Accroding to my understanding:
When we get the solution of Helmoltz equation using the function
UltrasoundProblem<dim>::solve ()
template <int dim>
void UltrasoundProblem<dim>::solve ()
{
deallog << "Solving linear system... ";
Timer <https://www.dealii.org/8.3.0/doxygen/deal.II/classTimer.html> timer;
timer.start
<https://www.dealii.org/8.3.0/doxygen/deal.II/classTimer.html#a3a8b5272198d029779dc9302a54305a8>
();
SparseDirectUMFPACK
<https://www.dealii.org/8.3.0/doxygen/deal.II/classSparseDirectUMFPACK.html>
A_direct;
A_direct.initialize
<https://www.dealii.org/8.3.0/doxygen/deal.II/classSparseDirectUMFPACK.html#a25b1d3c7dbb88158a76165a4a56a16d6>
(system_matrix);
A_direct.vmult
<https://www.dealii.org/8.3.0/doxygen/deal.II/classSparseDirectUMFPACK.html#ab50b0667127c0e5847bb125ae44800a4>
(solution, system_rhs);
timer.stop
<https://www.dealii.org/8.3.0/doxygen/deal.II/classTimer.html#a988f79aa183d9d5473c13106f5babe48>
();
deallog << "done ("
<< timer ()
<< "s)"
<< std::endl;
}
The output solution will be alpha and Beta from the function
UltrasoundProblem<dim>::solve
(). It will become of the input of the class
class ComputeIntensity : public DataPostprocessorScalar
<https://www.dealii.org/8.3.0/doxygen/deal.II/classDataPostprocessorScalar.html>
<dim>.
Using this class we will calculate the uh, duh, dduh etc.
Anyone can explain to me how it is calculating the uh? I don't understand
what is the input to this class after calculating the coeeficients Alpha
nad Beta in the tutorial.
template <int dim>
class ComputeIntensity : public DataPostprocessorScalar
<https://www.dealii.org/8.3.0/doxygen/deal.II/classDataPostprocessorScalar.html>
<dim>
{
public:
ComputeIntensity ();
virtual
void
compute_derived_quantities_vector
<https://www.dealii.org/8.3.0/doxygen/deal.II/classDataPostprocessor.html#aabfd7ef3eec0d636e0c69f8740af29f9>
(const std::vector<Vector<double>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classVector.html> > &uh,
const std::vector<std::vector<Tensor<1, dim>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classTensor.html> > > &duh,
const std::vector<std::vector<Tensor<2, dim>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classTensor.html> > > &dduh,
const std::vector<Point<dim>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classPoint.html> > &normals,
const std::vector<Point<dim>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classPoint.html> >
&evaluation_points,
std::vector<Vector<double>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classVector.html> >
&computed_quantities) const;
};
template <int dim>
ComputeIntensity<dim>::ComputeIntensity ()
:
DataPostprocessorScalar
<https://www.dealii.org/8.3.0/doxygen/deal.II/classDataPostprocessorScalar.html><dim>
("Intensity",
update_values
<https://www.dealii.org/8.3.0/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fa4057ca2f127aa619c65886a9d3ad4aea>
)
{}
template <int dim>
void
ComputeIntensity<dim>::compute_derived_quantities_vector (
const std::vector<Vector<double>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classVector.html> > &uh,
const std::vector<std::vector<Tensor<1, dim>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classTensor.html> > > &
/*duh*/,
const std::vector<std::vector<Tensor<2, dim>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classTensor.html> > > &
/*dduh*/,
const std::vector<Point<dim>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classPoint.html> > &
/*normals*/,
const std::vector<Point<dim>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classPoint.html> > &
/*evaluation_points*/,
std::vector<Vector<double>
<https://www.dealii.org/8.3.0/doxygen/deal.II/classVector.html> >
&computed_quantities
) const
{
Assert
<https://www.dealii.org/8.3.0/doxygen/deal.II/group__Exceptions.html#ga70a0bb353656e704acf927945277bbc6>(computed_quantities.size()
== uh.size(),
ExcDimensionMismatch (computed_quantities.size(), uh.size()));
for (unsigned int i=0; i<computed_quantities.size(); i++)
{
Assert
<https://www.dealii.org/8.3.0/doxygen/deal.II/group__Exceptions.html#ga70a0bb353656e704acf927945277bbc6>(computed_quantities[i].size()
== 1,
ExcDimensionMismatch (computed_quantities[i].size(), 1));
Assert
<https://www.dealii.org/8.3.0/doxygen/deal.II/group__Exceptions.html#ga70a0bb353656e704acf927945277bbc6>(uh[i].size()
== 2, ExcDimensionMismatch (uh[i].size(), 2));
computed_quantities[i](0) = std::sqrt(uh[i](0)*uh[i](0) +
uh[i](1)*uh[i](1));
}
}
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