Step-29

[Muhammad Adil]

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 timer;

timer.start ();

SparseDirectUMFPACK A_direct;

A_direct.initialize(system_matrix);

A_direct.vmult (solution, system_rhs);

timer.stop ();

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<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<dim>

{

public:

ComputeIntensity ();

virtual

void

compute_derived_quantities_vector (const std::vector<Vector<double> > &uh,

const std::vector<std::vector<Tensor<1, dim> > > &duh,

const std::vector<std::vector<Tensor<2, dim> > > &dduh,

const std::vector<Point<dim> > &normals,

const std::vector<Point<dim> > &evaluation_points,

std::vector<Vector<double> > &computed_quantities) const;

};

template <int dim>

ComputeIntensity<dim>::ComputeIntensity ()

:

DataPostprocessorScalar<dim> ("Intensity",

update_values)

{}

template <int dim>

void

ComputeIntensity<dim>::compute_derived_quantities_vector (

const std::vector<Vector<double> > &uh,

const std::vector<std::vector<Tensor<1, dim> > > & /*duh*/,

const std::vector<std::vector<Tensor<2, dim> > > & /*dduh*/,

const std::vector<Point<dim> > & /*normals*/,

const std::vector<Point<dim> > & /*evaluation_points*/,

std::vector<Vector<double> > &computed_quantities

) const

{

Assert(computed_quantities.size() == uh.size(),

ExcDimensionMismatch (computed_quantities.size(), uh.size()));

for (unsigned int i=0; i<computed_quantities.size(); i++)

{

Assert(computed_quantities[i].size() == 1,

ExcDimensionMismatch (computed_quantities[i].size(), 1));

Assert(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));

}

}

[Wolfgang Bangerth]

Muhammad,

> When we get the solution of Helmoltz equation using the function
> UltrasoundProblem<dim>::solve ()

> [...]

>
> 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.

The input uh to ComputeIntensity::compute_derived_quantities_vector() *is* the
solution at the points where we want to create output. You don't need to
compute it.

uh is of type std::vector<Vector<double> >. Specifically, the outer vector is
over all of the points on one cell where we want to create output; the inner
vector will, in your case, have size 2 and contain the pairs {alpha, beta} at
the output point.

I hope this makes it clear why the implementation of the function makes sense!

Best
W.


--
------------------------------------------------------------------------
Wolfgang Bangerth email: bang...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/

[Muhammad Adil]

Thank you Wolfgang Bangerth:

It means if I want to use duh, dduh or normal etc I don't need to compute just update the flags using get_needed_update_flags().

Please respond on this.

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[Wolfgang Bangerth]

On 8/18/19 2:46 AM, Muhammad Adil wrote:
> It means if I want to use duh, dduh or normal etc I don't need to compute just
> update the flags using get_needed_update_flags().

Yes, that is correct!