference.templates.h>
> in function
> void dealii::VectorTools::internal::do_integrate_difference(const
> dealii::hp::MappingCollection<dim, spacedim>&, const
> dealii::DoFHandler<dim, spacedim>&, const InVector&, const
> dealii::Function<spacedim, typename InVector::value_type>&, OutVector&,
> const dealii::hp::QCollection<dim>&, const dealii::VectorTools::NormType&,
> const dealii::Function<spacedim>*, double) [with int dim = 2; int spacedim
> = 2; InVector = dealii::Vector<double>; OutVector = dealii::Vector<double>;
> typename InVector::value_type = double]
> The violated condition was:
>
> ::dealii::deal_II_exceptions::internals::compare_for_equality(exact_solution.n_components,
> n_components)
> Additional information:
> Dimension 1 not equal to 2.
>
> Obviously, we have dimensionality mismatching between u_omega2 and the
> exact solution. which means that the mask is not really picking up the
> first component of the solution u_omega2. Do you have any suggestions to
> fix this issue?
>
> Appreciate your help,
> Najwa
> On Thursday, July 20, 2023 at 11:48:04 AM UTC+3 Najwa Alshehri wrote:
>
>> Thank you Daniel for the clear quick answer. I will follow it.
>>
>> Best,
>> Najwa
>>
>> On Wednesday, July 19, 2023 at 5:16:14 PM UTC+3 d.arnd...@gmail.com
>> wrote:
>>
>>> Najwa,
>>>
>>> The documentation of VectorTools::integrate_difference(
>>> https://www.dealii.org/current/doxygen/deal.II/namespaceVectorTools.html#a676190d2c897ac5da68a9c460fa95832)
>>> says
>>>
>>>
>>> The additional argument weight allows to evaluate weighted norms. The
>>> weight function may be scalar, establishing a spatially variable weight in
>>> the domain for all components equally. This may be used, for instance, to
>>> only integrate over parts of the domain. The weight function may also be
>>> vector-valued, with as many components as the finite element: Then,
>>> different components get different weights. A typical application is when
>>> the error with respect to only one or a subset of the solution variables is
>>> to be computed, in which case the other components would have weight values
>>> equal to zero. The ComponentSelectFunction
>>> <https://www.dealii.org/current/doxygen/deal.II/classComponentSelectFunction.html>
>>> class is particularly useful for this purpose as it provides such a "mask"
>>> weight. The weight function is expected to be positive, but negative values
>>> are not filtered. The default value of this function, a null pointer, is
>>> interpreted as "no weighting function", i.e., weight=1 in the whole domain
>>> for all vector components uniformly.
>>>
>>> Best,
>>> Daniel
>>>
>>> On Wed, Jul 19, 2023 at 8:01 AM Najwa Alshehri <najwaa...@gmail.com>
>>> wrote:
>>>
>>>> Dear group members,
>>>>
>>>> I have one question,
>>>>
>>>> I am trying to calculate the L2 norm of the error of a solution. In
>>>> particular, I have a *vector of the solution* u_omega and a *FeSystem*
>>>> with two fes.
>>>>
>>>> I am interested in computing the L2 norm of the error related to the
>>>> first fe using *integrate_difference * function. (Note here u_omega is *not
>>>> a blocked vector*, however, it has two solutions stacked together in
>>>> one vector). Can I extract the solution of the first part from u_omega?
>>>>
>>>>
>>>>
>>>> Thank you in advance for your help.
>>>>
>>>> Best,
>>>>
>>>> Najwa
>>>>
>>>> --
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>>>> .
>>>>
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