Dear all,
If I have a Vector-valued solution in 3D and I would like to get the size
of each vector in another smaller Vector, can I do it like this:
for (unsigned int i=0;i<solution.size();i=i+3)
{
unsigned int x=i;
unsigned int y=i+1;
unsigned int z=i+2;
unsigned int j = i / 3.0;
size(j)=pow(solution(x),2.0)+pow(solution(y),2.0)+pow(solution(z),2.0);
}
Where solution is the vector valued Vector that is 3 times bigger that the
scalar Vector called size.
Best,
Joel
On Tuesday, August 30, 2016 at 6:48:46 PM UTC+2, Jean-Paul Pelteret wrote:
>
> Dear Joel,
>
> No, this functionality doesn't exist. However, you can create a quadrature
> rule with the quadrature points located at the support points (see the FAQ
> <https://github.com/dealii/dealii/wiki/Frequently-Asked-Questions#how-to-get-the-mapped-position-of-support-points-of-my-element>),
>
> and could then extract the solution based on your custom quadrature rule.
>
> Regards,
> J-P
>
> On Tuesday, August 30, 2016 at 5:32:13 PM UTC+2, Joel Davidsson wrote:
>>
>> Dear Daniel,
>>
>> I was just wondering if their exist a similar function
>> to DoFTools::map_dofs_to_support_points, but that maps a vector-valued
>> solution Vector into to a std::vector<Point<dim>> instead?
>>
>> Best,
>> Joel
>>
>> On Monday, August 22, 2016 at 9:03:22 PM UTC+2, Daniel Arndt wrote:
>>>
>>> Joel,
>>>
>>> You should not rely on any particular sorting of the dofs in the
>>> solution vector. Instead you can ask the FiniteElement on each cell for the
>>> component of a local dof by
>>> const unsigned int component = fe.system_to_component_index(i).first;
>>>
>>> Apart from that the DataOut object knows about components and you can do
>>> some postprocessing on the solution vector using DataPostprocessor [1]
>>>
>>> Best,
>>> Daniel
>>>
>>> [1]
>>> https://dealii.org/8.4.1/doxygen/deal.II/classDataPostprocessor.html
>>>
>>> Am Montag, 22. August 2016 17:05:08 UTC+2 schrieb Joel Davidsson:
>>>>
>>>> Dear Daniel,
>>>>
>>>> Thank you for a very good answer, adding the fe_values_scalar and
>>>> cell_scalar fixed the problem.
>>>>
>>>> I have a follow-up question about the solution I get out, how is the
>>>> data organized in the solution vector? Say for example I want to loop over
>>>> all the x components, how would I do that?
>>>>
>>>> Best,
>>>> Joel
>>>>
>>>> On Friday, August 12, 2016 at 5:35:07 PM UTC+2, Daniel Arndt wrote:
>>>>>
>>>>> Joel,
>>>>>
>>>>> Yes the matrix you are assembling is a vector-valued mass matrix now.
>>>>> For me your code is failing with
>>>>>
>>>>> void dealii::FEValuesBase<dim, spacedim>::get_function_gradients(const
>>>>> InputVector&, std::vector<dealii::Tensor<1, spacedim, typename
>>>>> InputVector::value_type> >&) const [with InputVector =
>>>>> dealii::Vector<double>; int dim = 3; int spacedim = 3; typename
>>>>> InputVector::value_type = double]
>>>>> The violated condition was:
>>>>> (fe->n_components()) == (1)
>>>>> The name and call sequence of the exception was:
>>>>> dealii::ExcDimensionMismatch((fe->n_components()),(1))
>>>>> Additional Information:
>>>>> Dimension 3 not equal to 1
>>>>>
>>>>> and this is not surprising. What you are doing is to extract the
>>>>> gradients of a vector-valued finite element solution. The object that
>>>>> should store this should therefore be a
>>>>> std::vector<std::vector<Tensor<1,dim>> as you want to store for each
>>>>> quadrature point and each component a Tensor<1,dim>.
>>>>>
>>>>> What you want to do is really that in "Do not work". As you have two
>>>>> DoFHandlers, you should also have two FEValues objects and two
>>>>> cell_iterator corresponding to the correct DoFHandler. Then you can
>>>>> extract
>>>>> the gradient of your scalar field and project it onto the ansatz space
>>>>> for
>>>>> the vector-valued field. This should look like:
>>>>>
>>>>> typename DoFHandler<dim>::active_cell_iterator cell_scalar =
>>>>> dof_handler_scalar.begin_active();
>>>>> typename DoFHandler<dim>::active_cell_iterator cell =
>>>>> dof_handler.begin_active();
>>>>> ...
>>>>>
>>>>> for (; cell!=endc; ++cell, ++cell_vector)
>>>>> {
>>>>> fe_values.reinit (cell);
>>>>> fe_values_scalar.reinit (cell_scalar);
>>>>> fe_values_scalar.get_function_gradients(test,fe_function_grad);
>>>>> ...
>>>>> }
>>>>>
>>>>> Best,
>>>>> Daniel
>>>>>
>>>>
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