Dear Najwa,
how many components do the `ExactSolution2<dim>` function has?
The error complains about `exact_solution.n_components, n_components` not being
equal, in particular it tells you that `ExactSolution2<dim>` only has one
component.
If you built the ExactSolution class yourself, make sure at construction time
you tell Function<dim> to allocate two components:
ExactSolution2<dim>::ExactSolution2<dim>( … )
: Functions::Function<dim>(2)
Best,
Luca.
> On 20 Jul 2023, at 12:15, Najwa Alshehri <[email protected]> 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 [email protected] 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 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 <[email protected]> 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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